Abstract
Extending the qubit coherence times is a crucial task in building quantum information processing devices. In the three-dimensional cavity implementations of circuit QED, the coherence of superconducting qubits was improved dramatically due to cutting the losses associated with the photon emission. Next frontier in improving the coherence includes the mitigation of the adverse effects of superconducting quasiparticles. In these lectures, we review the basics of the quasiparticles dynamics, their interaction with the qubit degree of freedom, their contribution to the qubit relaxation rates, and approaches to control their effect.
Highlights
We will dispense with the spin-orbit coupling and associate the pair of states with the spin-up and spin-down electrons having the same orbital part of the wave function ψn(r)
L, m, n the product of wave functions is rapidly oscillating as a function or r suppressing the value of the integral and making it zero on average
Constructing a quantum information device calls for finding elementary building blocks capable of maintaining quantum coherence over extended time periods
Summary
The electron condensate in an isolated island accommodates an even number of particles. If the number of electrons on the island is even, they all reside in the condensate in a T = 0 equilibrium state. Ionization of the Cooper pairs results in a higher number of equilibrium quasiparticles, diminishing this even-odd effect. To see this we evaluate and compare the partition functions Z0 and Z1 for the even and odd numbers of electrons, respectively [3]. The origin of the excess quasiparticles is not known and remains under scrutiny It is worth assessing how harmful they are for the qubits operation and look for ways to mitigate their unwanted effects
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