No abstract

Quantum state transfer and teleportation, with qubits encoded in internal states of the atoms in cavities, among spatially separated nodes of a quantum network in decoherence-free subspace are proposed, based on a cavity-assisted interaction by single-photon pulses. We show in details the implementation of a logic-qubit Hadamard gate and a two-logic-qubit conditional gate, and discuss the experimental feasibility of our scheme.PACS numbers: 03.67. Hk, 42.50.Dv Quantum state transfer and teleportation are significant components in quantum information processing, especially for quantum network. As the confined atoms in cavity QED system are well suited for storing qubits in long-lived internal states, spatially separated cavities could be used to build a quantum network assisted by photons [1,2,3,4,5,6,7,11]. On the other hand, decoherence due to the inevitable interaction with environment destroys quantum coherence. So decoherence-free subspaces (DFSs) of Hilbert space has been introduced to protect against some errors due to environmental coupling with certain symmetry [8,9,10]. For example, Ref.[10] utilized two atoms to encode single-logic-qubit, i.e.,, which are robust to collective dephasing error caused by ambient magnetic fluctuation.In this Brief Report, for the quantum state encoded in DFS mentioned above, we present implementation of single-logic-qubit Hadamard gate and two-logic-qubit conditional gate based on cavity-assisted interaction with single-photon pulses. Based on these gates, we will carry out the quantum state transfer and teleportation between two spatially separated nodes in a quantum network. Compared with previous related works, our proposal does not rely on the synchronous optical lattices [4] in implementation of the single-logic-qubit Hadamard gate. In addition, auxiliary entangled photon pairs, as employed in [5], are unnecessary in our two-logic-qubit conditional gate. Moreover, for quantum state transfer, neither the entangled photon pairs [11] nor the special time-symmetric wave packet of the photons [1] is necessary in our scheme. So our scheme could not only protect quantum information from some decoherence, but also reduce the experimental difficulty compared to the previous schemes [1,4,5,11]. Furthermore, in our scheme, each node of the quantum network in DFS has individual input port for photons to complete necessary operations, and different operational results can be distinguished by * Electronic address: huawei.hw@gmail.com † Electronic address: mangfeng1968@yahoo.com detecting output photons.The main idea using cavity-assisted photon scattering to realize a controlled phase flip (CPF) between two atoms [3,4,5,6,11], is sketched below. Suppose that two identical atoms, each of which has a three-level configuration, are well located in a high-finesse cavity. The levels |0 and |e of the atom are resonantly coupled by the bare cavity mode with h polarization or by the h component of an input photon, while level |1 is decoupled because of the large detuning, as shown in Fi...

Following the proposal by F. Yamaguchi et al.[Phys. Rev. A 66, 010302 (R) (2002)], we present an alternative way to implement the two-qubit Grover search algorithm in cavity QED. Compared with F. Yamaguchi et al.'s proposal, with a strong resonant classical field added, our method is insensitive to both the cavity decay and thermal field, and doesn't require that the cavity remain in the vacuum state throughout the procedure. Moreover, the qubit definitions are the same for both atoms, which makes the experiment easier. The strictly numerical simulation shows that our proposal is good enough to demonstrate a two-qubit Grover's search with high fidelity.