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Journal ArticleDOI

How to Measure Squeezing and Entanglement of Gaussian States without Homodyning

06 Aug 2004-Physical Review Letters (American Institute of Physics)-Vol. 93, Iss: 6, pp 063601-063601
TL;DR: This work proposes a scheme for measuring the squeezing, purity, and entanglement of Gaussian states of light that does not require homodyne detection and needs only beam splitters and single-photon detectors.
Abstract: We propose a scheme for measuring the squeezing, purity, and entanglement of Gaussian states of light that does not require homodyne detection. The suggested setup needs only beam splitters and single-photon detectors. Two-mode entanglement can be detected from coincidences between photodetectors placed on the two beams.

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Citations
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Journal ArticleDOI
TL;DR: In this article, a detailed and comparative study of atom-atom entanglement for two cases corresponding to different injections of the two atoms one by one into the cavity field is presented.
Abstract: Entanglement properties of two uncoupled atoms embedded in a coherent field distribution through one quantum transition process are studied. A case of non-linear Hamiltonian of the problem is considered through which the effect of non-linear media is illustrated. Moreover, the effect of the frequency difference between the inter-atomic transition and the electromagnetic field is also analyzed. We show that, adjusting the considered parameters of the non-linear media and frequency difference leads to a strong control of the degree of entanglement where excellent periodicity of evolution with significant amplitudes maxima of entanglement can be obtained that is very important in predicting the behavior of transmitted information through the application of various information processing schemes. We present a detailed and comparative study of atom–atom entanglement for two cases corresponding to different injections of the two atoms one by one into the cavity field. In addition, we present an answer to the question: How is the quantum phase space structure for a composite system related to the entanglement characteristics of the corresponding quantum system? We demonstrate how can the entanglement in nonlinear tripartite systems be strongly associated with a delocalization in the phase space distribution.

4 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the generation and evolution of continuous-variable entanglement in an asymmetric coupled-quantum well (CQW) system and showed that this CQW system can be regarded as a source of macroscopic entangled light over a wide range of initial states of the cavity field.
Abstract: This paper investigates the generation and evolution of continuous-variable entanglement in an asymmetric coupled-quantum well (CQW) system. Our numerical results show that this CQW system can be regarded as a source of macroscopic entangled light over a wide range of initial states of the cavity field. This investigation can be used for achieving the macroscopic entangled light in the CQW solid-state medium, which is much more practical than that in an atomic medium because of its flexible design and the controllable interference strength.

4 citations

Journal ArticleDOI
TL;DR: A detailed analysis of the time evolution of the two-mode squeezing, entanglement and intensity of the cavity radiation of a two-photon correlated emission laser initially seeded with a thermal light is presented in this article.
Abstract: A detailed analysis of the time evolution of the two-mode squeezing, entanglement and intensity of the cavity radiation of a two-photon correlated emission laser initially seeded with a thermal light is presented. The dependences of the degree of two-mode squeezing and entanglement on the intensity of the thermal light and time are found to have a more or less similar nature, although the actual values differ, especially in the early stages of the process and when the atoms are initially prepared with nearly 50:50 probability to be in the upper and lower energy levels. Seeding the cavity degrades the nonclassical features significantly, particularly in the vicinity of t=0. It is also shown that the mean photon number in a wider time span has a dip when mode b is seeded but a peak when mode a is seeded. Moreover, it turns out that the effect of the seed light on the nonclassical features and intensity of the cavity radiation decreases significantly with time, an outcome essentially attributed to the pertinent emission–absorption mechanism. This can be taken as an encouraging aspect in the practical utilization of this model as a source of a bright entangled light.

4 citations

Posted Content
TL;DR: In this article, the authors studied the harmonic entanglement and squeezing in a two-mode radiation produced in a degenerate parametric down conversion process coupled to a twomode vacuum reservoir employing the linearization procedure.
Abstract: We study the harmonic entanglement and squeezing in a two-mode radiation produced in a degenerate parametric down conversion process coupled to a two-mode vacuum reservoir employing the linearization procedure. It is found that there is a quadrature entanglement between the harmonically related fundamental and second-harmonic modes and the superimposed radiation exhibits a significant two-mode squeezing. The entanglement exits even when there is no two-mode squeezing, since the correlation leading to these phenomena are essentially different. In addition, the more the external coherent light is down converted, the more stronger the entanglement and mean photon number of the two-mode radiation would be which is not generally true for squeezing.

3 citations

Posted Content
TL;DR: In this article, a new classification scheme is proposed to distinguish between effective discrete variable hybrid entanglement and so-called true hybrid entenglement, where the focus is on bipartite entanglements.
Abstract: Quantum information theory is a very young area of research offering a lot of challenging open questions to be tackled by ambitious upcoming physicists. One such problem is addressed in this thesis. Recently, several protocols have emerged which exploit both continuous variables and discrete variables. On the one hand, outperforming many of the established pure continuous variable or discrete variable schemes, these hybrid approaches offer new opportunities. However, on the other hand, they also lead to new, intricate, as yet uninvestigated, phenomena. An important ingredient of several of these hybrid protocols is a new kind of entanglement: The hybrid entanglement between continuous variable and discrete variable quantum systems, which is studied in detail in this work. An exhaustive analysis of this kind of entanglement is performed, where the focus is on bipartite entanglement. Nevertheless, also issues regarding multipartite hybrid entanglement are briefly discussed. The quintessence of this thesis is a new classification scheme which distinguishes between effective discrete variable hybrid entanglement and so-called true hybrid entanglement. However, along the way, also other questions are addressed, which have emerged during the studies. For example, entanglement witnessing is discussed not only for hybrid entangled states, but also for fully continuous variable two-mode Schroedinger cat states. Furthermore, subtleties regarding entanglement witnessing in a certain kind of mixed states are examined. Not only theoretical classification and analysis of hybrid entangled states are discussed, but also their generation is presented and a few applications are demonstrated.

