D-Wave Systems

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D-Wave Systems Inc.
Privately held company
Industry Computer hardware
Founded 1999
Headquarters Burnaby, British Columbia, Canada
Key people
  • Vern Brownell, CEO
  • Geordie Rose, CTO
  • Eric Ladizinsky, CS
  • V. Paul Lee, Chair
Products D-Wave One, D-Wave Two, D-Wave 2X
Revenue N/A
Number of employees
Approx. 100+
Subsidiaries None
Website dwavesys.com

D-Wave Systems, Inc. is a quantum computing company, based in Burnaby, British Columbia, Canada. D-Wave is the first company in the world to sell quantum computers.

The D-Wave One was built on early prototypes such as D-Wave's Orion Quantum Computer. The prototype was a 16-qubit quantum annealing processor, demonstrated on February 13, 2007 at the Computer History Museum in Mountain View, California.[1] D-Wave demonstrated what they claimed to be a 28-qubit quantum annealing processor on November 12, 2007.[2] The chip was fabricated at the NASA Jet Propulsion Laboratory Microdevices Lab in Pasadena, California.[3] These early prototypes were built upon the research papers by Umesh Vazirani, leading researcher on quantum complexity theory, who dismissed D-Wave’s claims of speedup as a misunderstanding of his work, and suggested that "even if it turns out to be a true quantum computer, and even if it could be scaled to thousands of qubits, [it] would likely not be more powerful than a cellphone".

On May 11, 2011, D-Wave Systems announced D-Wave One, described as "the world's first commercially available quantum computer", operating on a 128-qubit chipset[4] using quantum annealing (a general method for finding the global minimum of a function by a process using quantum fluctuations)[5][6][7][8] to solve optimization problems. In May 2013, a collaboration between NASA, Google and the Universities Space Research Association (USRA) launched a Quantum Artificial Intelligence Lab based on the D-Wave Two 512-qubit quantum computer that would be used for research into machine learning, among other fields of study.[9]

On August 20, 2015, D-Wave Systems announced[10] the general availability of the D-Wave 2X[11] system, a 1000+ qubit quantum computer. This was followed by an announcement[12] on September 28, 2015 that it had been installed at the Quantum Artificial Intelligence Lab at NASA Ames Research Center.

In January 2017, D-Wave has released Qbsolv[13][14][15] - a piece of open-source software for solving QUBO problems on both company's quantum processors and classic hardware architectures.


D-Wave was founded by Haig Farris (former chair of board), Geordie Rose (CTO and former CEO), Bob Wiens (former CFO), and Alexandre Zagoskin[16] (former VP Research and Chief Scientist). Farris taught a business course at the University of British Columbia (UBC), where Rose obtained his Ph.D., and Zagoskin was a postdoctoral fellow. The company name refers to their first qubit designs, which used d-wave superconductors.

D-Wave operated as an offshoot from UBC, while maintaining ties with the Department of Physics and Astronomy.[17] It funded academic research in quantum computing, thus building a collaborative network of research scientists. The company collaborated with several universities and institutions, including UBC, IPHT Jena, Université de Sherbrooke, University of Toronto, University of Twente, Chalmers University of Technology, University of Erlangen, and Jet Propulsion Laboratory. These partnerships were listed on D-Wave's website until 2005.[18][19] In June 2014 D-Wave announced a new quantum applications ecosystem with computational finance firm 1QB Information Technologies (1QBit) and cancer research group DNA-SEQ to focus on solving real-world problems with quantum hardware.[20]

D-Wave operated from various locations in Vancouver, British Columbia, and laboratory spaces at UBC before moving to its current location in the neighboring suburb of Burnaby. D-Wave also has offices in Palo Alto and Vienna, United States of America

Computer systems[edit]

Photograph of a chip constructed by D-Wave Systems Inc., designed to operate as a 128-qubit superconducting adiabatic quantum optimization processor, mounted in a sample holder.

The first commercially produced D-Wave processor was a programmable,[21] superconducting integrated circuit with up to 128 pair-wise coupled[22] superconducting flux qubits.[23][24][25] The 128-qubit processor was superseded by a 512-qubit processor in 2013.[26] The processor is designed to implement a special-purpose quantum annealing[5][6][7][8] as opposed to being operated as a universal gate-model quantum computer.

