Squeezed light enhances readout SNR in multilevel systems.

A widely used method for measuring qubits faces a fundamental challenge: qubit decay during the measurement itself, alongside limitations in signal-to-noise ratio. Researchers are now applying squeezed-light states to overcome these issues, a technique driven by the need for both speed and fidelity in quantum readout protocols. This approach encodes qubit information into a squeezed cavity, preventing state-dependent rotation and ensuring enhanced signal, and now extends to multilevel systems for advanced quantum information processing. Dispersive readout, a prevalent technique for measuring qubits in circuit quantum electrodynamics and optomechanical systems, contends with inherent limitations stemming from qubit-state decay during measurement and finite signal-to-noise ratios in single-shot readings. These challenges restrict the ultimate fidelity achievable with this widely implemented method, demanding innovative solutions to maintain qubit coherence throughout the readout process. The performance…