A device that produces individual atoms 'on demand' raises a number of exciting possibilities for nanotechnology, ranging from the controlled doping of nanostructures, to the opening of new pathways leading to the ultimate goal of atom-by-atom assembly. Using the techniques of laser cooling and trapping, we have realized a source of Cr atoms that can produce single atoms on demand with very high fidelity.
Our realization consists of a gated evaporative source of atoms and a magneto-optical trap that cools and captures these atoms. The presence of a single atom in the trap is detected by laser-induced fluorescence, and this signal is used in a feedback loop to control the gate on the atom source. When a fluorescence signal above a certain threshold is detected, signifying the presence of a single atom in the trap, the loading is turned off. If the atom leaves the trap, through intentional extraction or a random loss mechanism, the fluorescence rate drops below the threshold and the loading is turned on again. With this feedback control, the trap population remains at the single atom level at nearly all times, making a single atom available whenever it is required.
Performance of the source is measured by the fraction of time spent at the single atom population level, as compared with the fraction of time spent with zero or more atoms. Another figure of merit is the rate at which atoms can be extracted while still maintaining a given single-atom fraction. How well a source performs based on these measures depends on the signal-to-noise ratio of the detection, which in turn depends on the efficiency of fluorescence detection. The larger the fluorescence signal, the faster a measurement can be made and the faster the feedback loop can respond to either an extraction or a random event. We will present data for our first realization of a deterministic single-atom source of Cr showing single-atom population fractions over 95% at extraction rates up to 10 atoms per second. With advances in detection efficiency, we expect to reach even higher single-atom fractions at much faster extraction rates.
The atoms produced in our deterministic single-atom source are not only available 'on demand,' but are also extremely well localized (several micrometers) and extremely 'cold,' with mean kinetic energies corresponding to temperatures in the microkelvin range. These characteristics make this source especially interesting on one hand for applications such as quantum information processing, and on the other for high-resolution atom- or ion-optical imaging systems. We will discuss such applications, as well as other ways in which a deterministic source of atoms could be useful for studies in areas such as quantum electrodynamics and controlled collisions.
J. J. McClelland
Electron Physics Group, National Institute of Standards and Technology
100 Bureau Dr. STOP 8412, Gaithersburg, MD 20899 USA
Phone: 301-975-3721 Fax: 301-926-2746