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Journal of the Optical Society of America B

Efficient distributed controlled Z gate without ancilla single-photons via cross-phase modulation

Meng-Zheng Zhu, Liu Ye

Published Feb 3, 2014• 6 citations
Publisher

Abstract

A scheme is proposed to directly implement a controlled Z gate for two remote photonic qubits based on the weak cross-Kerr nonlinearity and intense coherent states of light. The distributed controlled Z gate can be used to achieve the remote creation of entangled states and can be extended to perform distributed quantum computation. The distinct advantage of the present scheme in contrast with the existing schemes is that ancilla single-photons are not needed. The total success probability and fidelity of the present controlled Z gate can approach unit in principle. We investigate photon losses of the qubus beam during the transmission and decoherence effects in the quantum gate caused by such photon losses. The scheme uses only basic tools in quantum optical laboratories and can be implemented in the regime of weak cross-Kerr nonlinearities. Therefore this makes us more confident in the feasibility of the proposed scheme.

DOI
10.1364/josab.31.000405

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A scheme is proposed to directly implement a controlled Z gate for two remote photonic qubits based on the weak cross-Kerr nonlinearity and intense coherent states of light. The distributed controlled Z gate can be used to achieve the remote creation of entangled states and can be extended to perform distributed quantum computation. The distinct advantage of the present scheme in contrast with the existing schemes is that ancilla single-photons are not needed. The total success probability and fidelity of the present controlled Z gate can approach unit in principle. We investigate photon losses of the qubus beam during the transmission and decoherence effects in the quantum gate caused by such photon losses. The scheme uses only basic tools in quantum optical laboratories and can be implemented in the regime of weak cross-Kerr nonlinearities. Therefore this makes us more confident in the feasibility of the proposed scheme.
We propose a protocol to direct implement the two-qubit controlled phase gate with cross-Kerr nonlinearity by using the interference of polarized photons. The protocol is based on optical elements, single polarization photons, cross-Kerr nonlinearity and the conventional photon detectors, which are feasible with existing experimental technology. Compared with Zou's protocol ( Phys. Rev. 2007 A 75 034302), this protocol is to replace the entangled state resources used by Zou with much simpler single-photon resources and has a higher success probability. All these advantages make this protocol more efficient and more convenient than others in the applications in quantum communication.
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The controlled phase gate is one of the most important logic gates in the quantum computation field. In this paper, we proposed a protocol for implementing the two-qubit controlled phase gates with the help of cross-Kerr nonlinearity, optical elements and the conventional photon detectors, which are feasible with existing experimental technology. The protocol also can be applied to implement the controlled phase gates of many different atomic and photonic degrees of freedom with successful probability of 100%, that is, our protocol is efficient and flexible.
We propose an efficient scheme for implementing the universal controlled-phase gate with logical qubits encoded in the superpositions of 2d2d2d circularly distributed coherent states (ddd is a positive integer), which have the advantage of protecting quantum information against the $(d\ensuremath{-}1)$-photon loss errors. We first demonstrate explicitly how to engineer dispersive interaction between the microwave cavity modes and multilevel transmon ancilla in circuit quantum electro-dynamical (QED) system. With the cat-state qubits, we realize the two-qubit controlled phase gate, and its operation time scales as 1/d1/d1/d. This means that it will be less susceptible to environmental disturbances if we employ larger ddd to encode information. Finally, we employ the experimentally reachable parameters in circuit QED system to numerically study the influence of the photon loss, the qubit relaxation, and the Kerr nonlinearity. The average fidelity for a controlled-phase gate has reached 0.9955 for d=8d=8d=8 when the system imperfections are considered. The results demonstrate the great potential of our scheme for quantum computation in circuit QED system.
We present a realization of two-qubit controlled-phase gate, based on the linear and nonlinear properties of the probe and signal optical pulses in an asymmetric GaAs/AlGaAs double quantum wells. It is shown that, in the presence of cross-phase modulation, a giant cross-Kerr nonlinearity and mutually matched group velocities of the probe and signal optical pulses can be achieved while realizing the suppression of linear and self-Kerr optical absorption synchronously. These characteristics serve to exhibit an all-optical two-qubit controlled-phase gate within efficiently controllable photon-photon entanglement by semiconductor mediation. In addition, by using just polarizing beam splitters and half-wave plates, we propose a practical experimental scheme to discriminate the maximally entangled polarization state of two-qubit through distinguishing two out of the four Bell states. This proposal potentially enables the realization of solid states mediated all-optical quantum computation and information processing.
The decoherence effect caused by the coupling between the system and the environment undoubtedly leads to the errors in efficient implementations of two (or three) qubit logical gates in quantum information processing. Fortunately, decoherence-free subspace (DFS) introduced can effectively decrease the influence of decoherence effect. In this paper, we propose some schemes for setting up a family of quantum control gates, including controlled-NOT (CNOT), Toffoli, and Fredkin gates for two or three logical qubits by means of cross-Kerr nonlinearities in DFS. These three logical gates require neither complicated quantum computational circuits nor auxiliary photons (or entangled states). The success probabilities of three logical gates are approximate 1 by performing the corresponding classical feed-forward operations based on the different measuring results of the X-homodyne detectors, and their fidelities are robust against the photon loss with the current technology. The proposed logical gates rely on only simple linear-optics elements, available single-qubit operations, and mature measurement methods, making our proposed gates be feasible and efficient in practical applications.