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Physical Review B

Optimal quantum gates for semiconductor qubits

Ulrich Hohenester

Published Oct 27, 2006• 45 citations
Publisher

Abstract

We employ optimal control theory to design optimized quantum gates for solid-state qubits subject to decoherence. At the example of a gate-controlled semiconductor quantum dot molecule we demonstrate that decoherence due to phonon couplings can be strongly suppressed. Our results suggest a much broader class of quantum control strategies in solids.

DOI
10.1103/physrevb.74.161307

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We employ optimal control theory to design optimized quantum gates for solid-state qubits subject to decoherence. At the example of a gate-controlled semiconductor quantum dot molecule we demonstrate that decoherence due to phonon couplings can be strongly suppressed. Our results suggest a much broader class of quantum control strategies in solids.
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We study phonon-assisted dephasing in optically excited semiconductor quantum dots within the frameworks of the independent Boson model and optimal control. Using a realistic description for the quantum dot states and the phonon coupling, we demonstrate that such dephasing has a drastic impact on the coherent optical response. We employ optimal control theory to search for control strategies that allow to fight decoherence, and show that appropriate tailoring of laser pulses allows a complete control of the optical excitation despite the phonon dephasing.
We have studied quantum coherence and control in solid-state qubits, mostly in superconductors. We have outlined several strategies to obtain high-fidelity quantum logic gates in the presence of decoherence. We have studied realistic, structured environments to qubits, including environments with resonances, slow noise, and non-Markovian effects. In all cases, we have formulated strategies how to master and engineer the decoherence properties. We have analyzed examples from superconducting charge and flux qubits as well as quantum dots.
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