Hong-Fu Wang

Converting two-atom singlet state into three-atom singlet state via quantum Zeno dynamics

An approach is presented for converting a two-atom singlet state into a three-atom singlet state based on the quantum Zeno dynamics induced by continuous coupling. The scheme can be achieved within one step through appropriately regulating the Rabi frequencies of the classical fields. The effects of decoherence such as atomic spontaneous emission and the loss of cavity are also considered in virtue of the master equation. The numerical simulation result shows that this proposal is especially robust against the cavity decay, since no cavity-photon population is involved during the whole process because of the quantum Zeno dynamics. Furthermore, if a multilevel atom and a multi-mode cavity are applicable, the N-atom singlet state could be derived directly from the (N−1)-atom singlet state with the same principle, which provides a scalable way for the preparation of |SN in theory.

Protocol and quantum circuit for implementing the N-bit discrete quantum Fourier transform in cavity QED

We present a simple protocol and quantum circuit for efficient implementation of the N-bit discrete quantum Fourier transform by using two-qubit controlled-NOT gate and SWCZ gate that is a combination of -SWAP and controlled-Z gates in cavity quantum electrodynamics. In this protocol long-lived electronic states in circular Rydberg atoms are used as quantum bits and the one-bit and two-bit quantum gate operations required for implementing the discrete quantum Fourier transform in the quantum circuit can be easily achieved with atom–microwave resonant interaction and atom–cavity interaction occurring only between two nearest-neighbour atoms. We present the detailed experimental procedure and analyse the experimental feasibility.

Schemes for the generation of multipartite entanglement of remote atoms trapped in separate optical cavities

Based on the interference effect of polarized photons leaking out of separate cavities, we propose schemes for the generation of the N-atom Greenberger–Horne–Zeilinger (GHZ) state, three-atom W state and a genuine four-atom entangled state |χ. In these schemes, each of the atoms is trapped separately in a remote optical cavity, and the possible spontaneous channels induced by the excited atoms lead to the coherent superposition of the states of the atoms. The desired multipartite entangled states can be generated with a certain success probability by the subsequent detection of the polarized photons in different modes. The schemes would be useful steps towards long-distance quantum communication, distributed quantum computation and constructing remote quantum information processing networks.

Distributed CNOT gate via quantum Zeno dynamics

We show how the quantum Zeno effect can be exploited to implement the CNOT gate in two separated cavities with two atomic four-level tripod systems. In respective subspaces of the total Hilbert space, the evolution of the quantum system exhibits different dynamical properties due to the continuous coupling between atoms and cavities. The strictly numerical simulation reveals that a high average gate fidelity can be obtained in the presence of decoherence.

Scheme for implementing linear optical quantum iSWAP gate with conventional photon detectors

A simple scheme is proposed to implement a two-qubit linear optical quantum iSWAP gate that is a universal gate in quantum computation and quantum information processing. By the interference effect of the polarized photons, a quantum iSWAP gate can be achieved with a low success probability (η4/32, with η being the quantum efficiency of photon detectors). The scheme is based only on simple linear optical elements, a pair of two-photon polarization entangled states, and conventional photon detectors that only distinguish the vacuum and nonvacuum Fock number states, which greatly decreases the experimental difficulty of implementing linear optical quantum computation.

Linear optical implementation of an ancilla-free quantum SWAP gate

We propose a simple linear optical scheme for directly implementing an ancilla-free two-qubit quantum SWAP gate with high success probability. The proposed setup consists of only simple linear optical elements and photon detectors without introducing additionally ancillary single photons or entangled photons sources. The scheme is feasible and within the reach of current experimental technology.

PHASE MATCHING IN FIXED-POINT QUANTUM SEARCH ALGORITHM

We investigate the phase matching problem in the fixed-point quantum search algorithm proposed by Grover [Phys. Rev. Lett.95 (2005) 150501]. We show that the optimal phase shift is π/3.61, which replaces the π/3 phase shift in fixed-point quantum search algorithm. The π/3.61-phase algorithm can be achieved in with the success probability of at least 94.11%, which offsets disadvantage that the success probability of getting correct results usually decreases with the increase of marked items when original Grover quantum search algorithm is applied to search an unordered database. In the meantime, this work also indicates that Grover quantum search algorithm is considerably robust to certain kinds of perturbations and is robust against modest noise in the initialization procedure.