FN	Thomson Reuters Web of Knowledge
VR	1.0

PT	J
AU	Wang, L Huang, JH Dowling, JP Zhu, SY
AF	Wang, Lei Huang, Jie-Hui Dowling, Jonathan P. Zhu, Shi-Yao
TI	Quantum information transmission
SO	QUANTUM INFORMATION PROCESSING
AB	We present a scheme of quantum information transmission, which transmits the quantum information contained in a single qubit via the quantum correlation shared by two parties (a two-qubit channel), whose quantum discord is non-zero. We demonstrate that quantum correlation, which may have no entanglement, is sufficient to transmit the information needed to reconstruct a quantum state. When the correlation matrix of the two-qubit channel is of full rank (rank three), the information of the qubit (in either a mixed state or a pure state) can be transmitted. The quantum discord of a channel with rank larger than or equal to three is always non-zero. Therefore, non-zero quantum discord is also necessary for our quantum information transmission protocol. The scheme may be useful in remote state tomography and remote state preparation.
TC	0
Z9	0
SN	1570-0755
PD	FEB
PY	2013
VL	12
IS	2
BP	899
EP	906
DI	10.1007/s11128-012-0435-2
UT	WOS:000313370000018
ER

PT	J
AU	Wang, XT Byrd, M Jacobs, K
AF	Wang, Xiaoting Byrd, Mark Jacobs, Kurt
TI	Numerical method for finding decoherence-free subspaces and its applications
SO	PHYSICAL REVIEW A
AB	In this work, inspired by the study of semidefinite programming for block-diagonalizing matrix *-algebras, we propose an algorithm that can find the algebraic structure of decoherence-free subspaces (DFS's) for a given noisy quantum channel. We prove that this algorithm will work for all cases with probability 1, and it is more efficient than the algorithm proposed by J. A. Holbrook, D. W. Kribs, and R. Laflamme, [Quantum. Inf. Proc. 80, 381 (2003)]. In fact, our results reveal that this previous algorithm only works for special cases. As an application, we discuss how this method can be applied to increase the efficiency of an optimization procedure for finding an approximate DFS. DOI: 10.1103/PhysRevA.87.012338
TC	0
Z9	0
SN	1050-2947
PD	JAN 31
PY	2013
VL	87
IS	1
AR	012338
DI	10.1103/PhysRevA.87.012338
UT	WOS:000314333500005
ER

PT	J
AU	Gao, Y Lee, H
AF	Gao, Yang Lee, Hwang
TI	Generalized limits for parameter sensitivity via quantum Ziv-Zakai bound
SO	JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
AB	We study the generalized limit for parameter sensitivity in quantum estimation theory considering the effects of repeated and adaptive measurements. Based on the quantum Ziv-Zakai bound, we derive some lower bounds for parameter sensitivity when the Hamiltonian of a system is unbounded and when the adaptive measurements are implemented on the system. We also prove that the parameter sensitivity is bounded by the limit of the minimum detectable parameter. In particular, we examine several known states in quantum phase estimation with non-interacting photons and show that they cannot perform better than the Heisenberg limit in a much simpler way with our result.
TC	2
Z9	2
SN	1751-8113
PD	OCT 19
PY	2012
VL	45
IS	41
AR	415306
DI	10.1088/1751-8113/45/41/415306
UT	WOS:000309550400013
ER

PT	J
AU	Horrom, T Singh, R Dowling, JP Mikhailov, EE
AF	Horrom, Travis Singh, Robinjeet Dowling, Jonathan P. Mikhailov, Eugeniy E.
TI	Quantum-enhanced magnetometer with low-frequency squeezing
SO	PHYSICAL REVIEW A
AB	We report the demonstration of a magnetometer with noise-floor reduction below the shot-noise level. This magnetometer, based on a nonlinear magneto-optical rotation effect, is enhanced by the injection of a squeezed vacuum state into its input. The noise spectrum shows squeezed noise reduction of about 2 +/- 0.35 dB spanning from close to 100 Hz to several megahertz. We also report on the observation of two different regimes of operation of such a magnetometer: one in which the detection noise is limited by the quantum noise of the light probe only, and one in which we see additional noise originating from laser noise which is rotated into the vacuum polarization.
TC	2
Z9	2
SN	1050-2947
PD	AUG 3
PY	2012
VL	86
IS	2
AR	023803
DI	10.1103/PhysRevA.86.023803
UT	WOS:000307125600008
ER

PT	J
AU	Boyd, RW Dowling, JP
AF	Boyd, Robert W. Dowling, Jonathan P.
TI	Quantum lithography: status of the field
SO	QUANTUM INFORMATION PROCESSING
AB	This contribution provides an analysis of progress in the field of quantum lithography. We review the conceptual foundations of this idea and the status of research aimed at implementing this idea in the laboratory. The selection of a highly sensitive recording material that functions by means of multiphoton absorption seems crucial to the success of the proposal of quantum lithography. This review thus devotes considerable attention to these materials considerations.
TC	2
Z9	2
SN	1570-0755
PD	AUG
PY	2012
VL	11
IS	4
SI	SI
BP	891
EP	901
DI	10.1007/s11128-011-0253-y
UT	WOS:000305530200002
ER

PT	J
AU	Howell, JC Anisimov, PM Dowling, JP Boyd, RW
AF	Howell, John C. Anisimov, Petr M. Dowling, Jonathan P. Boyd, Robert W.
TI	Single and biphoton imaging and high dimensional quantum communication
SO	QUANTUM INFORMATION PROCESSING
AB	Here, we present recent developments in the field of quantum imaging focusing on the high dimensionality aspects of single and biphoton imaging. We discuss some systems that have a "quantum advantage" over classical counterparts. We highlight some recent experiments in single-photon image discrimination, large alphabet quantum key distribution and image buffering.
TC	0
Z9	0
SN	1570-0755
PD	AUG
PY	2012
VL	11
IS	4
SI	SI
BP	925
EP	948
DI	10.1007/s11128-011-0299-x
UT	WOS:000305530200004
ER

PT	J
AU	Jiang, KB Brignac, CJ Weng, Y Kim, MB Lee, H Dowling, JP
AF	Jiang, Kebei Brignac, Chase J. Weng, Yi Kim, Moochan B. Lee, Hwang Dowling, Jonathan P.
TI	Strategies for choosing path-entangled number states for optimal robust quantum-optical metrology in the presence of loss
SO	PHYSICAL REVIEW A
AB	To acquire the best path-entangled photon Fock states for robust quantum-optical metrology with parity detection, we calculate phase information from a lossy interferometer by using twin entangled Fock states. We show that (a) when loss is less than 50% twin entangled Fock states with large photon number difference give higher visibility, while when loss is higher than 50%, the ones with less photon number difference give higher visibility; and (b) twin entangled Fock states with large photon number difference give sub-shot-noise limit sensitivity for phase detection in a lossy environment. This result provides a reference on what particular path-entangled Fock states are useful for real world metrology applications.
TC	0
Z9	0
SN	1050-2947
PD	JUL 19
PY	2012
VL	86
IS	1
AR	013826
DI	10.1103/PhysRevA.86.013826
UT	WOS:000306543200006
ER

Brown, KL
Horsman, C
Kendon, V
Munro, WJ

Brown, Katherine L.
Horsman, Clare
Kendon, Viv
Munro, William J.

Layer-by-layer generation of cluster states

PHYSICAL REVIEW A

Cluster states can be used to perform measurement-based quantum computation. The cluster state is a useful resource, because once it has been generated only local operations and measurements are needed to perform universal quantum computation. In this paper, we explore techniques for quickly and deterministically building a cluster state. In particular, we consider generating cluster states on a qubus quantum computer, a computational architecture which uses a continuous variable ancilla to generate interactions between qubits. We explore several techniques for building the cluster, with the number of operations required depending on whether we allow the ability to destroy previously created controlled-phase links between qubits. In the case where we cannot destroy these links, we show how to create an n x m cluster using just 3nm - 2n - inverted right perpendicular3m/2inverted left perpendicular + 3 operations. This gives more than a factor of 2 savings over a naive method. Further savings can be obtained if we include the ability to destroy links, in which case we only need inverted right perpendicular1/3(8nm - 4n - 4m - 8)inverted left perpendicular operations. Unfortunately, the latter scheme is more complicated so choosing the correct order to interact the qubits is considerably more difficult. A halfway scheme, that keeps a modular generation but saves additional operations over never destroying links requires only 3nm - 2n - 2m + 4 operations. The first scheme and the last scheme are the most practical for building a cluster state because they split up the generation into the repetition of simple sections.

Munro, William

A-8453-2011

1050-2947

MAY 7

2012

052305

10.1103/PhysRevA.85.052305

WOS:000303651200004

PT	J
AU	Richardson, CD Dowling, JP
AF	Richardson, Chris D. Dowling, Jonathan P.
TI	POPPER'S THOUGHT EXPERIMENT REINVESTIGATED
SO	INTERNATIONAL JOURNAL OF QUANTUM INFORMATION
AB	Popper's original thought experiment probed some fundamental and subtle rules of quantum mechanics. He claimed that quantum mechanics was incomplete and devised an experiment to prove it. Two experiments have directly and indirectly tested Popper's hypothesis, and they provide some evidence that Popper's prediction may have been correct. The equations governing these two experiments and Popper's thought experiment will be derived from basic quantum principles. The experimental constants will be inputted and it will show that the two experiments reinforce each other and agree completely with quantum theory.
TC	0
Z9	0
SN	0219-7499
PD	APR
PY	2012
VL	10
IS	3
AR	1250033
DI	10.1142/S0219749912500335
UT	WOS:000304611800008
ER

PT	J
AU	Bardhan, BR Anisimov, PM Gupta, MK Brown, KL Jones, NC Lee, H Dowling, JP
AF	Bardhan, Bhaskar Roy Anisimov, Petr M. Gupta, Manish K. Brown, Katherine L. Jones, N. Cody Lee, Hwang Dowling, Jonathan P.
TI	Dynamical decoupling in optical fibers: Preserving polarization qubits from birefringent dephasing
SO	PHYSICAL REVIEW A
AB	One of the major challenges in quantum computation has been to preserve the coherence of a quantum system against dephasing effects of the environment. The information stored in photon polarization, for example, is quickly lost due to such dephasing, and it is crucial to preserve the input states when one tries to transmit quantum information encoded in the photons through a communication channel. We propose a dynamical decoupling sequence, to protect photonic qubits from dephasing, by integrating wave plates into optical fiber at prescribed locations. We simulate random birefringent noise along realistic lengths of optical fiber and study preservation of polarization qubits through such fibers enhanced with Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling. This technique can maintain photonic qubit coherence at high fidelity, making a step toward achieving scalable and useful quantum communication with photonic qubits.
TC	0
Z9	0
SN	1050-2947
PD	FEB 28
PY	2012
VL	85
IS	2
AR	022340
DI	10.1103/PhysRevA.85.022340
UT	WOS:000300827200001
ER

