Experimental method of computing that makes use of quantum-mechanical phenomena. It incorporates quantum theory and the uncertainty principle. Quantum computers would allow a bit to store a value of 0 and 1 simultaneously. They could pursue multiple lines of inquiry simultaneously, with the final output dependent on the interference pattern generated by the various calculations. Seealso DNA computing, quantum mechanics.

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1970s

• 1970 - Stephen Wiesner invents conjugate coding.
• 1973 - Alexander Holevo publishes a paper showing that n qubits cannot carry more than n classical bits of information (a result known as "Holevo's theorem" or "Holevo's bound"). Charles H. Bennett shows that computation can be done reversibly.
• 1975 - R. P. Poplavskii publishes "Thermodynamical models of information processing" (in Russian), Uspekhi Fizicheskikh Nauk,115:3, 465–501 which showed the computational infeasibility of simulating quantum systems on classical computers, due to the superposition principle.
• 1976 - Polish mathematical physicist Roman Ingarden, in one of the first attempts at creating a quantum information theory, shows that Shannon information theory cannot directly be generalized to the quantum case, but rather that it is possible to construct a quantum information theory which is a generalization of Shannon's theory.

1980s

• 1980 - Yuri I. Manin, publishes Computable and uncomputable (in Russian), Moscow, Sovetskoye Radio.
• 1981
• Richard Feynman in his talk at the First Conference on the Physics of Computation, held at MIT, observed that it appeared to be impossible in general to simulate an evolution of a quantum system on a classical computer in an efficient way. He proposed a basic model for a quantum computer that would be capable of such simulations.
• Tommaso Toffoli introduced the reversible Toffoli gate, which, together with the NOT and XOR gates provides a universal set for quantum computation.

• 1984 - Charles Bennett and Gilles Brassard employ Wiesner's conjugate coding for distribution of cryptographic keys.
• 1985 - David Deutsch, at the University of Oxford, described the first universal quantum computer. Just as a universal Turing machine can simulate any other Turing machine efficiently, so the universal quantum computer is able to simulate any other quantum computer with at most a polynomial slowdown.

1990s

• 1991 - Artur Ekert invents entanglement based secure communication.
• 1993 - Dan Simon, at Université de Montréal, invented an oracle problem for which a quantum computer would be exponentially faster than conventional computer. This algorithm introduced the main ideas which were then developed in Peter Shor's factoring algorithm.
• 1994
• Peter Shor, at AT&T's Bell Labs in New Jersey, discovered a remarkable algorithm. It allowed a quantum computer to factor large integers quickly. It solved both the factoring problem and the discrete log problem. Shor's algorithm could theoretically break many of the cryptosystems in use today. Its invention sparked a tremendous interest in quantum computers.
• First United States Government workshop on quantum computing is organized by NIST in Gaithersburg, Maryland, in autumn.
• In December, Ignacio Cirac, at University of Castilla-La Mancha at Ciudad Real, and Peter Zoller at the University of Innsbruck proposed an experimental realization of the controlled-NOT gate with trapped ions.

• 1995
• First United States Department of Defense workshop on quantum computing and quantum cryptography is organized by United States Army physicists Charles M. Bowden, Jonathan P. Dowling, and Henry O. Everitt; it takes place in February at the University of Arizona in Tucson.
• Peter Shor and Andrew Steane simultaneously proposed the first schemes for quantum error correction. (An alternative to quantum error correction exploits special states that are immune to certain errors. This device is known as a decoherence-free subspaces.
• Christopher Monroe and David Wineland at NIST (Boulder, Colorado) experimentally realize the first quantum logic gate - the C-NOT gate - with trapped ions, according to Cirac and Zoller's proposal.

• 1996
• Lov Grover, at Bell Labs, invented the quantum database search algorithm. The quadratic speedup isn't as dramatic as the speedup for factoring, discrete logs, or physics simulations. However, the algorithm can be applied to a much wider variety of problems. Any problem that had to be solved by random, brute-force search, could now have a quadratic speedup.
• The United States Government, particularly in a joint partnership of the Army Research Office (now part of the Army Research Laboratory) and the National Security Agency, issues the first public call for research proposals in quantum information processing.

• 1997
• David Cory, Amr Fahmy and Timothy Havel, and at the same time Neil Gershenfeld and Isaac L. Chuang at MIT published the first papers on quantum computers based on bulk spin resonance, or thermal ensembles. The technology is based on a nuclear magnetic resonance (NMR) machine, which is similar to the medical magnetic resonance imaging machine. This room-temperature (thermal) collection of molecules (ensemble) maintains coherence for several seconds. However, this approach to quantum computing is not scalable beyond a few tens of qubits.
• Alexei Kitaev describes the principles of topological quantum computation as a method for combatting decoherence.

• 1998
• First working 2-qubit NMR computers demonstrated by Jonathan A Jones and Michele Mosca at Oxford University and at the same time by Isaac L. Chuang at IBM's Almaden Research Center together with coworkers at Stanford University and MIT.
• First working 3-qubit NMR computer.
• First execution of Grover's algorithm.

• 1999 - Samuel L. Braunstein and collaborators showed that there was no quantum entanglement in any bulk NMR experiment, implying that the NMR device is at best a classical simulator of a quantum computer.

2000-2004

• 2000
• First working 5-qubit NMR computer demonstrated at the Technical University of Munich.
• First execution of order finding (part of Shor's algorithm) at IBM's Almaden Research Center and Stanford University.
• First working 7-qubit NMR computer demonstrated at the Los Alamos National Laboratory.

