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Quantum computing with realistically noisy devices


In theory, quantum computers offer a means of solving problems that would be intractable on conventional computers. Assuming that a quantum computer could be constructed, it would in practice be required to function with noisy devices called ‘gates’. These gates cause decoherence of the fragile quantum states that are central to the computer's operation. The goal of so-called ‘fault-tolerant quantum computing’ is therefore to compute accurately even when the error probability per gate (EPG) is high. Here we report a simple architecture for fault-tolerant quantum computing, providing evidence that accurate quantum computing is possible for EPGs as high as three per cent. Such EPGs have been experimentally demonstrated, but to avoid excessive resource overheads required by the necessary architecture, lower EPGs are needed. Assuming the availability of quantum resources comparable to the digital resources available in today's computers, we show that non-trivial quantum computations at EPGs of as high as one per cent could be implemented.

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Figure 1: Block structure of C4/C6 concatenated codes.
Figure 2: Conditional logical errors with postselection.
Figure 3: Conditional and detected logical errors with error correction.
Figure 4: Estimating C4/C6 resource requirements.

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This work is a contribution of NIST, an agency of the US government, and is not subject to US copyright. Partial support from the DARPA QuIST programme is acknowledged.

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Correspondence to E. Knill.

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The author declares that he has no competing financial interests.

Supplementary information

Supplementary Methods

Contains Supplementary Figures 1 to 10 and references. (A) Graphical networks useful for implementing the architecture presented. (B) A discussion of how the architecture was simulated. (C) The details underlying the resource graph computations. (PDF 210 kb)

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Knill, E. Quantum computing with realistically noisy devices. Nature 434, 39–44 (2005).

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