Another paper, demonstrating some interesting techniques for overcoming practical problems in using D-Wave hardware. (Apologies Diana for the continuing lack of interpretation of these results :-) ). These techniques were applied to Low Density Parity Check problems.
Discrete optimization using quantum annealing on sparse Ising models
- 1D-Wave Systems, Burnaby, BC, Canada
- 2Department of Computer Science, Joint Center for Quantum Information and Computer Science, University of Maryland, College Park, MD, USA
This paper discusses techniques for solving discrete optimization problems using quantum annealing. Practical issues likely to affect the computation include precision limitations, finite temperature, bounded energy range, sparse connectivity, and small numbers of qubits. To address these concerns we propose a way of finding energy representations with large classical gaps between ground and first excited states, efficient algorithms for mapping non-compatible Ising models into the hardware, and the use of decomposition methods for problems that are too large to fit in hardware. We validate the approach by describing experiments with D-Wave quantum hardware for low density parity check decoding with up to 1000 variables.
More science on data from the D-Wave One system at USC.
Reexamining classical and quantum models for the D-Wave One processor
(Submitted on 12 Sep 2014)
We revisit the evidence for quantum annealing in the D-Wave One device (DW1) based on the study of random Ising instances. Using the probability distributions of finding the ground states of such instances, previous work found agreement with both simulated quantum annealing (SQA) and a classical rotor model. Thus the DW1 ground state success probabilities are consistent with both models, and a different measure is needed to distinguish the data and the models. Here we consider measures that account for ground state degeneracy and the distributions of excited states, and present evidence that for these new measures neither SQA nor the classical rotor model correlate perfectly with the DW1 experiments. We thus provide evidence that SQA and the classical rotor model, both of which are classically efficient algorithms, do not satisfactorily explain all the DW1 data. A complete model for the DW1 remains an open problem. Using the same criteria we find that, on the other hand, SQA and the classical rotor model correlate closely with each other. To explain this we show that the rotor model can be derived as the semiclassical limit of the spin-coherent states path integral. We also find differences in which set of ground states is found by each method, though this feature is sensitive to calibration errors of the DW1 device and to simulation parameters.
A new paper from users of the D-Wave Two at USC. Here’s the abstract:
We demonstrate that the performance of a quantum annealer on hard random Ising optimization problems can be substantially improved using quantum annealing correction (QAC). Our error correction strategy is tailored to the D-Wave Two device. We find that QAC provides a statistically significant enhancement in the performance of the device over a classical repetition code, improving as a function of problem size as well as hardness. Moreover, QAC provides a mechanism for overcoming the precision limit of the device, in addition to correcting calibration errors. Performance is robust even to missing qubits. We present evidence for a constructive role played by quantum effects in our experiments by contrasting the experimental results with the predictions of a classical model of the device. Our work demonstrates the importance of error correction in appropriately determining the performance of quantum annealers.
From the press release:
Cakebread will further manage and help sustain balance in D-Wave’s corporate expansion trajectory as it pursues its mission to solve the intractable problems of industry, security, aerospace and medicine. Before joining D-Wave, Cakebread served as chief financial officer of Pandora Media, Inc., a provider of personalized Internet radio and music discovery services. He was president and chief strategy officer of salesforce.com, a customer relationship management service provider. Other roles with salesforce.com include executive vice president and chief financial officer. Before that, Cakebread served as senior vice president and chief financial officer at Autodesk and Silicon Graphics World Trade. Cakebread holds a B.S. in business from the University of California at Berkeley and an M.B.A. from Indiana University.
“It’s a privilege to be part of the next big leap in computing,” stated Cakebread. “Classical processors have a new partner and there’s no limit to how far humanity can advance with the power of quantum computers. Clearly, D-Wave is leading this next generation of computing.”
This is cool. Check out this short promo vid for a new iPad app developed by Lockheed featuring D-Wave technology.
Here’s a link to the Lockheed Martin site which will take you directly to the App Store to get it.
New paper published in Phys Rev B last week showing a very cool new technique for examining quantum effects in big quantum systems. Here’s the arxiv link.
Here is the abstract:
We describe a quantum tunneling spectroscopy technique that requires only low bandwidth control. The method involves coupling a probe qubit to the system under study to create a localized probe state. The energy of the probe state is then scanned with respect to the unperturbed energy levels of the probed system. Incoherent tunneling transitions that flip the state of the probe qubit occur when the energy bias of the probe is close to an eigenenergy of the probed system. Monitoring these transitions allows the reconstruction of the probed system eigenspectrum. We demonstrate this method on an rf SQUID flux qubit.