Measurement of Many-Body Quantum Correlations in Superconducting Circuits

TL;DR

This paper introduces a novel measurement scheme for superconducting circuits that enables the detection of many-body quantum correlations, enhancing the capabilities of quantum simulators in analyzing complex quantum states.

Contribution

It proposes a probe circuit leveraging Josephson junction non-linearity to measure multi-point correlations in superconducting quantum simulators, expanding their analytical scope.

Findings

Successfully demonstrated measurement of two-point correlations in an LC-ladder with a quantum impurity.

The scheme can detect quantum properties like squeezing.

Potential to measure higher-order correlations in superconducting circuits.

Abstract

Recent advances in superconducting circuit technology have made the fabrication of large, customizable circuits routine. This has led to their application to areas beyond quantum information and, in particular, to their use as quantum simulators. A key challenge in this effort has been the identification of the quantum states realized by these circuits. Here, we propose a probe circuit capable of reading out many-body correlations in an analog quantum simulator. Our measurement scheme, designed for many-photon states, exploits the non-linearity of the Josephson junction to measure two-point (and potentially higher-order) correlation functions of the superconducting phase operator. We demonstrate the capabilities of this design in the context of an LC-ladder with a quantum impurity. The proposed probe allows for the measurement of inherently quantum correlations, such as squeezing, and has the potential to significantly expand the scope of analog quantum simulations using superconducting circuits.