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Optics Express

Implementation of controlled unitary gates and its application in a remote-controlled quantum gate

Byungjoo Kim, Seongjin Hong, Yong‐Su Kim, Kyunghwan Oh, Hyang‐Tag Lim

Published Oct 16, 2024• 3 citations
Publisher

Abstract

Recently, remote-controlled quantum information processing has been proposed for its applications in secure quantum processing protocols and distributed quantum networks. For remote-controlled quantum gates, the experimental realization of controlled unitary (CU) gates between any quantum gates is an essential task. Here, we propose and experimentally demonstrate a scheme for implementing CU gates between any pair of unitary gates using the polarization and time-bin degrees of freedom of single photons. Then, we experimentally implement remote-controlled single-qubit unitary gates by controlling either the state preparation or measurement of the control qubit with high process fidelities. We believe the proposed remote-controlled quantum gate model can pave the way for secure and efficient quantum information processing.

DOI
10.1364/oe.540199

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Recently, remote-controlled quantum information processing has been proposed for its applications in secure quantum processing protocols and distributed quantum networks. For remote-controlled quantum gates, the experimental realization of controlled unitary (CU) gates between any quantum gates is an essential task. Here, we propose and experimentally demonstrate a scheme for implementing CU gates between any pair of unitary gates using the polarization and time-bin degrees of freedom of single photons. Then, we experimentally implement remote-controlled single-qubit unitary gates by controlling either the state preparation or measurement of the control qubit with high process fidelities. We believe the proposed remote-controlled quantum gate model can pave the way for secure and efficient quantum information processing.
Recently, remote-controlled quantum information processing has been proposed for its applications in secure quantum processing protocols and distributed quantum networks. For remote-controlled quantum gates, the experimental realization of controlled unitary (CU) gates between any quantum gates is an essential task. Here, we propose and experimentally demonstrate a scheme for implementing CU gates between arbitrary pairs of unitary gates using the polarization and time-bin degrees of freedom of single-photons. Then, we experimentally implement remote-controlled single-qubit unitary gates by controlling either the state preparation or measurement of the control qubit with high process fidelities. We believe that the proposed remote-controlled quantum gate model can pave the way for secure and efficient quantum information processing.
Quantum entanglement enables measurement on one party to affect the other’s state. Based on this peculiar feature, we propose a model of remote-controlled quantum computing and design an optical scheme to realize this model for a single qubit. As an experimental demonstration of this scheme, we further implement three Pauli operators, Hardmard gate, phase gate, and π / 8 gate. The minimal fidelity obtained by quantum process tomography reaches 82%. Besides, as a potential application, our model contributes to secure remote quantum information processing.
Quantum gate teleportation enables the implementation of nonlocal quantum operations without direct interactions between distant nodes. We propose an efficient protocol for implementing arbitrary controlled-unitary (CU) gates acting on two spatially separated parties via indefinite causal order (ICO). By establishing a maximally entanglement between two remote nodes and coherently superposing orders of single-qubit gates, our protocol circumvents the drawback of complex local two-qubit operations. This ICO-based approach enables full programmability of CU gates by adjusting the inherent single-qubit operations, offering advantages over conventional fixed causal-order methods in terms of reduced circuit complexity and improved experimental flexibility. Furthermore, we develop an optical construction to implement the polarization CU gate using a stable and reciprocal Sagnac interferometer. Our work establishes a practical framework for scalable distributed quantum computation with flexible operations.
Optimizing the physical realization of quantum gates is important to build a quantum computer. Fredkin gate, also named controlled-swap gate, can be widely applicable in various quantum information processing schemes. In the present research, we propose and experimentally implement quantum Fredkin gate in a single-photon hybrid-degrees-of-freedom system. Polarization is used as the control qubit, and SWAP operation is achieved in a four-dimensional Hilbert space spanned by photonic orbital angular momentum. The effective conversion rate P\mathcal{P}P of the quantum Fredkin gate in our experiment is (95.4±2.6)%(95.4\pm 2.6)\%(95.4±2.6)%. Besides, we find that a kind of Greenberger-Horne-Zeilinger states can also be prepared by using our quantum Fredkin gate, and the Mermin inequality test shows its quantum contextual characteristic. Our experimental design paves the way for quantum computing and quantum fundamental study in high-dimensional and hybrid coding quantum systems.
The controlled quantum gate is an essential element for the realization of quantum computer and has been implemented in various types of two-level systems. However, high-dimensional controlled quantum gates are rarely investigated both theoretically and experimentally although high-dimensional quantum systems exhibit remarkable advantages over two-level systems for some of quantum information and computing tasks. Here we experimentally demonstrate the four-dimensional controlled X gate and its unique higher orders based on orbital-angular-momentum and polarization degrees of freedom of a single photon. The controlled gates have been examined with various input states, and all the conversion efficiency of the unitary operations are above 93% with 100% utility of photons. This work is an important step towards the goal of achieving arbitrary d-dimensional quantum circuit and paves a way for the implementation of quantum communication, computation in high-dimensional quantum systems.
We present a technique for remotely preparing an arbitrary single-photon hybrid state between two distant nodes. This remote state preparation (RSP) is accomplished with a hyper-entangled state in polarization and time-bin degrees of freedom (DoFs) using some experimentally available optical elements and devices. In our RSP, the sender performs unitary operations on her hyper-entangled photon in accordance with her knowledge of the desired state to be transmitted. By performing a single-photon projective measurement and classical communication, the target state will be reconstructed at the remote receiver’s quantum system. Furthermore, we discuss the RSP via a partially hyper-entangled state. We expect our study can pave the way towards the investigation of long-distance quantum communication scenarios.