Device-independent quantum memory certification in two-point measurement experiments

TL;DR

This paper introduces a device-independent method to certify quantum memories by testing temporal correlations against classical models, demonstrated with a trapped-ion system storing a qubit for 35 ms.

Contribution

It presents a novel, assumption-free approach for verifying quantum memories using causal inequalities and temporal correlations, validated experimentally.

Findings

Successfully certified 35 ms of qubit memory in a trapped-ion system.

Demonstrated the effectiveness of causal inequalities in quantum memory certification.

Established a practical framework for benchmarking quantum technologies.

Abstract

Quantum memories are key components of emerging quantum technologies. They are designed to store quantum states and retrieve them on demand without losing features such as superposition and entanglement. Verifying that a memory preserves these features is indispensable for applications such as quantum computation, cryptography and networks, yet no general and assumption-free method has been available. Here, we present a device-independent approach for certifying black-box quantum memories, requiring no trust in any part of the experimental setup. We do so by probing quantum systems at two points in time and then confronting the observed temporal correlations against classical causal models through violations of causal inequalities. We perform a proof-of-principle experiment in a trapped-ion quantum processor, where we certify 35 ms of a qubit memory. Our method establishes temporal correlations and causal modelling as practical and powerful tool for benchmarking key ingredients of quantum technologies, such as quantum gates or implementations of algorithms.