Abstract
The analysis of charge noise based on the Bloch-Redfield treatment of an ensemble of dissipative two-level fluctuators generally results in a violation of the fluctuation-dissipation theorem. The standard Markov approximation (when applied to the two-level fluctuators coupled to a bath) can be identified as the main origin of this failure. The resulting decoherence rates only involve the bath response at the fluctuator frequency, and thus completely neglect the effects of frequency broadening. A systematic and computationally convenient way to overcome this issue is to employ the spectator-qubit method: by coupling an auxiliary qubit to the two-level fluctuator ensemble, an analytical approximation for $S({\omega})$ fully consistent with the fluctuation-dissipation theorem can be obtained. We discuss the resulting characteristics of the noise which exhibits distinct behavior over several frequency ranges, including a $1/f$ to $1/f^2$ crossover with a $T^3$ temperature dependence of the crossover frequency.
Highlights
Random fluctuations of physical quantities in a qubit or its surrounding environment lead to decoherence limiting qubit performance
In widely used circuits such as the transmon [7] and fluxonium qubits [8], noise in different frequency ranges plays distinct roles in limiting coherence times: while dephasing rates are typically governed by low-frequency noise (e.g., 1/ f noise), relaxation processes are usually dominated by high-frequency noise (e.g., Nyquist noise)
While the presence of the spectator qubit is key to this method, we emphasize that the resulting noise spectral density is a property of the two-level fluctuators (TLFs) only, and independent of the spectator qubit
Summary
Random fluctuations of physical quantities in a qubit or its surrounding environment lead to decoherence limiting qubit performance. Inspection of the noise spectral density derived from Bloch-Redfield theory reveals violations of the fluctuation-dissipation theorem [28] This theorem directly relates the negative-frequency part of S(ω) to its positive-frequency counterpart, or equivalently, the symmetrized spectral density to the imaginary part of a response function. To overcome this issue, we abandon Bloch-Redfield theory and instead extract S(ω) by computing the depolarization rate of an auxiliary qubit weakly coupled to the noise source.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