PT	J
AU	Thanvanthri, S Kapale, KT Dowling, JP
AF	Thanvanthri, Sulakshana Kapale, Kishore T. Dowling, Jonathan P.
TI	Ultra-stable matter-wave gyroscopy with counter-rotating vortex superpositions in Bose-Einstein condensates
SO	JOURNAL OF MODERN OPTICS
AB	Matter-wave interferometers are, in principle, orders of magnitude more sensitive than their optical counterparts. Nevertheless, creation of matter-wave currents to achieve such a sensitivity is a continuing challenge. Here, we propose the use of Optical-Angular-Momentum (OAM) induced vortex superpositions in Bose-Einstein condensates (BECs) as an alternative to other atom interferometers for gyroscopy. The coherent superposition of two counter-rotating vortex states of a trapped condensate leads to an interference pattern that rotates by an angle proportional to the angular velocity of the rotating trap - in accordance with the Sagnac effect. We show that the rotation rate can be easily read out, and that the device is highly stable. The signal-to-noise ratio and sensitivity of the scheme are also estimated.
TC	0
Z9	0
SN	0950-0340
PY	2012
VL	59
IS	13
BP	1180
EP	1185
DI	10.1080/09500340.2012.702228
UT	WOS:000307873300009
ER

O'Brien, C
Anisimov, PM
Rostovtsev, Y
Kocharovskaya, O

O'Brien, Chris
Anisimov, Petr M.
Rostovtsev, Yuri
Kocharovskaya, Olga

Coherent control of refractive index in far-detuned Lambda systems

PHYSICAL REVIEW A

Enhancement and control of the index of refraction in a mixture of two three-level atomic species that form a pair of far-detuned Lambda schemes under two-photon resonance has been studied. We employ the density-matrix approach to properly take population relaxation into account and to describe the interaction of each Lambda system with the electromagnetic fields. Both Lambda systems are driven by a corresponding far-detuned coherent field at one atomic transition and are probed by the same weak field. In the dressed-state basis, it represents a superposition of effective two-level subsystems with the positions, widths, and amplitudes of the resonances controlled by the driving fields and allows for efficient control of the susceptibility of the total system; leading to refractive index (RI) enhancement with vanishing absorption in the absence of amplification. We analyze the experimental implementation of such a system in a cell of Rb atoms with a natural abundance of isotopes. An upper limit estimate of the RI enhancement is obtained.

O'Brien, Christopher

C-8232-2013

1050-2947

DEC 15

2011

063835

10.1103/PhysRevA.84.063835

WOS:000298113500005

Sete, EA
Dorfman, KE
Dowling, JP

Sete, Eyob A.
Dorfman, Konstantin E.
Dowling, Jonathan P.

Phase-controlled entanglement in a quantum-beat laser: application to quantum lithography

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS

We study entanglement generation and control in a quantum-beat laser coupled to a two-mode squeezed vacuum reservoir. We show that the generated entanglement is robust against cavity losses and environmental decoherence and can be controlled by tuning the phases of the microwave and the squeezed input fields. Moreover, we discuss two-photon correlations, absorption and implementations in quantum optical lithography.

Sete, Eyob

E-7813-2012

0953-4075

NOV 28

2011

225504

10.1088/0953-4075/44/22/225504

WOS:000296796600017

Wang, XT
Vinjanampathy, S
Strauch, FW
Jacobs, K

Wang, Xiaoting
Vinjanampathy, Sai
Strauch, Frederick W.
Jacobs, Kurt

Ultraefficient Cooling of Resonators: Beating Sideband Cooling with Quantum Control

PHYSICAL REVIEW LETTERS

The present state of the art in cooling mechanical resonators is a version of sideband cooling. Here we present a method that uses the same configuration as sideband cooling-coupling the resonator to be cooled to a second microwave (or optical) auxiliary resonator-but will cool significantly colder. This is achieved by varying the strength of the coupling between the two resonators over a time on the order of the period of the mechanical resonator. As part of our analysis, we also obtain a method for fast, high-fidelity quantum information transfer between resonators.

Jacobs, Kurt

E-7049-2011

0031-9007

OCT 19

2011

107

177204

10.1103/PhysRevLett.107.177204

WOS:000296984100017

Anisimov, PM
Dowling, JP
Sanders, BC

Anisimov, Petr M.
Dowling, Jonathan P.
Sanders, Barry C.

Objectively Discerning Autler-Townes Splitting from Electromagnetically Induced Transparency

PHYSICAL REVIEW LETTERS

Autler-Townes splitting (ATS) and electromagnetically induced transparency (EIT) both yield transparency in an absorption profile, but only EIT yields strong transparency for a weak pump field due to Fano interference. Empirically discriminating EIT from ATS is important but so far has been subjective. We introduce an objective method, based on Akaike's information criterion, to test ATS vs EIT from experimental data for three-level atomic systems and determine which pertains. We apply our method to a recently reported induced-transparency experiment in superconducting-circuit quantum electrodynamics.

Sanders, Barry

A-3891-2008

0031-9007

OCT 12

2011

107

163604

10.1103/PhysRevLett.107.163604

WOS:000296370800003

PT	J
AU	Seshadreesan, KP Anisimov, PM Lee, H Dowling, JP
AF	Seshadreesan, Kaushik P. Anisimov, Petr M. Lee, Hwang Dowling, Jonathan P.
TI	Parity detection achieves the Heisenberg limit in interferometry with coherent mixed with squeezed vacuum light
SO	NEW JOURNAL OF PHYSICS
AB	The interference between coherent and squeezed vacuum light effectively produces path entangled N00N states with very high fidelities. We show that the phase sensitivity of the above interferometric scheme with parity detection saturates the quantum Cramer-Rao bound, which reaches the Heisenberg limit when the coherent and squeezed vacuum light are mixed in roughly equal proportions. For the same interferometric scheme, we draw a detailed comparison between parity detection and a symmetric-logarithmic-derivative-based detection scheme suggested by Ono and Hofmann.
TC	5
Z9	5
SN	1367-2630
PD	AUG 24
PY	2011
VL	13
AR	083026
DI	10.1088/1367-2630/13/8/083026
UT	WOS:000294672800002
ER

PT	J
AU	Seshadreesan, KP Ghosh, S
AF	Seshadreesan, Kaushik P. Ghosh, Sibasish
TI	Constancy of maximal nonlocal probability in Hardy's nonlocality test for bipartite quantum systems
SO	JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
AB	We give the generic form of the entangled states of a system of two spin-1 (and two spin-3/2) particles and the appropriate set of spin observables that together exhibit maximum nonlocality under Hardy's nonlocality test. We show the maximum nonlocality to be 0.090 17 just as in the case of two spin-1/2 particles. We conjecture that this result holds good for a system of two spin-j particles for all values of j.
TC	2
Z9	2
SN	1751-8113
PD	AUG 5
PY	2011
VL	44
IS	31
AR	315305
DI	10.1088/1751-8113/44/31/315305
UT	WOS:000292736300013
ER

PT	J
AU	Stack, D Elgin, J Anisimov, PM Metcalf, H
AF	Stack, Daniel Elgin, John Anisimov, Petr M. Metcalf, Harold
TI	Numerical studies of optical forces from adiabatic rapid passage
SO	PHYSICAL REVIEW A
AB	We present a numerical study of the properties of optical forces on moving atoms derived from purely stimulated processes produced by multiple adiabatic rapid-passage sequences. The optical Bloch equations are solved for a carefully timed sequence of frequency-swept pulses that can produce a force much larger than the ordinary radiative force. We describe the effects of the sweep range, peak intensity, sweep direction, number of pulses, atomic velocity, and spontaneous emission. Since the momentum of thermal atoms is much larger than that transferred by a single absorption-stimulated emission cycle, multiple repetitions are needed to make a significant velocity change.
TC	1
Z9	1
SN	1050-2947
PD	JUL 25
PY	2011
VL	84
IS	1
AR	013420
DI	10.1103/PhysRevA.84.013420
UT	WOS:000293126500012
ER

Jacobs, K
Finn, J
Vinjanampathy, S

Jacobs, Kurt
Finn, Justin
Vinjanampathy, Sai

Real-time feedback control of a mesoscopic superposition

PHYSICAL REVIEW A

We show that continuous real-time feedback can be used to track, control, and protect a mesoscopic superposition of two spatially separated wave packets. The feedback protocol is enabled by an approximate state estimator and requires two continuous measurements, performed simultaneously. For nanomechanical and superconducting resonators, both measurements can be implemented by coupling the resonators to superconducting qubits.

Jacobs, Kurt

E-7049-2011

1050-2947

APR 20

2011

041801

10.1103/PhysRevA.83.041801

WOS:000290104500001

PT	J
AU	Yurtsever, U
AF	Yurtsever, Ulvi
TI	MODELING LOSSY PROPAGATION OF NON-CLASSICAL LIGHT
SO	INTERNATIONAL JOURNAL OF QUANTUM INFORMATION
AB	The lossy propagation law (generalization of Lambert-Beer's law for classical radiation loss) for non-classical, dual-mode entangled states is derived from first principles, using an infinite-series of beam splitters to model continuous photon loss. This model is general enough to accommodate stray-photon noise along the propagation, as well as amplitude attenuation. An explicit analytical expression for the density matrix as a function of propagation distance is obtained for completely general input states with bounded photon number in each mode. The result is analyzed numerically for various examples of input states. For N00N state input, the loss of coherence and entanglement is super exponential, as predicted by a number of previous studies. However, for generic input states, where the coefficients are generated randomly, the decay of coherence is very different; in fact no worse than the classical Beer-Lambert law. More surprisingly, there is a plateau at a mid-range interval in propagation distance where the loss is in fact sub-classical, following which it resumes the classical rate. The qualitative behavior of the decay of entanglement for two-mode propagation is also analyzed numerically for ensembles of random states using the behavior of negativity as a function of propagation distance.
TC	0
Z9	0
SN	0219-7499
PD	MAR
PY	2011
VL	9
IS	2
BP	739
EP	750
DI	10.1142/S0219749911006806
UT	WOS:000290857800009
ER