D-Wave maintains a list of peer-reviewed technical publications by their own scientists and others on their website.[27]

Orion prototype[edit]

On February 13, 2007, D-Wave demonstrated the Orion system, running three different applications at the Computer History Museum in Mountain View, California. This marked the first public demonstration of, supposedly, a quantum computer and associated service.

The first application, an example of pattern matching, performed a search for a similar compound to a known drug within a database of molecules. The next application computed a seating arrangement for an event subject to compatibilities and incompatibilities between guests. The last involved solving a Sudoku puzzle.

The processors at the heart of D-Wave's "Orion quantum computing system" are designed for use as hardware accelerator processors rather than general-purpose computer microprocessors. The system is designed to solve a particular NP-complete problem related to the two dimensional Ising model in a magnetic field.[1] D-Wave terms the device a 16-qubit superconducting adiabatic quantum computer processor.[28][29]

According to the company, a conventional front end running an application that requires the solution of an NP-complete problem, such as pattern matching, passes the problem to the Orion system.

According to Geordie Rose, founder and Chief Technology Officer of D-Wave, NP-complete problems "are probably not exactly solvable, no matter how big, fast or advanced computers get"; the adiabatic quantum computer used by the Orion system is intended to quickly compute an approximate solution.[30]

2009 Google demonstration[edit]

On December 8, 2009, at the Neural Information Processing Systems (NIPS) conference, a Google research team led by Hartmut Neven used D-Wave's processor to train a binary image classifier.

D-Wave One[edit]

On May 11, 2011, D-Wave Systems announced the D-Wave One, an integrated quantum computer system running on a 128-qubit processor. The processor used in the D-Wave One code-named "Rainier", performs a single mathematical operation, discrete optimization. Rainier uses quantum annealing to solve optimization problems. The D-Wave One is claimed to be the world's first commercially available quantum computer system.[31] The price will be approximately US$10,000,000.[32]

A research team led by Matthias Troyer and Daniel Lidar found that, while there is evidence of quantum annealing in D-Wave One, they saw no speed increase compared to classical computers. They implemented an optimized classical algorithm to solve the same particular problem as the D-Wave One.[33][34]

Lockheed Martin and D-Wave collaboration[edit]

On May 25, 2011, Lockheed Martin signed a multi-year contract with D-Wave Systems to realize the benefits based upon a quantum annealing processor applied to some of Lockheed's most challenging computation problems. The contract included purchase of the D-Wave One Quantum Computer System, maintenance, and associated professional services.[35]

Optimization problem-solving in protein structure determination[edit]

In August 2012, a team of Harvard University researchers presented results of the largest protein-folding problem solved to date using a quantum computer. The researchers solved instances of a lattice protein folding model, known as the Miyazawa–Jernigan model, on a D-Wave One quantum computer.[36][37]

D-Wave Two[edit]

Main article: D-Wave Two

In early 2012, D-Wave Systems revealed a 512-qubit quantum computer, code-named Vesuvius,[38] which was launched as a production processor in 2013.[39]

In May 2013, Catherine McGeoch, a consultant for D-Wave, published the first comparison of the technology against regular top-end desktop computers running an optimization algorithm. Using a configuration with 439 qubits, the system performed 3,600 times as fast as CPLEX, the best algorithm on the conventional machine, solving problems with 100 or more variables in half a second compared with half an hour. The results are presented at the Computing Frontiers 2013 conference.[40]

In March 2013 several groups of researchers at the Adiabatic Quantum Computing workshop at the Institute of Physics in London produced evidence, though only indirect, of quantum entanglement in the D-Wave chips.[41]

In May 2013 it was announced that a collaboration between NASA, Google and the USRA launched a Quantum Artificial Intelligence Lab at the NASA Advanced Supercomputing Division at Ames Research Center in California, using a 512-qubit D-Wave Two that would be used for research into machine learning, among other fields of study.[9][42]

D-Wave 2X[edit]

On August 20, 2015, D-Wave released general availability of their D-Wave 2X computer, with 1,152 qubits in a Chimera graph architecture (although, due to magnetic offsets and manufacturing variability inherent in the superconductor circuit fabrication fewer than 1152 qubits are functional and available for use. The exact number of qubits yielded will vary with each specific processor manufactured.) This was accompanied by a report comparing speeds with high-end single threaded CPUs. Unlike previous reports, this one explicitly stated that question of quantum speedup was not something they were trying to address, and focused on constant-factor performance gains over classical hardware. For general-purpose problems, a speedup of 15x was reported, but it is worth noting that these classical algorithms benefit efficiently from parallelization—so that the computer would be performing on par with, perhaps, 30 high-end single-threaded cores.

