Can quantum computers be commercially used in the near future? In February 2007, the company D-Wave Systems presented a working 16-qubit quantum computer. Many researchers are skeptical of this breakthrough, some because D-Wave does not use any protection against noise. If a quantum mechanical system suffers from too much noise, it becomes classical and cannot give any speed-ups over classical computers anymore.
This point was made by Wim van Dam in Nature Physics (vol. 3, April 2007). Van Dam cites recent results by four researchers from CWI − Harry Buhrman, Monique Laurent, Falk Unger and Alexander Schrijver − and two other collaborators − Richard Cleve and Noah Linden. These scientists showed that with a certain amount of imperfections in the devices the advantages of quantum computing are totally lost. For situations with more than 45% noise, quantum computers can be simulated by classical computers and can therefore not be more powerful than a standard desktop computer. Since the amount of imperfections in the company's demonstration is not yet known, it is impossible to say if D-Wave's quantum computer is intrinsically equivalent to a classical computer, Van Dam argues.
Wim van Dam refers to the article 'New Limits on Fault-Tolerant Quantum Computation', written by Harry Buhrman (CWI and Universiteit van Amsterdam), Richard Cleve (University of Waterloo), Monique Laurent (CWI), Noah Linden (University of Bristol), Alexander Schrijver (CWI and Universiteit van Amsterdam) and Falk Unger (CWI), published in the Proc. 47th Ann. Symp. Found. Comp. Sci. 411-419 (IEEE Press, 2006).
More information can be found on INS4's website, Wim van Dam's article in Nature Physics (for subscribers) or the original article of Buhrman and colleagues
