Prepare-and-measure scenarios with photon-number constraints

TL;DR

This paper develops a semidefinite programming approach to analyze quantum correlations in prepare-and-measure scenarios with photon-number constraints, enhancing certification and randomness generation in optical quantum communication.

Contribution

It introduces a novel method using semidefinite relaxations to bound quantum correlations under photon-number restrictions, applicable to various communication and randomness protocols.

Findings

Bounded quantum correlations under photon-number constraints.

Improved randomness extraction in optical protocols.

Demonstrated practical computation of optimal performance bounds.

Abstract

We study correlations in the prepare-and-measure scenario when quantum communication is constrained by photon-number statistics. Such constraints are natural and practical control parameters for semi-device-independent certification in optical platforms. To analyse these scenarios, we show how semidefinite programming relaxations for non-commutative polynomial optimization can be used to bound the set of quantum correlations under restrictions on the photon-number distribution. The practicality of this method is demonstrated by computing optimal performance bounds on several well-known communication tasks. We then apply the method to the certification of semi-device-inpependent random number generation protocols and show how to bound the conditional Shannon entropy. We showcase this versatile tool by improving randomness extraction in established protocols based on coherent states and homodyne measurements.