The D-Wave 2X processor is based on a 2,048-qubit chip with half of the qubits disabled, but these may be re-activated later on.[43][44]

Comparison of D-Wave systems[edit]

D-Wave One D-Wave Two D-Wave 2X D-Wave 2000Q[45][46]
Available May 2011 May 2013 August 2015 January 2017
Code-name Rainier Vesuvius
Qubits 128 512 1152 2048
Couplers 352 3000 5600
Josephson junctions 24,000 128,000
I/O / control lines 192
Operating temperature 0.02 K 0.015 K
Power consumption 15.5 kW 25 kW
Buyers Lockheed Martin Lockheed Martin


Lockheed Martin


Los Alamos National Laboratory

Temporal Defense Systems Inc.


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:[47]

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:[48] ″At the moment it is impossible to say if D-Wave's quantum computer is intrinsically equivalent to a classical computer or not. So until more is known about their error rates, caveat emptor is the least one can say″.

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.[49][50] 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[51] and later answered[52] 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.[53] In May 2011 he said that he was "retiring as Chief D-wave Skeptic",[54] 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.[51][55][56] In May 16, 2013 he resumed his skeptic post. He criticizes D-Wave for blowing 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.[33]

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).[57]

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.[58]

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." [59]

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.[60]

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"[61] 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.[62] The researchers, led by Matthias Troyer at the Swiss Federal Institute of Technology in Zurich, 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[63] 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 to find such problem classes.[64]

Notable alumni and collaborators[edit]

  • Jacob Biamonte[65] (University of Malta)
  • Alexandre Zagoskin[66] (Loughborough University)
  • Vern Brownell [67]

See also[edit]


