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Showing papers by "Jeffrey H. Shapiro published in 2007"


Journal ArticleDOI
TL;DR: In this article, a continuous-time multi-mode model for the input/output fields to/from the nonlinear medium was proposed, in which the full temporal content of the free-field input beams as well as the non-instantaneous response of the medium were taken into account.
Abstract: The weak nonlinear Kerr interaction between single photons and intense laser fields has been recently proposed as a basis for distributed optics-based solutions to few-qubit applications in quantum communication and computation. Here, we analyse the above Kerr interaction by employing a continuous-time multi-mode model for the input/output fields to/from the nonlinear medium. In contrast to previous single-mode treatments of this problem, our analysis takes into account the full temporal content of the free-field input beams as well as the non-instantaneous response of the medium. The main implication of this model, in which the cross-Kerr phase shift on one input is proportional to the photon flux of the other input, is the existence of phase noise terms at the output. We show that these phase noise terms will preclude satisfactory performance of the parity gate proposed by Munro et al (2005 New J. Phys. 7 137).

154 citations


Journal ArticleDOI
TL;DR: A minimum output entropy conjecture is proposed that, if proved to be correct, will establish that the capacity region of the bosonic broadcast channel equals the inner bound achieved using a coherent-state encoding and optimum detection.
Abstract: Previous work on the classical information capacities of bosonic channels has established the capacity of the single-user pure-loss channel, bounded the capacity of the single-user thermal-noise channel, and bounded the capacity region of the multiple-access channel. The latter is a multiple-user scenario in which several transmitters seek to simultaneously and independently communicate to a single receiver. We study the capacity region of the bosonic broadcast channel, in which a single transmitter seeks to simultaneously and independently communicate to two different receivers. It is known that the tightest available lower bound on the capacity of the single-user thermal-noise channel is that channel's capacity if, as conjectured, the minimum von Neumann entropy at the output of a bosonic channel with additive thermal noise occurs for coherent-state inputs. Evidence in support of this minimum output entropy conjecture has been accumulated, but a rigorous proof has not been obtained. We propose a minimum output entropy conjecture that, if proved to be correct, will establish that the capacity region of the bosonic broadcast channel equals the inner bound achieved using a coherent-state encoding and optimum detection. We provide some evidence that supports this conjecture, but again a full proof is not available.

96 citations


Journal ArticleDOI
TL;DR: This on-demand source of single photons on demand by means of a modular array of spontaneous parametric downconverters that are mediated by electro-optic polarization controls may significantly improve the performance of quantum key distribution, quantum communication, and quantum computation systems.
Abstract: We describe a method for generating single photons on demand by means of a modular array of spontaneous parametric downconverters that are mediated by electro-optic polarization controls. Our scheme allows easy addition of downconverter modules to improve single-photon generation performance while simultaneously further suppressing multiphoton events. We estimate that a single-photon generation probability of over 60% per pulse with a multiphoton probability of 1% is achievable with currently available technology. This on-demand source may significantly improve the performance of quantum key distribution, quantum communication, and quantum computation systems.

66 citations


Journal ArticleDOI
TL;DR: The most powerful individual-photon attack against the Bennett-Brassard 1984 quantum key distribution protocol is implemented, in good agreement with theoretical predictions for the eavesdropper¿s Rényi information.
Abstract: We have used deterministic single-photon two qubit (SPTQ) quantum logic to implement the most powerful individual-photon attack against the Bennett-Brassard 1984 (BB84) quantum key distribution protocol. Our measurement results, including physical source and gate errors, are in good agreement with theoretical predictions for the Renyi information obtained by Eve as a function of the errors she imparts to Alice and Bob's sifted key bits. The current experiment is a physical simulation of a true attack, because Eve has access to Bob's physical receiver module. This experiment illustrates the utility of an efficient deterministic quantum logic for performing realistic physical simulations of quantum information processing functions.

