# quantum computer

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Related to Quantum algorithms: Grover's algorithm

## quantum computer

[′kwän·təm kəm¦pyüd·ər] (computer science)

A computer in which the time evolution of the state of the individual switching elements of the computer is governed by the laws of quantum mechanics.

## quantum computer

(computer)A type of computer which uses the ability of
quantum systems, such as a collection of atoms, to be in many
different states at once. In theory, such superpositions
allow the computer to perform many different computations
simultaneously. This capability is combined with interference
among the states to produce answers to some problems, such as
factoring integers, much more rapidly than is possible with
conventional computers. In practice, such machines have not
yet been built due to their extreme sensitivity to noise.

A

**Oxford University**,**Stanford University**.A

**quantum search algorithm**for constraint satisfaction problems exhibits the phase transition for NP-complete problems.## quantum computing

A computer architecture based on quantum mechanics, the science of atomic structure and function. Quantum computing is radically different from ordinary computers ("classical computing"). It can only solve certain problems, all of which are mathematically based and represented as equations. Quantum computer processing emulates nature at the atomic level and one of its more auspicious uses is the analysis of molecular interactions to uncover nature's mysteries.In the late 1990s, the feasibility of quantum computing was demonstrated by MIT, the University of California at Berkeley and Stanford University. Because of the high cost of building and maintaining quantum computers, quantum computing is likely to be offered more as a cloud service than machinery for sale to individual companies. Time will tell. See quantum mechanics.

**Computations Can Be Staggering**

There are many problems that bog down even the fastest supercomputers because numbers tend to grow faster than one might imagine. An easy one to understand is the classic traveling salesman problem, which attempts to find the most efficient round trip between cities. The first thing is to compute all the possible routes, and if the trip involved 50 cities, the result is a number 63 digits long. Whereas classical computers may take days or even months to solve such problems, quantum computers are expected to have answers in mere minutes or seconds. See quantum supremacy, binary values and rice and chessboard legend.

**Qubit Superposition and Entanglement**

Quantum computing uses the "qubit," or quantum bit, comprising one or more electrons, and there are various approaches to their design. Quantum superposition is the condition that allows a qubit to be a 0 and 1 at the same time (see qubit). Entanglement is the property that allows one particle to relate to another over distance.

Gate model and quantum annealing are the two major categories of quantum computer architectures.

**Gate Model QC**

Gate model quantum computers use gates similar in concept to classical computers but with vastly different logic and architecture. Several companies are developing gate model machines, including Google, IBM, Intel and Rigetti, each with different qubit designs. The quantum chip is programmed by sending microwave pulses to the qubits. Digital-to-analog and analog-to-digital conversion takes place at the QC chip.

**IBM's Q Experience in the Cloud**

In 2016, IBM made a 5-qubit gate model quantum computer available in the cloud to allow scientists to experiment with gate model programming. A year later, the open source Qiskit development kit and a second machine with 16 qubits were added. The IBM Q Experience includes a library of educational materials.

IBM Q - Gate Model |
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Like the D-Wave computer, superconducting materials are used that must be kept at subzero temperatures, and both photos show the covers removed to expose the quantum chip at the bottom. See superconductor. (Image courtesy of IBM Research, www.research.ibm.com) |

Intel 49-Qubit Quantum Computer |
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In 2018, Intel announced its Tangle Lake gate model quantum chip with a unique architecture of single-electron transistors coupled together. Intel CEO Brian Krzanich shows the chip at CES 2018. (Image courtesy of Intel Corporation.) |

**Quantum Annealing**

D-Wave Systems in Canada offers the only "quantum annealing" computer. D-Wave computers are huge, refrigerated machines with up to 2,000 qubits that are used for optimization problems such as scheduling, financial analysis and medical research. Annealing is used to find the optimum route or the most efficient combination of settings to solve a problem.

D-Wave Chips Are Cool Too |
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D-Wave's latest quantum annealing chip has 2,000 qubits. Like gate model quantum computers, a refrigeration system is necessary. Using liquid nitrogen and liquid helium stages from top to bottom, it keeps getting colder all the way down to minus 459 degrees Fahrenheit. (Images courtesy of D-Wave Systems, Inc., www.dwavesys.com) |

D-Wave Chips Are Cool Too |
---|

D-Wave's latest quantum annealing chip has 2,000 qubits. Like gate model quantum computers, a refrigeration system is necessary. Using liquid nitrogen and liquid helium stages from top to bottom, it keeps getting colder all the way down to minus 459 degrees Fahrenheit. (Images courtesy of D-Wave Systems, Inc., www.dwavesys.com) |

**The Algorithms Are Critical**

The algorithms for solving real-world problems must be invented first, because new algorithms influence the design of the next generation of quantum architecture. There are hurdles to overcome with both gate model and annealing methods. However, scientists believe everyday quantum computing is inevitable.

**A Potential Catastrophe**

Eventually, quantum computers are expected to factor huge numbers and should be able to crack cryptographic keys in a matter of seconds. Scientists contend it is only a matter of time before this becomes a reality. When it does, it has menacing implications as every encrypted transaction as well as every cryptocurrency system in the world will be vulnerable to hacking unless quantum-safe methods are instituted beforehand. See quantum secure.

Are We at a Similar Stage? |
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Quantum computing is in the very early stages of development. When an eight-ton UNIVAC I in the 1950s evolved into a chip decades later, it makes one wonder what quantum computers might look like 50 years from now. See UNIVAC I and microcontroller. |

Are We at a Similar Stage? |
---|

Quantum computing is in the very early stages of development. When an eight-ton UNIVAC I in the 1950s evolved into a chip decades later, it makes one wonder what quantum computers might look like 50 years from now. See UNIVAC I and microcontroller. |

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