  1. ^ a b "Quantum Computing Demo Announcement". 2007-01-19. Retrieved 2007-02-11. 
  2. ^ "D-Wave Systems News". dwavesys.com. 
  3. ^ "A picture of the demo chip". Hack The Multiverse. 
  4. ^ M. W. Johnson et al (2011), Quantum annealing with manufactured spins (Nature)
  5. ^ a b T. Kadowaki; H. Nishimori (1998). "Quantum annealing in the transverse Ising model". Phys. Rev. E. 58: 5355–5363. doi:10.1103/physreve.58.5355. 
  6. ^ a b A. B. Finilla; M. A. Gomez; C. Sebenik; D. J. Doll (1994). "Quantum annealing: A new method for minimizing multidimensional functions". Chem. Phys. Lett. 219: 343–348. doi:10.1016/0009-2614(94)00117-0. 
  7. ^ a b G. E. Santoro; E. Tosatti (2006). "Optimization using quantum mechanics: quantum annealing through adiabatic evolution". J. Phys. A. 39: R393. doi:10.1088/0305-4470/39/36/r01. 
  8. ^ a b A. Das; B. K. Chakrabarti (2008). "Colloquium: Quantum annealing and analog quantum computation". Rev. Mod. Phys. 80: 1061–1081. doi:10.1103/revmodphys.80.1061. 
  9. ^ a b c d Choi, Charles (May 16, 2013). "Google and NASA Launch Quantum Computing AI Lab". MIT Technology Review. 
  10. ^ "D-Wave Systems Announces the General Availability of the 1000+ Qubit D-Wave 2X Quantum Computer | D-Wave Systems". www.dwavesys.com. Retrieved 2015-10-14. 
  11. ^ http://www.dwavesys.com/d-wave-two-system
  12. ^ "D-Wave Systems Announces Multi-Year Agreement To Provide Its Technology To Google, NASA And USRA's Quantum Artificial Intelligence Lab | D-Wave Systems". www.dwavesys.com. Retrieved 2015-10-14. 
  13. ^ Finley, Klint (11 January 2017). "Quantum Computing Is Real, and D-Wave Just Open-Sourced It". Wired (magazine). Condé Nast. Retrieved 14 January 2017. 
  14. ^ "D-Wave Initiates Open Quantum Software Environment". D-Wave Systems. Retrieved 14 January 2017. 
  15. ^ "dwavesystems/qbsolv". GitHub. Retrieved 14 January 2017. 
  16. ^ "Department staff - Dr Alexandre Zagoskin - Physics - Loughborough University". lboro.ac.uk. 
  17. ^ "UBC Physics & Astronomy -". ubc.ca. 
  18. ^ "D-Wave Systems at the Way Back Machine". 2002-11-23. Archived from the original on 2002-11-23. Retrieved 2007-02-17. 
  19. ^ "D-Wave Systems at the Way Back Machine". 2005-03-24. Archived from the original on 2005-03-24. Retrieved 2007-02-17. 
  20. ^ "D-Wave Systems Building Quantum Application Ecosystem, Announces Partnerships with DNA-SEQ Alliance and 1QBit". Retrieved 2014-06-09. 
  21. ^ M. W. Johnson et al., "A scalable control system for a superconducting adiabatic quantum optimization processor," Supercond. Sci. Technol. 23, 065004 (2010); preprint available: arXiv:0907.3757
  22. ^ Harris, R.; et al. (2009). "Compound Josephson-junction coupler for flux qubits with minimal crosstalk". Phys. Rev. B. 80: 052506. arXiv:0904.3784Freely accessible. doi:10.1103/physrevb.80.052506. 
  23. ^ Harris, R.; et al. (2010). "Experimental demonstration of a robust and scalable flux qubit". Phys. Rev. B. 81: 134510. arXiv:0909.4321Freely accessible. 
  24. ^ Next Big Future: Robust and Scalable Flux Qubit, [1], September 23, 2009
  25. ^ Next Big Future: Dwave Systems Adiabatic Quantum Computer [2], October 23, 2009
  26. ^ D-Wave Systems: D-Wave Two Quantum Computer Selected for New Quantum Artificial Intelligence Initiative, System to be Installed at NASA's Ames Research Center, and Operational in Q3, [3], May 16, 2013
  27. ^ "D-Wave Web site, list of technical publications". dwavesys.com. 
  28. ^ Kaminsky; William M. Kaminsky; Seth Lloyd (2002-11-23). "Scalable Architecture for Adiabatic Quantum Computing of NP-Hard Problems". Quantum Computing & Quantum Bits in Mesoscopic Systems. Kluwer Academic. arXiv:quant-ph/0211152Freely accessible. 
  29. ^ Meglicki, Zdzislaw (2008). Quantum Computing Without Magic: Devices. MIT Press. pp. 390–391. ISBN 0-262-13506-X. 
  30. ^ "Yeah but how fast is it? Part 3. OR some thoughts about adiabatic QC". 2006-08-27. Archived from the original on 2006-11-19. Retrieved 2007-02-11. 
  31. ^ "Learning to program the D-Wave One". Retrieved 11 May 2011. 
  32. ^ "First Ever Commercial Quantum Computer Now Available for $10 Million". Retrieved 25 May 2011. 
  33. ^ a b Scott Aaronson (16 May 2013). "D-Wave: Truth finally starts to emerge". 
