September 15, 2013

Scientific proof for quantumness for a special quantum system that does not yet exist

DWave Systems 512 qubit quantum annealing system was mentioned in an article that mainly talks about a new proof of quantumness for a specially built and as yet non-existent two qubit system. So the researchers are saying if you build a quantum system in the way that they describe then it would be easy to prove that it is or is not quantum. But their method is useless for the systems. So they mention the Dwave System controversy but present a proof which will do nothing to settle that argument.

Dwave has many research papers that provide proof of quantum entanglement and other quantum aspects to their calculations. However, many quantum researchers dispute speedup over classical and how much and how useful the quantumness that does exist contributes.

There is new work that would provide an improved error corrected system for Dwave like quantum annealers

Arxiv - Error corrected quantum annealing with hundreds of qubits

Quantum information processing o ffers dramatic speedups, yet is famously susceptible to decoherence, the process whereby quantum superpositions decay into mutually exclusive classical alternatives, thus robbing quantum computers of their power. This has made the development of quantum error correction an essential and inescapable aspect of both theoretical and experimental quantum computing. So far little is known about protection against decoherence in the context of quantum annealing, a computational paradigm which aims to exploit ground state quantum dynamics to solve
optimization problems more rapidly than is possible classically. Here we develop error correction for quantum annealing and provide an experimental demonstration using up to 344 superconducting flux qubits in processors which have recently been shown to physically implement programmable quantum annealing. We demonstrate a substantial improvement over the performance of the processors in the absence of error correction. These results pave a path toward large scale noise-protected adiabatic quantum optimization devices.

There is work towards an adiabatic version of Shor's Algorithm for calculating prime factors.

Arxiv - Period Finding with Adiabatic Quantum Computation

We outline an efficient quantum-adiabatic algorithm that solves Simon's problem, in which one has to determine the `period', or xor-mask, of a given black-box function. We show that the proposed algorithm is exponentially faster than its classical counterpart and has the same complexity as the corresponding circuit-based algorithm. Together with other related studies, this result supports a conjecture that the complexity of adiabatic quantum computation is equivalent to the circuit-based computational model in a stronger sense than the well-known, proven polynomial equivalence between the two paradigms. We also discuss the importance of the algorithm and its implications for the existence of an optimal-complexity adiabatic version of Shor's integer factorization algorithm and the experimental implementation of the latter.

Arxiv - Quantum Adiabatic Algorithms, Small Gaps, and Different Paths

We construct a set of instances of 3SAT which are not solved efficiently using the simplest quantum adiabatic algorithm. These instances are obtained by picking random clauses all consistent with two disparate planted solutions and then penalizing one of them with a single additional clause. We argue that by randomly modifying the beginning Hamiltonian, one obtains (with substantial probability) an adiabatic path that removes this difficulty. This suggests that the quantum adiabatic algorithm should in general be run on each instance with many different random paths leading to the problem Hamiltonian. We do not know whether this trick will help for a random instance of 3SAT (as opposed to an instance from the particular set we consider), especially if the instance has an exponential number of disparate assignments that violate few clauses. We use a continuous imaginary time Quantum Monte Carlo algorithm in a novel way to numerically investigate the ground state as well as the first excited state of our system. Our arguments are supplemented by Quantum Monte Carlo data from simulations with up to 150 spins

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