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96
Nuclear magnetic resonance spectroscopy: An experimentally accessible paradigm for quantum computing
 In Proceedings of the Fourth Workshop on Physics and Computation. New England Complex Systems Institute
, 1996
"... We present experimental results which demonstrate that nuclear magnetic resonance spectroscopy is capable of efficiently emulating many of the capabilities of quantum computers, including unitary evolution and coherent superpositions, but without attendant wavefunction collapse. This emulation is m ..."
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Cited by 64 (7 self)
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We present experimental results which demonstrate that nuclear magnetic resonance spectroscopy is capable of efficiently emulating many of the capabilities of quantum computers, including unitary evolution and coherent superpositions, but without attendant wavefunction collapse. This emulation is made possible by two facts. The first is that the spin active nuclei in each molecule of a liquid sample are largely isolated from the spins in all other molecules, so that each molecule is effectively an independent quantum computer. The second is the existence of a manifold of statistical spin states, called pseudopure states, whose transformation properties are identical to those of true pure states. These facts enable us to operate on coherent superpositions over the spins in each molecule using full quantum parallelism, and to combine the results into deterministic macroscopic observables via thermodynamic averaging. We call a device based on these principles an ensemble quantum computer. Our results show that it is indeed possible to prepare a pseudopure state
Decoherence, Einselection and the Existential Interpretation (The Rough Guide)
 PHIL. TRANS. R. SOC. LOND. A
, 1998
"... The roles of decoherence and environmentinduced superselection in the emergence of the classical from the quantum substrate are described. The stability of correlations between the einselected quantum pointer states and the environment allows them to exist almost as objectively as classical states ..."
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Cited by 40 (0 self)
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The roles of decoherence and environmentinduced superselection in the emergence of the classical from the quantum substrate are described. The stability of correlations between the einselected quantum pointer states and the environment allows them to exist almost as objectively as classical states were once thought to exist: there are ways of finding out what is the pointer state of the system which uses redundancy of its correlations with the environment, and which leave einselected states essentially unperturbed. This relatively objective existence of certain quantum states facilitates operational definition of probabilities in the quantum setting. Moreover, once there are states that ‘exist ’ and can be ‘found out’, a ‘collapse ’ in the traditional sense is no longer necessary—in effect, it has already happened. The role of the preferred states in the processing and storage of information is emphasized. The existential interpretation based on the relatively objective existence of stable correlations between the einselected states of observers’ memory and in the outside universe is formulated and discussed.
Building quantum wires: the long and the short of it
 In Proc. International Symposium on Computer Architecture (ISCA 2003
, 2003
"... As quantum computing moves closer to reality the need for basic architectural studies becomes more pressing. Quantum wires, which transport quantum data, will be a fundamental component in all anticipated silicon quantum architectures. In this paper, we introduce a quantum wire architecture based up ..."
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Cited by 33 (8 self)
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As quantum computing moves closer to reality the need for basic architectural studies becomes more pressing. Quantum wires, which transport quantum data, will be a fundamental component in all anticipated silicon quantum architectures. In this paper, we introduce a quantum wire architecture based upon quantum teleportation. We compare this teleportation channel with the traditional approach to transporting quantum data, which we refer to as the swapping channel. We characterize the latency and bandwidth of these two alternatives in a deviceindependent way and describe how the advanced architecture of the teleportation channel overcomes a basic limit to the maximum communication distance of the swapping channel. In addition, we discover a fundamental tension between the scale of quantum effects and the scale of the classical logic needed to control them. This “pitchmatching ” problem imposes constraints on minimum wire lengths and wire intersections, which in turn imply a sparsely connected architecture of coarsegrained quantum computational elements. This is in direct contrast to the “sea of gates ” architectures presently assumed by most quantum computing studies. 1
The Ion Trap Quantum Information Processor
 Appl. Phys. B
, 1997
"... An introductory review of the linear ion trap is given, with particular regard to its use for quantum information processing. The discussion aims to bring together ideas from information theory and experimental ion trapping, to provide a resource to workers unfamiliar with one or the other of these ..."
