Secure and robust randomness with sequential quantum measurements

TL;DR

This paper introduces a new framework for sequential quantum measurements that enhances randomness generation and security, demonstrating improved robustness and practical feasibility through theoretical analysis and photonic implementation.

Contribution

It provides a geometric and mathematical framework for sequential quantum correlations, establishing a Tsirelson-like boundary and demonstrating improved performance in secure randomness protocols.

Findings

Achieves maximum randomness certification with one remote and two sequential parties.

Establishes a Tsirelson-like boundary for sequential quantum correlations.

Demonstrates robustness under realistic noise and feasibility via photonic implementation.

Abstract

Quantum correlations between measurements of separated observers are crucial for applications like randomness generation and key distribution. Although device-independent security can be certified with minimal assumptions, current protocols have limited performances. Here, we exploit sequential measurements, defined with a precise temporal order, to enhance performances by reusing quantum states. We provide a geometric perspective and a general mathematical framework, analytically proving a Tsirelson-like boundary for sequential quantum correlations, which represents a trade-off in nonlocality shared by sequential users. This boundary is advantageous for secure quantum randomness generation, certifying maximum bits per state with one remote and two sequential parties, even if one sequential user shares no nonlocality. Our simple qubit protocol reaches this boundary, and numerical analysis shows improved robustness under realistic noise. A photonic implementation confirms feasibility and robustness. This study advances understanding of sequential quantum correlations and offers insights for efficient device-independent protocols.