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Quantum physics

Cruise control for a qubit

Nature volume 490, pages 43–44 (2012)Cite this article

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Continuous feedback control — monitoring a system and adjusting its dynamics — is widely used to keep systems 'on track'. This approach has now been used to maintain the cycling of a quantum bit almost indefinitely. See Letter p.77

In an ideal world, when the power supplied by a car's engine equals the power dissipated (for example, by air resistance and friction), the car's speed will remain steady. But in the real world, unpredictable fluctuations in the car and its environment (such as variations in wind speed, air pressure, tyre pressure, oil temperature, road surface and other variables) will cause the speed to vary even with constant power. With no feedback control, the position of the car around the track would, within an hour, become completely unrelated to the position of the second hand on the reference clock. In most modern cars, cruise control can do a good job of keeping the speed within a narrow range around a set value. But for the task in hand, a more sophisticated cruise-control mechanism would be needed, which compares the position of the car with the position of the second hand, as described above.

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Figure 1: Locking cycles to an external clock.

References

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Authors and Affiliations

  1. Howard M. Wiseman is at the Centre for Quantum Computation and Communication Technology (Australian Research Council), and the Centre for Quantum Dynamics, Griffith University, Brisbane 4111, Australia.,

    Howard M. Wiseman

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  1. Howard M. Wiseman
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Correspondence to Howard M. Wiseman.

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Wiseman, H. Cruise control for a qubit. Nature 490, 43–44 (2012). https://doi.org/10.1038/490043a

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