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Cited by 32 (2 self)
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An introductory review of the linear ion trap is given, with particular regard to its use for quantum information processing. The discussion aims to bring together ideas from information theory and experimental ion trapping, to provide a resource to workers unfamiliar with one or the other of these subjects. It is shown that information theory provides valuable concepts for the experimental use of ion traps, especially error correction, and conversely the ion trap provides a valuable link between information theory and physics, with attendant physical insights. Example parameters are given for the case of calcium ions. Passive stabilisation will allow about 200 computing operations on 10 ions; with error correction this can be greatly extended. 1
Architectural implications of quantum computing technologies
 ACM Journal on Emerging Technologies in Computing Systems (JETC
, 2006
"... In this article we present a classification scheme for quantum computing technologies that is based on the characteristics most relevant to computer systems architecture. The engineering tradeoffs of execution speed, decoherence of the quantum states, and size of systems are described. Concurrency, ..."
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Cited by 27 (4 self)
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In this article we present a classification scheme for quantum computing technologies that is based on the characteristics most relevant to computer systems architecture. The engineering tradeoffs of execution speed, decoherence of the quantum states, and size of systems are described. Concurrency, storage capacity, and interconnection network topology influence algorithmic efficiency, while quantum error correction and necessary quantum state measurement are the ultimate drivers of logical clock speed. We discuss several proposed technologies. Finally, we use our taxonomy to explore architectural implications for common arithmetic circuits, examine the implementation of quantum error correction, and discuss clusterstate quantum computation.
Polynomial Simulations of Decohered Quantum Computers
 37th Annual Symposium on Foundations of Computer Science
, 1996
"... Recently it has become clear, that a key issue in quantum computation is understanding how interaction with the environment, or "decoherence", effects the computational power of quantum computers. We adopt the standard physical method of describing systems which are interwound with their e ..."
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Cited by 24 (3 self)
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Recently it has become clear, that a key issue in quantum computation is understanding how interaction with the environment, or "decoherence", effects the computational power of quantum computers. We adopt the standard physical method of describing systems which are interwound with their environment by "density matrices", and within this framework define a model of decoherence in quantum computation.
Quantum Computing and Phase Transitions in Combinatorial Search
 J. of Artificial Intelligence Research
, 1996
"... We introduce an algorithm for combinatorial search on quantum computers that is capable of significantly concentrating amplitude into solutions for some NP search problems, on average. This is done by exploiting the same aspects of problem structure as used by classical backtrack methods to avoid un ..."
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Cited by 23 (7 self)
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We introduce an algorithm for combinatorial search on quantum computers that is capable of significantly concentrating amplitude into solutions for some NP search problems, on average. This is done by exploiting the same aspects of problem structure as used by classical backtrack methods to avoid unproductive search choices. This quantum algorithm is much more likely to find solutions than the simple direct use of quantum parallelism. Furthermore, empirical evaluation on small problems shows this quantum algorithm displays the same phase transition behavior, and at the same location, as seen in many previously studied classical search methods. Specifically, difficult problem instances are concentrated near the abrupt change from underconstrained to overconstrained problems. August
Imaging single atoms in a threedimensional array
, 2007
"... A single neutral atom trapped by light is a promising qubit. It has weak, wellunderstood interactions with the environment, its internal state can be precisely manipulated 1, interactions that entangle atoms can be varied from negligible to strong 2–4 and many single atoms can be trapped near each ..."
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Cited by 23 (0 self)
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A single neutral atom trapped by light is a promising qubit. It has weak, wellunderstood interactions with the environment, its internal state can be precisely manipulated 1, interactions that entangle atoms can be varied from negligible to strong 2–4 and many single atoms can be trapped near each other in an optical lattice 5. This collection of features would allow for a relatively large quantum computer 6 if each neutral atom qubit could be independently detected and addressed 7–10. A quantum computer with even 50 qubits would allow quantum simulations that are out of the reach of classical computers 11,12. So far, fewer than ten single atoms have been simultaneously imaged 13. Here we demonstrate trapping and imaging of 250 single atoms in a threedimensional optical lattice and show that imaging is highly unlikely to change the pattern of site occupancy. Our lattice spacing is large enough that, in principle, individual atoms can