Experimental Device-independent Tests of Classical and Quantum Dimensions

TL;DR

This paper demonstrates experimental methods to determine the classical or quantum dimension of a system in a device-independent manner, crucial for secure communication and understanding non-classical correlations.

Contribution

It introduces experimental techniques for device-independent dimension testing of systems emitted by black boxes, advancing secure quantum information protocols.

Findings

Dimension witnesses effectively distinguish classical and quantum systems.

Experimental results support the use of dimension witnesses in unreliable source scenarios.

The approach enhances the security and reliability of quantum communication systems.

Abstract

A fundamental resource in any communication and computation task is the amount of information that can be transmitted and processed. Information encoded in a classical system is limited by the dimension d_c of the system, i.e., the number of distinguishable states. A system with d_c=2^n classical states can carry n bits of classical information. Information encoded in a quantum system is limited by the dimension d_q of the Hilbert space of the system, i.e., the number of perfectly distinguishable quantum states. A system with d_q=2^n perfectly distinguishable quantum states can carry n qubits of quantum information. Physical systems of higher dimensions may enable more efficient and powerful information processing protocols. The dimension is fundamental in quantum cryptography and random number generation, where the security of many schemes crucially relies on the system's dimension. From a fundamental perspective, the dimension can be used to quantify the non-classicality of correlations, since classical simulation of correlations produced by a quantum system of dimension d_q may require a classical system of dimension d_c >> d_q. For all these reasons, a fundamental problem in information theory is to assess the (classical or quantum) dimension of a physical system in a "device-independent" scenario, i.e., without referring to the system's specifications, which may be under control of a dishonest supplier, eavesdropper or saboteur. In this contribution we report experiments realizing this goal for systems emitted by a black box. Our results indicate that dimension witnesses utilized in the experiments may become a powerful tool for testing systems provided by unreliable sources.