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Advanced Quantum Technologies

Construction of a Polarization Multiphoton Controlled One‐Photon Unitary Gate Assisted by the Spatial and Temporal Degrees of Freedom

Xiao‐Ming Xiu, Xue Geng, Sen‐Lin Wang, Cen Cui, Qing‐Yang Li, Yan‐Qiang Ji, Li Dong

Published Jul 9, 2019• 16 citations

Abstract

Abstract In order to fulfill quantum information processing tasks such as quantum computation and scalable quantum networks, quantum logic gates are indispensable parts. A multiqubit logic gate can efficiently reduce the cost of physical resources and complicated operations that are necessary in the combination of fewer‐qubit (e.g., two‐qubit) logic gates to fulfill the same tasks. However, the construction of multiphoton quantum logic gates is a large challenge. Assisted by spatial and temporal degrees of freedom, a polarization multiphoton controlled one‐photon unitary gate is proposed, which can be realized with three processes including the control‐path process based on weak cross‐Kerr nonlinearities, the unitary transformation process, and the output process. In the control‐path process, the control‐path modules are applied, where the entanglement between polarization, spatial and temporal degrees of freedom is generated by beam splitters, time delayers, and nonlinear interaction in cross‐Kerr media. The scheme presented here, assisted by spatial and temporal degrees of freedom reduces the experimental complexity of the schemes assisted by only spatial degree of freedom. Moreover, it will also be a useful reference in optimally constructing multiqubit quantum logic gates with other multiple degrees of freedom in many physical systems.

DOI: 10.1002/qute.201900066

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\sqrt[n]{cnot}

, controlled-phase, and Fredkin gates, and the preparation of one-photon, three-qubit Greenberger-Horne-Zeilinger (GHZ) and

W

states. This approach enables simple optical implementations of few-qubit tasks in quantum information processing.

We present a scheme of two-photon quantum Fourier transform at first, where the controlled π/2 phase gate and the Hadamard gates are applied. The indirect interaction between two photons can be realized through a coupling bus provided by a coherent state in Kerr media. Employing photon-number measurements and the corresponding classical feed-forward techniques, the task of low-error quantum Fourier transform can be fulfilled. With revision and modulation on the optical elements, controlled π/2n (n=2,3,…) phase gates are constructed, and the multiphoton quantum Fourier transform can be achieved by integrating these controlled phase gates and Hadamard gates.

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