PT	J
AU	Chiruvelli, A Lee, H
AF	Chiruvelli, Aravind Lee, Hwang
TI	Parity measurements in quantum optical metrology
SO	JOURNAL OF MODERN OPTICS
AB	We investigate the utility of parity detection to achieve Heisenberg-limited phase estimation for optical interferometry. We consider the parity detection with several input states that have been shown to exhibit subshot-noise interferometry with their respective detection schemes. We show that with parity detection, all these states achieve the sub-shot-noise limited phase uncertainty. Thus making the parity detection a unified detection strategy for quantum optical metrology. We also consider quantum states that are a combination of a NOON state and a dual-Fock state, which gives a great deal of freedom in the preparation of the input state, and is found to surpass the shot-noise limit.
TC	5
Z9	5
SN	0950-0340
PY	2011
VL	58
IS	11
BP	945
EP	953
DI	10.1080/09500340.2011.585251
UT	WOS:000294681500008
ER

PT	J
AU	Plick, WN Anisimov, PM Dowling, JP Lee, H Agarwal, GS
AF	Plick, William N. Anisimov, Petr M. Dowling, Jonathan P. Lee, Hwang Agarwal, Girish S.
TI	Parity detection in quantum optical metrology without number-resolving detectors
SO	NEW JOURNAL OF PHYSICS
AB	We present a method for directly obtaining the parity of a Gaussian state of light without recourse to photon-number counting. The scheme uses only a simple balanced homodyne technique and intensity correlation. Thus interferometric schemes utilizing coherent or squeezed light and parity detection may be practically implemented for an arbitrary photon flux. Specifically, we investigate a two-mode, squeezed light, Mach-Zehnder interferometer and show how the parity of the output state may be obtained. We also show that the detection may be described independently of the parity operator and that this 'parity-by-proxy' measurement has the same signal as traditional parity.
TC	7
Z9	7
SN	1367-2630
PD	NOV 11
PY	2010
VL	12
AR	113025
DI	10.1088/1367-2630/12/11/113025
UT	WOS:000284774100003
ER

PT	J
AU	Yurtsever, U
AF	Yurtsever, Ulvi
TI	Fundamental limits on the speed of evolution of quantum states
SO	PHYSICA SCRIPTA
AB	This paper reports on some new inequalities of Margolus-Levitin-Mandelstam-Tamm type involving the speed of quantum evolution between two orthogonal pure states. The clear determinant of the qualitative behavior of this time scale is the statistics of the energy spectrum.
TC	2
Z9	2
SN	0031-8949
PD	SEP
PY	2010
VL	82
IS	3
AR	035008
DI	10.1088/0031-8949/82/03/035008
UT	WOS:000281537200009
ER

PT	J
AU	Anisimov, PM Lum, DJ McCracken, SB Lee, H Dowling, JP
AF	Anisimov, Petr M. Lum, Daniel J. McCracken, S. Blane Lee, Hwang Dowling, Jonathan P.
TI	An invisible quantum tripwire
SO	NEW JOURNAL OF PHYSICS
AB	We present here a quantum tripwire, which is a quantum optical interrogation technique capable of detecting an intrusion with very low probability of the tripwire being revealed to the intruder. Our scheme combines interaction-free measurement (IFM) with the quantum Zeno effect in order to interrogate the presence of the intruder without interaction. The tripwire exploits a curious nonlinear behaviour of the quantum Zeno effect we discovered, which occurs in a lossy system. We also employ a statistical hypothesis testing protocol, allowing us to calculate a confidence level of IFM after a given number of trials. As a result, our quantum intruder alert system is robust against photon loss and dephasing under realistic atmospheric conditions and its design minimizes the probabilities of false positives and false negatives as well as the probability of becoming visible to the intruder.
TC	4
Z9	4
SN	1367-2630
PD	AUG 6
PY	2010
VL	12
AR	083012
DI	10.1088/1367-2630/12/8/083012
UT	WOS:000281278900001
ER

PT	J
AU	Plick, WN Dowling, JP Agarwal, GS
AF	Plick, William N. Dowling, Jonathan P. Agarwal, Girish S.
TI	Coherent-light-boosted, sub-shot noise, quantum interferometry
SO	NEW JOURNAL OF PHYSICS
AB	We present in this paper a new scheme for optical interferometry. We utilize coherent-beam-stimulated two-mode squeezed light, which interacts with a phase shifter and is then squeezed again before detection. Our theoretical device has the potential to reach far below the shot-noise limit in phase sensitivity. This new proposal avoids the pitfalls of other setups, such as difficulty in creating the required resource. Furthermore, our scheme requires no complicated detection protocol, relying instead only on simple intensity measurement. Also, bright, coherent sources 'boost' squeezed light, creating a very sensitive device. This hybrid scheme relies on no unknown components and can be constructed with current technology. In this paper, we present our analysis of this relatively straightforward device, using the operator propagation method. We derive the phase sensitivity and provide a simple numerical example of the power of our new proposal. Sensitivity to unknown phase shifts scales as a shot-noise-limited Mach-Zehnder interferometer, multiplied by a sub-Heisenberg contribution from the squeezed light.
TC	6
Z9	6
SN	1367-2630
PD	AUG 6
PY	2010
VL	12
AR	083014
DI	10.1088/1367-2630/12/8/083014
UT	WOS:000281278900003
ER

PT	J
AU	Gao, Y Anisimov, PM Wildfeuer, CF Luine, J Lee, H Dowling, JP
AF	Gao, Yang Anisimov, Petr M. Wildfeuer, Christoph F. Luine, Jerome Lee, Hwang Dowling, Jonathan P.
TI	Super-resolution at the shot-noise limit with coherent states and photon-number-resolving detectors
SO	JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
AB	There has been much recent interest in quantum optical interferometry for applications to metrology, subwavelength imaging, and remote sensing such as in quantum laser radar (LADAR). For quantum LADAR, atmospheric absorption rapidly degrades any quantum state of light, so that for high-photon loss the optimal strategy is to transmit coherent states of light, which suffer no worse loss than the Beer law for classical optical attenuation, and which provides sensitivity at the shot-noise limit. We show that coherent light coupled with photon-number-resolving detectors can provide a super-resolution much below the Rayleigh diffraction limit, with sensitivity no worse than shot noise in terms of the detected photon power. (C) 2010 Optical Society of America
TC	8
Z9	8
SN	0740-3224
PD	JUN
PY	2010
VL	27
IS	6
BP	A170
EP	A174
UT	WOS:000278433500047
ER

Jacobs, K

Jacobs, Kurt

Wave-function Monte Carlo method for simulating conditional master equations

PHYSICAL REVIEW A

Wave-function Monte Carlo methods are an important tool for simulating quantum systems, but the standard method cannot be used to simulate decoherence in continuously measured systems. Here I present a Monte Carlo method for such systems. This was used to perform the simulations of a continuously measured nanoresonator in [Phys. Rev. Lett. 102, 057208 (2009)].

Jacobs, Kurt

E-7049-2011

1050-2947

APR

2010

042106

10.1103/PhysRevA.81.042106

WOS:000277227300024

PT	J
AU	Pearlman, AJ Ling, A Goldschmidt, EA Wildfeuer, CF Fan, J Migdall, A
AF	Pearlman, A. J. Ling, A. Goldschmidt, E. A. Wildfeuer, C. F. Fan, J. Migdall, A.
TI	Enhancing image contrast using coherent states and photon number resolving detectors
SO	OPTICS EXPRESS
AB	We experimentally map the transverse profile of diffraction-limited beams using photon-number-resolving detectors. We observe strong compression of diffracted beam profiles for high detected photon number. This effect leads to higher contrast than a conventional irradiance profile between two Airy disk-beams separated by the Rayleigh criterion. (C) 2010 Optical Society of America
TC	5
Z9	5
SN	1094-4087
PD	MAR 15
PY	2010
VL	18
IS	6
BP	6033
EP	6039
UT	WOS:000276002500073
ER

PT	J
AU	Anisimov, PM Raterman, GM Chiruvelli, A Plick, WN Huver, SD Lee, H Dowling, JP
AF	Anisimov, Petr M. Raterman, Gretchen M. Chiruvelli, Aravind Plick, William N. Huver, Sean D. Lee, Hwang Dowling, Jonathan P.
TI	Quantum Metrology with Two-Mode Squeezed Vacuum: Parity Detection Beats the Heisenberg Limit
SO	PHYSICAL REVIEW LETTERS
AB	We study the sensitivity and resolution of phase measurement in a Mach-Zehnder interferometer with two-mode squeezed vacuum ((n) over bar photons on average). We show that superresolution and sub-Heisenberg sensitivity is obtained with parity detection. In particular, in our setup, dependence of the signal on the phase evolves (n) over bar times faster than in traditional schemes, and uncertainty in the phase estimation is better than 1/(n) over bar, and we saturate the quantum Cramer-Rao bound.
TC	33
Z9	33
SN	0031-9007
PD	MAR 12
PY	2010
VL	104
IS	10
AR	103602
DI	10.1103/PhysRevLett.104.103602
UT	WOS:000275543500020
ER

Lee, TW
Huver, SD
Lee, H
Kaplan, L
McCracken, SB
Min, CJ
Uskov, DB
Wildfeuer, CF
Veronis, G
Dowling, JP

Lee, Tae-Woo
Huver, Sean D.
Lee, Hwang
Kaplan, Lev
McCracken, Steven B.
Min, Changjun
Uskov, Dmitry B.
Wildfeuer, Christoph F.
Veronis, Georgios
Dowling, Jonathan P.

