Towards Quantum Superpositions of a Mirror

We propose an experiment for creating quantum superposition states involving of the order of ${10}^{14}$ atoms via the interaction of a single photon with a tiny mirror. This mirror, mounted on a high-quality mechanical oscillator, is part of a high-finesse optical cavity which forms one arm of a Michelson interferometer. By observing the interference of the photon only, one can study the creation and decoherence of superpositions involving the mirror. A detailed analysis of the requirements shows that the experiment is within reach using a combination of state-of-the-art technologies.

Figure 1

The proposed setup: a Michelson interferometer for a single photon, where in each arm there is a high-finesse cavity. The cavity in arm A has a very small end mirror mounted on a micromechanical oscillator. The single photon comes in through I. If the photon is in arm A, the motion of the small mirror is affected by its radiation pressure. The photon later leaks out of either cavity and is detected at D1 or D2.

Figure 2

Time evolution of the interference visibility $V$ of the photon over one period of the mirror’s motion for the case where the mirror has been optically cooled close to its ground state ($\overline{n}=2$, solid line) and for $T=2\mathrm{m}\mathrm{K}$, which corresponds to $\overline{n}=100000$ (dashed line—see also inset). The visibility decays after $t=0$, but in the absence of decoherence there is a revival of the visibility after a full period. The width of the revival peak scales like $1/\sqrt{\overline{n}}$.