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	NIST: Physics Laboratory's - Quantum Information
		That is, in quantum information processing, the processing capacity scales exponentially as the number of available qubits, as opposed to classical information processing, which scales linearly with the number of classical bits.
		Quantum information science offers a new paradigm for information processing, exchange and storage, and provides a basis for the development of quantum computers and physically secure communication; i.e., communication whose resistance to eavesdropping is guaranteed by physical law.
		The primary challenge, therefore, is to construct a logic device that meets the criteria for a quantum processor, namely: state preparation, scalability, two-qubit gates for entangling operations, efficient readout, and small decoherence.
	physics.nist.gov /MajResProj/QuantumInfo/quantum.html (1072 words)

	Quantum gate - Wikipedia, the free encyclopedia
		A quantum gate or quantum logic gate is a rudimentary quantum circuit operating on a small number of qubits.
		Quantum logic gates are represented by unitary matrices.
		The controlled-U gate is a gate that operates on two qubits in such a way that the first qubit serves as a control.
	en.wikipedia.org /wiki/Quantum_gate (416 words)

	Quantum Computing (Site not responding. Last check: 2007-10-19)
		Although early demonstrations of quantum computing explored a wide variety of experimental methods, quantum computers based on solid-state systems, in spite of the potentially larger interactions limiting coherence, are believed to be worth serious investigation.
		Analogously, the readout of the qubit state is accomplished by measuring the spin-dependent current from the quantum dot to the magnetic material.
		The computation process utilizes the three lowest levels of a quantum dot; two of them represent a state of a qubit, while the third one is used to arrange an electron interaction with the electromagnetic field.
	www.ece.ncsu.edu /nano/quantum_computing.htm (1897 words)

	PhysicsWeb - Quantum logic gate lights up
		Quantum computers, on the other hand, exploit the ability of quantum particles to be in two or more states at the same time.
		A quantum bit or "qubit" can therefore be "0" or "1" or any combination of the two.
		Quantum logic: to be or NOT to be
	www.physics.lsa.umich.edu /nea/news/articles/August03/logic.htm (462 words)

	Quantum Optics and Spectroscopy - Recent Results - Cirac Zoller Gate
		In a quantum computer, the information is stored in qubits (quantum bits of information) which can take values of 0 and 1 like their classical couterparts, but also any coherent superposition of 0 and 1.
		In this scheme, each ion's electronic state represents a qubit, and a quantum gate between any pair of ions is realised by coupling them through their collective motion.
		The CNOT quantum logical gate corresponds to the XOR gate operation of classical logic which flips the state of a target bit conditioned on the state of a control bit.
	heart-c704.uibk.ac.at /recent/ciraczollere.html (486 words)

	NEC, RIKEN demonstrate quantum logic gate
		The quantum computer, when it is finally brought to fruition, will far surpass the capabilities of even the most modern of today’s supercomputers, as it utilises a “qubit,” a quantum superposition of the “0” and “1” states, as the basic information unit.
		Information processing in a quantum computer is conducted by a series of quantum gate operations to the qubit, and it has been theoretically proven that only two kinds of gate operations are sufficient for quantum computation, no matter how complicated the algorithms are and no matter how many qubits they require.
		Having realised both the one-qubit rotation gate and the two-qubit conditional gate, the research laboratory will work toward achieving further integration of the qubit to demonstrate a quantum algorithm, an effort which is expected to contribute to the practical realisation of a quantum computer.
	www.ferret.com.au /articles/61/0C01B761.asp (347 words)

	UO Research to Create 'Quantum Computer' Building Block
		Once a single logic gate is developed, it could be used to create quantum processing devices with capabilities that potentially could be used in practical applications.
		Quantum computing has been recognized in the past five or so years as one of the most exciting areas of research, combining computer science theory and quantum physics.
		Raymer notes that while the development of the quantum computer is still perhaps 20 years in the future, if one were ever built, it would be used "for certain special tasks and might operate thousands to millions of times faster than the largest parallel processor computer" available today.
	www.uoregon.edu /newscenter/quantum.html (559 words)

	Japanese boffins advance quantum computing \| The Register
		Quantum computing (whose basic concepts are enough to make your head spin) has the potential to revolutionise computing as never before.
		The quantum computer, when it is finally brought to fruition, will likely far surpass the capabilities of even the most modern of today's supercomputers, as it utilizes a "qubit," a quantum superposition of the "0" and "1" states, as the basic information unit.
		Having succeeded in realizing both the one-qubit rotation gate and the two-qubit conditional gate, the research laboratory will continue to strive toward achieving further integration of the qubit to demonstrate quantum algorithm, an effort which is expected to contribute significantly to the practical realisation of a quantum computer.
	theregister.com /2003/10/31/japanese_boffins_advance_quantum_computing (598 words)

