title: A quantum Fredkin gate.
abstract: 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.
authors.affiliation: CQC T (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia.
authors.forename: Raj B
authors.initials: RB
authors.lastname: Patel
authors.affiliation: CQC T (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia.
authors.forename: Joseph
authors.identifier: 0000-0002-5346-3872
authors.initials: J
authors.lastname: Ho
authors.affiliation: CQCT (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia.; Laboratoire Photonique, Numerique et Nanosciences, Institut d'Optique, CNRS and Université de Bordeaux, 33400 Talence, France.
authors.forename: Franck
authors.identifier: 0000-0003-1057-6276
authors.initials: F
authors.lastname: Ferreyrol
authors.affiliation: CQC T and School of Mathematics and Physics, University of Queensland, Brisbane 4072, Australia.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Ralph
authors.affiliation: CQC T (Centre for Quantum Computation & Communication Technology) and Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia.
authors.forename: Geoff J
authors.initials: GJ
authors.lastname: Pryde
mesh_terms: D000465:Algorithms; D008962:Models, Theoretical; D011789:Quantum Theory
keywords: Fredkin (controlled-SWAP) gate; GHZ states; circuits; downconversion; entanglement; logic gate; photons; quantum computers; quantum optics; qubits