Effects of imperfect noise correlations on decoherence-free subsystems: SU(2) diffusion model

Abstract

We present a model of an N-qubit channel where consecutive qubits experience correlated random rotations. Our model is an extension to the standard decoherence-free subsystems approach (DFS) which assumes that all the qubits experience the same disturbance. The variation of rotations acting on consecutive qubits is modeled as diffusion on the SU(2) group. The model may be applied to spins traveling in a varying magnetic field, or to photons passing through a fiber whose birefringence fluctuates over the time separation between photons. We derive an explicit formula describing the action of the channel on an arbitrary N-qubit state. For N=3 we investigate the effects of diffusion on both classical and quantum capacity of the channel. We observe that nonorthogonal states are necessary to achieve the optimal classical capacity. Furthermore we find the threshold for the diffusion parameter above which coherent information of the channel vanishes.

11 pages, 6 figures, improved clarity, more discussion, many new references and the title changed

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Cited by in corpus (5)

• Quantum channels and memory effects
• Memory effects in attenuation and amplification quantum processes
• Classical capacity of Gaussian thermal memory channels
• Decoherence and Quantum Error Correction for Quantum Computing and Communications
• Suppressing correlated noise in signals transmitted over the Gaussian memory channels using $2N$-port splitter and phase flips