H. S. Song

Quantum gate operations using atomic qubits through cavity input-output process

We propose two deterministic schemes to implement quantum swap gate and Fredkin gate encoded by atomic qubits through the input-output process of the cavity. We show that these schemes can be extended to realize multi-qubit gate operations. By numerical calculation, the fidelity and photon loss probability for implementing quantum swap gate between photon and atom are also discussed.

Preparation of a stable and maximally entangled state of two distant qutrits trapped in separate cavities

Abstract. We have proposed a simple scheme to entangle two distantnqutrits trapped in separate optical cavities. The quantumninformation of each qutrit is skillfully encoded on the degeneratenground states of a pair of atoms, hence the entanglement betweennthem is relatively stable against spontaneous emission. InnLamb-Dicke limits, it is not necessary to require coincidencendetections, which will relax the conditions for the experimentalnrealization. The scheme is robust against the inefficientndetections. nn

Remote preparation of N photon GHZ polarization entangled states within a network

We propose a new linear optical protocol for remote state preparation (RSP) between two parties under control of a number of controllers in terms of optical elements. The proposed setup involves simple linear optical elements, a N-photon polarization entangled state, and photon de tectors, witch have been widely used in experiment. The realization of this protocol is appealing due to the fact that quantum state of light is robust against the decoherence and photons are ideal carriers for transmitting quantum information over long distances.

Bounds on bipartitely shared entanglement reduced from superposed tripartite quantum states

For a tripartite pure state superposed by two individual states, the bipartitely shared entanglement can always be achieved by local measurements of the third party. Consider the different aims of the third party, i.e. maximizing or minimizing the bipartitely shared entanglement, we find bounds on both the possible bipartitely shared entanglement of the superposition state in terms of the corresponding entanglement of the two states being superposed. In particular, by choosing the concurrence as bipartite entanglement measure, we obtain calculable bounds for tripartite (2 ⊗ 2 ⊗ n)-dimensional cases.

Full separability criterion for tripartite quantum systems

Abstract.In this paper, an intuitive approach is employed tongeneralize the full separability criterion of tripartite quantumnstates of qubits to the higher-dimensional systems [Phys. Rev. An72, 022333 (2005)]. A distinct characteristic of thenpresent generalization is that less restrictive conditions arenneeded to characterize the properties of full separability.nFurthermore, the formulation for pure states can be convenientlynextended to the case of mixed states by utilizing the Kroneckernproduct approximate technique. As applications, we give the analyticnapproximation of the criterion for weakly mixed tripartite quantumnstates and investigate the full separability of some weakly mixednstates. n nn n

Weak measurement combined with quantum delayed-choice experiment and implementation in optomechanical system

Weak measurement [Y. Aharonov, D.Z. Albert, L. Vaidman, Phys. Rev. Lett. 60, 1351 (1988); C. Simon, E.S. Polzik, Phys. Rev. A 83, 040101(R) (2011)] combined with quantum delayed-choice experiment that use Controlled Hadamard gate instead of Hadamard gate in quantum networks give rise to a surprising amplification effect, i.e., counterintuitive negative amplification effect. We show that this effect is caused by the wave and particle behaviours of the system, and it can’t be explained by a semiclassical wave theory [D. Suter, Phys. Rev. A 51, 45 (1995); J.C. Howell, D.J. Starling, P.B. Dixon, P.K. Vudyasetu, A.N. Jordan, Phys. Rev. A 81, 033813 (2010); N. Brunner, A. Acín, D. Collins, N. Gisin, V. Scarani, Phys. Rev. Lett. 91, 180402 (2003)] and by the statistical feature of preselection and postselection with disturbance [C. Ferrie, J. Combes, Phys. Rev. Lett. 113, 120404 (2014)], due to the entanglement of the system and the ancilla in Controlled Hadamard gate. The generation mechanism with wave-particle duality in quantum mechanics lead us to a scheme for implementation of weak measurement in optomechanical system.

Amplification effects in optomechanics via weak measurements

We revisit the scheme of single-photon weak-coupling optomechanics using post-selection, proposed by Pepper, Ghobadi, Jeffrey, Simon and Bouwmeester [Phys. Rev. Lett. 109, 023601 (2012)], by analyzing the exact solution of the dynamical evolution. Positive and negative amplification effects of the displacement of the mirrors position can be generated when the Kerr phase is considered. This effect occurs when the post-selected state of the photon is orthogonal to the initial state, which can not be explained by the usual weak measurement results. The amplification effect can be further modulated by a phase shifter, and the maximal displacement state can appear within a short evolution time.

Simply quantum information processing with RF superconducting qubit

Utilizing rf superconducting quantum interference devices coupled with transmission line resonator, we propose a scheme to implementing quantum information processing. In this system, the high fidelity two-qubit maximally entangled states and quantum logic gate are realized. Under the large detuning condition, the excited state of an rf superconducting quantum interference device is adiabatically eliminated. So the excited state spontaneous emission of the superconducting qubit can be effectively avoided in this paper. At last, the experimental feasibility and the challenge of our schemes have been discussed.