Abstract
Over the past several decades, quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future.
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References
Nielsen, M. A. & Chuang, I. L. Quantum Computation and Quantum Information (Cambridge University Press, 2000)
Knill, E. Quantum computing with realistically noisy devices. Nature 434, 39â44 (2005)
DiVincenzo, D. P. The physical implementation of quantum computation. Fortschr. Phys. 48, 771â783 (2000)
Mizel, A., Lidar, D. A. & Mitchell, M. Simple proof of equivalence between adiabatic quantum computation and the circuit model. Phys. Rev. Lett. 99, 070502 (2007)
Raussendorf, R. & Briegel, H. J. A one-way quantum computer. Phys. Rev. Lett. 86, 5188â5191 (2001)
Cory, D. G., Fahmy, A. F. & Havel, T. F. Ensemble quantum computing by NMR-spectroscopy. Proc. Natl Acad. Sci. USA 94, 1634â1639 (1997)
Gershenfeld, N. A. & Chuang, I. L. Bulk spin resonance quantum computation. Science 275, 350â356 (1997)
Ryan, C. A., Moussa, O., Baugh, J. & Laflamme, R. Spin based heat engine: demonstration of multiple rounds of algorithmic cooling. Phys. Rev. Lett. 100, 140501 (2008)
Shor, P. W. & Jordan, S. P. Estimating Jones polynomials is a complete problem for one clean qubit. Quant. Inform. Comput. 8, 681â714 (2008)
Braunstein, S. L. & van Loock, P. Quantum information with continuous variables. Rev. Mod. Phys. 77, 513â577 (2005)
Schmidt, H. & Imamoglu, A. Giant Kerr nonlinearities obtained by electromagnetically induced transparency. Opt. Lett. 21, 1936â1938 (1996)
Duan, L. M. & Kimble, H. J. Scalable photonic quantum computation through cavity-assisted interactions. Phys. Rev. Lett. 92, 127902 (2004)
Knill, E., Laflamme, R. & Milburn, G. J. A scheme for efficient quantum computation with linear optics. Nature 409, 46â52 (2001)
Politi, A., Matthews, J. C. F. & OâBrien, J. L. Shorâs quantum factoring algorithm on a photonic chip. Science 325, 1221 (2009)
OâBrien, J. L. Optical quantum computing. Science 318, 1567â1570 (2007)
Migdal, A. & Dowling, J. eds. Single-photon detectors, applications, and measurement. J. Mod. Opt. 51, (2004)
Hadfield, R. H. Single-photon detectors for optical quantum information applications. Nature Photon. 3, 696â705 (2009)
Grangier, P., Sanders, B. & Vuckovic, J. eds. Focus on single photons on demand. New J. Phys. 6, (2004)
Shields, A. J. Semiconductor quantum light sources. Nature Photon. 1, 215â223 (2007)
Matthews, J. C. F., Politi, A., Stefanov, A. & OâBrien, J. L. Manipulation of multiphoton entanglement in waveguide quantum circuits. Nature Photon. 3, 346â350 (2009)
Kistner, C. et al. Demonstration of strong coupling via electro-optical tuning in high-quality QD-micropillar systems. Opt. Express 16, 15006â15012 (2008)
Fushman, I. et al. Controlled phase shifts with a single quantum dot. Science 320, 769â772 (2008)
Gruber, A. et al. Scanning confocal optical microscopy and magnetic resonance on single defect centers. Science 276, 2012â2014 (1997)
Devitt, S. J. et al. Photonic module: an on-demand resource for photonic entanglement. Phys. Rev. A 76, 052312 (2007)
Wineland, D. J. et al. Experimental issues in coherent quantum-state manipulation of trapped atomic ions. J. Res. Natl. Inst. Stand. Technol. 103, 259â328 (1998)
Wineland, D. & Blatt, R. Entangled states of trapped atomic ions. Nature 453, 1008â1014 (2008)
Ospelkaus, C. et al. Trapped-ion quantum logic gates based on oscillating magnetic fields. Phys. Rev. Lett. 101, 090502 (2008)
Garcia-Ripoll, J. J., Zoller, P. & Cirac, J. I. Speed optimized two-qubit gates with laser coherent control techniques for ion trap quantum computing. Phys. Rev. Lett. 91, 157901 (2003)
Leibfried, D., Blatt, R., Monroe, C. & Wineland, D. Quantum dynamics of single trapped ions. Rev. Mod. Phys. 75, 281â324 (2003)
Home, J. P. et al. Complete methods set for scalable ion trap quantum information processing. Science 325, 1227â1230 (2009)
