Information trade-offs for optical quantum communication (original) (raw)
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Quantum trade-off coding for bosonic communication
2011
Recent work has precisely characterized the achievable trade-offs between three key information processing tasks-classical communication (generation or consumption), quantum communication (generation or consumption), and shared entanglement (distribution or consumption), measured in bits, qubits, and ebits per channel use respectively. Slices and corner points of this three-dimensional region reduce to several well-known quantum communication protocols over noisy channels. A single trade-off coding technique can attain any point in the region and can outperform timesharing between the best known protocols for accomplishing each information processing task alone. Previously, the benefits of trade-off coding that had been found were too small to be of much practical value (for the dephasing and the universal cloning machine channels, for instance). In this article, we demonstrate that the associated performance gains are nonetheless remarkably high for several physically relevant bosonic channels that model free-space / fiber-optic links, thermalizing channels, or amplifiers (or even relativistic communication). We show that significant performance gains from trade-off coding also apply when trading photon-number resources between transmitting public and private classical information simultaneously over secret-key-assisted bosonic channels.
Energy and bandwidth efficiency optimization of quantum-enabled optical communication channels
npj Quantum Information
We present a systematic study of quantum receivers and modulation methods enabling resource efficient quantum-enhanced optical communication. We introduce quantum-inspired modulation schemes that theoretically yield a better resource efficiency than legacy protocols. Experimentally, we demonstrate below the shot-noise limit symbol error rates for M ≤ 16 legacy and quantum-inspired communication alphabets using software-configurable optical communication time-resolving quantum receiver testbed. Further, we experimentally verify that our quantum-inspired modulation schemes boost the accuracy of practical quantum measurements and significantly optimize the combined use of energy and bandwidth for communication alphabets that are longer than M = 4 symbols.
Information Transmission and Entanglement Distribution Over Bosonic Channels
2008
Abstract: High-sensitivity photodetection systems have long been limited by noises of quantum-mechanical origin. Nevertheless, analyses and designs of optical communication systems have seldom employed fully quantum treatments. As a result, these works do not establish the ultimate limits on optical communication performance.
Optimal encoding capacity of a linear optical quantum channel
Physical Review A, 2015
Here, we study the classical information capacity of a quantum channel, assuming linear optical encoding, as a function of available photons and optical modes. We present a formula for general channel capacity and show that this capacity is achieved without requiring the use of entangling operations typically required for scalable universal quantum computation, e.g. KLM measurementassisted transformations. As an example, we provide an explicit encoding scheme using the resources required of standard dense coding using two dual-rail qubits (2 photons in 4 modes). In this case, our protocol encodes one additional bit of information. Greater gains are expected for larger systems.
Multiple-user quantum information theory for optical communication channels
2008
Abstract: Research has established capacity theorems for point-to-point bosonic channels with additive thermal noise, under the presumption of a conjecture on the minimum output von Neumann entropy. In the first part of this thesis, we evaluate the optimum capacity for free-space line-of-sight optical communication using Gaussian-attenuation apertures. Optimal power allocation across all the spatio-temporal modes is studied, in both the far-field and near-field propagation regimes.
Optimized quantum-optical communications in the presence of loss
Optics Communications, 1998
We consider the effect of loss on quantum-optical communication channels. The channel based on direct detection of number states, which for a lossless transmission line would achieve the ultimate quantum channel capacity, is easily degraded by loss. The same holds true for the channel based on homodyne detection of squeezed states, which also is very fragile to loss. On the contrary, the ''classical'' channel based on heterodyne detection of coherent states is loss-invariant. We optimize the a priori probability for the squeezed-state and the number-state channels, taking the effect of loss into account. In the low power regime we achieve a sizeable improvement of the mutual information, and both the squeezed-state and the number-state channels overcome the capacity of the coherent-state channel. In particular, the squeezed-state channel beats the classical channel for total average number of photons N-8. However, for sufficiently high power the classical channel always performs as the best one. For the number-state channel we show that with a loss h Q 0.6 the optimized a priori probability departs from the usual thermal-like behavior, and develops gaps of zero probability, with a considerable Ž. improvement of the mutual information up to 70% of improvement at low power for attenuation h s 0.15. q 1998 Elsevier Science B.V.
Compact Coding Using Multi-Photon Tolerant Quantum Protocols For Quantum Communication
International Journal on Cryptography and Information Security, 2016
This paper presents a new encryption scheme called Compact Coding that encodes information in time, phase, and intensity domains, simultaneously. While these approaches have previously been used one at a time, the proposed scheme brings to bear for the first time their strengths simultaneously leading to an increase in the secure information transfer rate. The proposed scheme is applicable to both optical fibers and free space optics, and can be considered as an alternative to polarization coding. This paper applies the proposed compact coding scheme to multi-photon tolerant quantum protocols in order to produce quantum-level security during information transfer. We present the structure of the proposed coding scheme in a multi-photon environment and address its operation.
We analyze a long-distance entanglement based quantum key distribution (QKD) architecture, which uses multiple linear-optic quantum repeaters, frequency-multiplexed entanglement sources, and classical error correction. We find an exact expression for the secret-key rate, and an analytical characterization of how errors propagate through noisy repeater links, as a function of all loss and noise parameters, when the sources have zero multi-pair emissions, i.e., g2(0)=0g^2(0)=0g2(0)=0. We also present numerical results that show that two-pair-emission rates of a downconversion source has an unworkably poor rate-distance scaling, and show how the performance improves as g2(0)g^2(0)g2(0) of the source decreases. Our analysis of how the entangled state held by the two distant parties evolves through multiple swap operations, can in principle be applied to other repeater architectures as well. The exact results and scaling laws we present, may provide new quantitative insights useful not only for designing lo...
Public and private resource trade-offs for a quantum channel
Arxiv preprint arXiv:1005.3818, 2010
Collins and Popescu realized a powerful analogy between several resources in classical and quantum information theory. The Collins-Popescu analogy states that public classical communication, private classical communication, and secret key interact with one another somewhat similarly to the way that classical communication, quantum communication, and entanglement interact. This paper discusses the information-theoretic treatment of this analogy for the case of noisy quantum channels. We determine a capacity region for a quantum channel interacting with the noiseless resources of public classical communication, private classical communication, and secret key. We then compare this region with the classical-quantum-entanglement region from our prior efforts and explicitly observe the informationtheoretic consequences of the strong correlations in entanglement and the lack of a super-dense coding protocol in the public-private-secret-key setting. The region simplifies for several realistic, physicallymotivated channels such as entanglement-breaking channels, Hadamard channels, and quantum erasure channels, and we are able to compute and plot the region for several examples of these channels.
Physical Review A, 2015
It is well known that the efficiency of linear optical implementations of the dense coding is limited by one's ability to discriminate between the four optically encoded Bell states.The best experimental demonstration up to date reports the transmission of ≈ 1.63 bits of information per single optical qubit which is less than the theoretical bound of 2.0 bits for a generic qubit. We show that besides the Bell states there is a class of bipartite two-photon entangled states that can also facilitate dense coding. However, in contrast to the Bell states, they can be deterministically discriminated by means of linear optics and coincidence photo detection without using any auxiliary entanglement resources. We discuss how the proposed dense coding scheme can be generalized to the case of two-photon N -mode entangled states for N = 6, 8.