Atomic cloud key to controlling a quantum state without measuring it

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.