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physica status solidi (b)

Decoherence in flux qubits on mesoscopic nonsuperconducting rings

Marcin Kurpas, Jerzy Dajka, E. Zipper

Published May 7, 2007• 2 citations
Publisher

Abstract

Abstract The problem of decoherence in recently proposed flux qubits built on mesoscopic normal metal rings is studied. The relaxation and dephasing times coming from the interaction of the qubit with the measuring device are calculated within the weak coupling spin‐boson model. We analyze the effect of the measuring apparatus on the relaxation and dephasing times. The possibility of ohmic approximation for the bath is investigated. Considerably long decoherence times are found. The work is limited to the weak damping regime in low temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI
10.1002/pssb.200674641

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We investigate the decoherence and dephasing of two coupled Josephson qubits. With the interaction between the qubits being generated by current–current correlations, two different situations in which the qubits are coupled to the same bath, or to two independent baths, are considered. Upon focussing on dissipation being caused by the fluctuations of voltage sources, the relaxation and dephasing rates are explicitly evaluated. Analytical and numerical results for the coupled qubits dynamics are provided.
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Abstract A three level scheme based on S–P polaron intersublevel transitions in n‐doped InAs/GaAs self‐assembled quantum dots is proposed to obtain laser effect around 25 µm wavelength under optical pumping. Temperature dependence of the optical gain is theoretically analysed. Lasing effect is expected up to 300 K. To probe the T 2 decoherence time, one of the key parameter driving the laser performances, an optical Rabi oscillation experiment is performed on the pumping transition. Transmission variation is measured as a function of the pump pulse area and modelled by 2‐level optical Bloch equations considering inhomogeneous contributions. We show that the non‐monotonous population dependence and damping of the oscillation is only compatible with a T 2 ∼ 5 ps dephasing time, one order of magnitude longer than in quantum wells and one order of magnitude shorter than the 45 ps relaxation time of the S–P transition, demonstrating a non relaxation‐limited decoherence for the transition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)