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arXiv:2301.02513 · Physical Review A

Information carried by a single particle in quantum multiple-access channels

Xinan Chen, Yujie Zhang, Andreas Winter, Virginia O. Lorenz, Eric Chitambar

Published Jun 13, 2024• 2 citations
arXivHTMLPDF

Abstract

Nonclassical features of quantum systems have the potential to strengthen the way we currently exchange information. In this paper, we explore this enhancement on the most basic level of single particles. To be more precise, we compare how well multiparty information can be transmitted to a single receiver using just one classical or quantum particle. Our approach is based on a multiple-access communication model in which messages can be encoded into a single particle that is coherently distributed across multiple spatial modes. Theoretically, we derive lower bounds on the accessible information in the quantum setting that strictly separate it from the classical scenario. This separation is found whenever there is more than one sender, and also when there is just a single sender who has a shared phase reference with the receiver. When there is only one sender, the separation is impossible without a shared phase reference due to the famous Holevo's bound. Experimentally, we present a proof-of-principle demonstration of such quantum advantage in single-particle communication by implementing a multiport interferometer with messages being encoded along the different trajectories. Specifically, we consider a two-sender communication protocol built by a three-port optical interferometer. In this scenario, the rate sum achievable with a classical particle is upper bounded by one bit, while we experimentally observe a rate sum of $1.0152\ifmmode\pm\else\textpm\fi{}0.0034$ bits in the quantum setup.

DOI
10.1103/physreva.109.062420

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Nonclassical features of quantum systems have the potential to strengthen the way we currently exchange information. In this paper, we explore this enhancement on the most basic level of single particles. To be more precise, we compare how well multiparty information can be transmitted to a single receiver using just one classical or quantum particle. Our approach is based on a multiple-access communication model in which messages can be encoded into a single particle that is coherently distributed across multiple spatial modes. Theoretically, we derive lower bounds on the accessible information in the quantum setting that strictly separate it from the classical scenario. This separation is found whenever there is more than one sender, and also when there is just a single sender who has a shared phase reference with the receiver. When there is only one sender, the separation is impossible without a shared phase reference due to the famous Holevo's bound. Experimentally, we present a proof-of-principle demonstration of such quantum advantage in single-particle communication by implementing a multiport interferometer with messages being encoded along the different trajectories. Specifically, we consider a two-sender communication protocol built by a three-port optical interferometer. In this scenario, the rate sum achievable with a classical particle is upper bounded by one bit, while we experimentally observe a rate sum of 1.0152\ifmmode±\else\textpm\fi0.00341.0152\ifmmode\pm\else\textpm\fi{}0.00341.0152\ifmmode±\else\textpm\fi0.0034 bits in the quantum setup.
A multiple access channel describes a situation in which multiple senders are trying to forward messages to a single receiver using some physical medium. In this paper we consider scenarios in which this medium consists of just a single classical or quantum particle. In the quantum case, the particle can be prepared in a superposition state thereby allowing for a richer family of encoding strategies. To make the comparison between quantum and classical channels precise, we introduce an operational framework in which all possible encoding strategies consume no more than a single particle. We apply this framework to an N -port interferometer experiment in which each party controls a path the particle can traverse. When used for the purpose of communication, this setup embodies a multiple access channel (MAC) built with a single particle.We provide a full characterization of the N -party classical MACs that can be built from a single particle, and we show that every non-classical particle can generate a MAC outside the classical set. To further distinguish the capabilities of a single classical and quantum particle, we relax the locality constraint and allow for joint encodings by subsets of 1
We introduce and analyze an information theoretical task that we call the quantum multiple-access one-time pad. Here, a number of senders initially share a correlated quantum state with a receiver and an eavesdropper. Each sender performs a local operation to encode a classical message and sends their system to the receiver, who subsequently performs a measurement to decode the messages. The receiver will be able to decode the messages almost perfectly, while the eavesdropper must not be able to extract information about the messages even if they have access to the quantum systems transmitted. We consider a “conditional” scenario in which a portion of the receiver’s side information is also accessible to the eavesdropper. We investigate the maximum amount of classical information that can be encoded by each of the senders. We derive a single-letter characterization for the achievable rate region in an asymptotic limit of infinitely many copies and vanishingly small error.
We investigate two senders and one receiver multiparty communication scenario. Following Phys.Rev.A83, 062112 and arXiv : 2506.07699, we study multiparty communication bounded by dimension and distinguishability. We provide an explicit characterization of the classical correlations achievable under these constraints. We then demonstrate that quantum communication systematically exceeds these classical limits, even in the absence of preshared entanglement and without any input choice for the receiver. Furthermore, we implement semidefinite hierarchy tools tailored to the two-sender, one-receiver setting for both types of constraints considered. Our results reveal a clear quantum advantage in multiparty communication under those restrictions.
Abstract The extension of point-to-point communication to multi-node configurations has significant applications in internet and telecommunication networks. Quantum resources promise notable advantages in such settings. Here, we demonstrate a novel quantum advantage in simulating multiple access channels (MACs)-a common network configuration where multiple distant senders transmit messages to a single receiver (e.g. the uplink from several mobile phones to a server). Specifically, we show that qubit transmission outperforms its classical counterpart, even when the latter is supplemented with classical shared randomness. Remarkably, unlike the seminal quantum superdense coding protocol, this advantage is achieved without any pre-shared entanglement between the senders and the receiver-a feat prohibited by Holevo and Frenkel–Weiner no-go theorems in the one-sender-one-receiver scenario. The receiver’s ability to simultaneously decode quantum systems from multiple senders underpins this distinct advantage in the MAC setup. Some of our MAC designs are inspired by constructs in quantum foundations, such as the Pusey–Barrett–Rudolph theorem and ‘quantum nonlocality without entanglement’. Beyond network applications, this quantum advantage reveals a deeper connection to ‘quantum nonlocality without inputs’ phenomenon and suggests potential for semi-device-independent certification of entangled measurements.
Quantum mechanics allows operations to be in indefinite causal order, leading to advantages in computational and communication tasks. However, basic notions such as communication capacity have not yet been formalized. In light of this, through the process matrix formalism, we formulate different classical capacities for a bipartite quantum process. For one-way communication, we find that general quantum processes satisfy a generalization of the Holevo bound, i.e., we can send, at most, one bit per qubit. The result also holds for processes with indefinite causal order and with shared entanglement between the sender and the receiver. We further extend known bounds to classical channel capacities, showing that general processes cannot outperform causally separable ones. Next, we study bidirectional communication through a causally separable process. Our result shows that a bidirectional protocol cannot exceed the limit of a one-way communication protocol. Finally, we generalize this result to a multiparty broadcast communication protocol through a definite ordered process.
We consider the one-shot coding of multiple access channels one-time pad. Suppose that the senders and the receiver share an entangled state in the multi-party systems. Using the position-based coding, each sender encodes the classical messages on their systems, then they transmit their systems over the ideal quantum channels. The receiver applies a decoding operator to all the systems in order to figure out which message was transmitted with respect to the quantum joint typicality lemma. We provide the upper bound of the information leakage by the convex split lemma. Combining quantum max-information with quantum hypothesis testing mutual information, we give the inner bound of the achievable rate.