Optimization of quantum interferometric metrological sensors in the presence of photon loss

PHYSICAL REVIEW A

We optimize two-mode entangled number states of light in the presence of loss in order to maximize the extraction of the available phase information in an interferometer. Our approach optimizes over the entire available input Hilbert space with no constraints, other than fixed total initial photon number. We optimize to maximize the Fisher information, which is equivalent to minimizing the phase uncertainty. We find that in the limit of zero loss, the optimal state is the maximally path-entangled (so-called N00N) state, for small loss, the optimal state gradually deviates from the N00N state, and in the limit of large loss, the optimal state converges to a generalized two-mode coherent state, with a finite total number of photons. The results provide a general protocol for optimizing the performance of a quantum optical interferometer in the presence of photon loss, with applications to quantum imaging, metrology, sensing, and information processing.

min, changjun

E-6699-2011

1050-2947

DEC

2009

063803

10.1103/PhysRevA.80.063803

WOS:000273233800154

PT	J
AU	Plick, WN Wildfeuer, CF Anisimov, PM Dowling, JP
AF	Plick, William N. Wildfeuer, Christoph F. Anisimov, Petr M. Dowling, Jonathan P.
TI	Optimizing the multiphoton absorption properties of maximally path-entangled number states
SO	PHYSICAL REVIEW A
AB	In this paper we examine the N-photon absorption properties of maximally path-entangled number states (N00N states). We consider two cases. The first involves the N-photon absorption properties of the ideal N00N state, one that does not include spectral information. We study how the N-photon absorption probability of this state scales with N, confirming results presented by others in a previous paper by a different method. We compare this to the absorption probability of various other states. The second case is that of two-photon absorption for an N=2 N00N state generated from a type-II spontaneous down-conversion event. In this situation we find that the absorption probability is both better than analogous coherent light (due to frequency entanglement) and highly dependent on the optical setup. We show that the poor production rates of quantum states of light may be partially mitigated by adjusting the spectral parameters to improve their two-photon absorption rates. This work has application to quantum imaging, particularly quantum lithography, where the N- photon absorbing process in the lithographic resist must be optimized for practical applications.
TC	3
Z9	3
SN	1050-2947
PD	DEC
PY	2009
VL	80
IS	6
AR	063825
DI	10.1103/PhysRevA.80.063825
UT	WOS:000273233800176
ER

Cable, H
Vyas, R
Singh, S
Dowling, JP

Cable, Hugo
Vyas, Reeta
Singh, Surendra
Dowling, Jonathan P.

An optical parametric oscillator as a high-flux source of two-mode light for quantum lithography

NEW JOURNAL OF PHYSICS

We investigate the use of an optical parametric oscillator (OPO), which can generate relatively high-flux light with strong non-classical features, as a source for quantum lithography. This builds on the proposal of Boto et al (2000 Phys. Rev. Lett. 85 2733), for etching simple patterns on multi-photon absorbing materials with sub-Rayleigh resolution, using two-mode entangled states of light. We consider an OPO with two down-converted modes that share the same frequency but differ in field polarization or direction of propagation, and derive analytical expressions for the multi-photon absorption rates when the OPO is operated below, near and above its threshold. Because of strong non-classical correlations between the two modes of the OPO, the interference patterns resulting from the superposition of the two modes are characterized by an effective wavelength that is half of their actual wavelength. The interference patterns resulting when the two modes of the OPO are used for etching are also characterized by an effective wavelength half that for the illuminating modes. We compare our results with those for the case of a high-gain optical amplifier source and discuss the relative merit of the OPO.

Cable, Hugo

C-2346-2011

1367-2630

NOV 30

2009

113055

10.1088/1367-2630/11/11/113055

WOS:000272153400006

PT	J
AU	Wildfeuer, CF Pearlman, AJ Chen, J Fan, JY Migdall, A Dowling, JP
AF	Wildfeuer, Christoph F. Pearlman, Aaron J. Chen, Jun Fan, Jingyun Migdall, Alan Dowling, Jonathan P.
TI	Resolution and sensitivity of a Fabry-Perot interferometer with a photon-number-resolving detector
SO	PHYSICAL REVIEW A
AB	With photon-number resolving detectors, we show compression of interference fringes with increasing photon numbers for a Fabry-Perot interferometer. This feature provides a higher precision in determining the position of the interference maxima compared to a classical detection strategy. We also theoretically show supersensitivity if N-photon states are sent into the interferometer and a photon-number resolving measurement is performed.
TC	13
Z9	13
SN	1050-2947
PD	OCT
PY	2009
VL	80
IS	4
AR	043822
DI	10.1103/PhysRevA.80.043822
UT	WOS:000271351000178
ER

PT	J
AU	Wilde, MM
AF	Wilde, Mark M.
TI	Can classical noise enhance quantum transmission?
SO	JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
AB	A modified quantum teleportation protocol broadens the scope of the classical forbidden-interval theorems for stochastic resonance. The fidelity measures performance of quantum communication. The sender encodes the two classical bits for quantum teleportation as weak bipolar subthreshold signals and sends them over a noisy classical channel. Two forbidden-interval theorems provide a necessary and sufficient condition for the occurrence of the nonmonotone stochastic resonance effect in the fidelity of quantum teleportation. The condition is that the noise mean must fall outside a forbidden interval related to the detection threshold and signal value. An optimal amount of classical noise benefits quantum communication when the sender transmits weak signals, the receiver detects with a high threshold and the noise mean lies outside the forbidden interval. Theorems and simulations demonstrate that both finite-variance and infinite-variance noise benefit the fidelity of quantum teleportation.
TC	1
Z9	1
SN	1751-8113
PD	AUG 14
PY	2009
VL	42
IS	32
AR	325301
DI	10.1088/1751-8113/42/32/325301
UT	WOS:000268342600013
ER

Jacobs, K
Landahl, AJ

Jacobs, Kurt
Landahl, Andrew J.

Engineering Giant Nonlinearities in Quantum Nanosystems

PHYSICAL REVIEW LETTERS

We describe a method to engineer giant nonlinearities in, and probes to measure nonlinear observables of, mesoscopic quantum resonators. This involves tailoring the Hamiltonian of a simple auxiliary system perturbatively coupled to the resonator, and has the potential to engineer a wide range of nonlinearities to high accuracy. We give a number of explicit examples, including a readily realizable two-qubit auxiliary system that creates an x(4) potential and a chi((3)) (Kerr) nonlinearity, valid to fifth order in the perturbative coupling.

Jacobs, Kurt

E-7049-2011

0031-9007

AUG 7

2009

103

067201

10.1103/PhysRevLett.103.067201

WOS:000268809300065

PT	J
AU	Uskov, DB Kaplan, L Smith, AM Huver, SD Dowling, JP
AF	Uskov, Dmitry B. Kaplan, Lev Smith, A. Matthew Huver, Sean D. Dowling, Jonathan P.
TI	Maximal success probabilities of linear-optical quantum gates
SO	PHYSICAL REVIEW A
AB	Numerical optimization is used to design linear-optical devices that implement a desired quantum gate with perfect fidelity, while maximizing the success rate. For the two-qubit controlled-sign [or controlled NOT (CNOT)] gate, we provide numerical evidence that the maximum success rate is S=2/27 using two unentangled ancilla resources; interestingly, additional ancilla resources do not increase the success rate. For the three-qubit Toffoli gate, we show that perfect fidelity is obtained with only three unentangled ancilla photons-less than in any existing scheme-with a maximum S=0.003 40. This compares well to S=(2/27)(2)/2 approximate to 0.002 74, obtainable by combining two CNOT gates and a passive quantum filter [T. C. Ralph, K. J. Resch, and A. Gilchrist, Phys. Rev. A 75, 022313 (2007)]. The general optimization approach can easily be applied to other areas of interest, such as quantum error correction, cryptography, and metrology [M. M. Wilde and D. B. Uskov, Phys. Rev. A 79, 022305 (2009); G. A. Durkin and J. P. Dowling, Phys. Rev. Lett. 99, 070801 (2007)].
TC	13
Z9	13
SN	1050-2947
PD	APR
PY	2009
VL	79
IS	4
AR	042326
DI	10.1103/PhysRevA.79.042326
UT	WOS:000265946900058
ER

Jacobs, K
Tian, L
Finn, J

Jacobs, Kurt
Tian, Lin
Finn, Justin

Engineering Superposition States and Tailored Probes for Nanoresonators via Open-Loop Control

PHYSICAL REVIEW LETTERS

We show that a nanoresonator can be prepared in mesoscopic superposition states merely by monitoring a qubit coupled to the square of the resonator's position. This works for thermal initial states, and does not require a third-order nonlinearity. The required coupling can be generated using a simple open-loop control protocol, obtained with optimal control theory. We simulate the complete preparation process, including environmental noise. Our results indicate the power of open-loop control for state engineering and measurement in quantum nanosystems.

Jacobs, Kurt

E-7049-2011

0031-9007

FEB 6

2009

102

057208

10.1103/PhysRevLett.102.057208

WOS:000263166400061

PT	J
AU	Wilde, MM Uskov, DB
AF	Wilde, Mark M. Uskov, Dmitry B.
TI	Linear-optical hyperentanglement-assisted quantum error-correcting code
SO	PHYSICAL REVIEW A
AB	We propose a linear-optical implementation of a hyperentanglement-assisted quantum error-correcting code. The code is hyperentanglement assisted because the shared entanglement resource is a photonic state hyperentangled in polarization and orbital angular momentum. It is possible to encode, decode, and diagnose channel errors using linear-optical techniques. The code corrects for polarization "flip" errors and is thus suitable only for a proof-of-principle experiment. The encoding and decoding circuits use a Knill-Laflamme-Milburn-like scheme for transforming polarization and orbital angular momentum photonic qubits. A numerical optimization algorithm finds a unit-fidelity encoding circuit that requires only three ancilla modes and has success probability equal to 0.0097.
TC	9
Z9	9
SN	1050-2947
PD	FEB
PY	2009
VL	79
IS	2
AR	022305
DI	10.1103/PhysRevA.79.022305
UT	WOS:000263815000050
ER

PT	J
AU	Huver, SD Wildfeuer, CF Dowling, JP
AF	Huver, Sean D. Wildfeuer, Christoph F. Dowling, Jonathan P.
TI	Entangled Fock states for robust quantum optical metrology, imaging, and sensing
SO	PHYSICAL REVIEW A
AB	We propose a class of path-entangled photon Fock states for robust quantum optical metrology, imaging, and sensing in the presence of loss. We model propagation loss with beam splitters and derive a reduced density-matrix formalism from which we examine how photon loss affects coherence. It is shown that particular entangled number states, which contain a special superposition of photons in both arms of a Mach-Zehnder interferometer, are resilient to environmental decoherence. We demonstrate an order of magnitude greater visibility with loss than possible with path-entangled parallel to N,0 >+parallel to 0,N > states. We also show that the effectiveness of a detection scheme is related to super-resolution visibility.
TC	45
Z9	45
SN	1050-2947
PD	DEC
PY	2008
VL	78
IS	6
AR	063828
DI	10.1103/PhysRevA.78.063828
UT	WOS:000262243500078
ER

PT	J
AU	Wildfeuer, CF Dowling, JP
AF	Wildfeuer, Christoph F. Dowling, Jonathan P.
TI	Strong violations of Bell-type inequalities for Werner-like states
SO	PHYSICAL REVIEW A
AB	We investigate the violation of Bell-type inequalities for two-qubit Werner-like states parametrized by the positive parameter 0 <= p <= 1. We use an unbalanced homodyne detection scheme to obtain the quantum mechanical probabilities. A violation of the Bell-Wigner and Janssens inequalities is obtained for a large range of the parameter p. The range given by these inequalities is greater than the one given by the Clauser-Horne inequality. The range in which a violation is attained actually coincides with the range where the Werner-like states are known to be nonseparable, i.e., for p > 1/3. However, the improvement over the Clauser-Horne inequality is achieved at the price of restricting the class of possible local hidden variable theories.
TC	2
Z9	2
SN	1050-2947
PD	SEP
PY	2008
VL	78
IS	3
AR	032113
DI	10.1103/PhysRevA.78.032113
UT	WOS:000259689400025
ER