  34. ^ Boixo, Sergio; Rønnow, Troels F.; Isakov, Sergei V.; Wang, Zhihui; Wecker, David; Lidar, Daniel A.; Martinis, John M.; Troyer, Matthias (16 April 2013). "Quantum annealing with more than one hundred qubits". Nature Physics. 10 (3): 218–224. arXiv:1304.4595Freely accessible. doi:10.1038/nphys2900. 
  35. ^ "Lockheed Martin Signs Contract with D-Wave Systems". Retrieved 2011-05-25
  36. ^ "D-Wave quantum computer solves protein folding problem". nature.com. 
  37. ^ "D-Wave uses quantum method to solve protein folding problem". phys.org. 
  38. ^ "D-Wave Defies World of Critics With 'First Quantum Cloud' - WIRED". WIRED. 22 February 2012. 
  39. ^ "The black box that could change the world". The Globe and Mail. 
  40. ^ McGeoch, Catherine; Wang, Cong (May 2013). "Experimental Evaluation of an Adiabatic Quantum System for Combinatorial Optimization". 
  41. ^ Aron, Jacob (8 March 2013). "Controversial quantum computer aces entanglement tests". New Scientist. Retrieved 14 May 2013. 
  42. ^ Hardy, Quentin (16 May 2013). "Google Buys a Quantum Computer". Bits. The New York Times. Retrieved 3 June 2013. 
  43. ^ The Future Of Quantum Computing: Vern Brownell, D-Wave CEO @ Compute Midwest on YouTube 4 December 2014
  44. ^ brian wang. "Next Big Future: Dwave Systems shows off quantum chip with 2048 physical qubits". nextbigfuture.com. 
  45. ^ "D-Wave Announces D-Wave 2000Q Quantum Computer and First System Order | D-Wave Systems". www.dwavesys.com. Retrieved 2017-01-25. 
  46. ^ D-Wave Systems, PDF, 01-2017, http://www.dwavesys.com/sites/default/files/D-Wave%202000Q%20Tech%20Collateral_0117F.pdf
  47. ^ "Shtetl-Optimized: D-Wave Easter Spectacular". 2007-04-07. Retrieved 2007-05-17. 
  48. ^ "Quantum computing: In the 'death zone'?". 2007-04-07. Retrieved 2008-12-23. 
  49. ^ Quantum annealing with manufactured spins Nature 473, 194–198, 12 May 2011
  50. ^ The CIA and Jeff Bezos Bet on Quantum Computing Technology Review October 4, 2012 by Tom Simonite
  51. ^ a b "Shtetl-Optimized". scottaaronson.com. 
  52. ^ "Entanglement in a quantum annealing processor". prx. 2014-05-29. 
  53. ^ "Shtetl-Optimized: The Orion Quantum Computer Anti-Hype FAQ". 2007-02-09. Retrieved 2007-05-17. 
  54. ^ "Shtetl-Optimized". scottaaronson.com. 
  55. ^ "Shtetl-Optimized: Thanksgiving Special: D-Wave at MIT". 2007-11-22. Retrieved 2007-12-03. 
  56. ^ "In Defence of D-Wave". 
  57. ^ "D-Wave: comment on comparison with classical computers". 2013-06-10. Retrieved 2013-06-20. 
  58. ^ Shin, Seung Woo; Graeme Smith; John A. Smolin; Umesh Vazirani (28 January 2014). "How 'Quantum' is the D-Wave Machine?". arXiv:1401.7087Freely accessible [quant-ph]. 
  59. ^ Walter Vinci, Tameem Albash, Anurag Mishra, Paul A. Warburton, Daniel A. Lidar "Distinguishing Classical and Quantum Models for the D-Wave Device" (17 Mar 2014) http://arxiv.org/abs/1403.4228
  60. ^ Lanting, T.; Przybysz, A. J.; Smirnov, A. Yu.; Spedalieri, F. M.; Amin, M. H.; Berkley, A. J.; Harris, R.; Altomare, F.; Boixo, S.; Bunyk, P.; Dickson, N.; Enderud, C.; Hilton, J. P.; Hoskinson, E.; Johnson, M. W.; Ladizinsky, E.; Ladizinsky, N.; Neufeld, R.; Oh, T.; Perminov, I.; Rich, C.; Thom, M. C.; Tolkacheva, E.; Uchaikin, S.; Wilson, A. B.; Rose, G. (2014). "Verification Required". aps.org. doi:10.1103/PhysRevX.4.021041. 
  61. ^ Helmut Katzgraber, quoted in (Cho 2014).
  62. ^ Cho, Adrian (20 June 2014), "Quantum or not, controversial computer yields no speedup", Science, 344 (6190): 1330–1331, doi:10.1126/science.344.6190.1330, PMID 24948715 .
  63. ^ Mohammad H. Amin, "Searching for quantum speedup in quasistatic quantum annealers" arXiv:1503.04216
  64. ^ Steiger, Damian; Heim, Bettina; Rønnow, Troels; Troyer, Matthias (October 22, 2015), "Performance of quantum annealing hardware", Electro-Optical and Infrared Systems: Technology and Applications XII; and Quantum Information Science and Technology, doi:10.1117/12.2202661 
  65. ^ "Faculty | Prof Jacob Biamonte | Physics | University of Oxford". qubit.org. Retrieved 2013-09-04. 
  66. ^ "Department staff | Dr Alexandre Zagoskin | Physics | Loughborough University". Lboro.ac.uk. Retrieved 2013-05-16. 
  67. ^ "CrunchBase". 

External links[edit]