Quantum-enhanced Information Retrieval from Reflective Intelligent Surfaces

TL;DR

The paper tackles energy-constrained backscatter information retrieval by introducing a time-resolving quantum receiver fed by multi-color probing and RIS-based modulation to surpass the standard quantum limit (SQL) for large-alphabet readout. It proposes a practical scheme that relies on coherent multi-color probes and an adaptive displacement receiver, optimized via Bayesian MAP updates, to discriminate RIS-encoded symbols. Simulations show the approach beats the SQL for modulations up to $M=2^8$, achieving about 2x energy savings or a $\sqrt{2}$ improvement in reading distance, with two spectral modes found to be sufficient. This work improves the feasibility of high-capacity, energy-efficient passive backscatter systems and highlights a viable path toward practical quantum-enhanced information retrieval.

Abstract

Information retrieval from passive backscatter systems is widely used in digital applications with tight energy budgets, short communication distances, and low data rates. Due to the fundamental limits of classical wireless receivers, the achievable data rate cannot be increased without compromising either energy efficiency or communication range, thereby hindering the broader adoption of this technology. In this work, we present a novel time-resolving quantum receiver combined with a multi-mode probing signal to extract large-alphabet information modulated by a passive reconfigurable intelligent surface (RIS). The adaptive nature of the proposed receiver yields significant quantum advantages over classical receivers without relying on complex or fragile quantum resources such as entanglement. Simulation results show that the proposed technique surpasses the classical standard quantum limit (SQL) for modulation sizes up to M = 2^8, meanwhile halving the probing energy or increasing the communication distance by a factor of 1.41.

Figures (10)

• Figure 1: RIS-modulated information retrieval system with an adaptive time-resolving quantum receiver.
• Figure 2: An example showing an arrival light mode is adaptively displaced by the LO signal in 5 rounds, creating an increasingly sparse photon statistics in the SPD.
• Figure 3: Constellation of RIS modulation.
• Figure 4: Symbol error probability under different modulation schemes for $S=1$.
• Figure 5: Symbol error probability with varying RIS element number.