Decoherence Control for Optical Qubits

Chunyan Li, Zu-Rong Zhang, Shi‐Hai Sun +2 more

The implementation of an optical system universal logic-qubit controlled-NOT gate of decoherence-free subspaces (DFSs) using the cross-Kerr nonlinearity effect is discussed. Both the control qubit and the target qubit contain two photons, the states of which are DFSs of collective-rotating noise or collective-dephasing noise. A three-qubit parity-check circuit, which is the most important unit of the quantum gate, is proposed first, and only one ancillary photon is needed in our scheme. A single-photon source, linear optical apparatus, and quantum nondemolition detector are used to perform the process. Its efficiency may approach 100% with a feed-forward process. The experimental feasibility of the strategy with current technology is also considered.

K. M. Fonseca-Romero, Sigmund Kohler, Peter Hänggi A

Yan‐Ling Li, Mao-Fa Fang, Xing Mao Xiao +1 more

We propose a scheme for implementing a remote three-qubit controlled-Z gate with three atoms separately trapped in three distant cavities coupled by optical fibres. The influences of various decoherence processes, such as spontaneous emission of the atoms and photon leakage of the cavities and the optical fibres, on the fidelity are also investigated. It is found that the gate can be implemented with high fidelity even when these decoherence processes are considered. This scheme can be extended to the implementation of a remote N -qubit controlled-Z gate with N atoms separately trapped in N distant cavities coupled by optical fibres.

J. I. Cirac, Thomas Pellizzari, J. F. Poyatos +1 more

R. B. Dalton, Geoff Gillett, Geoff J. Pryde +4 more

Paweł Machnikowski, Anna Grodecka, Weber, Carsten +1 more

We discuss various methods of all-optical spin control in semiconductor quantum dots. We present different ways of rotating a single confined electron spin by optical coupling to a trion state. We also discuss a method for controlling the polarization of a confined exciton via a two-photon transition. Finally, we analyze the effect of phonon-induced decoherence on the fidelity of these optical spin control protocols.