Enhanced qubit readout using locally-generated squeezing and inbuilt Purcell-decay suppression

Abstract

We introduce and analyze a dispersive qubit readout scheme where two-mode squeezing is generated directly in the measurement cavities. The resulting suppression of noise enables fast, high- fidelity readout of naturally weakly coupled qubits, and the possibility to protect strongly coupled qubits from decoherence by weakening their coupling. Unlike other approaches exploiting squeezing, our setup avoids the difficult task of transporting and injecting with high fidelity an externally-generated squeezed state. Our setup is also surprisingly robust against unwanted non-QND backaction effects, as interference naturally suppresses Purcell decay: the system acts as its own Purcell filter. Our setup is compatible with the experimental state-of-the-art in circuit QED systems, but the basic idea could also be realized in other systems.

6 pages main text, 4 figures, 8 pages supplementary appendices

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• Photon-noise-tolerant dispersive readout of a superconducting qubit using a nonlinear Purcell filter
• Stabilizing two-qubit entanglement by mimicking a squeezed environment
• Exponentially Improved Dispersive Qubit Readout with Squeezed Light
• Nuclear spin readout in a cavity-coupled hybrid quantum dot-donor system
• Interferometric Purcell suppression of spontaneous emission in a superconducting qubit
• Hybrid phase-space--Fock-space approach to evolution of a driven nonlinear resonator
• Beating the 3 dB Limit for Intracavity Squeezing and Its Application to Nondemolition Qubit Readout