Li-Jun Xie

Photonic two-qubit parity gate with tiny cross–Kerr nonlinearity

The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in an experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits.

Nondestructive Greenberger-Horne-Zeilinger-state analyzer

We propose a method to construct a nondestructive n-qubit Greenberger– Horne–Zeilinger (GHZ)-state analyzer. The method is applied to any systems in which two-qubit parity gates, controlled-phase gates, or controlled-NOT gates can be realized. We also present a simplified two-photon parity gate with which a nondestructive n-photon GHZ-state analyzer could be largely simplified. The nondestructive GHZ-state analyzer is expected to find useful applications for economical quantum-information processing.

Remote information concentration and multipartite entanglement in multilevel systems

Remote information concentration (RIC) in

Multiparty hierarchical quantum-information splitting

d

Generation of three-atom W state via nonresonant Jaynes-Cummings model

-level systems (qudits) is studied. It is shown that the quantum information initially distributed in three spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. The entangled channel can be different types of genuine multipartite pure entangled states which are inequivalent under local operations and classical communication. The entangled channel can also be a mixed entangled state, even a bound entangled state which has a similar form to the Smolin state, but has different features from the Smolin state. A common feature of all these pure and mixed entangled states is found; i.e., they have

A simple scheme for realizing six-photon entangled state based on cavity quantum electrodynamics

{d}^{2}

Nondestructive two-photon parity detector with near unity efficiency

common commuting stabilizers. The differences of qudit-RIC and qubit-RIC (

Many-to-one remote information concentration for qudits and multipartite entanglement

d=2

Generation of four-photon GHZ states based on interaction between a four-level atom and two bimodal cavities

) are also analyzed.

Effect of a Nonideal Initial-State of the Ancillary System on Optimal Universal Quantum Cloning

We propose a scheme for multiparty hierarchical quantum-information splitting (QIS) with a multipartite entangled state, where a boss distributes a secret quantum state to two grades of agents asymmetrically. The agents who belong to different grades have different authorities for recovering the bosss secret. Except for the bosss Bell-state measurement, no nonlocal operation is involved. The presented scheme is also shown to be secure against eavesdropping. Such a hierarchical QIS is expected to find useful applications in the field of modern multipartite quantum cryptography.