Widening the sharpness modulation region of an entanglement-assisted sequential quantum random access code: Theory, experiment, and application

TL;DR

This paper introduces an entanglement-assisted sequential quantum random access code protocol that broadens the measurement sharpness modulation region, demonstrates experimental success surpassing classical bounds, and explores applications in device-independent randomness and quantum decoding.

Contribution

It presents a novel entanglement-assisted sequential QRAC scheme with an expanded sharpness modulation region and experimental validation, enabling advanced quantum information tasks.

Findings

Achieved over 27 standard deviations above classical success probability.

Widened the sharpness modulation region from a line to a triangle in measurement parameters.

Demonstrated applications in device-independent randomness expansion.

Abstract

The sequential quantum random access code (QRAC) allows two or more decoders to obtain a desired message with higher success probability than the best classical bounds by appropriately modulating the measurement sharpness. Here, we propose an entanglement-assisted sequential QRAC protocol which can enable device-independent tasks. By relaxing the equal sharpness and mutually unbiased measurement limits, we widen the sharpness modulation region from a one-dimensional interval to a two-dimensional triangle. Then, we demonstrate our scheme experimentally and get more than 27 standard deviations above the classical bound even when both decoders perform approximately projective measurements. We use the observed success probability to quantify the connection among sequential QRAC, measurement sharpness, measurement biasedness, and measurement incompatibility. Finally, we show that our protocol can be applied to sequential device-independent randomness expansion and our measurement strategy can enhance the success probability of decoding the entire input string. Our results may promote a deeper understanding of the relationship among quantum correlation, quantum measurement, and quantum information processing.