Olmschenk, S. et al. Quantum teleportation between distant matter qubits. Science 323, 486â489 (2009)
Dür, W., Briegel, H. J., Cirac, J. I. & Zoller, P. Quantum repeaters based on entanglement purification. Phys. Rev. A 59, 169â181 (1999)
Duan, L.-M. & Raussendorf, R. Efficient quantum computation with probabilistic quantum gates. Phys. Rev. Lett. 95, 080503 (2005)
Morsch, O. & Oberthaler, M. Dynamics of Bose-Einstein condensates in optical lattices. Rev. Mod. Phys. 78, 179â215 (2006)
Anderlini, M. et al. Controlled exchange interaction between pairs of neutral atoms in an optical lattice. Nature 448, 452â456 (2007)
Urban, E. et al. Observation of Rydberg blockade between two atoms. Nature Phys. 5, 110â114 (2009)
Gaëtan, A. et al. Observation of collective excitation of two individual atoms in the Rydberg blockade regime. Nature Phys. 5, 115â118 (2009)
Negrevergne, C. et al. Benchmarking quantum control methods on a 12-qubit system. Phys. Rev. Lett. 96, 170501 (2006)
Vandersypen, L. M. K. et al. Experimental realization of Shorâs quantum factoring algorithm using nuclear magnetic resonance. Nature 414, 883â887 (2001)
Khaneja, N., Reiss, T., Kehlet, C., Schulte-Herbruggen, T. & Glaser, S. J. Optimal control of coupled spin dynamics: design of NMR pulse sequences by gradient ascent algorithms. J. Magn. Reson. 172, 296â305 (2005)
Braunstein, S. L. et al. Separability of very noisy mixed states and implications for NMR quantum computing. Phys. Rev. Lett. 83, 1054â1057 (1999)
Mehring, M., Mende, J. & Scherer, W. Entanglement between an electron and a nuclear spin 1/2. Phys. Rev. Lett. 90, 153001 (2003)
Hanson, R., Kouwenhoven, L. P., Petta, J. R., Tarucha, S. & Vandersypen, L. M. K. Spins in few-electron quantum dots. Rev. Mod. Phys. 79, 1217â1265 (2007)
Uhrig, S. G. Keeping a quantum bit alive by optimized Ï-pulse sequences. Phys. Rev. Lett. 98, 100504 (2007)
Liu, H. W. et al. A gate-defined silicon quantum dot molecule. Appl. Phys. Lett. 92, 222104 (2008)
Simmons, C. B. et al. Charge sensing and controllable tunnel coupling in a Si/SiGe double quantum dot. Nano Lett. 9, 3234â3238 (2009)
Kane, B. E. A silicon-based nuclear spin quantum computer. Nature 393, 133â137 (1998)
Vrijen, R. et al. Electron-spin-resonance transistors for quantum computing in silicon-germanium heterostructures. Phys. Rev. A 62, 012306 (2000)
Tyryshkin, A. M. & Lyon, S. A. Data presented at the Silicon Qubit Workshop, 24â25 August (University of California, Berkeley; sponsored by Lawrence Berkeley National Laboratory and Sandia National Laboratory, 2009)
Ladd, T. D., Maryenko, D., Yamamoto, Y., Abe, E. & Itoh, K. M. Coherence time of decoupled nuclear spins in silicon. Phys. Rev. B 71, 14401 (2005)
Yang, A. et al. Simultaneous subsecond hyperpolarization of the nuclear and electron spins of phosphorus in silicon by optical pumping of exciton transitions. Phys. Rev. Lett. 102, 257401 (2009)
Batra, A., Weis, C. D., Reijonen, J., Persaud, A. & Schenkel, T. Detection of low energy single ion impacts in micron scale transistors at room temperature. Appl. Phys. Lett. 91, 193502 (2007)
OâBrien, J. L. et al. Towards the fabrication of phosphorus qubits for a silicon quantum computer. Phys. Rev. B 64, 161401 (2001)
Schneider, C. et al. Lithographic alignment to site-controlled quantum dots for device integration. Appl. Phys. Lett. 92, 183101 (2008)
Atatüre, M. et al. Quantum-dot spin-state preparation with near-unity fidelity. Science 312, 551â553 (2006)
Gerardot, B. D. et al. Optical pumping of a single hole spin in a quantum dot. Nature 451, 441â444 (2008)
Press, D., Ladd, T. D., Zhang, B. Y. & Yamamoto, Y. Complete quantum control of a single quantum dot spin using ultrafast optical pulses. Nature 456, 218â221 (2008)
Berezovsky, J. et al. Nondestructive optical measurements of a single electron spin in a quantum dot. Science 314, 1916â1920 (2006)
