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Quantum Computers


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The editors are well aware that his type of computing is not yet in existence at the time this page is written. At least not on a commercial scale. However there are some prototypes in laboratories, in a very rudimentary form though.
Still the editors find this type of computing such a fascinating idea that it is made part of the architecture series as well.

It is around 2000 that Quantum computing articles show up in magazines and newspapers but not so much in professional magazines. Why? Because Quantum computing is a very controversial type of computing of which some say that it will never be realized in a practical way. Others find the idea fascinating and try to realize a quantum computer one way or another.

Einstein once said: "If you can think about it, it will be possible now or in the future".

Bearing this in mind, and fantasizing about the possibilities, the History of Computing Project decided to include this chapter into the series on hardware platforms. Besides why not?!

Related Articles
Quantum Informationsystem
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Quantum computers
Grid computers
Mini computers
Embedded computers

The ranking of a quantumcomputer is as you can see at the top of the computing spectrum. Scientist predict that this will be the fastest but also smallest computer we will know.

A quantum computer is not simply to describe because the scientist are only developing theories and practical implementation since recent years.


Chronology of Quantum Computing

Reference: (2)(3)


Planck proposed that light is emitted and absorbed in quanta of energy Hw, thereby explaining the spectrum of black body radiation.


Einstein interpreted the photoelectric effect by postulating that light comes in particles — photons.


Einstein proposes quantum theory of the specific heat of solids.

Rutherford scatters particles off gold foil, leading to the discovery of the atomic nucleus.


The “old quantum theory”: Bohr model successfully describes spectrum of hydrogen atom.


Einstein publishes the general theory of relativity, the culmination of classical (pre-quantum) physics.


de Broglie proposes that matter particles of energy E and momentum p behave as waves of angular frequency E/¯h and wave vector p/¯h.


Bose proposes statistical law for photons; Einstein extends this to matter particles (of integer spin, it will turn out).


Beginnings of the “new quantum theory”: Heisenberg’s matrix mechanics describes relations between observable quantities.

Uhlenbeck and Goudsmit discover the spin of the electron.

Pauli proposes exclusion principle.


Schroedinger proposes wave equation for the time-evolution of the wave function. Born interprets wave function as probability amplitude.

Dirac attempts to quantise the electromagnetic field. Fermi distribution for electrons derived.


Bohr and Heisenberg develop the now orthodox Copenhagen interpretation of quantum mechanics. Heisenberg proposes uncertainty
principle xp  h/2

Davisson and Germer observe diffraction of electrons: particles can behave as waves.


Dirac proposes a relativistic wave equation for the electron, which leads to the prediction of antimatter.

Bloch and Sommerfeld develop the theory of electron bands and Fermi surfaces in solids.


“The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that exact application of these laws leads to equations much too complicated to be solved.” (Dirac)


Anderson discovers the positron, predicted by Dirac.


Einstein, Podolsky and Rosen (EPR) propose thought experiment to show that quantum mechanics is incomplete.


Feynman, Schwinger and Tomonaga develop quantum electrodynamics (QED), the quantum theory of the electromagnetic field. Predictions
for electrons will be consistent with experiment to parts in 1012.


Everett proposes many-worlds interpretation of quantum mechanics.


Bell inequalities between correlations are satisfied by local realistic theories but violated by quantum mechanics, answering PR’sobjections of 1935.


Alexander Holevo publishes a paper showing that n qubits cannot carry more than n classical bits of information.


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.


Richard Feynman gave the first proposal for using quantum phenomena to perform computations. The speech was entitled "Simulating Physics With Computers". It was in a talk he gave at the First Conference on the Physics of Computation at MIT. He pointed out that it would probably take a classical computer an extremely long time to simulate a simple experiment in quantum physics. If so, then simple quantum systems are essentially performing huge calculations all the time. It might even be possible to harness that for something useful.


Aspect performs EPR experiment, showing that Bell’s inequalities are violated and hence refuting local realism.

Binnig and Rohrer image atoms with scanning tunneling microscope.

Feynman proposes the idea of a quantum computer.



Penrose proposes that the brain is a quantum computer.


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. This raised the hope that a simple device might be able to perform many different quantum algorithms.



Dan Simon, at Universite de Montreal, invented an oracle problem for which 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.


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, even outside the physics community.

Shor's algorithm for prime factorisation on a quantum computer can (in principle) perform calculations impossible on a classical computer.


Shor proposed the first scheme for quantum error correction. This is an approach to making quantum computers that can compute with large numbers of qubits for long periods of time. Errors are always introduced by the environment, but quantum error correction might be able to overcome those errors. This could be a key technology for building large-scale quantum computers that work. These early proposals had a number of limitations. They could correct for some errors, but not errors that occur during the correction process itself. A number of improvements have been suggested, and active research on this continues. An alternative to quantum error correction has been found. Instead of actively correcting the errors induced by the interaction with the environment, special states that are immune to the errors can be used. This approach, known as decoherence free subspaces, assumes that there is some symmetry in the computer-environment interaction.


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.


David Cory, A.F. Fahmy and Timothy Havel, and at the same time Neil Gershenfeld and Isaac Chuang at MIT published the first papers on quantum computers based on bulk spin resonance, or thermal ensembles. The computer is actually a single, small molecule, which stores qubits in the spin of its protons and neutrons. Trillions of trillions of these can float in a cup of water. That cup is placed in a nuclear magnetic resonance machine, similar to the magnetic resonance imaging machines used in hospitals. This room-temperature (thermal) collection of molecules (ensemble) has massive amounts of redundancy, which allows it to maintain coherence for thousands of seconds, much better than many other proposed systems.

Grover develops an algorithm for fast database search.

Quantum cryptography successfully is demonstrated over a distance of 23 km.

First quantum teleportation of a photon.


First working 2-qubit NMR computer demonstrated at University of California, Berkeley.


First working 3-qubit NMR computer demonstrated at IBM's Almaden Research Center. First execution of Grover's algorithm.


First working 5-qubit NMR computer demonstrated at IBM's Almaden Research Center. First execution of order finding (part of Shor's algorithm).

Quantum tunneling is observed in a macroscopic system (currents in superconducting devices).

Tau neutrino observed, completing verification of standard model of elementary particles (if initial hints of a Higgs boson are correct).

The idea of quantum now exists 100 years.


First working 7-qubit NMR computer demonstrated at IBM's Almaden Research Center. First execution of Shor's algorithm. The number 15 was factored using 10^18 identical molecules, each containing 7 atoms.


Dr. Isaac Chuang, research staff member at IBM's Almaden Research Center (San Jose, Calif.), holds a quantum computer -- the glass tube contains special designed molecules.

Quantum computers promised to solve some of the most difficult mathematical problems exponentially faster than a conventional computer(4)



This is the first working quantum computer.

The multi billion question is: when will quantum computers be consumer ripe in the next future. Some think it will never be the case others predict the emergence within two decades.



First financial transaction transmitted with the use of entangled photons.




Operating systems


Programming quantumcomputers








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