YQI Colloquium - Alexandre Blais - Université de Sherbrooke

Circuit quantum electrodynamics (cQED) has emerged as a powerful platform for quantum computation and for investigating quantum optics at microwave frequencies. A critical aspect of all cQED experiments is qubit readout, which relies on microwave drives. In principle, higher drive amplitudes should lead to faster and more accurate readout. However, an unexplained degradation in readout fidelity occurs even with moderate drive amplitudes, limiting the improvement of superconducting qubit readout. In this talk, we investigate the behavior of qubit readout in cQED. We begin by reviewing the measurement process in this architecture and presenting numerical results of the dynamics of a transmon-resonator system under measurement. Our findings reveal signatures of transmon ionization where the qubit escapes from its cosine potential. We further explore the connections between these observations and chaos in the classically driven transmon. Finally, we propose an approach to mitigating the impact of strong drives on the system by controllably decoupling the qubit from the cavity’s photon population. This technique effectively cloaks the qubit from the cavity, offering a promising avenue for improving readout fidelity in circuit QED systems.

 

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