Dephasing of Majorana qubits due to quasistatic disorder

Quantum bits based on Majorana zero modes are expected to be robust against certain noise types, and hence provide a quantum computing platform that is superior to conventional qubits. This robustness is not complete, though: imperfections can still lead to qubit decoherence and hence to information loss. In this work, we theoretically study Majorana-qubit dephasing in a minimal model: in a Kitaev chain with quasistatic disorder. Our approach, based on numerics as well as first-order nondegenerate perturbation theory, provides a conceptually simple physical picture and predicts Gaussian dephasing. We show that as system parameters are varied, the dephasing rate due to disorder oscillates out-of-phase with respect to the oscillating Majorana splitting of the clean system. In our model, first-order dephasing sweet spots are absent if disorder is uncorrelated. We describe the crossover between uncorrelated and highly correlated disorder, and show that dephasing measurements can be used to characterize the disorder correlation length. We expect that our results will be utilized for the design and interpretation of future Majorana-qubit experiments.