Atom Detection and Photon Production in a Scalable, Open, Optical Microcavity

A microfabricated Fabry-Perot optical resonator has been used for atom detection and photon production with less than 1 atom on average in the cavity mode. Our cavity design combines the intrinsic scalability of microfabrication processes with direct coupling of the cavity field to single-mode optical waveguides or fibers. The presence of the atom is seen through changes in both the intensity and the noise characteristics of probe light reflected from the cavity input mirror. An excitation laser passing transversely through the cavity triggers photon emission into the cavity mode and hence into the single-mode fiber. These are first steps toward building an optical microcavity network on an atom chip for applications in quantum information processing.

Figure 1

Apparatus (not to scale). Graph: change in reflected probe light as atoms traverse the cavity. Averaging window: $250\mu \mathrm{s}$. Laser, cavity, and atom frequencies are equal: ${\omega }_L={\omega }_C={\omega }_A$. Atoms are released from optical molasses at time $t=0$, and 34 identical drops are averaged. There are $\sim 0.7$ atoms in the cavity on average at the peak.

Figure 2

Peak probe laser reflection with ${\omega }_C={\omega }_A$ versus detuning $({\omega }_L-{\omega }_A)/2\pi$ for different initial MOT numbers. (a) $⟨N⟩=1.1$ atoms in the cavity; full-width at half-maximum $2.1\times 2\gamma$. (b) $⟨N⟩=0.6$; width $1.7\times 2\gamma$. Solid curves are Monte Carlo fits to the data using Eq. (1).

Figure 3

Normalized variance of the photon counts reflected from the cavity as a function of time, determined from 48 drops. (a) Nonresonant cavity. (b) Resonant cavity. Horizontal line: shot-noise limit. Vertical dashed line: arrival time of the peak number of atoms.

Figure 4

(a) Probe reflection signal showing abrupt atom loss when the excitation laser is turned on. (b) Cavity-stimulated decay generates a pulse of photons in the fiber when the atom cloud is excited. The dotted line shows coincidence of the photon pulse with the turn-on of the excitation laser.