Demonstration of quantum advantage by a joint detection receiver for optical communications using quantum belief propagation on a trapped-ion device

TL;DR

This paper demonstrates a quantum advantage in optical communication by implementing a joint detection receiver using quantum belief propagation on a trapped-ion device, surpassing classical limits in error probability.

Contribution

It presents the first experimental realization of a quantum joint detection scheme for optical codewords using a trapped-ion quantum computer, bridging photonic and ion-based quantum information.

Findings

Successfully implemented quantum joint detection on a trapped-ion system.

Surpassed the quantum limit on minimum average decoding error.

Demonstrated feasibility of quantum advantage in optical communication.

Abstract

Demonstrations of quantum advantage have largely focused on computational speedups and on quantum simulation of many-body physics, limited by fidelity and capability of current devices. Discriminating laser-pulse-modulated classical-communication codewords at the minimum allowable probability of error using universal-quantum processing presents a promising parallel direction, one that is of both fundamental importance in quantum state discrimination, as well as of technological relevance in deep-space laser communications. Here we present an experimental realization of a quantum joint detection receiver for binary phase shift keying modulated codewords of a 3-bit linear tree code using a recently-proposed quantum algorithm: belief propagation with quantum messages. The receiver, translated to a quantum circuit, was experimentally implemented on a trapped-ion device -- the recently released Honeywell LT-1.0 system using ${}^{171}Yb+ $ ions, which possesses all-to-all connectivity and mid-circuit measurement capabilities that are essential to this demonstration. We conclusively realize a previously postulated but hitherto not-demonstrated joint quantum detection scheme, and provide an experimental framework that surpasses the quantum limit on the minimum average decoding error probability associated with pulse-by-pulse detection in the low mean photon number limit. The full joint-detection scheme bridges across photonic and trapped-ion based quantum information science, mapping the photonic coherent states of the modulation alphabet onto inner product-preserving states of single-ion qubits. Looking ahead, our work opens new avenues in hybrid realizations of quantum-enhanced receivers with applications in astronomy and emerging space-based platforms.