Jalani Fox

The non-paradox of superluminal tunneling, and a planned experiment to study the real mystery

Although the now well-established fact of superluminal tunneling may be somewhat surprising, we maintain that as in previous cases of quantum nonlocality, there is in fact no paradox. No signal, in the sense of previously unpredictable information, may be transmitted faster than c by making use of anomalously fast tunneling. On the other hand, we believe that mysteries persist about where a particle is while it is tunneling, how long it spends there, and whether (in a carefully defined sense, but less restricted than that of the familiar two-slit discussions) it can be in two places at the same time. We are setting up a series of atom optics experiments which we believe will provide direct experimental evidence about some of these issues.

Classical and quantum analysis of one-dimensional velocity selection for ultracold atoms

We discuss a velocity selection technique for obtaining cold atoms, in which all atoms below a certain energy are spatially selected from the surrounding atom cloud. Velocity selection can in some cases be more efficient than other cooling techniques for the preparation of ultracold atom clouds in one dimension. With quantum mechanical and classical simulations and theory we present a scheme using a dipole force barrier to select the coldest atoms from a magnetically trapped atom cloud. The dipole and magnetic potentials create a local minimum which traps the coldest atoms. A unique advantage of this technique is the sharp cut-off in the velocity distribution of the sample of selected atoms. Such a non-thermal distribution should prove useful for a variety of experiments, including proposed studies of atomic tunnelling and scattering from quantum potentials. We show that when the rms size of the atom cloud is smaller than the local minimum in which the selected atoms are trapped, the velocity selection technique can be more efficient in one dimension than some common techniques such as evaporative cooling. For example, one simulation shows nearly 6% of the atoms retained at a temperature 100 times lower than the starting condition.

Motional quantum state reconstruction in an optical lattice

Summary form only given. We demonstrate reconstruction of the quantum center-of-mass motion of laser-cooled atoms confined in an optical lattice. We examine time-evolution of the density matrix to study decoherence effects in the lattice.

Efficient 1-D Velocity Selection in Laser-Cooled Atom Clouds

In this paper we demonstrate a “velocity-selection” technique which selects the lowest energy atoms from a laser-cooled cloud. The technique selects in one dimension, and confines the colder, selected atoms in a small auxiliary trap, spatially separated from hotter atoms. For one dimensional experiments, velocity selection can have an efficiency (defined as the fraction of the initial cloud which remains after selection) that varies as √U/kBT, where U defines a maximum energy and T is a cloud temperature, making it more efficient than 3D cooling methods such as evaporative cooling, which typically retains less than 1% of the atoms when cooling to 1% of the initial temperature [1]. The process of selection creates non-thermal distributions with a sharp cutoff in velocity, which can be important for experiments on effects such as tunneling [2] and quantum collisions [3].