REDUCING DECOHERENCE IN QUANTUM-COMPUTER MEMORY WITH ALL QUANTUM BITSCOUPLING TO THE SAME ENVIRONMENT

Decoherence in quantum-computer memory due to the inevitable coupling to the external environment is examined. We make the assumption that a ll quantum bits (qubits) interact with the same environment rather tha n the assumption of separate environments for different qubits. It is found that the qubits decohere collectively. For some kinds of entangl ed input states, no decoherence occurs at all in the memory, even if t he qubits are interacting with the environment. Based on this phenomen on, a scheme is proposed for reducing the collective decoherence. We a lso discuss possible implications of this decoherence model for quantu m measurements.