26 citations


Posted Content
TL;DR: It is shown that the preceding minimum output entropy conjectures are simple consequences of an entropy photon-number inequality, which is a conjectured quantum-mechanical analog of the entropy power inequality from classical information theory.
Abstract: Determining the ultimate classical information carrying capacity of electromagnetic waves requires quantum-mechanical analysis to properly account for the bosonic nature of these waves. Recent work has established capacity theorems for bosonic single-user, broadcast, and wiretap channels, under the presumption of two minimum output entropy conjectures. Despite considerable accumulated evidence that supports the validity of these conjectures, they have yet to be proven. Here we show that the preceding minimum output entropy conjectures are simple consequences of an Entropy Photon-Number Inequality, which is a conjectured quantum-mechanical analog of the Entropy Power Inequality (EPI) from classical information theory.

23 citations


Journal ArticleDOI
TL;DR: In this paper, an off-resonant nonadiabatic approach to loading trapped-atom memories is proposed, and the ensuing trade-offs between the atom-light coupling rate and input photon bandwidth for achieving a high loading probability are identified.
Abstract: Entanglement distribution between trapped-atom quantum memories, viz. single atoms in optical cavities, is addressed. In most scenarios, the rate of entanglement distribution depends on the efficiency with which the state of traveling single photons can be transferred to trapped atoms. This loading efficiency is analytically studied for two-level, V-level, {lambda}-level, and double-{lambda}-level atomic configurations by means of a system-reservoir approach. An off-resonant nonadiabatic approach to loading {lambda}-level trapped-atom memories is proposed, and the ensuing trade-offs between the atom-light coupling rate and input photon bandwidth for achieving a high loading probability are identified. The nonadiabatic approach allows a broad class of optical sources to be used, and in some cases it provides a higher system throughput than what can be achieved by adiabatic loading mechanisms. The analysis is extended to the case of two double-{lambda} trapped-atom memories illuminated by a polarization-entangled biphoton.

14 citations


Proceedings ArticleDOI
07 Jun 2007
TL;DR: This work considers a laser radar system in which a series of N-photon entangled-state pulses are prepared with only one photon from each pulse being used to interrogate the target while the others are detected within the radar itself.
Abstract: High time-bandwidth product waveforms have long been used in radar systems to achieve high-resolution ranging at high signal-to-noise ratio under a peak power constraint on the radar transmitter. We consider a laser radar system in which a series of N-photon entangled-state pulses are prepared with only one photon from each pulse being used to interrogate the target while the others are detected within the radar itself. This send-one-detectall protocol (SODAP) achieves high time-bandwidth product pulse compression in a cryptographic quantum manner, i.e., the entanglement precludes any passive receiver from performing pulse compression on the target return.

11 citations


Patent
12 Jun 2007
TL;DR: In this article, a control module is configured to receive one or more input signals, and in response to the control signals, the control module provides a high transmission path for the operative wavelength from an optical input port, determined by the inputs, to the optical output port at a predetermined time with respect to a time reference in at least one of the input signals.
Abstract: A control module is configured to receive one or more input signals. An optical selection network includes a plurality of optical input ports configured to receive respective optical waves at an operative wavelength, and at least one optical output port configured to provide an optical wave at the optical wavelength. The optical selection network is configured to receive one or more control signals from the control module, and in response to the control signals, provide a high transmission path for the operative wavelength from an optical input port, determined by the input signals, to the optical output port at a predetermined time with respect to a time reference in at least one of the input signals, and provide a low transmission path for the operative wavelength from each of a plurality of optical input ports, determined by the input signals, to the optical output port at the predetermined time.

6 citations


Proceedings ArticleDOI
06 May 2007
TL;DR: The most powerful individual-photon attack against the Bennett-Brassard 1984 quantum key distribution protocol is implemented and results are in good agreement with theoretical predictions for the eavesdropper?s Renyi information.
Abstract: We have implemented the most powerful individual-photon attack against the Bennett-Brassard 1984 quantum key distribution protocol. Our measurement results are in good agreement with theoretical predictions for the eavesdropper?s Renyi information.