	Quantum Computing (Stanford Encyclopedia of Philosophy)
		Indeed, quantum mysteries such as entanglement and nonlocality were historically considered a philosophical quibble, until physicists discovered that these mysteries might be harnessed to devise new efficient algorithms.
		Observables—in the quantum circuit model there are only two, the preparation of the initial state and the observation of the final state, in the same basis, and of the same variable, at the end of the computation—are not as important here as in Bell's case since any measurement commutes with itself.
		Consequently, in the quantum circuit model one should count the number of computational steps in the computation not by counting the number of transformations of the state, but by counting the number of one- or two-qubit local transformations that are required to create the ‘clever’ superposition that ensures the desired "speed-up".
	plato.stanford.edu /entries/qt-quantcomp (9666 words)

	Semiconductor Magazine - Future Technology: Quantum Computing
		Quantum gates, like their classical analogs, are the building blocks of computation.
		However, quantum gates must be implemented in a way that depends only on unitary manipulations of the initial qubits.
		To summarize, quantum computers are unlikely to replace binary logic in the near, or distant, future, except for a small set of specialized problems.
	dom.semi.org /web/wmagazine.nsf/4f55b97743c2d02e882565bf006c2459/ff63d037584b327888256ace007f3613!OpenDocument (2551 words)

	1
		Quantum reversibility means that quantum computers drive themselves forward in infinitesimal (reversible) steps, much the same way that molecules of perfume would diffuse from a perfume bottle.
		Quantum computer programs are not "run", but are said to "evolve," as they process the program’s inputs to outputs.
		Although quantum computers were predicted some years ago, the engineering obstacles were considered prohibitive, and quantum computers were not expected to be produced, even in prototype, until sometime in the year 2025.
	www.carolla.com /quantum/QuantumComputers.htm (4488 words)

	ScienceDaily: Next Step To The Quantum Computer: University Of Bonn Physicists Build Quantum Data Memory
		Their next aim is to construct a quantum gate in which two or more atoms interact with each other in a controlled way.
		Quantum computer -- A quantum computer is any device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on...
		Quantum number -- A quantum number is any one of a set of numbers used to specify the full quantum state of any system in quantum mechanics.
	www.sciencedaily.com /releases/2004/10/041007082711.htm (2006 words)

	Quantum Computation
		These gates could be addressed in parallel by unitary transformations, which must be carried out reversibly, implying no loss of energy in a gate operation.
		However, for a quantum computer there is the famous Grover algorithm for which the running time scales only as the square root of N. Since many computer algorithms involve search as one of their components, this speed up potentially has broad application.
		The enemy of the qubits of a quantum system is interaction with the environment, which leads to decoherence and destroys the coherent superposition states.
	www.csr.umd.edu /csrpage/research/quantum/index.htm (4105 words)

	NIST Ion Storage Group (Site not responding. Last check: 2007-10-19)
		However, there is a drawback to this sort of computation: according to quantum mechanics, whenever we read the state of a quantum register, we effectively collapse the superposition to one particular value and immediately destroy the parallelism.
		A quantum logic gate is a fundamental building block of a quantum computer, just as conventional logic gates (AND, OR, Exclusive-OR, etc.) are the building blocks for traditional digital logic.
		Here, the motional state is the "control qubit," which is unchanged by the gate (this qubit is necessary to make the gate reversible and preserve the unitarity required by quantum mechanics).
	tf.nist.gov /ion/qucomp/quan_log.htm (992 words)

	Simulating Quantum Circuits - Quantum Gates
		Gates are called universal gates if they can be used to create any logic circuit, such as the NAND gate in classical circuits.
		The square root of NOT gate is the first purely quantum gate that we shall examine and, from a classical point of view, is unusual in its behaviour.
		However two such gates linked sequentially produce an output that is the inverse of the input, and thus behave in the same way as the a classical NOT gate.
	www.themilkyway.com /quantum/FinalReport/QuantumGates.html (787 words)

	The Initialization Problem in Quantum Computing
		In the recursive development of the S-matrices for the various gates, Deutsch[1] failed to include the unknown phase with the embedded S-terms, assuming thereby that the gates were initialized.
		Quantum errors, on the other hand, perturb the information bits, in a nonlocal sense, to a superposition of many states so the concept of controlling all errors by using a higher dimensional codeword space cannot be directly applied.
		According to the positivist understanding of quantum mechanics, it is essential to speak from the point of view of the observer and not ask about any intrinsic information in a quantum state[6].
	www.ee.lsu.edu /kak/pubs/inf4 (3811 words)

	Quantum info
		Quantum theory has been put to test and has predicted the proper statistics for every experiment from the lowest to the highest energies in the universe.
		Quantum mechanics is a theory of probabilities, and probabilities in modern Bayesian statistics are statements of information – predicting outcomes given our prior knowledge – what we know and what we don’t know.
		Quantum logic gates map input states to output states (they are unitary transformations).
	www.ieee.org /organizations/pubs/newsletters/leos/apr02/academic.html (3332 words)

