Project Leader

Light falling on a tiny mirror exerts a pressure, causing the mirror to move and potentially revealing its quantum-mechanical behaviour. But at room temperature the effects are masked because the mirror is in a constant state of thermal agitation. Markus Aspelmeyer at the Institute for Quantum Optics and Quantum Information in Vienna, Austria, and his team have found a way to cool the micromirror using radiation pressure, and thus damp down this random agitation. Furthermore, their system can self-regulate its own cooling, removing the need for any active feedback loops. Their work on page 67 creates an important avenue for physicists to combine micromechanical motion and radiation to improve the sensitivity of high-precision measures — or one day even demonstrate quantum behaviour.

Why has no one achieved self-cooling by radiation pressure in a micromechanical system until now?

There have been attempts over the past 5 to 10 years, but no one had a micromirror that was lightweight enough, or highly reflecting. We were lucky to collaborate with guys from the United States and Austria who could work with our initially rough ideas for such high-sensitivity systems — which are only now possible because of nano- and microfabrication techniques.

What was the key breakthrough?

It was really a series of minor breakthroughs, but we did celebrate at our first successful attempt to fabricate the mirror used in the experiment. Our celebratory, now empty, bottle of champagne has a plot of our first characterization of the mirror on it.

The paper was put on hold while control experiments were reworked — during the World Cup no less. What happened?

We were ambitiously trying to provide the first full quantum description, rather than follow previous classical-physics attempts, so we had to be extremely careful. At one point we realized there seemed to be a factor of two missing when we compared our findings with results in the classical literature. It turned out that our original data were correct, and luckily we were able to settle all experimental and theoretical issues before the World Cup semi-finals.

What's the next step?

Classical physics offers no means to describe the quantum ground state, or lowest possible energy state. By continuing the work described in this paper and eliminating the current mirror imperfections, we will get there straight away.