Practical Tests of Quantumness Using Multipartite Bell-Type Inequalities

Abstract:

As time has progressed, quantum processing units (QPUs) have become increasingly accessible, offering anyone the opportunity to run programs on real quantum hardware. However, the extent to which current QPUs demonstrate genuine quantum behavior still remains a vital question to address- after all it is important to know if real quantum computers are using quantum mechanics and not just expensive classical machines. To do this, the Bell inequalities can be used. Bell inequalities are mathematical tools used to detect entanglement and nonlocality; their violation confirms that the correlations produced by a QPU cannot be explained by any classical theory, allowing the confirmation of genuine quantum behavior. As a result, it is possible to use these tools to investigate the efficiency of Bell inequalities and their ability to withstand noise, in effect, allowing the evaluation of whether they make beneficial quantum tests. By generating three to five qubit GHZ states and applying optimized measurement settings designed to maximize inequality violation under both ideal and noisy conditions on a locally run simulator allows the graphing of how quickly Bell inequalities fall under the classical boundary based on the noise strength, conveying how easily they can test for quantumness despite noise. In conclusion, by evaluating multipartite Bell inequalities as a quantitative benchmark, this work contributes to the foundational understanding of testing how “quantum” today’s quantum computers truly are. This study demonstrates that multipartite Bell inequalities provide a quantitative benchmark for assessing the genuine quantumness of contemporary quantum computers.