Convex combinations of bosonic pure-loss channels

• URL: http://arxiv.org/abs/2604.26874v1
• Date: Wed, 29 Apr 2026 16:42:12 GMT
• Title: Convex combinations of bosonic pure-loss channels
• Abstract summary: We show that entanglement distribution and quantum key distribution can always be achieved at a strictly positive rate over any fading channel.<n>We identify regimes where the coherent information of thermal inputs vanishes, while optimized non-Gaussian states achieve strictly positive values.
• Score: 4.458381173954051
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: The pure-loss channel is a fundamental model for describing noise in bosonic quantum platforms. It is characterised by a single parameter, the transmissivity, which quantifies the fraction of the input energy that reaches the output of the channel. In realistic scenarios, however, such as free-space quantum communication, the transmissivity is not fixed but fluctuates from one channel use to another. In this setting, the overall channel is effectively described as a convex combination of pure-loss channels, known as a fading channel. Despite its practical relevance, the quantum Shannon theory of the fading channel has remained largely unexplored. Here, we address this gap, specifically investigating degradability, anti-degradability, entanglement breakingness, and capacities of the fading channel. Of particular relevance to practical quantum-internet applications, we prove that entanglement distribution and quantum key distribution can always be achieved at a strictly positive rate over any fading channel, no matter how noisy it is or how strongly the transmissivity fluctuates, provided the channel is not completely noisy. Moreover, we prove that thermal states, which are optimal for a broad class of static bosonic Gaussian channels, fail to achieve the entanglement-assisted classical capacity of fading channels: non-Gaussian Fock-diagonal states strictly outperform all Gaussian encodings. Most strikingly, we identify regimes where the coherent information of thermal inputs vanishes, while optimized non-Gaussian states achieve strictly positive values, thereby activating the channel for quantum communication. For a paradigmatic binary fading model we establish this result analytically, deriving the exact capacity-achieving state in closed form. For general fading distributions, we design an iterative variational algorithm to optimize the coherent and mutual information.

Related papers

• Asymptotic Limits of Entanglement Distribution [43.748379918040854]
  We investigate the limits of entanglement distribution across quantum networks utilizing intermediate stations and local operations.<n>We establish a strict dichotomy: the preservation of entanglement over arbitrarily long distances is possible if the underlying quantum channel admits a correctable subspace.<n>We derive a fundamental lower bound on the physical resource requirements, proving that for channels without a correctable subspace, the number of parallel channels per link must scale at least logarithmically with the number of intermediate stations to sustain a non-zero amount of entanglement.
  arXiv  Detail & Related papers  (2026-05-22T09:56:38Z)
• Experimental Quantum Channel Purification [6.303535911712495]
  Channel purification emerges as a promising technique for suppressing noise in quantum channels without complex encoding and decoding operations.<n>We introduce an experimental setup for efficient channel purification, harnessing the spatial and polarization properties of photons.
  arXiv  Detail & Related papers  (2025-10-31T15:08:16Z)
• Optimizing entanglement distribution via noisy quantum channels [44.99833362998488]
  Entanglement distribution is a crucial problem in quantum information science.<n>We investigate strategies for distributing quantum entanglement between two distant parties through noisy quantum channels.
  arXiv  Detail & Related papers  (2025-06-06T13:48:20Z)
• String commitment from unstructured noise [46.40786209841718]
  We introduce the unstructured noisy channel model as a generalization of the unfair noisy channel model.<n>We show that the entropic constraints in the unstructured noisy channel model can be derived from physical assumptions such as noisy quantum storage.
  arXiv  Detail & Related papers  (2024-12-31T05:28:05Z)
• Resolvability of classical-quantum channels [54.825573549226924]
  We study the resolvability of classical-quantum channels in two settings, for the channel output generated from the worst input, and form the fixed independent and identically distributed (i.i.d.) input. For the fixed-input setting, while the direct part follows from the known quantum soft covering result, we exploit the recent alternative quantum Sanov theorem to solve the strong converse.
  arXiv  Detail & Related papers  (2024-10-22T05:18:43Z)
• Improving Gaussian channel simulation using non-unity gain heralded quantum teleportation [1.5945487609983366]
  Quantum teleportation provides an avenue to effectively simulate Gaussian channels. We demonstrate the simulation of non-physical Gaussian channels otherwise inaccessible using conventional means. We report Gaussian noise suppression, effectively converting an imperfect quantum channel into a near-identity channel.
  arXiv  Detail & Related papers  (2024-08-16T11:19:51Z)
• Classical capacity of quantum non-Gaussian attenuator and amplifier channels [0.8409980020848168]
  We consider a quantum bosonic channel that couples the input mode via a beam splitter or two-mode squeezer to an environmental mode prepared in an arbitrary state. We investigate the classical capacity of this channel, which we call a non-Gaussian attenuator or amplifier channel.
  arXiv  Detail & Related papers  (2023-12-25T06:05:51Z)
• Improving Continuous-variable Quantum Channels with Unitary Averaging [37.69303106863453]
  We present a scheme of passive linear optical unitary averaging for protecting unknown Gaussian states transmitted through an optical channel. The scheme reduces the effect of phase noise on purity, squeezing and entanglement, thereby enhancing the channel via a probabilistic error correcting protocol.
  arXiv  Detail & Related papers  (2023-11-17T10:10:19Z)
• Fault-tolerant Coding for Entanglement-Assisted Communication [46.0607942851373]
  This paper studies the study of fault-tolerant channel coding for quantum channels. We use techniques from fault-tolerant quantum computing to establish coding theorems for sending classical and quantum information in this scenario. We extend these methods to the case of entanglement-assisted communication, in particular proving that the fault-tolerant capacity approaches the usual capacity when the gate error approaches zero.
  arXiv  Detail & Related papers  (2022-10-06T14:09:16Z)
• Detecting positive quantum capacities of quantum channels [9.054540533394926]
  A noisy quantum channel can be used to reliably transmit quantum information at a non-zero rate. This is because it requires computation of the channel's coherent information for an unbounded number of copies of the channel. We show that a channel's ability to transmit information is intimately connected to the relative sizes of its input, output, and environment spaces.
  arXiv  Detail & Related papers  (2021-05-13T14:26:45Z)
• Coherent control and distinguishability of quantum channels via PBS-diagrams [59.94347858883343]
  We introduce a graphical language for coherent control of general quantum channels inspired by practical quantum optical setups involving polarising beam splitters (PBS) We characterise the observational equivalence of purified channels in various coherent-control contexts, paving the way towards a faithful representation of quantum channels under coherent control.
  arXiv  Detail & Related papers  (2021-03-02T22:56:25Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.