A two-level system (gubit, shown in blue) with energy splitting ωq is affected by noise δωq (red) and is placed inside a single-mode electromagnetic cavity with frequency ωc. Partially transparent mirrors allow for the interaction of the qubit-cavity system with external modes. An input field binðtÞ enters at port 1, causing an output field boutðtÞ that leaves the cavity at port 2, thereby creating a time-dependent transmission through the system from left to right.

Fingerprints of Qubit Noise in Transient Cavity Transmission

P. M. Mutter, G. Burkard
Phys. Rev. Lett. 128, 236801 (2022)

Noise affects the coherence of qubits and thereby places a bound on the performance of quantum computers. We theoretically study a generic two-level system with fluctuating control parameters in a photonic cavity and find that basic features of the noise spectral density are imprinted in the transient transmission through the cavity. We obtain analytical expressions for generic noise and proceed to study the cases of quasistatic, white and 1/fα noise in more detail. Additionally, we propose a way of extracting the noise power spectral density in a frequency band only bounded by the range of the qubit-cavity detuning and with an exponentially decaying error due to finite measurement times. Our results suggest that measurements of the time-dependent transmission probability represent a novel way of extracting noise characteristics.

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