Harrison, J., Sellars, M. J. & Manson, N. B. Measurement of the optically induced spin polarisation of N-V centres in diamond. Diamond Related Mater. 15, 586â588 (2006)
Dutt, M. V. G. et al. Quantum register based on individual electronic and nuclear spin qubits in diamond. Science 316, 1312â1316 (2007)
Neumann, P. et al. Multipartite entanglement among single spins in diamond. Science 320, 1326â1329 (2008)
Jiang, L. et al. Repetitive readout of a single electronic spin via quantum logic with nuclear spin ancillae. Science 326, 267â272 (2009)
Hanson, R., Dobrovitski, V. V., Feiguin, A. E., Gywat, O. & Awschalom, D. D. Coherent dynamics of a single spin interacting with an adjustable spin bath. Science 320, 352â355 (2008)
Takahashi, S., Hanson, R., van Tol, J., Sherwin, M. S. & Awschalom, D. D. Quenching spin decoherence in diamond through spin bath polarization. Phys. Rev. Lett. 101, 047601 (2008)
Balasubramanian, G. et al. Ultralong spin coherence time in isotopically engineered diamond. Nature Mater. 8, 383â387 (2009)
Neumann, P. et al. Scalable quantum register based on coupled electron spins in a room temperature solid. Nature Phys. 10.1038/nphys1536 (in the press)
Wang, C. F. et al. Fabrication and characterization of two-dimensional photonic crystal microcavities in nanocrystalline diamond. Appl. Phys. Lett. 91, 201112 (2007)
Wu, E. et al. Room temperature triggered single-photon source in the near infrared. New J. Phys. 9, 434 (2007)
Wang, C., Kurtsiefer, C., Weinfurter, H. & Burchard, B. Single photon emission from SiV centres in diamond produced by ion implantation. J. Phys. At. Mol. Opt. Phys. 39, 37â41 (2006)
Sanaka, K., Pawlis, A., Ladd, T. D., Lischka, K. & Yamamoto, Y. Indistinguishable photons from independent semiconductor nanostructures. Phys. Rev. Lett. 103, 053601 (2009)
Nakamura, Y., Pashkin, Yu. A. & Tsai, J. S. Coherent control of macroscopic quantum states in a single-Cooper-pair box. Nature 398, 786â788 (1999)
Vion, D. et al. Manipulating the quantum state of an electrical circuit. Science 296, 886â889 (2002)
Schreier, J. A. et al. Suppressing charge noise decoherence in superconducting charge qubits. Phys. Rev. B 77, 180502 (2008)
Chiorescu, I., Nakamura, Y., Harmans, C. J. P. M. & Mooij, J. E. Coherent quantum dynamics of a superconducting flux qubit. Science 299, 1869â1871 (2003)
Martinis, J. M., Nam, S., Aumentado, J. & Urbina, C. Rabi oscillations in a large Josephson-junction qubit. Phys. Rev. Lett. 89, 117901 (2002)
Niskanen, A. O. et al. Quantum coherent tunable coupling of superconducting qubits. Science 316, 723â726 (2007)
Harris, R. et al. Experimental demonstration of a robust and scalable flux qubit. Preprint at ãhttp://arxiv.org/abs/0909.4321ã (2009)
Wallraff, A. et al. Strong coupling of a single photon to a superconducting qubit using circuit quantum electrodynamics. Nature 431, 162â167 (2004)
DiCarlo, L. et al. Demonstration of two-qubit algorithms with a superconducting quantum processor. Nature 260, 240â244 (2009)
Ansmann, M. et al. Violation of Bellâs inequality in Josephson phase qubits. Nature 461, 504â506 (2009)
Chow, J. M. et al. Entanglement metrology using a joint readout of superconducting qubits. Preprint at ãhttp://arxiv.org/abs/0908.1955ã (2009)
Lupascu, A. et al. Quantum non-demolition measurement of a superconducting two-level system. Nature Phys. 3, 119â123 (2007)
Micheli, A., Brennen, G. K. & Zoller, P. A toolbox for lattice-spin models with polar molecules. Nature Phys. 2, 341â347 (2006)
Rippe, L., Julsgaard, B., Walther, A., Ying, Y. & Kroll, S. Experimental quantum-state tomography of a solid-state qubit. Phys. Rev. A 77, 022307 (2008)
de Riedmatten, H., Afzelius, M., Staudt, M. U., Simon, C. & Gisin, N. A solid-state light-matter interface at the single-photon level. Nature 456, 773â777 (2008)
