We have studied the deflection of ground-state sodium atoms passing through a micron-sized parallel-plate cavity by measuring the intensity of a sodium atomic beam transmitted through the cavity as a function of cavity plate separation. This experiment provides clear evidence for the existence of the Casimir-Polder force, which is due to modification of the ground-state Lamb shift in the confined space of a cavity. Our results confirm the magnitude of the force and the distance dependence predicted by quantum electrodynamics. PACS numbers: 42.50.Wm, 32.70Jz, 42.50.Lc Physicists have long been intrigued by the idea that the electromagnetic vacuum interacts with charged particles to produce observable effects. The first experimental verification of this idea was the discovery [1] that the 251/2 and 2P\/2 states of hydrogen are not degenerate. Crudely speaking, the degeneracy is split by the ac Stark effect due to the interaction with the vacuum. Energy shifts of this type are now well established and are generally known as Lamb shifts. The vacuum field in the vicinity of a conducting plate is different from that of free space. In particular, at a distance L from the plate, the spatial distribution, polarization, and spectral density of the vacuum field are substantially altered for frequencies below ~~c/L because of the boundary conditions imposed by the plate. The first discussion of a physical effect due to this modification of the vacuum dates back to 1948 and the seminal work of Casimir [2]. Casimir and Polder [3] discussed the interaction of a neutral atom with a plane conducting plate and showed that the modified vacuum gives rise to a spatially varying Lamb shift whose gradient corresponds to an attractive long-range force. Similar long-range forces are found between any pair of neutral objects, the most famous example being perhaps the Casimir force between two conducting plates. We refer to any such force on an isolated atom as a Casimir-Polder force.Although some quantitative measurements exist on the long-range forces between macroscopic dielectrics [4], the Casimir force has been studied only qualitatively [5], and the Casimir-Polder interaction has eluded detection altogether [6]. Recent experiments on the Rydberg states of helium [7] have yielded precise measurements of the long-range interaction between the Rydberg electron and the He + core, but have not yet reached the point of testing the Casimir-Polder interaction [8], known in that system as K r 'et. In the experiment reported here we have probed the vacuum field in a parallel-plate cavity using a beam of ground-state sodium atoms. Since the vacuum field varies with position, the atoms experience a Casimir-Polder force which pushes them towards the cavity walls. We have used the deflection of the beam to demonstrate the existence of this force and to confirm quantitatively the strength predicted by quantum electrodynamics.For a spherical ground-state atom (3s sodium) between parallel ideal mirrors, the position-dependent atom-cavity interacti...

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We have performed spectroscopy on sodium atoms that are optically channeled in the single node of a laser standing wave set up across a parallel-plate cavity. Using this technique we have extended our previous measurement of the Lennard-Jones van der Waals energy-level shift ͓Sandoghdar et al., Phys. Rev. Lett. 68, 3432 ͑1992͔͒ down to a cavity width of ϳ500 nm. We discuss the applications of this technique to the precise measurement of atom-surface distances.

We have investigated the application of an electronic feedback technique recently reported by Repasky et al. [Appl. Opt. 45, 9013 (2006)] to an injection-locked semiconductor diode laser. We find that without electronic feedback, the injection-locked slave laser will only follow the master for less than 1 GHz, but once the electronic feedback is applied, the slave laser is capable of following for more than 20 GHz, corresponding to the full scan range of the master laser.

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