• 2001
• First execution of Shor's algorithm at IBM's Almaden Research Center and Stanford University. The number 15 was factored using 10¹⁸ identical molecules, each containing seven active nuclear spins. However all these NMR results do not represent true quantum computing as no quantum entanglement is present (see 1999 above).

• 2002 - The Quantum Information Science and Technology Roadmapping Project, involving some of the main participants in the field, laid out the Quantum computation roadmap
• 2003 Todd D. Pittman and collaborators at Johns Hopkins University, Applied Physics Laboratory and independently Jeremy L. O'Brien and collaborators at the University of Queensland, demonstrate quantum controlled-not gates using only linear optical elements.,
• 2004 - First working pure state NMR quantum computer (based on parahydrogen) demonstrated at Oxford University and University of York.

Since the NMR experiments cannot prepare pure quantum states and exhibit no quantum entanglement during computation, concerns have arisen about their quantum nature. In particular, it has been proved that the presence of entanglement is a necessary condition for quantum computation.

2005

• University of Illinois at Urbana-Champaign scientists demonstrate quantum entanglement of multiple characteristics, potentially allowing multiple qubits per particle.
• Two teams of physicists have measured the capacitance of a Josephson junction for the first time. The methods could be used to measure the state of quantum bits in a quantum computer without disturbing the state.
• In December, the first quantum byte, or qubyte, is announced to have been created by scientists at The Institute of Quantum Optics and Quantum Information at the University of Innsbruck in Austria, with the formal paper published in the December 1st issue of Nature.
• Harvard University and Georgia Institute of Technology researchers succeeded in transferring quantum information between "quantum memories" – from atoms to photons and back again.

2006

• Materials Science Department of Oxford University, cage a qubit in a buckyball (a Buckminster fullerene particle), and demonstrated quantum "bang-bang" error correction.
• Researchers from the University of Illinois at Urbana-Champaign use the Zeno Effect, repeatedly measuring the properties of a photon to gradually change it without actually allowing the photon to reach the program, to search a database without actually "running" the quantum computer.
• Vlatko Vedral of the University of Leeds and colleagues at the universities of Porto and Vienna found that the photons in ordinary laser light can be quantum mechanically entangled with the vibrations of a macroscopic mirror.
• Professor Samuel L.Braunstein at the University of York along with the University of Tokyo and the Japan Science and Technology Agency gave the first experimental demonstration of quantum telecloning.
• Professors at the University of Sheffield develop a means to efficiently produce and manipulate individual photons at high efficiency at room temperature.
• New error checking method theorized for Josephson junction computers.
• First 12 qubit quantum computer benchmarked.
• Two dimensional ion trap developed for quantum computing.
• Seven atoms placed in stable line, a step on the way to constructing a quantum gate, at the University of Bonn.
• A team at Delft University of Technology in the Netherlands created a device that can manipulate the "up" or "down" spin-states of electrons on quantum dots.
• University of Arkansas develops quantum dot molecules.
• Spinning new theory on particle spin brings science closer to quantum computing.
• University of Copenhagen develops quantum teleportation between photons and atoms.
• University of Southern California develops new quantum error correction method.
• University of Camerino scientists develop theory of macroscopic object entanglement, which has implications for the development of quantum repeaters.
• Scientists at Illinois at Urbana-Champaign find that quantum coherence is possible in incommensurate electronic systems.
• University of Utah Scientist shows it's feasible to read data stored as nuclear spins.

2007

• Subwavelength waveguide developed for light.
• Single photon emitter for optical fibers developed.
• New material proposed for quantum computing.
• Single atom single photon server devised.
• First use of Deutsch's Algorithm in a cluster state quantum computer.
• University of Cambridge develops electron quantum pump.
• Superior method of qubit coupling developed.
• Successful Demonstration of Controllably Coupled Qubits.
• Breakthrough in applying spin-based electronics to silicon.
• Scientists demonstrate quantum state exchange between light and matter.
• Diamond quantum register developed.
• Controlled-NOTquantum gates on a pair of superconducting quantum bits realized.
• Scientists contain, study hundreds of individual atoms in 3D array.
• Nitrogen in buckyball used in quantum computing.
• Large number of electrons quantum coupled.
• Spin-orbit interaction of electrons measured.
• Atoms quantum manipulated in laser light.
• Light pulses used to control electron spins.
• Quantum effects demonstrated across tens of nanometers.
• Light pulses used to accelerate quantum computing development.
• Quantum RAM blueprint unveiled.
• Model of quantum transistor developed.
• Long distance entanglement demonstrated.
• Photonic quantum computing used to factor number by two independent labs.
• Quantum bus developed by two independent labs.
• Superconducting quantum cable developed.
• Transmission of qubits demonstrated.
• Superior qubit material devised.
• Single electron qubit memory.
• Bose-Einstein condensate quantum memory developed
• D-Wave Systems claims to have working 28-qubit quantum computer.
• New cryonic method reduces decoherence and increases interaction distance.(and thus quantum computing speed)
• Photonic quantum computer demonstrated.

2008

• Graphene quantum dot qubits
• Quantum bit stored
• 3D qubit-qutrit entanglement demonstrated
• Analog quantum computing devised
• Control of quantum tunneling
• Entangled memory developed
• Superior NOT gate developed
• Qutrits developed
• Quantum logic gate in optical fiber
• Nano-Diamonds devised
• Superior quantum Hall Effect discovered
• Enduring spin states in quantum dots
• Molecular magnets proposed for quantum RAM
• Quasiparticles offer hope of stable quantum computer
• Image storage may have better storage of qubits
• Quantum entangled images
• Quantum state intentionally altered in molecule
• Electron position controlled in silicon circuit
• Superconducting Electronic Circuit Pumps Microwave Photons
• Amplitude spectroscopy developed

References