Sunday, October 3, 2010

The Challenge to make quantum computers

The challenge to implement a completely scalable  quantum computer is tied with the understanding of the quantum/classical transition where quantum mechanics dominates the explanation of the microscopic world (up to the molecular scale more or less), but classical mechanics explains very well the ordinary macroscopic world. A completely scalable quantum computer would eventually give us a macroscopic taste of the imaginable strange quantum effects that so far have been seen only in the microscopic world.

"Because there are no known fundamental obstacles to such scalability (practical quantum computer with large number of qubits), it has been suggested that failure to achieve it would reveal new physics" -Emanuel Knill

I feel that the most recent papers are becoming more conservative about their predictions on the feasibility of quantum computing despite fact that there is work stating that fault tolerant quantum computation is possible with two ingredients:

  • Maximum Error/Gate about 10^-4 to 10^-5
  • Effective error correction codes with ancillary qubits.
The last ingredient seems to be more or less accomplished  and the former one does not seem to be fundamentally unattainable despite the fact that we are currently very far. A paper that summarizes these facts with a high degree of scepticism is

Is Fault-Tolerant Quantum Computation Really Possible?

which I also like for its entertaining and straightforward writing style. 

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