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Benchmarking quantum devices based on fingerprints of quantum chaos
We have developed a new method to quantify the performance of analog quantum simulators, using insights from quantum chaos.
The state fidelity quantifies the closeness of two quantum states. While theoretically simple, the fidelity is difficult to measure in experiments since most conventional approaches require sophisticated controls not accessible in existing devices. CUA researchers and collaborators developed a new simple method that is ready to implement in existing analog quantum simulators.
The new protocol exploits a ubiquitous nature of quantum dynamics: chaos and information scrambling. Usually seen as a hindrance, measurement outcomes obtained from chaotic quantum dynamics look random, yet we have discovered that this randomness in fact exhibits a subtle and delicate pattern, so-called speckle pattern, obeying universal statistical properties. The idea is to utilize speckle patterns as fingerprints of quantum states in order to quantitatively compare different states.
The simplicity of our method makes it suitable for a diverse range of quantum devices available in laboratories today. Our work enables further applications including the simultaneous calibration of multiple experimental parameters, with applications to the precise characterization of quantum devices, as well as to quantum sensors.
Figure: (a) The method applies to a wide range of quantum devices, including analog devices which have minimal controls. (b) It is enabled by a theoretical discovery that measurements on a quantum state after chaotic evolution exhibit universal statistical properties, serving as a fingerprint of the original state. (c) The method can be used to measure the degradation of the quantum state over time in the presence of a fixed error (green) or continuously occurring errors (blue).