Pavia писал(а):
D-Wave это обычный аналоговый процессор.
Любой квантовый компьютер является по своей сути аналоговым, Вопрос в том есть ли плюсы от квантовой механики в расчетах,
D-wave основан на "quantum annealing", почитайте английскую викопедию и google arXiv D-wave quantum annealing.
Цитата:
In December 2015, Google announced that the D-Wave machine outperforms both simulated annealing and Quantum Monte Carlo by up to a factor of 100,000,000 on a set of hard optimization problems.[27]
Quantum annealing (QA) is a metaheuristic for finding the global minimum of a given objective function over a given set of candidate solutions (candidate states), by a process using quantum fluctuations. Quantum annealing is used mainly for problems where the search space is discrete (combinatorial optimization problems) with many local minima; such as finding the ground state of a spin glass.[1] It was formulated in its present form by T. Kadowaki and H. Nishimori in "Quantum annealing in the transverse Ising model"[2] though a proposal in a different form had been proposed by A. B. Finilla, M. A. Gomez, C. Sebenik and J. D. Doll, in "Quantum annealing: A new method for minimizing multidimensional functions".[3]
Quantum annealing starts from a quantum-mechanical superposition of all possible states (candidate states) with equal weights. Then the system evolves following the time-dependent Schrödinger equation, a natural quantum-mechanical evolution of physical systems. The amplitudes of all candidate states keep changing, realizing a quantum parallelism, according to the time-dependent strength of the transverse field, which causes quantum tunneling between states. If the rate of change of the transverse-field is slow enough, the system stays close to the ground state of the instantaneous Hamiltonian, i.e., adiabatic quantum computation.[4] If the rate of change of the transverse-field is accelerated, the system may leave the ground state temporarily but produce a higher likelihood of concluding in the ground state of the final problem Hamiltonian, i.e., diabatic quantum computation.[5][6] The transverse field is finally switched off, and the system is expected to have reached the ground state of the classical Ising model that corresponds to the solution to the original optimization problem. An experimental demonstration of the success of quantum annealing for random magnets was reported immediately after the initial theoretical proposal.[7]
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In 2007 Umesh Vazirani, a professor at University of California (UC) Berkeley and one of the founders of quantum complexity theory upon which D-Wave is based, made the following criticism:[43]
Their claimed speedup over classical algorithms appears to be based on a misunderstanding of a paper my colleagues van Dam, Mosca and I wrote on "The power of adiabatic quantum computing." That speed up unfortunately does not hold in the setting at hand, and therefore D-Wave's "quantum computer" even if it turns out to be a true quantum computer, and even if it can be scaled to thousands of qubits, would likely not be more powerful than a cell phone.
Wim van Dam, a professor at UC Santa Barbara, summarized the scientific community consensus as of 2008 in the journal Nature Physics:[44]
An article in the May 12, 2011 edition of Nature gives details which critical academics say proves that the company's chips do have some of the quantum mechanical properties needed for quantum computing.[45][46] Prior to the 2011 Nature paper, D-Wave was criticized for lacking proof that its computer was in fact a quantum computer. Nevertheless, questions were raised[47] and later answered[48] regarding experimental proof of quantum entanglement inside D-Wave devices.
MIT professor Scott Aaronson, who describes himself as "Chief D-Wave Skeptic", said that D-Wave's 2007 demonstration did not prove anything about the workings of the Orion computer, and that its marketing claims were deceptive.[49] In May 2011 he said that he was "retiring as Chief D-wave Skeptic",[50] and reporting his "skeptical but positive" views based on a visit to D-Wave in February 2012. Aaronson said that one of the most important reasons for his new position on D-Wave was the 2011 Nature article.[47][51][52] In May 16, 2013 he resumed his skeptic post. He criticizes D-Wave for blowing up results out of proportion on press releases that claim speedups of three orders of magnitude, in light of a paper by scientists from ETH Zurich reporting a 128-qubit D-Wave computer being outperformed by a factor of 15 using regular digital computers and applying classical metaheuristics (particularly simulated annealing) to the problem that D-Wave's computer was specifically designed to solve.[30]
On May 16, 2013 NASA and Google, together with a consortium of universities, announced a partnership with D-Wave to investigate how D-Wave's computers could be used in the creation of artificial intelligence. Prior to announcing this partnership, NASA, Google, and Universities Space Research Association put a D-Wave computer through a series of benchmark and acceptance tests, which it passed.[9] Independent researchers found that D-Wave's computers could solve some problems as much as 3,600 times faster than particular software packages running on conventional digital computers.[9] Other independent researchers found that different software packages running on a single core of a desktop computer can solve those same problems as fast or faster than D-Wave's computers (at least 12,000 times faster for quadratic assignment problems, and between 1 and 50 times faster for quadratic unconstrained binary optimization problems).[53]
In January 2014 researchers at UC Berkeley and IBM published a classical model reproducing the D-Wave machine's observed behavior, suggesting that it may not be a quantum computer.[54]
In March 2014, researchers at University College London and the University of Southern California (USC) published a paper comparing data obtained from a D-Wave Two computer with three possible explanations from classical physics and one quantum model. They found that their quantum model was a better fit to the experimental data than the Shin-Smith-Smolin-Vazirani classical model, and a much better fit than any of the other classical models. The authors conclude that "This suggests that an open system quantum dynamical description of the D-Wave device is well-justified even in the presence of relevant thermal excitations and fast single-qubit decoherence." [55]
In May 2014, researchers at D-Wave, Google, USC, Simon Fraser University, and National Research Tomsk Polytechnic University published a paper containing experimental results that demonstrated the presence of entanglement among D-Wave qubits. Qubit tunneling spectroscopy was used to measure the energy eigenspectrum of two and eight-qubit systems, demonstrating their coherence during a critical portion of the quantum annealing procedure.[56]
A study published in Science in June 2014, described as "likely the most thorough and precise study that has been done on the performance of the D-Wave machine"[57] and "the fairest comparison yet", attempted to define and measure quantum speedup. Several definitions were put forward as some may be unverifiable by empirical tests, while others, though falsified, would nonetheless allow for the existence of performance advantages. The study found that the D-Wave chip "produced no quantum speedup" and did not rule out the possibility in future tests.[58] The researchers, led by Matthias Troyer at the Swiss Federal Institute of Technology, found "no quantum speedup" across the entire range of their tests, and only inconclusive results when looking at subsets of the tests. Their work illustrated "the subtle nature of the quantum speedup question." Further work[59] has advanced understanding of these test metrics and their reliance on equilibrated systems, thereby missing any signatures of advantage due to quantum dynamics.
There are many open questions regarding quantum speedup. The ETH reference in the previous section is just for one class of benchmark problems. Potentially there may be other classes of problems where quantum speedup might occur. Researchers at Google, USC, Texas A&M, and DW are working hard to find such problem classes.[60]
