Experimental Test of Sequential Weak Measurements for Certified Quantum Randomness Extraction

TL;DR

This paper experimentally tests the use of sequential weak measurements on entangled photons to potentially extract unlimited certified quantum randomness, analyzing their feasibility and robustness under realistic conditions.

Contribution

It demonstrates the practical implementation of sequential weak measurements for quantum randomness extraction and evaluates their performance with real optical setups.

Findings

Weak measurements can be implemented with current optical technology.

Performance improvement is limited to near-ideal quantum states.

Sequential weak measurements can preserve entanglement for multiple measurements.

Abstract

Quantum nonlocality offers a secure way to produce random numbers: their unpredictability is intrinsic and can be certified just by observing the statistic of the measurement outcomes, without assumptions on how they are produced. To do this, entangled pairs are generated and measured to violate a Bell inequality with the outcome statistics. However, after a projective quantum measurement, entanglement is entirely destroyed and cannot be used again. This fact poses an upper bound to the number of random numbers that can be produced from each quantum state when projective measurements are employed. Instead, by using weak measurements, some entanglement can be maintained and reutilized, and a sequence of weak measurements can extract an unbounded amount of randomness from a single state as predicted in Phys. Rev. A 95, 020102(R) (2017). We study the feasibility of these weak measurements, analyze the robustness to imperfections in the quantum state they are applied to, and then test them using an optical setup based on polarization-entangled photon pairs. We show that the weak measurements are realizable, but can improve the performance of randomness generation only in close-to-ideal conditions.