3 citations

References
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Journal ArticleDOI
TL;DR: A measure of entanglement that can be computed effectively for any mixed state of an arbitrary bipartite system is presented and it is shown that it does not increase under local manipulations of the system.
Abstract: We present a measure of entanglement that can be computed effectively for any mixed state of an arbitrary bipartite system. We show that it does not increase under local manipulations of the system, and use it to obtain a bound on the teleportation capacity and on the distillable entanglement of mixed states.

3,889 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the Deutsch-Jozsa algorithm for continuous variables, and a deterministic version of it is used for quantum information processing with continuous variables.
Abstract: Preface. About the Editors. Part I: Quantum Computing. 1. Quantum computing with qubits S.L. Braunstein, A.K. Pati. 2. Quantum computation over continuous variables S. Lloyd, S.L. Braunstein. 3. Error correction for continuous quantum variables S.L. Braunstein. 4. Deutsch-Jozsa algorithm for continuous variables A.K. Pati, S.L. Braunstein. 5. Hybrid quantum computing S. Lloyd. 6. Efficient classical simulation of continuous variable quantum information processes S.D. Bartlett, B.C. Sanders, S.L. Braunstein, K. Nemoto. Part II: Quantum Entanglement. 7. Introduction to entanglement-based protocols S.L. Braunstein, A.K. Pati. 8. Teleportation of continuous uantum variables S.L. Braunstein, H.J. Kimble. 9. Experimental realization of continuous variable teleportation A. Furusawa, H.J. Kimble. 10. Dense coding for continuous variables S.L. Braunstein, H.J. Kimble. 11. Multipartite Greenberger-Horne-Zeilinger paradoxes for continuous variables S. Massar, S. Pironio. 12. Multipartite entanglement for continuous variables P. van Loock, S.L. Braunstein. 13. Inseparability criterion for continuous variable systems Lu-Ming Duan, G. Giedke, J.I. Cirac, P. Zoller. 14. Separability criterion for Gaussian states R. Simon. 15. Distillability and entanglement purification for Gaussian states G. Giedke, Lu-Ming Duan, J.I. Cirac, P. Zoller. 16. Entanglement purification via entanglement swapping S. Parke, S. Bose, M.B. Plenio. 17. Bound entanglement for continuous variables is a rare phenomenon P. Horodecki, J.I. Cirac, M. Lewenstein. Part III: Continuous Variable Optical-Atomic Interfacing. 18. Atomic continuous variable processing and light-atoms quantum interface A. Kuzmich, E.S. Polzik. Part IV: Limits on Quantum Information and Cryptography. 19. Limitations on discrete quantum information and cryptography S.L. Braunstein, A.K. Pati. 20. Quantum cloning with continuous variables N.J. Cerf. 21. Quantum key distribution with continuous variables in optics T.C. Ralph. 22. Secure quantum key distribution using squeezed states D. Gottesman, J. Preskill. 23. Experimental demonstration of dense coding and quantum cryptography with continuous variables Kunchi Peng, Qing Pan, Jing Zhang, Changde Xie. 24. Quantum solitons in optical fibres: basic requisites for experimental quantum communication G. Leuchs, Ch. Silberhorn, E. Konig, P.K. Lam, A. Sizmann, N. Korolkova. Index.

2,940 citations

Journal ArticleDOI
TL;DR: The Peres-Horodecki criterion of positivity under partial transpose is studied in the context of separability of bipartite continuous variable states and turns out to be a necessary and sufficient condition for separability.
Abstract: The Peres-Horodecki criterion of positivity under partial transpose is studied in the context of separability of bipartite continuous variable states. The partial transpose operation admits, in the continuous case, a geometric interpretation as mirror reflection in phase space. This recognition leads to uncertainty principles, stronger than the traditional ones, to be obeyed by all separable states. For all bipartite Gaussian states, the Peres-Horodecki criterion turns out to be a necessary and sufficient condition for separability.

1,796 citations

Journal ArticleDOI
TL;DR: An inseparability criterion based on the total variance of a pair of Einstein-Podolsky-Rosen type operators is proposed for continuous variable systems and turns out to be a necessary and sufficient condition for inseparability.
Abstract: As with discrete systems, quantum entanglement also plays the basic role in quantum information protocols with continuous variables. A problem of great importance is then to check whether a continuous variable state, generally mixed, is entangled (inseparable). For discrete systems, there is the Peres-Horodecki inseparability criterion [1,2], based on the negativity of the partial transpose of the composite density operator. This negativity provides a necessary and sufficient condition for inseparability of 2 × 2 or 2 × 3 —dimensional systems. In this section, we will describe an entirely different inseparability criterion for continuous variable states, which was first proposed in Ref. [3]. The Peres-Horodecki criterion was also successfully extended to the continuous variable systems shortly afterwards, which will be described in the next section by Simon.

1,670 citations

Book
13 Mar 1998
TL;DR: In this paper, the authors present a survey of classical models of light experiments with Photons, as well as non-demolition experiments with light and non-quantum noise.
Abstract: Classical Models of Light Experiments with Photons Quantum Models of Light Basic Optical Components Photo-currents: Generation and Detection The Laser Quantum Noise: Basic Measurements Sub-Poissonian Light Squeezing Experiments Quantum Non-demolition Experiments Applications of Quantum Optics Summary and Outlook Appendices Index.

817 citations