It is shown that the magnetic state decoherence produced by collisions in a thermal vapor can be suppressed by the application of a train of ultrafast optical pulses.In a beautiful experiment, Itano et al. demonstrated the Quantum Zeno effect [1]. A radio frequency pi pulse having a duration on the order of 250 ms was applied to a ground state hyperfine transition. At the same time, a series of radiation pulses was used to drive a strongly coupled ground to excited state uv transition. The rf and strong transitions shared the same ground state level. Itano et al. showed that excitation of the rf transition could be suppressed by the uv pulses. They interpreted the result in terms of collapse of the wave functionspontaneous emission from the excited state during the uv pulses is a signature that the uv pulse projected the atom into its ground state; the lack of such spontaneous emission implies projection into the final state of the rf transition. This paper triggered a great deal of discussion, especially with regards to the interpretation of the results [2].A necessary condition for a quantum Zeno effect is a perturbation of a state amplitude on a time scale that is short compared with the correlation time of the process inducing the transition. In the experiment of Itano et al., this time scale is simply the duration of the pi pulse, 256 ms. On the other hand, if one wished to inhibit particle decay or spontaneous emission [3], it would be necessary to apply perturbations on a time scale that is short compared with the correlation time of the vacuum, an all but impossible task. In this paper,we consider the inhibition of collisional, magnetic state decoherence, by the application of a train of ultrafast, optical pulses. This correlation time of the collisional perturbations resulting in magnetic state decoherence is of order of the duration of a collision and is intermediate between that for the coherent pi pulse applied by Itano et al. and the almost instantaneous, quantum jump-like process produced by the vacuum field. It should be noted that related schemes have been proposed for inhibiting decoherence in systems involving quantum computation [4], but the spirit of these proposals differs markedly from the one presented herein.The rapid perturbations of the system are a necessary, but not sufficient, condition for a mechanism to qualify as a Quantum Zeno effect. The perturbations must involve some "measurement" on the system for the "Quantum Zeno" label to apply. The suppression of magnetic state coherence discussed in this paper is not a Quantum Zeno effect in this sense. We will return to this point below.We envision an experiment in which "active atoms" in a thermal vapor undergo collisions with a bath of foreign gas perturbers. A possible level scheme for the active atoms is depicted in Fig. 1. At some initial time, an ultrashort pulse excites an atom from its ground state, having angular momentum J = 0, to the m = 0 sublevel of an excited state having J = 1. The duration of the excitation pulse τ p is ...

We analyze the sensitivity to inertial rotations Ω of a micron scale integrated gyroscope consisting of a coupled resonator optical waveguide (CROW). We show here that by periodic modulation of the evanescent coupling between resonators, the sensitivity to rotations can be enhanced by a factor up to 10(9) in comparison to a conventional CROW with uniform coupling between resonators. Moreover, the overall shape of the transmission through this CROW superlattice is qualitatively changed resulting in a single sharp transmission resonance located at Ω = 0s-1 instead of a broad transmission band. The modulated coupling therefore allows the CROW gyroscope to operate without phase biasing and with sensitivities suitable for inertial navigation even with the inclusion of resonator losses.

We describe a matter-wave amplifier for vibrational ground state molecules, which uses a Feshbach resonance to first form quasi-bound molecules starting from an atomic Bose-Einstein condensate. The quasi-bound molecules are then driven into their stable vibrational ground state via a twophoton Raman transition inside an optical cavity. The transition from the quasi-bound state to the electronically excited state is driven by a classical field. Amplification of ground state molecules is then achieved by using a strongly damped cavity mode for the transition from the electronically excited molecules to the molecular ground state.

The spin dynamics of atomic Bose-Einstein condensates confined in a one-dimensional optical lattice is studied. The condensates at each lattice site behave like spin magnets that can interact with each other through both the light-induced dipole-dipole interaction and the static magnetic dipole-dipole interaction. We show how these site-to-site dipolar interactions can distort the ground-state spin orientations and lead to the excitation of spin waves. The dispersion relation of the spin waves is studied and possible detection schemes are proposed.