PT	J
AU	Han, MX Olson, SJ Dowling, JP
AF	Han, Muxin Olson, S. Jay Dowling, Jonathan P.
TI	Generating entangled photons from the vacuum by accelerated measurements: Quantum-information theory and the Unruh-Davies effect
SO	PHYSICAL REVIEW A
AB	Building on the well-known Unruh-Davies effect, we examine the effects of projective measurements and quantum communications between accelerated and stationary observers. We find that the projective measurement by a uniformly accelerated observer can excite real particles from the vacuum in the inertial frame, even if no additional particles are created by the measurement process in the accelerating frame. Furthermore, we show that the particles created by this accelerating measurement can be highly entangled in the inertial frame, and it is also possible to use this process to generate even maximally entangled two-qubit states by a certain arrangement of measurements. As a by-product of our analysis, we also show that a single qubit of information can be perfectly transmitted from the accelerating observer to the inertial one. In principle, such an effect could be exploited in designing an entangled-state generator for quantum communication.
TC	6
Z9	6
SN	1050-2947
PD	AUG
PY	2008
VL	78
IS	2
AR	022302
DI	10.1103/PhysRevA.78.022302
PN	Part a
UT	WOS:000259263400038
ER

Glasser, RT
Cable, H
Dowling, JP
De Martini, F
Sciarrino, F
Vitelli, C

Glasser, Ryan T.
Cable, Hugo
Dowling, Jonathan P.
De Martini, Francesco
Sciarrino, Fabio
Vitelli, Chiara

Entanglement-seeded, dual, optical parametric amplification: Applications to quantum imaging and metrology

PHYSICAL REVIEW A

The study of optical parametric amplifiers (OPAs) has been successful in describing and creating nonclassical light for use in fields such as quantum metrology and quantum lithography [Agarwal , J. Opt. Soc. Am. B 24, 2 (2007)]. In this paper we present the theory of an OPA scheme utilizing an entangled state input. The scheme involves two identical OPAs seeded with the maximally path-entangled vertical bar N00N > state (vertical bar 2,0 >+vertical bar 0,2 >)/root 2. The stimulated amplification results in output state probability amplitudes that have a dependence on the number of photons in each mode, which differs greatly from two-mode squeezed vacuum. A large family of entangled output states are found. Specific output states allow for the heralded creation of N=4 N00N states, which may be used for quantum lithography, to write sub-Rayleigh fringe patterns, and for quantum interferometry, to achieve Heisenberg-limited phase measurement sensitivity.

Cable, Hugo

C-2346-2011

1050-2947

JUL

2008

012339

10.1103/PhysRevA.78.012339

WOS:000258180300084

PT	J
AU	Thanvanthri, S Kapale, KT Dowling, JP
AF	Thanvanthri, Sulakshana Kapale, Kishore T. Dowling, Jonathan P.
TI	Arbitrary coherent superpositions of quantized vortices in Bose-Einstein condensates via orbital angular momentum of light
SO	PHYSICAL REVIEW A
AB	We recently proposed a scheme for the creation of coherent superpositions of vortex states in Bose-Einstein condensates (BECs) using orbital angular momentum (OAM) states of light [Phys. Rev. Lett. 95, 173601 (200.5)], Here we discuss further technical details of the proposal, provide an alternative, time-reversal-symmetric scheme for transfer of a superposition of OAM states of light to the BEC via a procedure analogous to the traditional stimulated Raman adiabatic passage technique, and discuss an alternative trap configuration conducive for sustaining large charge vortices. Superpositions of OAM states of light, that can be created using the existing experimental techniques, can be transferred to an initially nonrotating BEC via a specially devised Raman coupling scheme. The techniques proposed here open up avenues to study coherent interaction of OAM states of light with matter. The study could also be employed for performing various quantum-information-processing tasks with OAM states of light-including a memory for a quantum state of the initial superposition.
TC	15
Z9	15
SN	1050-2947
PD	MAY
PY	2008
VL	77
IS	5
AR	053825
DI	10.1103/PhysRevA.77.053825
PN	Part b
UT	WOS:000257024100060
ER

Combes, J
Wiseman, HM
Jacobs, K

Combes, Joshua
Wiseman, Howard M.
Jacobs, Kurt

Rapid measurement of quantum systems using feedback control

PHYSICAL REVIEW LETTERS

We introduce a feedback control algorithm that increases the speed at which a measurement extracts information about a d-dimensional system by a factor that scales as d(2). Generalizing this algorithm, we apply it to a register of n qubits and show an improvement of O(n). We derive analytical bounds on the benefit provided by the feedback and perform simulations that confirm that this speedup is achieved.

Combes, Joshua	D-3790-2009
Wiseman, Howard	A-7266-2008
Jacobs, Kurt	E-7049-2011

0031-9007

APR 25

2008

100

160503

10.1103/PhysRevLett.100.160503

WOS:000255457600009

Jacobs, K
Jordan, AN
Irish, EK

Jacobs, K.
Jordan, A. N.
Irish, E. K.

Energy measurements and preparation of canonical phase states of a nano-mechanical resonator

EPL

We show that a continuous quantum non-demolition measurement of the energy of a nanomechanical resonator can be achieved by monitoring the resonator with a single-electron transistor, or a quantum point contact, via a Cooper-pair box. This technique can further be used to prepare highly entangled states of two resonators, such as canonical phase reference states, and so-called noon states. Copyright (c) EPLA, 2008.

Jordan, Andrew	E-4558-2011
Jacobs, Kurt	E-7049-2011

0295-5075

APR

2008

18003

10.1209/029-5075/82/18003

WOS:000255369300029

Wilde, MM
Brun, TA
Dowling, JP
Lee, H

Wilde, Mark M.
Brun, Todd A.
Dowling, Jonathan P.
Lee, Hwang

Coherent communication with linear optics

PHYSICAL REVIEW A

We show how to implement several continuous-variable coherent protocols with linear optics. Noise can accumulate when implementing each coherent protocol with realistic optical devices. Our analysis bounds the level of noise accumulation. We highlight the connection between a coherent channel and a nonlocal quantum nondemolition interaction and give two new protocols that implement a coherent channel. One protocol is superior to a previous method for a nonlocal quantum nondemolition interaction because it requires fewer communication resources. We then show how continuous-variable coherent superdense coding implements two nonlocal quantum nondemolition interactions with a quantum channel and bipartite entanglement. We finally show how to implement continuous-variable coherent teleportation experimentally and provide a way to verify the correctness of its operation.

Brun, Todd

C-3943-2008

1050-2947

FEB

2008

022321

10.1103/PhysRevA.77.022321

WOS:000253763900048

PT	J
AU	Dowling, JP
AF	Dowling, Jonathan P.
TI	Quantum optical metrology - the lowdown on high-N00N states
SO	CONTEMPORARY PHYSICS
AB	Quantum states of light, such as squeezed states or entangled states, can be used to make measurements (metrology), produce images, and sense objects with a precision that far exceeds what is possible classically, and also exceeds what was once thought to be possible quantum mechanically. The primary idea is to exploit quantum effects to beat the shot-noise limit in metrology and the Rayleigh diffraction limit in imaging and sensing. Quantum optical metrology has received a boost in recent years with an influx of ideas from the rapidly evolving field of optical quantum information processing. Both areas of research exploit the creation and manipulation of quantum-entangled states of light. We will review some of the recent theoretical and experimental advances in this exciting new field of quantum optical metrology, focusing on examples that exploit a particular two-mode entangled photon state-the High-N00N state.
TC	89
Z9	89
SN	0010-7514
PY	2008
VL	49
IS	2
BP	125
EP	143
DI	10.1080/00107510802091298
UT	WOS:000257343400003
ER

PT	J
AU	Gao, Y Lee, H
AF	Gao, Yang Lee, Hwang
TI	Sub-shot-noise quantum optical interferometry: a comparison of entangled state performance within a unified measurement scheme
SO	JOURNAL OF MODERN OPTICS
CT	38th Winter Colloquium on the Physics of Quantum Electronics
CY	JAN 06-FEB 10, 2008
CL	Snowbird, UT
AB	Phase measurement using a lossless Mach-Zehnder interferometer with certain entangled N-photon states can lead to a phase sensitivity of the order of 1/N, the Heisenberg limit. However, previously considered output measurement schemes are different for different input states to achieve this limit. We show that it is possible to achieve this limit just by the parity measurement for all the commonly proposed entangled states. Based on the parity measurement scheme, the reductions of the phase sensitivity in the presence of photon loss are examined for the various input states.
TC	6
Z9	6
SN	0950-0340
PY	2008
VL	55
IS	19-20
BP	3319
EP	3327
DI	10.1080/09500340802428298
UT	WOS:000261803300022
ER

Chiruvelli, A
Jacobs, K

Chiruvelli, Aravind
Jacobs, Kurt

Rapid-purification protocols for optical homodyning

PHYSICAL REVIEW A

We present a number of rapid-purification feedback protocols for optical homodyne detection of a single optical qubit. We derive first a protocol that speeds up the rate of increase of the average purity of the system, and find that as in the equivalent protocol for a nondissipative measurement, this generates a deterministic evolution for the purity in the limit of strong feedback. We also consider two analogs of the Wiseman-Ralph rapid-purification protocol in this setting, and show that as in that protocol they speed up the average time taken to reach a fixed level of purity. We also examine how the performance of these algorithms changes with detection efficiency, being an important practical consideration.

Jacobs, Kurt

E-7049-2011

1050-2947

JAN

2008

012102

10.1103/PhysRevA.77.012102

WOS:000252862000017

Sciarrino, F
Vitelli, C
De Martini, F
Glasser, R
Cable, H
Dowling, JP

Sciarrino, Fabio
Vitelli, Chiara
De Martini, Francesco
Glasser, Ryan
Cable, Hugo
Dowling, Jonathan P.

