1973 – Alexander Holevo publishes a paper showing that nqubits 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 Stanisław Ingarden publishes a seminal paper entitled "Quantum Information Theory" in Reports on Mathematical Physics, vol. 10, 43–72, 1976. (The paper was submitted in 1975.) It is one of the first attempts at creating a quantum information theory, showing 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, within the formalism of a generalized quantum mechanics of open systems and a generalized concept of observables (the so-called semi-observables).
1980s
1981
Richard Feynman in his talk at the First Conference on the Physics of Computation, held at MIT in May, 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 [1]
Tommaso Toffoli introduced the reversible Toffoli gate, which, together with the NOT and XOR gates provides a universal set for quantum computation.
1982 - Paul Benioff proposes the first recognisable theoretical framework for a quantum computer [2]
Peter Shor, at AT&T's Bell Labs in New Jersey, discovers an important 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.
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.[3]
1996
Lov Grover, at Bell Labs, invented the quantum database search algorithm. The quadratic speedup is not 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.
1999 – Samuel L. Braunstein and collaborators showed that there was no mixed state quantum entanglement in any bulk NMR experiment. Pure state quantum entanglement is necessary for any quantum computational speedup, and thus this gave evidence that NMR computers would not yield benefit over classical computer. It was still an open question as to whether mixed state entanglement is necessary for quantum computational speedup[6]
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.
Noah Linden and Sandu Popescu proved that the presence of entanglement is a necessary condition for a large class of quantum protocols. This, coupled with Brauenstein's result (see 1999 above), called the validity of NMR quantum computation into question.[7]
Emanuel Knill, Raymond Laflamme, and Gerard Milburn show that optical quantum computing is possible with single photon sources, linear optical elements, and single photon detectors, launching the field of linear optical quantum computing.
2002 – The Quantum Information Science and Technology Roadmapping Project, involving some of the main participants in the field, laid out the Quantum computation roadmap.
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.[10]
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 1 issue of Nature.
Materials Science Department of Oxford University, cage a qubit in a buckyball (a Buckminster fullerene particle), and demonstrated quantum "bang-bang" error correction.[11]
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.[12]
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.[13]
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.[14]
Professors at the University of Sheffield develop a means to efficiently produce and manipulate individual photons at high efficiency at room temperature.[15]
New error checking method theorized for Josephson junction computers.[16]
Two dimensional ion trap developed for quantum computing.[18]
Seven atoms placed in stable line, a step on the way to constructing a quantum gate, at the University of Bonn.[19]
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.[20]
University of Arkansas develops quantum dot molecules.[21]
Spinning new theory on particle spin brings science closer to quantum computing.[22]
University of Copenhagen develops quantum teleportation between photons and atoms.[23]
University of Camerino scientists develop theory of macroscopic object entanglement, which has implications for the development of quantum repeaters.[24]
Tai-Chang Chiang, at Illinois at Urbana-Champaign, finds that quantum coherence can be maintained in mixed-material systems.[25]
Cristophe Boehme, University of Utah, demonstrates the feasibility of reading spin-data on a silicon-phosphorus quantum computer.[26]
NIST demonstrates multiple computing operations on qubits[95]
A combination of all of the fundamental elements required to perform scalable quantum computing through the use of qubits stored in the internal states of trapped atomic ions shown[96]
Researchers at University of Bristol demonstrate Shor's algorithm on a silicon photonic chip [97]
Quantum Computing with an Electron Spin Ensemble[98]
Photon machine gun developed for quantum computing[100]
Quantum algorithm developed for differential equation systems[101]
First universal programmable quantum computer unveiled[102]
Scientists electrically control quantum states of electrons[103]
Google collaborates with D-Wave Systems on image search technology using quantum computing[104]
A method for synchronizing the properties of multiple coupled CJJ rf-SQUID flux qubits with a small spread of device parameters due to fabrication variations was demonstrated[105]
D-Wave claims to have developed quantum annealing and introduces their product called D-Wave One. The company claims this is the first commercially available quantum computer[128]
Repetitive error correction demonstrated in a quantum processor[129]
^ June 14, 2007 NaturePlantenberg, J. H.; De Groot, P. C.; Harmans, C. J. P. M.; Mooij, J. E. (2007). "Demonstration of controlled-NOT quantum gates on a pair of superconducting quantum bits". Nature447 (7146): 836–839. doi:10.1038/nature05896. PMID17568742.
^Thomas Monz, Philipp Schindler, Julio T. Barreiro, Michael Chwalla, Daniel Nigg, William A. Coish, Maximilian Harlander, Wolfgang Hänsel, Markus Hennrich1, and Rainer Blatt (2011). "14-Qubit Entanglement: Creation and Coherence". Physical Review Letters106 (13): 130506. doi:10.1103/PhysRevLett.106.130506.