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arXiv:1807.06065

Experimental realization of a quantum CNOT gate for orbital angular momentum and polarization with linear optical elements

J. H. Lopes, W. C. Soares, Bertúlio de Lima Bernardo, D. P. Caetano, Askery Canabarro

Published Jul 16, 2018• 0 citations
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Abstract

We propose and experimentally demonstrate that a Mach-Zehnder interferometer composed of polarized beam splitters and a pentaprism in the place of one of the mirrors works as a linear optical quantum controlled-NOT (CNOT) gate. To perform the information processing, the polarization and orbital angular momentum (OAM) of the photons act as the control and target qubits, respectively. The readout process is simple, requiring only a linear polarizer and a triangular diffractive aperture before detection. The viability and stability of the experiment makes the present proposal a valuable candidate for future implementations in optical quantum computation protocols.

DOI
10.48550/arxiv.1807.06065

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We describe an optical implementation of a CNOT gate in which the control qubit is the polarization of a single photon and the target qubit is the spatial parity of the same photon. The gate is implemented with a polarization- sensitive spatial light modulator. We characterize the operation of the gate using quantum process tomography and the spatial parity is analyzed with a modified Mach-Zehnder interferometer. We also demonstrate the CNOT-gate operation with arbitrary rotation of the target qubit and discuss the possibility of implementing multi-qubit CNOT gates using the same approach.
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Implementation of quantum logic gates with linear optical elements plays a prominent role in quantum computing due to their relatively easy manipulation and realization. We present efficient schemes to implement controlled-not (cnot) gates and controlled-swap (Fredkin) gates by using solely linear optics. We encode the control qubits and target qudits in photonic polarization (two-level) and spatial degrees of freedom (ddd level), respectively. On the basis of the hybrid encoding, cnot and Fredkin gates are constructed in a deterministic way without any borrowed ancillary photons or measurement-induced nonlinearities. Remarkably, the number of linear optics required to implement a cnot gate has been reduced to one polarizing beam splitter, while only ddd polarizing beam splitters are necessary to implement a generalized Fredkin gate. The optical depths of all schemes are reduced to 1 and and are dimension independent. Besides, the fidelity of our three-qubit Fredkin gate is higher than 99.7% under realistic conditions, which is higher than in previous schemes.
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