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Abstract
The fluxonium qubit has arisen as one of the most promising candidate devices for implementing quantum information in superconducting devices, since it is both insensitive to charge noise (like flux qubits) and insensitive to flux noise (like charge qubits). Here, we investigate the stability of the quantum information to quasiparticle tunneling through a Josephson junction. Microscopically, this dephasing is due to the dependence of the quasiparticle transmission probability on the qubit state. We argue that on a phenomenological level the dephasing mechanism can be understood as originating from heat currents, which are flowing in the device due to possible effective temperature gradients, and their sensitivity to the qubit state. The emerging dephasing time is found to be insensitive to the number of junctions with which the superinductance of the fluxonium qubit is realized. Furthermore, we find that the dephasing time increases quadratically with the shunt-inductance of the circuit which highlights the stability of the device to this dephasing mechanism.
Highlights
Among the various types of superconducting qubits [1,2,3], the recently developed fluxonium qubit [4, 5] has the unique advantage of being protected against both charge and flux noise
We have studied the impact of the phase sensitivity of the quasiparticle transport on the coherence properties of the fluxonium qubit
Using a phenomenological approach, based on the study of heat currents carried by quasiparticles and the associated heat conductance, we have shown that the dephasing time is inversely proportional to the sensitivity, a quantity describing to which extent possible heat currents flowing in the device depend on the state of the qubit
Summary
Among the various types of superconducting qubits [1,2,3], the recently developed fluxonium qubit [4, 5] has the unique advantage of being protected against both charge and flux noise This is important since both effects in general limit the performance of the qubits by introducing relaxation and dephasing processes. Our approach has the advantage that we are able to consider very small temperature gradients—corresponding to superconducting qubit segments with identical superconducting gaps In this regime, the dominating effect of the heat-current sensitivity to the qubit state stems from the phase-dependence of a weak bound state originating from Andreev reflection.
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