Morton, J. J. L. et al. Bang-bang control of fullerene qubits using ultrafast phase gates. Nature Phys. 2, 40â43 (2006)
Mason, N., Biercuk, M. J. & Marcus, C. M. Local gate control of a carbon nanotube double quantum dot. Science 303, 655â658 (2004)
Trauzettel, B., Bulaev, D. V., Loss, D. & Burkard, G. Spin qubits in graphene quantum dots. Nature Phys. 3, 192â196 (2007)
Platzman, P. M. & Dykman, M. I. Quantum computing with electrons floating on liquid helium. Science 284, 1967â1969 (1999)
Leuenberger, M. N. & Loss, D. Quantum computing in molecular magnets. Nature 410, 789â793 (2001)
Tian, L., Rabl, P., Blatt, R. & Zoller, P. Interfacing quantum-optical and solid-state qubits. Phys. Rev. Lett. 92, 247902 (2004)
Andre, A. et al. A coherent all-electrical interface between polar molecules and mesoscopic superconducting resonators. Nature Phys. 2, 636â642 (2006)
Recher, P., Sukhorukov, E. V. & Loss, D. Andreev tunneling, Coulomb blockade, and resonant transport of nonlocal spin-entangled electrons. Phys. Rev. B 63, 165314 (2001)
Privman, V., Vagner, I. D. & Kventsel, G. Quantum computation in quantum-Hall systems. Phys. Lett. A 239, 141â146 (1998)
Smelyanskiy, V. N., Petukhov, A. G. & Osipov, V. V. Quantum computing on long-lived donor states of Li in Si. Phys. Rev. B 72, 081304 (2005)
Tian, L. & Zoller, P. Coupled ion-nanomechanical systems. Phys. Rev. Lett. 93, 266403 (2004)
Piermarocchi, C., Chen, P., Sham, L. J. & Steel, D. G. Optical RKKY interaction between charged semiconductor quantum dots. Phys. Rev. Lett. 89, 167402 (2002)
Quinteiro, G. F., Fernandez-Rossier, J. & Piermarocchi, C. Long-range spin-qubit interaction mediated by microcavity polaritons. Phys. Rev. Lett. 97, 097401 (2006)
Khitun, A., Ostroumov, R. & Wang, K. L. Spin-wave utilization in a quantum computer. Phys. Rev. A 64, 062304 (2001)
Barnes, C. H. W., Shilton, J. M. & Robinson, A. M. Quantum computation using electrons trapped by surface acoustic waves. Phys. Rev. B 62, 8410â8419 (2000)
Chang, D. E., Sørensen, A. S., Hemmer, P. R. & Lukin, M. D. Quantum optics with surface plasmons. Phys. Rev. Lett. 97, 053002 (2006)
Raussendorf, R. & Harrington, J. Fault-tolerant quantum computation with high threshold in two dimensions. Phys. Rev. Lett. 98, 190504 (2007)
Nayak, C., Simon, S. H., Stern, A., Freedman, M. & Das Sarma, S. Non-abelian anyons and topological quantum computation. Rev. Mod. Phys. 80, 1083â1159 (2008)
Langer, C. et al. Long-lived qubit memory using atomic ions. Phys. Rev. Lett. 95, 060502 (2005)
Knill, E. et al. Randomized benchmarking of quantum gates. Phys. Rev. A 77, 012307 (2008)
Benhelm, J., Kirchmair, G., Roos, C. F. & Blatt, R. Towards fault-tolerant quantum computing with trapped ions. Nature Phys. 4, 463â466 (2008)
Treutlein, P., Hommelhoff, P., Steinmetz, T., Hänsch, T. W. & Reichel, J. Coherence in microchip traps. Phys. Rev. Lett. 92, 203005 (2004)
Ryan, C. A., Laforest, M. & Laflamme, R. Randomized benchmarking of single- and multi-qubit control in liquid-state NMR quantum information processing. New J. Phys. 11, 013034 (2009)
Bertet, P. et al. Dephasing of a superconducting qubit induced by photon noise. Phys. Rev. Lett. 95, 257002 (2005)
Emerson, J. et al. Symmetrized characterization of noisy quantum processes. Science 317, 1893â1896 (2007)
Hanson, R. & Awschalom, D. D. Coherent manipulation of single spins in semiconductors. Nature 453, 1043â1049 (2008)
Acknowledgements
We thank R. Hanson, M. D. Lukin, and W. D. Oliver for comments. We acknowledge support from NSF, EPSRC, QIP IRC, IARPA, ERC, the Leverhulme Trust, CREST-JST, DFG, BMBF and Landesstiftung BW. J.L.OâB. acknowledges a Royal Society Wolfson Merit Award.
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Ladd, T., Jelezko, F., Laflamme, R. et al. Quantum computers. Nature 464, 45â53 (2010). https://doi.org/10.1038/nature08812
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DOI: https://doi.org/10.1038/nature08812