The Effect of Local Structure and Nonuniformity on DecoherenceFree States of Charge Qubit.pdfVIP

The Effect of Local Structure and Non-uniformity on Decoherence-Free States of Charge Qubits Tetsufumi Tanamoto and Shinobu Fujita Advanced LSI Technology Laboratory, Toshiba Corporation, Kawasaki 212-8582, Japan We analyze robustness of decoherence-free (DF) subspace in charge qubits when there are a local structure and non-uniformity that violate collective decoherence measurement condition. We solve master equations of up to four charge qubits and a detector as two serially coupled quantum point contacts (QPC) with an island structure. We show that robustness of DF states is strongly affected by local structure as well as by non-uniformities of qubits. 5 I. INTRODUCTION 0 0 2 Decoherence-free(DF) states1 are useful for collective c decoherence environment, even if there is a small sym- e metry breaking perturbation parameterized by η in the 2 D order of O(η) (η ≪ 1) . Nowadays, experiments for DF 8 states have been successful up to four qubits in pho- 3 4 2 ton system and in nuclear magnetic resonance (NMR) . FIG. 1: Qubits that use double dot charged states are capac- However, in solid-state qubits, it seems to be more dif- itively coupled to a QPC detector. 1 ficult to realize the collective decoherence environment v than in the case of optical or NMR qubits. This is be- 4 cause we could not prepare plenty of qubits with math- the robustness of four-qubit DF states writ