By Serge-Paul Carrasco on August 7, 2011

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 simultaneously, 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 factorization 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 a large number of interacting qubits, and second because of the interaction of those qubits with their surrounding 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 controlled 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 a 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 Systems
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 optimization processor.