Atomic cloud key to controlling a quantum state without measuring it

Enlarge / The atoms (center foreground) alter a laser so it extracts energy from a membrane (blue). (credit: Departement Physik, Universitat Basel)

Way back when I was still working in the lab, there was a lot of buzz about something called "coherent control." The basic idea was to take the principles of traditional control theory-the same theory that makes things like cruise control work-and apply them to quantum systems.

Some very cool ideas and insights came out of that early work, but it has taken a while to put them into practice. Now, we might be starting to see some practical applications emerging, with researchers demonstrating in a new paper the active cooling of a membrane using coherent control.

Measurement is bad

A traditional control system has something like a desired state, such as the target speed of a car. By repeatedly measuring the speed of a car and accelerating or decelerating, the control system can bring the car to the target speed.

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