进不同分系统, + B 或 D + E 的合成系统 C 的分解,可以在避免 decoherence 帮助。例如,为 + B 系统不必破坏的 A 的导致环境的 decoherence 在 D+E 系统(A+B = C = D+E ) 在场的纠纷。这条新途径在可能最后导致量计算的一个新模型的量计算理论的基础也开一些问题。
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.