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Seeing the news about 14 entangled states today @ Innsbruck:

I haven't found a clear guide online to how many qubits we are aiming for a first practical quantum computer, e.g. Factorization, Search or re-implementing large scale computing problems?

  1. Given the relatively few algorithms we have, and the fact that algorithms don't necessarily have to map 1:1 with the size of the domain (i.e. be multi-step), can we make any reasonable guesses for the above use cases?

The Wikipedia entry for Shor's algorithm seems to state "The input and output qubit registers need ... twice as many qubits as necessary ..." so we would need 1024 qubits for common encryption in use today e.g. AES. Is this a correct understanding?

references: http://en.wikipedia.org/wiki/Shor%27s_algorithm http://en.wikipedia.org/wiki/Key_size

Are more info on any quantum algorithms suitable for large scale computing problems yet? e.g. 50-100 qubits for 'useful' (1999) eigen* calculations http://prl.aps.org/abstract/PRL/v83/i24/p5162_1 - only have access to the abstract

Cheers

velniukas
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2 Answers2

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For modeling of physical (and chemical) systems on quantum computer even 25-30 qubits would be already quite nice, see Lanyon, et al, “Towards Quantum Chemistry on a Quantum Computer”, Nature Chemistry 2, 106 - 111 (2009) (see also http://arxiv.org/abs/0905.0887 )

Really, quant-ph section in arXiv.org is standard place for papers about quantum computers, the paper from PRL you mentioned also may be found there (but seems I may post only one link).

Alex 'qubeat'
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In this paper you can find a way to drastically reduce number of required qubits:

arxiv.org: Shor's algorithm with fewer (pure) qubits

Christof Zalka (Submitted on 15 Jan 2006)

stackexchanger
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