Experimental sub-Rayleigh resolution by an unseeded high-gain optical parametric amplifier for quantum lithography

PHYSICAL REVIEW A

Quantum lithography proposes to adopt entangled quantum states in order to increase resolution in interferometry. In the present paper we experimentally demonstrate that the output of a high-gain optical parametric amplifier can be intense yet exhibits quantum features, namely, sub-Rayleigh fringes, as proposed by [Agarwal , Phys. Rev. Lett. 86, 1389 (2001)]. We investigate multiphoton states generated by a high-gain optical parametric amplifier operating with a quantum vacuum input for gain values up to 2.5. The visibility has then been increased by means of three-photon absorption. The present paper opens interesting perspectives for the implementation of such an advanced interferometrical setup.

Cable, Hugo

C-2346-2011

1050-2947

JAN

2008

012324

10.1103/PhysRevA.77.012324

WOS:000252862000056

VanMeter, NM
Lougovski, P
Uskov, DB
Kieling, K
Eisert, J
Dowling, JP

VanMeter, N. M.
Lougovski, P.
Uskov, D. B.
Kieling, K.
Eisert, J.
Dowling, Jonathan P.

General linear-optical quantum state generation scheme: Applications to maximally path-entangled states

PHYSICAL REVIEW A

We introduce schemes for linear-optical quantum state generation. A quantum state generator is a device that prepares a desired quantum state using product inputs from photon sources, linear-optical networks, and postselection using photon counters. We show that this device can be concisely described in terms of polynomial equations and unitary constraints. We illustrate the power of this language by applying the Grobner-basis technique along with the notion of vacuum extensions to solve the problem of how to construct a quantum state generator analytically for any desired state, and use methods of convex optimization to identify bounds to success probabilities. In particular, we disprove a conjecture concerning the preparation of the maximally path-entangled vertical bar n,0 >+vertical bar 0,n > (NOON) state by providing a counterexample using these methods, and we derive a new upper bound on the resources required for NOON-state generation.

Quantum, CQD at IMS

D-2115-2010

1050-2947

DEC

2007

063808

10.1103/PhysRevA.76.063808

WOS:000251985900108

Jacobs, K
Lougovski, P

Jacobs, Kurt
Lougovski, Pavel

Emergent quantum jumps in a nano-electro-mechanical system

JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL

We describe a nano-electro-mechanical system that exhibits the 'retroactive' quantum jumps discovered by Mabuchi and Wiseman ( 1998 Phys. Rev. Lett. 81 4620). This system consists of a Cooper-pair box coupled to a nano-mechanical resonator, in which the latter is continuously monitored by a single-electron transistor or quantum point contact. Further, we show that these kinds of jumps, and the jumps that emerge in a continuous quantum non-demolition measurement, are one and the same phenomena. We also consider manipulating the jumps by applying feedback control to the Cooper-pair box.

Jacobs, Kurt

E-7049-2011

1751-8113

NOV 16

2007

F987

F993

10.1088/1751-8113/40/46/F02

WOS:000250687700002

PT	J
AU	Dowling, JP
AF	Dowling, Jonathan P.
TI	Quantum optics - Kittens catch phase
SO	NATURE
TC	2
Z9	2
SN	0028-0836
PD	NOV 15
PY	2007
VL	450
IS	7168
BP	362
EP	363
DI	10.1038/450362b
UT	WOS:000250918600036
ER

Wildfeuer, CF
Lund, AP
Dowling, JP

Wildfeuer, Christoph F.
Lund, Austin P.
Dowling, Jonathan P.

Strong violations of Bell-type inequalities for path-entangled number states

PHYSICAL REVIEW A

We show that nonlocal correlation experiments on the two spatially separated modes of a maximally path-entangled number state may be performed. They lead to a violation of a Clauser-Horne Bell inequality for any finite photon number N. We also present an analytical expression for the two-mode Wigner function of a maximally path-entangled number state and investigate a Clauser-Horne-Shimony-Holt Bell inequality for such a state. We test other Bell-type inequalities. Some are violated by a constant amount for any N.

Lund, Austin

A-3623-2011

1050-2947

NOV

2007

052101

10.1103/PhysRevA.76.052101

WOS:000251326400013

Cable, H
Dowling, JP

Cable, Hugo
Dowling, Jonathan P.

Efficient generation of large number-path entanglement using only linear optics and feed-forward

PHYSICAL REVIEW LETTERS

We show how an idealized measurement procedure can condense photons from two modes into one and how, by feeding forward the results of the measurement, it is possible to generate efficiently superposition states commonly called N00N states. For the basic procedure sources of number states leak onto a beam splitter, and the output ports are monitored by photodetectors. We find that detecting a fixed fraction of the input at one output port suffices to direct the remainder to the same port, with high probability, however large the initial state. When instead photons are detected at both ports, macroscopic quantum superposition states are produced. We describe a linear-optical circuit for making the components of such a state orthogonal, and another to convert the output to a N00N state. Our approach scales exponentially better than existing proposals. Important applications include quantum imaging and metrology.

Cable, Hugo

C-2346-2011

0031-9007

OCT 19

2007

163604

10.1103/PhysRevLett.99.163604

WOS:000250296000030

Florescu, M
Lee, H
Puscasu, I
Pralle, M
Florescu, L
Ting, DZ
Dowling, JP

Florescu, Marian
Lee, Hwang
Puscasu, Irina
Pralle, Martin
Florescu, Lucia
Ting, David Z.
Dowling, Jonathan P.

Improving solar cell efficiency using photonic band-gap materials

SOLAR ENERGY MATERIALS AND SOLAR CELLS

The potential of using photonic crystal structures for realizing highly efficient and reliable solar-cell devices is presented. We show that due their ability to modify the spectral and angular characteristics of thermal radiation, photonic crystals emerge as one of the leading candidates for frequency- and angular-selective radiating elements in thermophotovoltaic devices. We show that employing photonic crystal-based angle- and frequency-selective absorbers facilitates a strong enhancement of the conversion efficiency of solar cell devices without using concentrators. (c) 2007 Elsevier B.V. All rights reserved.

Florescu, Marian

E-9009-2010

0927-0248

OCT 15

2007

1599

1610

10.1016/j.solmat.2007.05.001

WOS:000249835800002

PT	J
AU	Han, MX Ma, YG Huang, WM
AF	Han, Muxin Ma, Yongge Huang, Weiming
TI	Fundamental structure of loop quantum gravity
SO	INTERNATIONAL JOURNAL OF MODERN PHYSICS D
AB	In the recent twenty years, loop quantum gravity, a background independent approach to unify general relativity and quantum mechanics, has been widely investigated. The aim of loop quantum gravity is to construct a mathematically rigorous, background independent, non-perturbative quantum theory for a Lorentzian gravitational field on a four-dimensional manifold. In the approach, the principles of quantum mechanics are combined with those of general relativity naturally. Such a combination provides us a picture of, so-called, quantum Riemannian geometry, which is discrete on the fundamental scale. Imposing the quantum constraints in analogy from the classical ones, the quantum dynamics of gravity is being studied as one of the most important issues in loop quantum gravity. On the other hand, the semi-classical analysis is being carried out to test the classical limit of the quantum theory. In this review, the fundamental structure of loop quantum gravity is presented pedagogically. Our main aim is to help non-experts to understand the motivations, basic structures, as well as general results. It may also be beneficial to practitioners to gain insights from different perspectives on the theory. We will focus on the theoretical framework itself, rather than its applications, and do our best to write it in modern and precise langauge while keeping the presentation accessible for beginners. After reviewing the classical connection dynamical formalism of general relativity, as a foundation, the construction of the kinematical Ashtekar-Isham-Lewandowski representation is introduced in the content of quantum kinematics. The algebraic structure of quantum kinematics is also discussed. In the content of quantum dynamics, we mainly introduce the construction of a Hamiltonian constraint operator and the master constraint project. At last, some applications and recent advances are outlined. It should be noted that this strategy of quantizing gravity can also be extended to obtain other background-independent quantum gauge theories. There is no divergence within this background-independent and diffeomorphism-invariant quantization program of matter coupled to gravity.
TC	40
Z9	42
SN	0218-2718
PD	SEP
PY	2007
VL	16
IS	9
BP	1397
EP	1474
DI	10.1142/S0218271807010894
UT	WOS:000252849400001
ER

Lougovski, P
Casagrande, F
Lulli, A
Solano, E

Lougovski, P.
Casagrande, F.
Lulli, A.
Solano, E.

Strongly driven one-atom laser and decoherence monitoring

PHYSICAL REVIEW A

We propose the implementation of a strongly driven one-atom laser, based on the off-resonant interaction of a three-level atom in Lambda configuration with a single cavity mode and three laser fields. We show that the system can be described equivalently by a two-level atom resonantly coupled to the cavity and driven by a strong effective coherent field. The effective dynamics can be solved exactly, including a thermal field bath, allowing an analytical description of field statistics and entanglement properties. We also show the possible generation of quantum superposition (Schrodinger cat) states for the whole atom-field system and for the field alone after atomic measurement. We propose a way to monitor the system decoherence by measuring atomic populations. Finally, we confirm the validity of our model through numerical solutions.

Solano, Enrique

C-1132-2013

1050-2947

SEP

2007

033802

10.1103/PhysRevA.76.033802

WOS:000249786000143

PT	J
AU	Durkin, GA Dowling, JP
AF	Durkin, Gabriel A. Dowling, Jonathan P.
TI	Local and global distinguishability in quantum interferometry
SO	PHYSICAL REVIEW LETTERS
AB	A statistical distinguishability based on relative entropy characterizes the fitness of quantum states for phase estimation. This criterion is employed in the context of a Mach-Zehnder interferometer and used to interpolate between two regimes of local and global phase distinguishability. The scaling of distinguishability in these regimes with photon number is explored for various quantum states. It emerges that local distinguishability is dependent on a discrepancy between quantum and classical rotational energy. Our analysis demonstrates that the Heisenberg limit is the true upper limit for local phase sensitivity. Only the "NOON" states share this bound, but other states exhibit a better trade-off when comparing local and global phase regimes.
TC	36
Z9	36
SN	0031-9007
PD	AUG 17
PY	2007
VL	99
IS	7
AR	070801
DI	10.1103/PhysRevLett.99.070801
UT	WOS:000248866900007
ER

PT	J
AU	Kapale, KT Dowling, JP
AF	Kapale, Kishore T. Dowling, Jonathan P.
TI	Bootstrapping approach for generating maximally path-entangled photon states
SO	PHYSICAL REVIEW LETTERS
AB	We propose a bootstrapping approach to the generation of maximally path-entangled states of photons, so-called "NOON states." The strong atom-light interaction of cavity QED can be employed to generate NOON states with about 100 photons. These can then be used to boost the existing experimental Kerr nonlinearities based on quantum coherence effects, to facilitate NOON generation with an arbitrarily large number of photons. We also offer an alternative scheme that uses an atom-cavity dispersive interaction to obtain a sufficiently high Kerr nonlinearity necessary for arbitrary NOON generation.
TC	24
Z9	24
SN	0031-9007
PD	AUG 3
PY	2007
VL	99
IS	5
AR	053602
DI	10.1103/PhysRevLett.99.053602
UT	WOS:000248597500019
ER

PT	J
AU	Wilde, MM Spedalieri, F Dowling, JP Lee, H
AF	Wilde, Mark M. Spedalieri, Federico Dowling, Jonathan P. Lee, Hwang
TI	Alternate scheme for optical cluster-state generation without number-resolving photon detectors
SO	INTERNATIONAL JOURNAL OF QUANTUM INFORMATION
AB	We design a controlled-phase gate for linear optical quantum computing by using photodetectors that cannot resolve photon number. An intrinsic error-correction circuit corrects errors introduced by the detectors. Our controlled-phase gate has a 1/4 success probability. Recent development in cluster-state quantum computing has shown that a two-qubit gate with non-zero success probability can build an arbitrarily large cluster state only with polynomial overhead. Hence, it is possible to generate optical cluster states without number-resolving detectors and with polynomial overhead.
TC	1
Z9	1
SN	0219-7499
PD	AUG
PY	2007
VL	5
IS	4
BP	617
EP	626
DI	10.1142/S0219749907003080
UT	WOS:000251175600012
ER

Jacobs, K
Lund, AP

Jacobs, Kurt
Lund, Austin P.

