Unbounded Communication Power of a Qubit

TL;DR

This paper demonstrates that a single qubit can retain accessible information through multiple measurements, enabling an indefinite sequence of receivers to maintain quantum advantage by leveraging preparation distinguishability and measurement incompatibility.

Contribution

It introduces the concept of preparation distinguishability as a resource and shows how it, combined with measurement incompatibility, allows repeated quantum advantage in information retrieval.

Findings

Repeated measurements can preserve quantum advantage in a qubit.

Preparation distinguishability mitigates measurement disturbance.

Quantum advantage can be maintained over arbitrarily long sequences.

Abstract

Quantum mechanics enables information-processing advantages even at the level of a single qubit. A paradigmatic example is the 2$\to$1 random access code (RAC), where a qubit outperforms a classical bit in retrieving encoded information. In the standard form, however, this quantum advantage is restricted to a single receiver, since decoding measurements inevitably destroy the encoded information. Contrary to this, we address how long the information encoded in a single qubit remains accessible even after multiple decoding, each with a quantum advantage. Introducing preparation distinguishability as an operational resource associated with the sender, we show that its interplay with measurement incompatibility on the receiver's side can mitigate measurement-induced disturbance, thereby enabling an arbitrarily long sequence of receivers to each retain a quantum advantage. Our results show that, even under repeated measurements, the information encoded in a qubit need not be entirely exhausted, revealing a stronger communication feature than previously recognised.