Quantum communication with coherent states (original) (raw)

Quantum communication with continuum single-photon, two-photon and coherent states

Quantum Information and Computation, 2017

In this work, we analyze the behavior of continuum single-photon, two-photon and coherent states in some quantum communication schemes. In particular, we consider the single-photon in a Mach-Zenhder interferometer, the Hong-Ou-Mandel interference, the quantum bit commitment protocol and a new protocol for secure transmission of sampled analog signals. Furthermore, it is shown an equation for estimating the spectral distribution of the single-photon produced by a heralded single-photon source using four-wave mixing in an optical fiber.

Quantum Communications in New Telecommunications Systems

Quantum Communications in New Telecommunications Systems, 2017

Concepts in Communications 2.1. Quantum limits Quantum coherence and quantum correlation applications in optics have been discussed by [KNI 01]. Coherent states are an ideal tool for handling the boundary between classic and quantum properties; it can be shown that by using coherent states, analytical solutions can be found to previously unsolvable nonlinear quantum problems. Quantum optics has generated new applications that use the possibilities of quantum states of light, such as coherence and quantum correlation. The latter is known as entanglement. It can be shown how it is possible to obtain images of objects at weak intensity with a sensitivity that exceeds the standard quantum limits. The authors also show that the biphotons that are created in the process of parametric decay exhibit a space-time correlation phenomenon, which is called entanglement. Applications based on the impossibility of cloning unknown quantum states are unique; they have been developed in the field of quantum cryptography. An EPR experiment with entangled and polarized photons has been developed to test its feasibility. In line with this, the quantum correlations between spatially separated events are due to the propagation of a signal in superluminal communication in a chosen context: the coincidences between the entangled photons pass through two polarizers aligned along an east-west axis and are measured as a time function over 21 sidereal days. No deviation from this prediction of quantum theory has been observed. Taking account of the experimental uncertainties, we infer that if a chosen framework for super-luminal signals exists, then this moves at a velocity v depending on the Earth. The velocity module of quantum communications in this context is greater than v t ≈ 0.6 × 10 4 c for v < 0.1 c for any arbitrary direction of v. A lower limit for the velocity of quantum communications has been identified by [COQ 01]. Another aspect in determining limits has been observed with the famous g factor in quantum communications for semiconductors III.V [KAS 01].

Quantum communication with coherent states of light

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 2017

Quantum communication offers long-term security especially, but not only, relevant to government and industrial users. It is worth noting that, for the first time in the history of cryptographic encoding, we are currently in the situation that secure communication can be based on the fundamental laws of physics (information theoretical security) rather than on algorithmic security relying on the complexity of algorithms, which is periodically endangered as standard computer technology advances. On a fundamental level, the security of quantum key distribution (QKD) relies on the non-orthogonality of the quantum states used. So even coherent states are well suited for this task, the quantum states that largely describe the light generated by laser systems. Depending on whether one uses detectors resolving single or multiple photon states or detectors measuring the field quadratures, one speaks of, respectively, a discrete- or a continuous-variable description. Continuous-variable QKD ...

Mathematical techniques for quantum communication theory

Open Systems & Information Dynamics, 1995

We present mathematical techniques for addressing two closely related questions in quantum communication theory. In particular, we give a statistically motivated derivation of the Bures-Uhlmann measure of distinguishability for density operators, and we present a simplified proof of the Holevo upper bound to the mutual information of quantum communication channels. Both derivations give rise to novel quantum measurements.

Realizable receivers for discriminating coherent and multicopy quantum states near the quantum limit

Coherent states of light, and methods for distinguishing between them, are central to all applications of laser light. We obtain the ultimate quantum limit on the error probability exponent for discriminating among any M multimode coherent-state waveforms via the quantum Chernoff exponent in M -ary multi-copy state discrimination. A receiver, i.e., a concrete realization of a quantum measurement, called the Sequential Waveform Nulling (SWN) receiver, is proposed for discriminating an arbitrary coherent-state ensemble using only auxiliary coherent-state fields, beam splitters, and non-number-resolving single photon detectors. An explicit error probability analysis of the SWN receiver is used to show that it achieves the quantum limit on the error probability exponent, which is shown to be a factor of four greater than the error probability exponent of an ideal heterodyne-detection receiver on the same ensemble. We generalize the philosophy of the SWN receiver, which is itself adapted from some existing coherent-state receivers, and propose a receiver -the Sequential Testing (ST) receiver-for discriminating n copies of M pure quantum states from an arbitrary Hilbert space. The ST receiver is shown to achieve the quantum Chernoff exponent in the limit of a large number of copies, and is remarkable in requiring only local operations and classical communication (LOCC) to do so. In particular, it performs adaptive copy-by-copy binary projective measurements. Apart from being of fundamental interest, these results are relevant to communication, sensing, and imaging systems that use laser light and to photonic implementations of quantum information processing protocols in general.

Demonstration of Near-Optimal Discrimination of Optical Coherent States

Physical Review Letters, 2008

The optimal discrimination of non-orthogonal quantum states with minimum error probability is a fundamental task in quantum measurement theory as well as an important primitive in optical communication. In this work, we propose and experimentally realize a new and simple quantum measurement strategy capable of discriminating two coherent states with smaller error probabilities than can be obtained using the standard measurement devices; the Kennedy receiver and the homodyne receiver.

Quantum Detection of Signals in the Presence of

The classical communications model assumes that deterministic signals are observed in the presence of additive Gaussian noise. Thls model is adequate for describing communications at radio frequencies, where quantum effects are not readily detectable. However, at optical frequencies quantum effects become the dominant source of error, and must be taken into account. An approach consistent with the principles of quantum mechanics starts by quantizing the received electromagnetic field, and seeks to determine those measurements on the received field that achieve best results, such as minimizing the average probability of detection error. Exact solutions for the case of pure coherent states for both binary and higher-dimensional signals can be found in the literature (l, 2, 3, 41. The quantum mechanical solution for pure-state signals can be formulated in terms of Kennedy's orthogonal "measurement states", involving optimization of the detection operator over the signal ...

Coherent states in Quantum Information: An example of experimental manipulations

Journal of Physics: Conference Series, 2010

A part of difficulties in implementing communication in Quantum Information stems from the fragility of Shroedinger cat-like superpositions. We describe here a recent experiment in Quantum Optics proving the feasibility of a feedback-mediated quantum measurement for discriminating between optical coherent states under photodetection. The measurements validate theoretical prediction by Helstrom ("Helstrom bound"), Dolinar and Geremia. This contribution gives an account of the implementation achieved by Cook, Martin and Geremia (2007) and explains the theoretical approaches to the subject.