Criticality-Enhanced Quantum Sensing with a Parametric Superconducting Resonator

Quantum metrology, a cornerstone of quantum technologies, exploits entanglement and superposition to achieve higher precision than classical protocols in parameter estimation tasks. When combined with critical phenomena such as phase transitions, the divergence of quantum fluctuations is predicted to enhance the performance of quantum sensors. Here, we implement a critical quantum sensor using a superconducting parametric (i.e., two-photon driven) Kerr resonator. The sensor, a linear resonator terminated by a supercondicting quantum interference device, operates near the critical point of a finite-component second-order dissipative phase transition obtained by scaling the system parameters. We analyze the performance of a frequency-estimation protocol and show that quadratic precision scaling with respect to the system size can be achieved with finite values of the Kerr nonlinearity. Since each photon emitted from the cavity carries more information about the parameter to be estimated compared to its classical counterpart, our protocol opens perspectives for faster or more precise metrological protocols. Our results demonstrate that quantum advantage in a sensing protocol can be achieved by exploiting a finite-component phase transition.

💡 Research Summary

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The authors present a concrete implementation of a critical‑enhanced quantum sensor using a superconducting parametric (two‑photon driven) Kerr resonator. The device consists of a λ/4 microwave cavity whose non‑linearity and resonance frequency are tunable via a SQUID terminating one end of the resonator. By applying a static magnetic flux to the SQUID they control the Kerr coefficient (U) and the bare cavity frequency (\omega_r). Simultaneously, a coherent pump at nearly twice the cavity frequency provides a two‑photon drive of amplitude (G), establishing the Hamiltonian
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