6 citations


Patent
17 Jul 2007
TL;DR: The phase-conjugate optical coherence tomography (PC-OCT) as mentioned in this paper is a three-dimensional imaging technique of interest for biomedical and other imaging applications, which shares much of the source and detection convenience of conventional OCT employing classical light sources and is being developed for a variety of endoscopic optical biopsy instruments.
Abstract: Phase-conjugate optical coherence tomography (PC-OCT) methods and apparatus. PC-OCT may be employed as a three-dimensional imaging technique of interest for biomedical and other imaging applications. It shares much of the source and detection convenience of conventional OCT employing classical light sources, which is in clinical use in ophthalmology and is being developed for a variety of endoscopic optical biopsy instruments. PC-OCT offers a two-fold improvement in axial resolution and immunity to group velocity dispersion, when compared with conventional OCT, that is available from quantum optical coherence tomography (Q-OCT). PC-OCT does this without Q-OCT's need for a non-classical light source and the attendant requirement of photon-coincidence counting detection. Thus, in comparison with Q-OCT, PC-OCT is capable of producing images in measurement times similar to those of conventional OCT.

5 citations


Patent
12 Jun 2007
TL;DR: In this article, a delay module and a time-dependent module are used to convert information encoding on an electromagnetic wave to a time dependent one. But the delay module is configured to respond to a control signal to apply a first transformation to the first component at a first time and a second transformation at a second time that is later than the first time by the difference between the first transformation and the second time delay.
Abstract: An apparatus that converts information encoding on an electromagnetic wave includes a delay module and a time-dependent module. The delay module is configured to apply a first time delay to a first component of an electromagnetic wave and to apply a second time delay different from the first time delay to a second component of the electromagnetic wave. The time-dependent module is configured to respond to a control signal to apply a first transformation to the first component at a first time and to apply a second transformation to the second component at a second time that is later than the first time by the difference between the first time delay and the second time delay.

Proceedings ArticleDOI
13 Jun 2007
TL;DR: In this article, it was shown that almost all the characteristics of quantum optical coherence tomography and quantum ghost imaging are due to phase-sensitive cross correlations, and hence are obtainable with classical phase sensitive sources.
Abstract: We show that almost all the characteristics of quantum optical coherence tomography and quantum ghost imaging are due to phase-sensitive cross correlations, and hence are obtainable with classical phase-sensitive sources.

Proceedings ArticleDOI
06 May 2007
TL;DR: In this article, a continuous-time model for cross-phase modulation was proposed to analyze quantum parity gates that use weak nonlinearity between single photons and intense coherent pulses, and an inevitable phase noise was shown to degrade gate fidelity.
Abstract: Quantum parity gates that use weak nonlinearity between single photons and intense coherent pulses are analyzed using a continuous-time model for cross-phase modulation. An inevitable phase noise is shown to degrade gate fidelity.

Proceedings ArticleDOI
TL;DR: In this paper, quantum limits on optics-based precision measurements are described, contrasting single-mode, multi-mode and continuous-time paradigms, and it is shown that 1/N is not the ultimate quantum limit on precision.
Abstract: Quantum limits on optics-based precision measurements are described, contrasting single-mode, multi-mode, and continuous-time paradigms. The latter suggests that 1/N, where N is the measurement's average photon number, is not the ultimate quantum limit on precision.

Proceedings ArticleDOI
10 Jun 2007
TL;DR: In this article, the authors demonstrate a pulsed entanglement source whose flux is sufficiently high that it leads to reduced quantum-interference visibility due to multiple-pair emissions, and an array of such pulsed downconverters can be configured to yield single photons on demand.
Abstract: We demonstrate a pulsed entanglement source whose flux is sufficiently high that it leads to reduced quantum-interference visibility due to multiple-pair emissions. An array of such pulsed downconverters can be configured to yield single photons on demand.