Ya-Fei Yu

Quantum entanglement distribution with hybrid parity gate

We propose a scheme for entanglement distribution among different single atoms trapped in separated cavities. In our scheme, by reflecting an input coherent optical pulse from a cavity with a single trapped atom, a controlled phase-shift gate between the atom and the coherent optical pulse is achieved. Based on this gate and homodyne detection, we construct an n-qubit parity gate and show its use for the distribution of a large class of entangled states in one shot, including the GHZ state |GHZ{sub n}>, W state |W{sub n}>, Dicke state |D{sub n,k}>, and certain sums of Dicke states |G{sub n,k}>. We also show that such a distribution could be performed with high success probability and high fidelity even in the presence of channel loss.

Optical quantum computation with cavities in the intermediate coupling region

Large-scale quantum computation is currently a hot area of research. The scalable quantum computation scheme with cavities originally proposed by Duan and Kimble (Phys. Rev. Lett., 92 (2004) 127902) is further developed here to operate in the intermediate coupling region, which not only greatly relaxes experimental demands on the Purcell factor, but also eliminates the need to consider internal trade-off between cavity quality and efficiency. In our scheme, by controlling the reflectivity of the input single-photon pulse in the cavity, we can realize local atom-photon and nonlocal atom-atom controlled phase-flip (CPF) gates. We also introduce a theoretical model to analyze the performance of our scheme under practical noise. Furthermore, we show that the nonlocal CPF gate can be used to realize a quantum repeater.

Scalable quantum information processing with atomic ensembles and flying photons

We present a scheme for scalable quantum information processing with atomic ensembles and flying photons. Using the Rydberg blockade, we encode the qubits in the collective atomic states, which could be manipulated fast and easily due to the enhanced interaction in comparison to the single-atom case. We demonstrate that our proposed gating could be applied to generation of two-dimensional cluster states for measurement-based quantum computation. Moreover, the atomic ensembles also function as quantum repeaters useful for long-distance quantum state transfer. We show the possibility of our scheme to work in bad cavity or in weak coupling regime, which could much relax the experimental requirement. The efficient coherent operations on the ensemble qubits enable our scheme to be switchable between quantum computation and quantum communication using atomic ensembles.

Generation of a genuine four-particle entangled state of trap ions

We present a scheme for the generation of a genuine four-qubit entangled state in an ion trap. This state has many interesting entanglement properties and possible applications in quantum information processing and fundamental tests of quantum physics. In our scheme, the ion is driven by a standing-wave field, whose frequency is resonant with the ion carrier transition. By adjusting the phase of the field, both the vibration mode population and the ionic carrier excitation can be avoided. So our scheme is insensitive to the vibration states, which is important in view of decoherence.

Realization of universal quantum cloning with superconducting quantum-interference device qubits in a cavity

We propose a scheme to realize 1 → 2 universal quantum cloning machine (UQCM) with superconducting quantum interference device (SQUID) qubits, embeded in a high-Q cavity. CNOT operations are derived to present our scheme, and the two-photon Raman resonance processes are used to increase the operation rate. Compared with previous works, our scheme has advantages in the experimental realization and further utilization.

Generating entanglement of photon-number states with coherent light via cross-Kerr nonlinearity

We propose a scheme for generating entangled states of light fields. This scheme only requires the cross-Kerr nonlinear interaction between coherent light beams, followed by a homodyne detection. Therefore, this scheme is within the reach of current technology. We study in detail the generation of the entangled states between two modes, and that among three modes. In addition to the Bell states between two modes and the W states among three modes, we find plentiful new kinds of entangled states. Finally, the scheme can be extended to generate the entangled states among more than three modes.

Decoherence-free quantum memory for photonic state using atomic ensembles

Large scale quantum information processing requires stable and long-lived quantum memories. Here, using atom-photon entanglement, we propose an experimentally feasible scheme to realize decoherence-free quantum memory with atomic ensembles, and show one of its applications, remote transfer of unknown quantum state, based on laser manipulation of atomic ensembles, photonic state operation through optical elements, and single-photon detection with moderate efficiency. The scheme, with inherent fault-tolerance to the practical noise and imperfections, allows one to retrieve the information in the memory for further quantum information processing within the reach of current technology.

Entanglement generation with coherent light via cross-Kerr-nonlinearity

We propose a scheme for generating entangled states of light fields. This scheme only requires the cross-Kerr nonlinear interaction between coherent light-beams, followed by a homodyne detection. Therefore, this scheme is within the reach of current technology. We study in detail the generation of the entangled states between two modes, and that among three modes. In addition to the Bell states between two modes and the W states among three modes, we find plentiful new kinds of entangled states. Finally, the scheme can be extend to generate the entangled states among more than three modes.