Feedback control of nonlinear quantum systems: A rule of thumb

PHYSICAL REVIEW LETTERS

We show that in the regime in which feedback control is most effective-when measurements are relatively efficient, and feedback is relatively strong-then, in the absence of any sharp inhomogeneity in the noise, it is always best to measure in a basis that does not commute with the system density matrix than one that does. That is, it is optimal to make measurements that disturb the state one is attempting to stabilize.

Lund, Austin	A-3623-2011
Jacobs, Kurt	E-7049-2011

0031-9007

JUL 13

2007

020501

10.1103/PhysRevLett.99.020501

WOS:000248021000006

PT	J
AU	Zink, B Stergioulas, N Hawke, I Ott, CD Schnetter, E Muller, E
AF	Zink, Burkhard Stergioulas, Nikolaos Hawke, Ian Ott, Christian D. Schnetter, Erik Mueller, Ewald
TI	Nonaxisymmetric instability and fragmentation of general relativistic quasitoroidal stars
SO	PHYSICAL REVIEW D
AB	In a recent publication, we have demonstrated that differentially rotating stars admit new channels of black hole formation via fragmentation instabilities. Since a higher order instability of this kind could potentially transform a differentially rotating supermassive star into a multiple black hole system embedded in a massive accretion disk, we investigate the dependence of the instability on parameters of the equilibrium model. We find that many of the models constructed exhibit nonaxisymmetric instabilities with corotation points, even for low values of T/\|W\|, which lead to a fission of the stars into one, two, or three fragments, depending on the initial perturbation. At least in the models selected here, an m=1 mode becomes unstable at lower values of T/\|W\|, which would seem to favor a scenario where one black hole with a massive accretion disk forms. In this case, we have gained evidence that low values of compactness of the initial model can lead to a stabilization of the resulting fragment, thus preventing black hole formation in this scenario.
TC	11
Z9	11
SN	1550-7998
PD	JUL
PY	2007
VL	76
IS	2
AR	024019
DI	10.1103/PhysRevD.76.024019
UT	WOS:000248545200045
ER

Shizume, K
Jacobs, K
Burgarth, D
Bose, S

Shizume, Kosuke
Jacobs, Kurt
Burgarth, Daniel
Bose, Sougato

Quantum communication via a continuously monitored dual spin chain

PHYSICAL REVIEW A

We analyze a recent protocol for the transmission of quantum states via a dual spin chain [Burgarth and Bose, Phys. Rev. A 71, 052315 (2005)] under the constraint that the receiver's measurement strength is finite. That is, we consider the channel where the ideal, instantaneous, and complete von Neumann measurements are replaced with a more realistic continuous measurement. We show that for optimal performance the measurement strength must be "tuned" to the channel spin-spin coupling, and once this is done, one is able to achieve a similar transmission rate to that obtained with ideal measurements. The spin chain protocol thus remains effective under measurement constraints.

Burgarth, Daniel	A-5965-2009
Jacobs, Kurt	E-7049-2011

1050-2947

JUN

2007

062328

10.1103/PhysRevA.75.062328

WOS:000247624300066

Jacobs, K
Lougovski, P
Blencowe, M

Jacobs, Kurt
Lougovski, Pavel
Blencowe, Miles

Continuous measurement of the energy eigenstates of a nanomechanical resonator without a nondemolition probe

PHYSICAL REVIEW LETTERS

We show that it is possible to perform a continuous measurement that continually projects a nanoresonator into its energy eigenstates by employing a linear coupling with a two-state system. This technique makes it possible to perform a measurement that exposes the quantum nature of the resonator by coupling it to a Cooper-pair box and a superconducting transmission line resonator.

Jacobs, Kurt

E-7049-2011

0031-9007

APR 6

2007

147201

10.1103/PhysRevLett.98.147201

WOS:000245512100058

Agarwal, GS
Chan, KW
Boyd, RW
Cable, H
Dowling, JP

Agarwal, Girish S.
Chan, Kam Wai
Boyd, Robert W.
Cable, Hugo
Dowling, Jonathan P.

Quantum states of light produced by a high-gain optical parametric amplifier for use in quantum lithography

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS

We present a theoretical analysis of the properties of an unseeded optical parametic amplifier (OPA) used as the source of entangled photons for applications in quantum lithography. We first study the dependence of the excitation rate of a two-photon absorber on the intensity of the light leaving the OPA. We find that the rate depends linearly on intensity only for output beams so weak that they contain fewer than one photon per mode. We also study the use of an N-photon absorber for arbitrary N as the recording medium to be used with such a light source. We find that the contrast of the interference pattern and the sharpness of the fringe maxima tend to increase with increasing values of N, but that the density of fringes and thus the limiting resolution does not increase with N. We conclude that the output of an unseeded OPA exciting an N-photon absorber provides an attractive system in which to perform quantum lithography. (c) 2007 Optical Society of America.

Cable, Hugo

C-2346-2011

0740-3224

FEB

2007

270

274

10.1364/JOSAB.24.000270

WOS:000244281200016

PT	J
AU	Kapale, KT
AF	Kapale, K. T.
TI	Polarization preserving quantum nondemolition photodetector
SO	JOURNAL OF MODERN OPTICS
AB	A polarization preserving quantum nondemolition photodetector is proposed based on nonlinearities obtainable through quantum coherence effects. An atomic level scheme is devised such that in the presence of strong linearly polarized drive field a coherent weak probe field acquires a phase proportional to the number of photons in the signal mode immaterial of its polarization state. It is also shown that the unavoidable phase-kicks resulting due to the measurement process are insensitive to the polarization state of the incoming signal photon. It is envisioned that such a device would have tremendous applicability in photonic quantum information proposals where quantum information in the polarization qubit is to be protected.
TC	1
Z9	1
SN	0950-0340
PD	JAN 20
PY	2007
VL	54
IS	2-3
BP	327
EP	335
DI	10.1080/09500340600753822
UT	WOS:000244387900013
ER

Kok, P
Munro, WJ
Nemoto, K
Ralph, TC
Dowling, JP
Milburn, GJ

Kok, Pieter
Munro, W. J.
Nemoto, Kae
Ralph, T. C.
Dowling, Jonathan P.
Milburn, G. J.

Linear optical quantum computing with photonic qubits

REVIEWS OF MODERN PHYSICS

Linear optics with photon counting is a prominent candidate for practical quantum computing. The protocol by Knill, Laflamme, and Milburn [2001, Nature (London) 409, 46] explicitly demonstrates that efficient scalable quantum computing with single photons, linear optical elements, and projective measurements is possible. Subsequently, several improvements on this protocol have started to bridge the gap between theoretical scalability and practical implementation. The original theory and its improvements are reviewed, and a few examples of experimental two-qubit gates are given. The use of realistic components, the errors they induce in the computation, and how these errors can be corrected is discussed.

MIlburn, Gerard	B-6381-2008
Kok, Pieter	B-1658-2010
Nemoto, Kae	A-8833-2011
Munro, William	A-8453-2011
Ralph, Timothy	A-1858-2011

453

465

0034-6861

JAN-MAR

2007

135

174

10.1103/RevModPhys.79.135

WOS:000244867600004

Jacobs, K
Dowling, JP

Jacobs, Kurt
Dowling, Jonathan P.

Concatenated beam splitters, optical feed-forward, and the nonlinear sign gate

PHYSICAL REVIEW A

We consider a nonlinear sign gate implemented using a sequence of two beam splitters, and consider the use of further sequences of beam splitters to implement feed-forward so as to correct an error resulting from the first beam splitter. We obtain similar results to Scheel [Phys. Rev. A 73, 034301 (2006)], in that we also find that our feed-forward procedure is only able to produce a very minor improvement in the success probability of the original gate.

Jacobs, Kurt

E-7049-2011

1050-2947

DEC

2006

064304

10.1103/PhysRevA.74.064304

WOS:000243166700175

PT	J
AU	Agarwal, GS Kapale, KT
AF	Agarwal, G. S. Kapale, K. T.
TI	Subwavelength atom localization via coherent population trapping
SO	JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
AB	We present an atom localization scheme based on coherent population trapping. We consider atomic transitions in a Lambda configuration where the control field is a standing-wave field. The probe field and the control field produce coherence between the two ground states and prepare the atom in a pure state. We show that the population in one of the ground states has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of this population would localize the atom. Interestingly enough the role of the cavity finesse is played by the ratio of the intensities of the pump and probe. This is in fact the reason for obtaining extreme subwavelength localization.
TC	53
Z9	53
SN	0953-4075
PD	SEP 14
PY	2006
VL	39
IS	17
BP	3437
EP	3446
DI	10.1088/0953-4075/39/17/002
UT	WOS:000240490700005
ER

Jacobs, K
Steck, DA

Jacobs, Kurt
Steck, Daniel A.