	Trapped ion quantum computers - Wikipedia, the free encyclopedia
		The fundamental operations of a quantum computer have been demonstrated experimentally with high accuracy (or "high fidelity" in quantum computing language) in trapped ion systems, and a strategy has been developed for scaling the system to arbitrarily large number of qubits by shuttling ions in an array of ion traps.
		The electrodynamic trap currently used in trapped ion quantum computing research was invented in the 1960's by Wolfgang Paul (who received the Nobel Prize in 1989 for his work).
		The first implementation scheme for a controlled-NOT quantum gate was proposed by Ignacio Cirac and Peter Zoller in 1995, specifically for the trapped ion system.
	en.wikipedia.org /wiki/Trapped_ion_quantum_computers (1435 words)

	NIST: Physics Laboratory's - Quantum Information
		The starting point for quantum information at NIST was in 1995 when the Ion Storage Group demonstrated the first quantum-logic gate.
		This effort entitled A Scalable Quantum Information Network is led by Carl Williams and includes representatives of the Electronics and Electrical Engineering Laboratory, the Information Technology Laboratory, and the Physics Laboratory.
		The figure shows memory qubits in a quantum register and an accumulator where the qubits in the quantum register can be moved together to undergo quantum operations.
	qubit.nist.gov (1058 words)

	Research News: Making Quantum Computing Work in Silicon
		With quantum computing, says Schenkel, "The idea is to find the solution by first acting on all the entangled qubits in parallel through clever quantum gate operations, and then to extract the solution in measurements that simultaneously 'collapse' the superpositions of the entire system to a series of classical zeros and ones."
		But in the long run, quantum computers based on silicon could be manufactured with familiar materials and methods — maybe even mass produced — and could prove easier to scale up.
		Schenkel and his colleagues are developing a field-effect transistor made of isotopically enriched silicon, in which the flow of current through the device is sensitive to the spin state of a single donor atom — a "single-spin readout" device.
	www.lbl.gov /Science-Articles/Archive/AFRD-quantum-logic.html (1319 words)

	EETimes.com - Quantum entanglement demonstrated, quantum gate, computer could be next
		Chang next plans to build the world's first quantum gate in an electronically controlled semiconductor device, enabling the creation of a key building block in quantum computation.
		Quantum computers operate on q-bits, rather than digital bits, which can only be "0" or "1," because q-bits can superimpose any number of parallel computations.
		According to quantum computational theory, the exact state of the quantum dot cannot be determined because of the simultaneous superimposed logic states.
	www.eetimes.com /at/news/showArticle.jhtml?articleID=19900040 (797 words)

	Brian's Quantum Gates Paper (Site not responding. Last check: 2007-10-19)
		A crucial part of quantum computing is the manipulation of the relevant qubits by what are called quantum gates.
		A quantum gate is formally defined as a device which performs a fixed unitary operation on selected qubits in a fixed period of time and a quantum network is a device consisting of quantum logic gates whose computational steps are synchronized in time [2].
		Mathematically, a qubit is represented as a vector with two dimensions, a and b, and a quantum gate on k qubits is a unitary matrix U of dimensions 2k x 2k [3].
	www.cs.iastate.edu /~patterbj/cs/quantum/fp/index.htm (172 words)

	Realization of the Cirac-Zoller controlled-NOT quantum gate : Abstract : Nature
		Quantum computers have the potential to perform certain computational tasks more efficiently than their classical counterparts.
		In this scheme, quantum logical gates involving any subset of ions are realized by coupling the ions through their collective quantized motion.
		The CNOT quantum logical gate corresponds to the XOR gate operation of classical logic that flips the state of a target bit conditioned on the state of a control bit.
	www.nature.com /nature/journal/v422/n6930/abs/nature01494.html (256 words)

	Media Vision : Quantum Gate (PC CD Boxed) (Site not responding. Last check: 2007-10-19)
		Quantum Gate does contain a VR simulation mini-game that offers the player a limited shooting game experience.
		Despite all of Quantum Gate's flaws, the game is redeemed by two somber side-stories.
		More than anything else, Quantum Gate is like an extended demo of the multimedia abilities that CDROM technology could bring to the PC.
	videogames.mysic.com /B0002TKOO6++Quantum+Gate+(pc+Cd+Boxed) (559 words)

	Quantum circuit - Wikipedia, the free encyclopedia
		Quantum circuits are also theoretically interesting as a tool for understanding the power and limitations of quantum computation.
		However, as a first step in describing a quantum computing device it is instructive to observe that reversible gates are theoretically possible; moreover, these are actually of practical interest, since they do not increase entropy.
		Examples of these logic gates which have been studied are the controlled NOT gate (also called CNOT gate), the Toffoli gate and the Fredkin gate.
	en.wikipedia.org /wiki/Quantum_circuit (1638 words)

	EETimes.com - Quantum entanglement demonstrated, quantum gate, computer could be next
		Chang next plans to build the world's first quantum gate in an electronically controlled semiconductor device, enabling the creation of a key building block in quantum computation.
		Quantum computers operate on q-bits, rather than digital bits, which can only be "0" or "1," because q-bits can superimpose any number of parallel computations.
		According to quantum computational theory, the exact state of the quantum dot cannot be determined because of the simultaneous superimposed logic states.
	eetimes.com /article/showArticle.jhtml?articleId=19900040 (587 words)

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