There are two major differences between qubits.
There is an ensemble qubit which contain a large number of particles that together act as a single qubit and there is what one typically thinks of as a qubit, which is a single particle or material.
Possible qubits include single photons, trapped atomic ions, neutral atoms, nuclear spins, quantum dots, impurities in silicon and diamond, etc...
It was the unorthodox theories of quantum mechanics, born out of the 20th Century, which were later to spawn quantum computing. The concept of using quantum entities to process data and solve complex problems, much like a classical computer, can be traced back to the 1980s.
Quantum computing is still very much in its nascent stage. There is a long way to go before a usefully functioning quantum computer can be built, let alone brought to market. But advances in this new technology are occurring frequently, and no chronological record can ever be complete. What follows is an accurate timeline explaining key advances in quantum computing. As you will discover, much of the technological progress has been made this century. Most of the major theoretical concepts were laid down in the late 20th Century.
In 1980, U.S. scientist, Paul Benioff, was the first to propose a computer which operated under quantum mechanical principles. His idea of a quantum computer was based on Alan Turing’s famous paper tape computer described in his 1936 paper.
The next year, physicist Richard Feynman, proved it was impossible to simulate quantum systems on a classical computer. His argument hinged on Bell’s theorem, written in 1964. He showed how classical mechanics fails to account for the full range of predictions arising from quantum mechanics. Feynman did propose how a quantum computer might be able to simulate any quantum system, including the physical world in a 1984 lecture. His concept borrowed from Benioff’s quantum Turing computer.
In 1985, David Deutsch, a physicist, published a paper describing the world's first universal quantum computer. He showed how such a quantum machine could reproduce any realizable physical system. What’s more it could do this by finite means and much faster than a classical computer. He was the first to set down the mathematical concepts of a quantum Turing machine, one which could model a quantum system.
Enthusiasm for creating the first quantum computer really kicked off with Shor’s algorithm in 1994. Peter Shor, a mathematician at Bell Labs, proposed a method for factorizing large integers. This had serious implications for cryptography, which relies on this operation being hard to keep codes secure. Shor’s algorithm searched for periodicities in long integers -
With the help of Andrew Steane, Peter Shor later devised quantum codes which can be used to offset errors caused by decoherence. When qubits interact with ‘noise’ from the outside world they can stop behaving in a quantum mechanical sense, creating errors.
The following year saw Christopher Monroe and David Wineland of NIST demonstrate the first quantum logic gate, the C-
In 1996, another Bell researcher, Lov Grover, used quantum mechanics to solve an old problem: unstructured search. Say, for example, you want to match a large database of names with a long list of telephone numbers. A classical computer could only solve this problem by querying each name with a telephone number until it got the right one. If N is the number of queries undertaken, then on average a classical computer would need N/2 queries to match each telephone record. Grover’s algorithm uses the theory of quantum superposition to reduce the number of queries to √N, significantly faster. This algorithm boosted interest in building quantum computers by revealing yet another use for them.
1998 saw the first experimental demonstration of a quantum algorithm, Deutsch’s problem, by a quantum computer. Oxford researchers used a working 2-
In 2000, the first working 5-
2001 is famous for being the year that the landmark Shor’s algorithm was first demonstrated. A team at the IBM Almaden Research Center in California succeeded in factorizing the integer 15 into 5 and 3. They used a thimbleful of a bespoke liquid containing billions of molecules. The molecules were constructed from five fluoride and two carbon atoms, each with their own nuclear spin state. The molecules worked as a 7-
In 2006, scientists at the Institute for Quantum Computing and Perimeter Institute for Theoretical Physics presented a new operational standard by controlling a 12-
The same year, Bonn researchers took a step closer to the building of a quantum gate, the quantum representation of a mathematical rule. By using ‘laser tweezers’ they succeeded in lining up seven cesium atoms in a row, all at precisely the same distance from each other.
Also in 2006, researchers at the University of Arkansas created molecules of quantum dot pairs. These have great potential for quantum computers, especially if more complex molecules can be created.
At the University of Camerino, scientists developed a theory for entangling macroscopic objects. Their experiment employed lasers and mirrors. The results could one day lead to quantum computers operating on a macroscopic, ie, visible, scale.
2007 saw the first use of Deutsch’s algorithm in a cluster state quantum computer. Belfast and Vienna researchers studied the superposed interaction of four quantum encoded photons.
Later the same year, a company called D-
In 2011, D-
Quantum annealing is a process where sequences of coupled qubits are set up to find their lowest energy state. Shunning the much faster Shor’s algorithm, D-
2011 went down in quantum computer history as the year when a quantum computer was devised with Von Neumann architecture. This is the classical computer set up with a central processing unit (CPU) and a memory which stores data and processing instructions. The Chinese team's quantum computer contained seven quantum components, including two superconducting qubits.
The following year, D-
In 2013, D-
2013’s landmark advance was the beating of the record for avoiding qubit decoherence at room temperature. The previous two second record, set the year before, was smashed by 39 minutes. The researchers also managed to keep qubits from decohering for three hours at cryogenic temperatures. Even a 39 minute lifespan would allow over 20 million quantum computations to be performed before they had decayed by 1%.
In 2015, D-
Recent advances have brought the prospect of a first general-
Timeline of quantum computing -
Bell’s theorem -
Quantum Dot Molecules -
Controversial quantum computer beats factoring record, by Stephen Battersby, 13 April 2012
Researchers smash through quantum computer storage record, by Jacob Kastrenakes, 14 November, 2013
Diamonds could be building blocks for quantum computers, by Agam Shah, 7 November, 2011
Computing With Quantum Cats From Colossus To Qubits, by John Gribbin, published 2013, Bantam Press
The Quantum Age -
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