A straightforward introduction to continuous quantum measurement

CONTEMPORARY PHYSICS

We present a pedagogical treatment of the formalism of continuous quantum measurement. Our aim is to show the reader how the equations describing such measurements are derived and manipulated in a direct manner. We also give elementary background material for those new to measurement theory, and describe further various aspects of continuous measurements that should be helpful to those wanting to use such measurements in applications. Specifically, we use the simple and direct approach of generalized measurements to derive the stochastic master equation describing the continuous measurements of observables, give a tutorial on stochastic calculus, treat multiple observers and inefficient detection, examine a general form of the measurement master equation.. and show how the master equation leads to information gain and disturbance. To conclude, we give a detailed treatment of imaging the resonance fluorescence from a single atom as a concrete example of how a continuous position measurement arises in a physical system.

Jacobs, Kurt

E-7049-2011

0010-7514

SEP-OCT

2006

279

303

10.1080/00107510601101934

WOS:000243585400004

Steck, DA
Jacobs, K
Mabuchi, H
Habib, S
Bhattacharya, T

Steck, Daniel A.
Jacobs, Kurt
Mabuchi, Hideo
Habib, Salman
Bhattacharya, Tanmoy

Feedback cooling of atomic motion in cavity QED

PHYSICAL REVIEW A

We consider the problem of controlling the motion of an atom trapped in an optical cavity using continuous feedback. In order to realize such a scheme experimentally, one must be able to perform state estimation of the atomic motion in real time. While in theory this estimate may be provided by a stochastic master equation describing the full dynamics of the observed system, integrating this equation in real time is impractical. Here we derive an approximate estimation equation for this purpose, and use it as a drive in a feedback algorithm designed to cool the motion of the atom. We examine the effectiveness of such a procedure using full simulations of the cavity QED system, including the quantized motion of the atom in one dimension.

Jacobs, Kurt

E-7049-2011

1050-2947

JUL

2006

012322

10.1103/PhysRevA.74.012322

WOS:000239425900039

PT	J
AU	Han, MX Ma, YG
AF	Han, MX Ma, YG
TI	Master constraint operators in loop quantum gravity
SO	PHYSICS LETTERS B
AB	We introduce a master constraint operator (M) over cap densely defined in the diffeomorphism invariant Hilbert space in loop quantum gravity, which corresponds classically to the master constraint in the programme. It is shown that (M) over cap is positive and symmetric, and hence has its Friedrichs self-adjoint extension. The same conclusion is tenable for an alternative master operator (M) over cap', whose quadratic form coincides with the one proposed by Thiemann. So the master constraint programme for loop quantum gravity can be carried out in principle by employing either of the two operators. (c) 2006 Elsevier B.V. All rights reserved.
TC	17
Z9	18
SN	0370-2693
PD	APR 13
PY	2006
VL	635
IS	4
BP	225
EP	231
DI	10.1016/j.physletb.2006.03.004
UT	WOS:000236630600008
ER

PT	J
AU	Han, MX Ma, YG
AF	Han, MX Ma, YG
TI	Dynamics of a scalar field in a polymer-like representation
SO	CLASSICAL AND QUANTUM GRAVITY
AB	In the last 20 years, loop quantum gravity, a background- independent approach to unify general relativity and quantum mechanics, has been widely investigated. We consider the quantum dynamics of a real massless scalar field coupled to gravity in this framework. A Hamiltonian operator for the scalar field can be well defined in the coupled diffeomorphism-invariant Hilbert space, which is both self-adjoint and positive. On the other hand, the Hamiltonian constraint operator for the scalar field coupled to gravity can be well defined in the coupled kinematical Hilbert space. There are one-parameter ambiguities due to scalar field in the construction of both operators. The results heighten our confidence that there is no divergence within this background- independent and diffeomorphism-invariant quantization approach of matter coupled to gravity. Moreover, to avoid possible quantum anomaly, the master constraint programme can be carried out in this coupled system by employing a self-adjoint master constraint operator on the diffectmorphism-invariant Hilbert space.
TC	9
Z9	10
SN	0264-9381
PD	APR 7
PY	2006
VL	23
IS	7
BP	2741
EP	2760
DI	10.1088/0264-9381/2317/031
UT	WOS:000236932700031
ER

PT	J
AU	Guillaume, A Dowling, JP
AF	Guillaume, A Dowling, JP
TI	Heisenberg-limited measurements with superconducting circuits
SO	PHYSICAL REVIEW A
AB	We describe an assembly of N superconducting qubits contained in a single- mode cavity. In the dispersive regime, the correlation between the cavity field and each qubit results in an effective interaction between qubits that can be used to dynamically generate maximally entangled states. With only collective manipulations, we show how to create maximally entangled quantum states and how to use these states to reach the Heisenberg limit in the determination of the qubit bias control parameter (gate charge for charge qubits, external magnetic flux for rf-superconducting quantum interference devices).
TC	1
Z9	1
SN	1050-2947
PD	APR
PY	2006
VL	73
IS	4
AR	040304
DI	10.1103/PhysRevA.73.040304
UT	WOS:000237147700004
ER

PT	J
AU	Dowling, JP
AF	Dowling, JP
TI	Quantum information - To compute or not to compute?
SO	NATURE
TC	6
Z9	6
SN	0028-0836
PD	FEB 23
PY	2006
VL	439
IS	7079
BP	919
EP	920
DI	10.1038/439919a
UT	WOS:000235486100025
ER

PT	J
AU	Spedalieri, FM Lee, H Dowling, JP
AF	Spedalieri, FM Lee, H Dowling, JP
TI	High-fidelity linear optical quantum computing with polarization encoding
SO	PHYSICAL REVIEW A
AB	We show that the KLM scheme [Knill, Laflamme, and Milburn, Nature 409, 46 (2001)] can be implemented using polarization encoding, thus reducing the number of path modes required by half. One of the main advantages of this new implementation is that it naturally incorporates a loss detection mechanism that makes the probability of a gate introducing a non-detected error, when non-ideal detectors are considered, dependent only on the detector dark-count rate and independent of its efficiency. Since very low dark-count rate detectors are currently available, a high-fidelity gate (probability of error of order 10(-6) conditional on the gate being successful) can be implemented using polarization encoding. The detector efficiency determines the overall success probability of the gate but does not affect its fidelity. This can be applied to the efficient construction of optical cluster states with very high fidelity for quantum computing.
TC	14
Z9	14
SN	1050-2947
PD	JAN
PY	2006
VL	73
IS	1
AR	012334
DI	10.1103/PhysRevA.73.012334
UT	WOS:000235008900063
ER

PT	J
AU	Kapale, KT Dowling, JP
AF	Kapale, KT Dowling, JP
TI	Vortex phase qubit: Generating arbitrary, counterrotating, coherent superpositions in bose-einstein condensates via optical angular momentum beams
SO	PHYSICAL REVIEW LETTERS
AB	We propose a scheme for the generation of arbitrary coherent superpositions of vortex states in Bose-Einstein condensates (BEC) using the orbital-angular-momentum states of light. We devise a scheme to generate coherent superpositions of two such counterrotating states of light using well-known experimental techniques. We show that a specially designed Raman scheme allows for transfer of the optical vortex-superposition state onto an initially nonrotating BEC. This creates an arbitrary and coherent superposition of a vortex and antivortex pair in the BEC. The ideas presented here could be extended to generate entangled vortex states, design memories for the orbital-angular-momentum states of light, and perform other quantum information tasks. Applications to inertial sensing are also discussed.
TC	60
Z9	60
SN	0031-9007
PD	OCT 21
PY	2005
VL	95
IS	17
AR	173601
DI	10.1103/PhysRevLett.95.173601
UT	WOS:000232724400031
ER

Florescu, M
Lee, H
Stimpson, AJ
Dowling, J

Thermal emission and absorption of radiation in finite inverted-opal photonic crystals

PHYSICAL REVIEW A

We study theoretically the optical properties of a finite inverted-opal photonic crystal. The light-matter interaction is strongly affected by the presence of the three-dimensional photonic crystal and the alterations of the light emission and absorption processes can be used to suppress or enhance the thermal emissivity and absorptivity of the dielectric structure. We investigate the influence of the absorption present in the system on the relevant band edge frequencies that control the optical response of the photonic crystal. Our study reveals that the absorption processes cause spectral broadening and shifting of the band edge optical resonances, and determine a strong reduction of the photonic band gap spectral range. Using the angular and spectral dependence of the band edge frequencies for stop bands along different directions, we argue that by matching the blackbody emission spectrum peak with a prescribed maximum of the absorption coefficient, it is possible to achieve an angle-sensitive enhancement of the thermal emission/absorption of radiation. This result opens a way to realize a frequency-sensitive and angle-sensitive photonic crystal absorbers/emitters.

Florescu, Marian

E-9009-2010

1050-2947

SEP

2005

033821

10.1103/PhysRevA.72.033821

WOS:000232228300171

PT	J
AU	Sun, QQ Rostovtsev, YV Dowling, JP Scully, MO Zubairy, MS
AF	Sun, QQ Rostovtsev, YV Dowling, JP Scully, MO Zubairy, MS
TI	Optically controlled delays for broadband pulses
SO	PHYSICAL REVIEW A
AB	We propose a scheme that provides large controllable delays for broadband optical pulses. The system is based on the steep dispersion of a coherently driven medium, in which the narrow electromagnetically induced transparency (EIT) band is overcome by using spatial and temporal processing.
TC	45
Z9	46
SN	1050-2947
PD	SEP
PY	2005
VL	72
IS	3
AR	031802
DI	10.1103/PhysRevA.72.031802
UT	WOS:000232228300015
ER

Florescu, M
Scheel, S
Haffner, HH
Lee, H
Strekalov, D
Knight, PL
Dowling, JP

Single photons on demand from 3D photonic band-gap structures

EUROPHYSICS LETTERS

We describe a practical implementation of a (semi-deterministic) photon gun based on stimulated Raman adiabatic passage pumping and the strong enhancement of the photonic density of states in a photonic band-gap material. We show that this device allows deterministic and unidirectional production of single photons with a high repetition rate of the order of 100 kHz. We also discuss specific 3D photonic micro-structure architectures in which our model can be realized and the feasibility of implementing such a device using Er(3+) ions that produce single photons at the telecommunication wavelength of 1.55 mu m.

Florescu, Marian	E-9009-2010
Haeffner, Hartmut	D-8046-2012

0295-5075

MAR

2005

945

951

10.1209/epl/i2004-10453-5

WOS:000228445900014

PT	J
AU	Ghali, JK
AF	Ghali, JK
TI	Contemporary issues in heart failure
SO	AMERICAN HEART JOURNAL
TC	4
Z9	5
SN	0002-8703
PD	JUL
PY	1999
VL	138
IS	1
BP	5
EP	8
DI	10.1016/S0002-8703(99)70235-8
PN	Part 1
UT	WOS:000081395400003
ER