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arXiv:quant-ph/0202014

Realization of Fredkin Gate by Three Transition Pulses in NMR Quantum Information Processor

Fei, Xue, Du Jiangfeng, Mingjun, Shi, Xianyi Zhou, Han RongDian, Jihui Wu

Published Feb 2, 2002• 2 citations
arXivHTMLPDF

Abstract

The three-qubit conditional swap gate(Fredkin gate) is a universal gate that can be used to create any logic circuit and has many direct usages. In this paper, we experimentally realized Fredkin gate with only three transition pulses in solution of alanine. It appears that no experimental realization of Fredkin gate with fewer pulses has yet been reported up to now. In addition, the simple structure of our scheme makes it easy to be implemented in experiments.

DOI
10.48550/arxiv.quant-ph/0202014

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The three-qubit conditional swap gate(Fredkin gate) is a universal gate that can be used to create any logic circuit and has many direct usages. In this paper, we experimentally realized Fredkin gate with only three transition pulses in solution of alanine. It appears that no experimental realization of Fredkin gate with fewer pulses has yet been reported up to now. In addition, the simple structure of our scheme makes it easy to be implemented in experiments.
Minimizing the resources required to build logic gates into useful processing circuits is key to realizing quantum computers. Although the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analog has been realized. By adding control to the SWAP unitary, we use photonic qubit logic to demonstrate the first quantum Fredkin gate, which promises many applications in quantum information and measurement. We implement example algorithms and generate the highest-fidelity three-photon Greenberger-Horne-Zeilinger states to date. The technique we use allows one to add a control operation to a black-box unitary, something that is impossible in the standard circuit model. Our experiment represents the first use of this technique to control a two-qubit operation and paves the way for larger controlled circuits to be realized efficiently.
Quantum information science addresses how the processing and transmission of information are affected by uniquely quantum mechanical phenomena. Combination of two-qubit gates has been used to realize quantum circuits, however, scalability is becoming a critical problem. The use of three-qubit gates may simplify the structure of quantum circuits dramatically. Among them, the controlled-SWAP (Fredkin) gates are essential since they can be directly applied to important protocols, e.g., error correction, fingerprinting, and optimal cloning. Here we report a realization of the Fredkin gate for photonic qubits. We achieve a fidelity of 0.85 in the computational basis and an output state fidelity of 0.81 for a 3-photon Greenberger-Horne-Zeilinger state. The estimated process fidelity of 0.77 indicates that our Fredkin gate can be applied to various quantum tasks.
Quantum information science addresses how the storage, processing, and transmission of information are affected by uniquely quantum mechanical phenomena, such as superposition and entanglement. New technologies that harness these quantum effects are beginning to be realized in the areas of communication, information processing and precision measurement. For the realization of a universal gate set, by which, in principle, any quantum information task can be realized, two-qubit gates have been demonstrated and have been used to realize small-scale quantum circuits. However, scalability is becoming a critical problem. It may therefore be helpful to consider the use of three-qubit gates, which can simplify the structure of quantum circuits dramatically. Although both the controlled-SWAP (CSWAP) gate (also called Fredkin gate) and the controlled-controlled-NOT gate (also called Toffoli gate) are representative three-qubit gates, the Fredkin gates can be directly applied to many important quantum information protocols, e.g., error correction, fingerprinting, optimal cloning, and controlled entanglement filtering. Here we report a realization of the Fredkin gate using a photonic quantum circuit, following the theoretical proposal by Fiurasek. We achieve a fidelity of 0.85 for the classical truth table of CSWAP operation and an output state fidelity of 0.81 for a generated 3-photon Greenberger-Horne-Zeilinger (GHZ) state. We also confirmed that the gate is capable of genuine tripartite entanglement with a quantum coherence corresponding to a visibility of 0.69 for three-photon interferences. From these results, we estimate a process fidelity of 0.77, which indicates that our Fredkin gate can be applied to various quantum tasks.