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Natural Quantum Computation

(T) D-Wave, a start-up based in British Columbia and a spin-off of the University of British Columbia, has been working for over 11 years on quantum computation. In 2007, D-Wave presented an early prototype of its quantum computing system at the Computer Museum in Mountain View, CA. And in May this year, D-Wave announced the first sale of its quantum computing system to Lockheed Martin based on a quantum annealing processor. At the same time, D-Wave scientists published the results of their research “quantum annealing with manufactured spins” in Nature Magazine.

As its name implies, a quantum computer attempts to process information leveraging the fundamental laws of quantum mechanics. In traditional computers, information can have two digital states 0 or 1. In quantum computers, information is modeled after atoms that can have more than one state simultaenously, a fundamental law in quantum mechanics called quantum superposition. As early as 1982, well-known physicist Richard Feynman pioneered the idea of simulating quantum mechanical objects. In 1985, Oxford University Physic Professor David Deutsch proposed a simple abstract machine, that he called the quantum Turing machine, that captures all the power of quantum computation based on quantum gates (qbits). And in 1994, Peter Schor from AT&T Bell Labs developed the first quantum algorithm to perform efficient factorisation of integers, a very useful computing application in particular in cryptography, and out of reach for traditional computing systems.

Building “universal” quantum computers is still a challenge (if you are optimistic) or a dream (if you are pessimistic) first because of the complexity of designing large number of interacting qubits, and second because of the interaction of those qubits with their surronding environment that can prevent them from efficient quantum computation, an effect called decoherence.

D-Wave natural quantum computer (NQC™) is built around superconducting processors designed to enable quantum annealing algorithms. Many computationally impossible problems can be reduced to finding the ground state of a system of interacting spins such as the Travelling Sales Man or the Spin Glass. Or quantum annealing enables the search for the ground state of a quantum system. To that end, D-Wave NQC implements a programmable quantum spin system, in which controled individual spins and their couplings perform quantum annealing, and then determines the state of each spin. D-Wave NQC implements an artificial Ising spin system involving an array of eight superconducting flux quantum bits (qbits) interconnected as a bipartite graph.

Simplified schematic of a superconducting flux qubit acting as a quantum mechanical spin in the D-Wave system - circulating current in the qubit loop rise to a flux inside, encoding two distinct spin states that can exist in superposition

D-Wave NQC demonstrates that a programmable artificial spin system can be manufactured as an integrated circuit implementing a quantum algorithm to solve hard combinatorial optimization problems found for instance in software engineering, financial risk analysis, or bioinformatics. D-Wave’s experiments provide a valuable framework for investigating the physics of interacting quantum spins, and a brilliant step toward the exciting quest for a universal quantum computer.

References:

D-Wave Blog: “Hack the Multiverse”

Nature Magazine, “Quantum annealing with manufactured spins”, May 2011

D-Wave,“Implementation of a quantum annealing algorithm using a superconducting circuit”, March 2009

Note: the picture above is D-Wave 128 qubit superconducting adiabatic quantum optmization processor.

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Sunday, August 7, 2011