Generation of squeezed states of microwave radiation in a superconducting resonant circuit

TL;DR

This paper presents a theoretical method to generate squeezed microwave states in superconducting resonators with tunable parameters, enhancing measurement precision and quantum readout fidelity.

Contribution

It introduces a novel approach to produce squeezed states by dynamically tuning the resonance frequency of superconducting circuits using an RF SQUID.

Findings

Squeezed states can be generated in the 0.1-10 GHz range.

Small frequency shifts are sufficient for squeezing.

Protocols for experimental verification are proposed.

Abstract

High-quality superconducting oscillators have been successfully used for quantum control and readout devices in conjunction with superconducting qubits. Also, it is well known that squeezed states can improve the accuracy of measurements to subquantum, or at least subthermal, levels. Here we show theoretically how to produce squeezed states of microwave radiation in a superconducting oscillator with tunable parameters. The circuit impedance, and thus the resonance frequency, can be changed by controlling the state of an RF SQUID inductively coupled to the oscillator. By repeatedly shifting the resonance frequency between any two values, it is possible to produce squeezed and subthermal states of the electromagnetic field in the (0.1--10) GHz range, even when the relative frequency change is small. We propose experimental protocols for the verification of squeezed state generation, and for their use to improve the readout fidelity when such oscillators serve as quantum transducers.