Decoherence-Free Subspaces for Multiple-Qubit Errors: (I) Characterization

Abstract

Coherence in an open quantum system is degraded through its interaction with a bath. This decoherence can be avoided by restricting the dynamics of the system to special decoherence-free subspaces. These subspaces are usually constructed under the assumption of spatially symmetric system-bath coupling. Here we show that decoherence-free subspaces may appear without spatial symmetry. Instead, we consider a model of system-bath interactions in which to first order only multiple-qubit coupling to the bath is present, with single-qubit system-bath coupling absent. We derive necessary and sufficient conditions for the appearance of decoherence-free states in this model, and give a number of examples. In a sequel paper we show how to perform universal and fault tolerant quantum computation on the decoherence-free subspaces considered in this paper.

18 pages, no figures. Major changes. Section on universal fault tolerant computation removed. This section contained a crucial error. A new paper [quant-ph/0007013] presents the correct analysis

References in corpus (5)

• Universal Fault-Tolerant Computation on Decoherence-Free Subspaces
• On Universal and Fault-Tolerant Quantum Computing
• Decoherence-Free Subspaces for Multiple-Qubit Errors: (II) Universal, Fault-Tolerant Quantum Computation
• Protecting Quantum Information Encoded in Decoherence Free States Against Exchange Errors
• Pauli Exchange Errors in Quantum Computation

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