Atom confinement traps

Atoms are provided from an rf discharge source, at cryogenic temperatures. After thermalization on the cold cell walls, typically 250 mK, the low field seeking states, c and d (Fig. 1) are attracted to the center of a Ioffe-Pritchard trap, a linear quadrupole trap with a coil at each end to confine the atoms axially. The trapping field is initially about 0.9 T, sufficient to capture atoms with a temperature of about 0.5 K. Once the temperature of the walls is reduced, the temperature of the trapped gas rapidly falls by evaporation, the escaping atoms being trapped on the helium surface. At about 60 mK, the gas becomes isolated from the wall and evaporation ceases. 

The author became interested in the models of confinement of the hydrogen atom inside finite volumes [2,14,17,18] in connection with the measurements of the hyperfine structure of atomic hydrogen trapped in a-quartz [19,20]. Ten years later, he extended his interests to confinement in semi-infinite spaces limited by a paraboloid [21], a hyperboloid [9] and a cone [22] in connection with the exoelectron emission by compressed rocks [23,24], Jaskolski s report [1] cited several of the above-mentioned works [9,14,17, 18,21], each one of which had formulated and constructed exact solutions for new types of confinement for the hydrogen atom. This subsection is focussed on his citation of our article [9] ... 

Three questions have motivated significant developments in cold collisions (1) How do collisions lead to loss of atom confinement in traps (2) How can photoassociation spectroscopy yield precision measurements of atomic properties and insight into the quantum nature of the scattering process itself (3) How can optical fields be used to control the outcome of a collisional encounter The first question will be largely ignored in this chapter. The answer to the second question has proved to be fruitful not only for molecular spectroscopy but has also contributed to real advances in the precision measurement of atomic properties. 

Cavity QED has led to many new effects, including the realization of a quantmn phase gate (Turchette et al. 1995), the creation of Fock states of the radiation field (Varcoe et al. 2000), and a demonstration of quantum nondemolition detection of single photons (Nogues et al. 1999). Ye et al. (1999) have noted that all serious schemes for quantum computation and communication via cavity QED rely on developing techniques for atom confinement. This explains the importance of the experiments on the trapping of single atoms under conditions of cavity QED. 

A far-off resonance trap (FORT), in contrast, uses tire dipole force ratlier tlian tire spontaneous force to confine atoms and can therefore operate far from resonance witli negligible population of excited states. A hybrid MOT/dipole-force trap was used by a NIST-Maryland collaboration [26] to study cold collisions, and a FORT was... 

Single atomic ions confined in radio frequency traps and cooled by laser beams (Figure 7.4a) formed the basis for the first proposal of a CNOT quantum gate with an explicit physical system [14]. The first experimental realization of a CNOT quantum gate was in fact demonstrated on a system inspired by this scheme [37]. In this proposal, two internal electronic states of alkaline-earth or transition metal ions (e.g. Ba2+ or Yb3+) define the qubit basis. These states have excellent coherence properties, with T2 and T2 in the range of seconds [15]. Each qubit can be... 

Electron donors and acceptors for reversible redox systems must invariably exhibit at least two stable oxidation states, or the net result will be an irreversible chemical reaction. The donor or acceptor components of the redox system need not be confined to independent atoms, ions, or molecules but could even be imperfections in crystal lattices capable of functioning as electron traps. The well-known color centers in alkali halides are just such acceptor systems. 

Fig. 2. Schematic diagram of the apparatus. The superconducting magnetic coils create trapping potential that confines atoms near the focus of the 243 nm laser beam. The beam is focused to a 50 pm waist radius and retro-reflected to allow for Doppler-free excitation. After excitation, fluorescence is induced by an applied electric field. A small fraction of the 122 nm fluorescence photons are counted on a microchannel plate detector. Not shown is the trapping cell which surrounds the sample and is thermally anchored to a dilution refrigerator. The actual trap is longer and narrower than indicated in the diagram...

The density and the number of trapped atoms can be inferred from the decay of the sample. Atoms are dumped from the trap by lowering one of the axial confining fields. The emerging atoms recombine rapidly on the walls of the cell, releasing an energy of 4.6 eV per recombination. A fraction of this energy is collected on a small quartz bolometer [24]. The total integrated power is proportional to the total number of atoms in the trap. 

Once an antiproton and positron have combined, electrical confinement forces cease and the antihydrogen atom will escape, hit an electrode, and annihilate. During the early stages of the experiment no attempt will be made to trap the produced antihydrogen and the annihilation signature will be one of the most important diagnostics tools. 

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