The promise of tremendous computational power, coupled with the development of robust error-correcting schemes1, has fuelled extensive efforts2 to build a quantum computer. The requirements for realizing such a device are confounding: scalable quantum bits (two-level quantum systems, or qubits) that can be well isolated from the environment, but also initialized, measured and made to undergo controllable interactions to implement a universal set of quantum logic gates3. The usual set consists of single qubit rotations and a controlled-NOT (CNOT) gate, which flips the state of a target qubit conditional on the control qubit being in the state 1. Here we report an unambiguous experimental demonstration and comprehensive characterization of quantum CNOT operation in an optical system. We produce all four entangled Bell states as a function of only the input qubits' logical values, for a single operating condition of the gate. The gate is probabilistic (the qubits are destroyed upon failure), but with the addition of linear optical quantum non-demolition measurements, it is equivalent to the CNOT gate required for scalable all-optical quantum computation4.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Nielsen, M. A. & Chuang, I. L. Quantum Computation and Quantum Information (Cambridge Univ. Press, Cambridge, 2000)
Clark, R. G. (ed.) Quant. Inform. Comput. 1 (special issue on implementation of quantum computation) 1–50 (2001)
DiVincenzo, D. P. & Loss, D. Quantum information is physical. Superlatt. Microstruct. 23, 419–432 (1998)
Knill, E., Laflamme, R. & Milburn, G. J. A scheme for efficient quantum computation with linear optics. Nature 409, 46–52 (2001)
Vandersypen, L. M. K. et al. Experimental realisation of Shor's quantum factoring algorithm using nuclear magnetic resonance. Nature 414, 883–887 (2001)
Schmidt-Kaler, F. et al. Realisation of the Cirac–Zoller controlled-NOT quantum gate. Nature 422, 408–411 (2003)
Leibfried, D. et al. Experimental demonstration of a robust, high-fidelity geometric two ion-qubit phase gate. Nature 422, 412–415 (2003)
Kane, B. E. A silicon-based nuclear spin quantum computer. Nature 393, 133–137 (1998)
Pashkin, Yu. A. et al. Quantum oscillations in two coupled charge qubits. Nature 421, 823–826 (2003)
Gisin, N., Ribordy, G., Tittel, W. & Zbinden, H. Quantum cryptography. Rev. Mod. Phys. 74, 145–195 (2002)
Turchette, Q. A., Hood, C. J., Lange, W., Mabuchi, H. & Kimble, H. J. Measurement of conditional phase shifts for quantum logic. Phys. Rev. Lett. 75, 4710–4713 (1995)
Gottesman, D. & Chuang, I. L. Demonstrating the viability of universal quantum computation using teleportation and single-qubit operations. Nature 402, 390–393 (1999)
Koashi, M., Yamamoto, T. & Imoto, N. Probabilistic manipulation of entangled photons. Phys. Rev. A 63, 030301 (2001)
Pan, J.-W., Simon, C., Brukner, Č. & Zeilinger, A. Entanglement purification for quantum communication. Nature 410, 1067–1070 (2001)
Pittman, T. B., Jacobs, B. C. & Franson, J. D. Probabilistic quantum logic operations using polarizing beam splitters. Phys. Rev. A 64, 062311 (2001)
Santori, C., Fattal, D., Vučković, J., Solomon, G. S. & Yamamoto, Y. Indistinguishable photons from a single-photon device. Nature 419, 594–597 (2002)
Kuhn, A., Hennrich, M. & Rempe, G. Deterministic single-photon source for distributed quantum networking. Phys. Rev. Lett. 89, 067901 (2002)
Kuzmich, A. et al. Generation of nonclassical photon pairs for scalable quantum communication with atomic ensembles. Nature 423, 731–734 (2003)
James, D. F. V. & Kwiat, P. G. Atomic-vapor-based high efficiency optical detectors with photon number resolution. Phys. Rev. Lett. 89, 183601 (2002)
Imamoglu, A. High efficiency photon counting using stored light. Phys. Rev. Lett. 89, 163602 (2002)
Ralph, T. C., Langford, N. K., Bell, T. B. & White, A. G. Linear optical controlled-NOT gate in the coincidence basis. Phys. Rev. A 65, 062324 (2001)
Hofmann, H. F. & Takeuchi, S. Quantum phase gate for photonic qubits using only beam splitters and postselection. Phys. Rev. A 66, 024308 (2001)
Kok, P., Lee, H. & Dowling, J. P. Single-photon quantum-nondemolition detectors constructed with linear optics and projective measurements. Phys. Rev. A 66, 063814 (2002)
Hong, C. K., Ou, Z. Y. & Mandel, L. Measurement of subpicosecond time intervals between two photons by interference. Phys. Rev. Lett. 59, 2044–2046 (1987)
Kurtsiefer, C., Oberparleiter, M. & Weinfurter, H. High-efficiency entangled photon pair collection in type-II parametric fluorescence. Phys. Rev. A 64, 023802 (2001)
James, D. F. V., Kwiat, P. G., Munro, W. J. & White, A. G. Measurement of qubits. Phys. Rev. A 64, 052312 (2001)
Munro, W. J., Nemoto, K. & White, A. G. The Bell inequality: A measure of entanglement? J. Mod. Opt. 48, 1239–1246 (2001)
Pittman, T. B., Fitch, M. J., Jacobs, B. C. & Franson, J. D. Experimental controlled-NOT logic gate for single photons. Preprint at 〈http://arXiv.org/quant-ph/0303095〉 (2003)
Dodd, J. L., Ralph, T. C. & Milburn, G. J. Experimental requirements for Grover's algorithm in optical quantum computation. Phys. Rev. A (in the press); preprint at 〈http://arXiv.org/quant-ph/0306081〉 (2003)
Takeuchi, S. Beamlike twin-photon generation by use of type II parametric downconversion. Opt. Lett. 26, 843–845 (2001)
We thank N. K. Langford for experimental work related to non-classical interference, T. B. Bell for work on the quantum state tomography system, and P. T. Cochrane, J. L. Dodd, A. Gilchrist, P. G. Kwiat, G. J. Milburn, W. J. Munro and M. A. Nielsen for discussions. This work was supported by the Australian government, the Australian Research Council, the US National Security Agency (NSA) and Advanced Research and Development Activity (ARDA) under the Army Research Office (ARO).
The authors declare that they have no competing financial interests.
About this article
Cite this article
O'Brien, J., Pryde, G., White, A. et al. Demonstration of an all-optical quantum controlled-NOT gate. Nature 426, 264–267 (2003). https://doi.org/10.1038/nature02054
Quantum Information Processing (2021)
Quantum hyper-CPHASE gates with polarisation and orbital angular momentum degrees of freedom and generalisation to arbitrary hyper-conditional gates
Quantum Information Processing (2020)
Quantum Information Processing (2020)
Nature Physics (2019)
Nature Reviews Physics (2019)