Test one to test many: a unified approach to quantum benchmarks

TL;DR

This paper introduces a unified method to efficiently test quantum benchmarks involving infinite input states using a single experimental setup, improving validation of quantum information protocols.

Contribution

It presents a universal approach to validate quantum benchmarks with a single entangled state and measurement, applicable to various quantum protocols involving coherent states.

Findings

Single setup can probe average fidelity over all coherent states

Method applies to teleportation, storage, amplification, and purification

Provides rigorous validation of quantum protocols using minimal resources

Abstract

Quantum benchmarks are routinely used to validate the experimental demonstration of quantum information protocols. Many relevant protocols, however, involve an infinite set of input states, of which only a finite subset can be used to test the quality of the implementation. This is a problem, because the benchmark for the finitely many states used in the test can be higher than the original benchmark calculated for infinitely many states. This situation arises in the teleportation and storage of coherent states, for which the benchmark of 50% fidelity is commonly used in experiments, although finite sets of coherent states normally lead to higher benchmarks. Here we show that the average fidelity over all coherent states can be indirectly probed with a single setup, requiring only two-mode squeezing, a 50-50 beamsplitter, and homodyne detection. Our setup enables a rigorous experimental validation of quantum teleportation, storage, amplification, attenuation, and purification of noisy coherent states. More generally, we prove that every quantum benchmark can be tested by preparing a single entangled state and measuring a single observable.