Quantum computing

The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers.

Quantum computing is computing usingquantum-mechanical phenomena, such assuperposition and entanglement.[1] Aquantum computer is a device that performs quantum computing. They are different frombinary digital electronic computers based ontransistors. Whereas common digital computing requires that the data be encoded into binary digits (bits), each of which is always in one of two definite states (0 or 1), quantum computation uses quantum bits, which can be in superpositions of states. Aquantum Turing machine is a theoretical model of such a computer, and is also known as the universal quantum computer. The field of quantum computing was initiated by the work of Paul Benioff (de)[2] and Yuri Manin in 1980,[3]Richard Feynman in 1982,[4] and David Deutsch in 1985.[5] A quantum computer with spins as quantum bits was also formulated for use as a quantum spacetime in 1968.[6]

As of 2017, the development of actual quantum computers is still in its infancy, but experiments have been carried out in which quantum computational operations were executed on a very small number of quantum bits.[7] Both practical and theoretical research continues, and many national governments and military agencies are funding quantum computing research in additional effort to develop quantum computers for civilian, business, trade, environmental and national security purposes, such as cryptanalysis.[8] A small 16-qubit quantum computer exists and is available for hobbyists to experiment with via the IBM quantum experience project. Along with the IBM computer a company called D-Wave has also been developing their own version of a quantum computer that uses a process called annealing.[9]

One of the more fascinating developments in the Quantum Computing field is the fact that in December of 2017, Microsoft released a preview version of a "Quantum Development Kit".[10] It includes a programming language Q# that they have developed which can take advantage of the unusual and potentially incredible power of the Quantum Computer. The remarkable thing about this release is that there does not exist yet a quantum computer that can run programs beyond the trivial ones that can be run on the very small, experimental IBM and D-Wave quantum computers described in the previous paragraph. So as Lewis D. Eigen has said, "We can write, debug, and perfect quantum programs that not only cannot be run today, but might not be able to be run for a decade or more. The fact that Microsoft has invested substantial resources in a new language, and many programmers will actually write programs in that language that cannot now be run, is an indication of the enormous theoretical potential of quantum computing and the faith that someone soon will find a way to construct a large scale quantum computer. This is the future of computing, and Microsoft has given new meaning to the phrase 'getting ahead of the curve'." [11] To allow the "quantum programmers" to debug and see the results of their quantum programs, Microsoft has programmed a normal modern computer to behave like and simulate a quantum computer only it does not have the incredible speed that the real quantum computer will have when created. So quantum programmers will be creating their programs in "slow motion" until the development for which so many are awaiting.

Large-scale quantum computers would theoretically be able to solve certain problems much more quickly than any classical computers that use even the best currently known algorithms, like integer factorization using Shor's algorithm or thesimulation of quantum many-body systems. There exist quantum algorithms, such asSimon's algorithm, that run faster than any possible probabilistic classical algorithm.[12]A classical computer could in principle (withexponential resources) simulate a quantum algorithm, as quantum computation does not violate the Church–Turing thesis.[13]:202 On the other hand, quantum computers may be able to efficiently solve problems which are not practically feasible on classical computers.