Curator's Take
AI Commentary
This article shows that applying squeezed‑microwave fields during the dispersive readout of a superconducting‑qubit magnetometer can reclaim up to 27 % of the Fisher information lost in state‑assignment errors, directly tightening the magnetic‑field sensitivity bound without altering the Ramsey encoding stage. By framing the effect in terms of an effective detected mode that balances squeezed and anti‑squeezed quadrature noise, the work builds on recent demonstrations of microwave squeezing for qubit readout and provides a concrete recipe for hardware‑level error mitigation in quantum sensors. The result is especially relevant for near‑term superconducting platforms where measurement fidelity remains a bottleneck, although the benefit hinges on precise alignment between the squeezed quadrature and the discrimination axis.
— Mark Eatherly
Summary
The performance of superconducting-qubit magnetometers depends not only on magnetic-field encoding during Ramsey interrogation, but also on how efficiently the encoded information is recovered during readout. Here we quantify how squeezed-microwave-assisted dispersive readout can recover magnetic-field information lost during qubit-state assignment. We develop an effective detected-mode framework linking projected quadrature noise, state-assignment error, and the classical Fisher information accessible from binary readout outcomes. A finite mismatch between the squeezed quadrature and the discrimination axis produces an optimal squeezing strength through the competition between squeezed and anti-squeezed fluctuations. For representative parameters, squeezed readout reduces the readout-limited magnetic-field sensitivity bound by $27.3\%$. This improvement arises from recovering information lost in the readout stage rather than from increasing the information encoded during Ramsey interrogation. These results may provide a practical route for mitigating measurement-stage information loss in superconducting quantum sensing.