Interplay and optimization of decoherence mechanisms in the optical
  control of spin quantum bits implemented on a semiconductor quantum dot

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Abstract

We study the influence of the environment on an optically induced rotation of a single electron spin in a charged semiconductor quantum dot. We analyze the decoherence mechanisms resulting from the dynamical lattice response to the charge evolution induced in a trion-based optical spin control scheme. Moreover, we study the effect of the finite trion lifetime and of the imperfections of the unitary evolution such as off-resonant excitations and the nonadiabaticity of the driving. We calculate the total error of the operation on a spin-based qubit in an InAs/GaAs quantum dot system and discuss possible optimization against the different contributions. We indicate the parameters which allow for coherent control of the spin with a single qubit gate error as low as \(10^{-4}\).

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Phonon-Assisted Damping of Rabi Oscillations in Semiconductor Quantum Dots

J. Förstner, C. Weber, J. Danckwerts … (2003)

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Phonon-induced decay of the electron spin in quantum dots

, , (2003)

We study spin relaxation and decoherence in a GaAs quantum dot due to spin-orbit interaction. We derive an effective Hamiltonian which couples the electron spin to phonons or any other fluctuation of the dot potential. We show that the spin decoherence time \(T_2\) is as large as the spin relaxation time \(T_1\), under realistic conditions. For the Dresselhaus and Rashba spin-orbit couplings, we find that, in leading order, the effective magnetic field can have only fluctuations transverse to the applied magnetic field. As a result, \(T_2=2T_1\) for arbitrarily large Zeeman splittings, in contrast to the naively expected case \(T_2\ll T_1\). We show that the spin decay is drastically suppressed for certain magnetic field directions and values of the Rashba coupling constant. Finally, for the spin coupling to acoustic phonons, we show that \(T_2=2T_1\) for all spin-orbit mechanisms in leading order in the electron-phonon interaction.