Suppression of energy-relaxation-induced decoherence in Λ-type three-level SQUID flux qubits: A dark-state approach

Abstract

We report a theoretical investigation of decoherence induced by energy relaxation of the auxiliary level in the Λ-type three-level SQUID flux qubits. We show that the energy-relaxation-induced decoherence in this particular case is proportional to the average population of the auxiliary level and thus can be effectively suppressed by the use of a dark-state approach in which the auxiliary level is unpopulated. We demonstrate through bit-flip operation that the dark state can be realized by means of the stimulated Raman adiabatic passage (STIRAP). An extension of the dark-state scheme to create any superposition state is straightforward.