1. Creation of Fock States of Atoms
This is an ongoing project where the goal is to create Fock sates of atoms ie: a known number of atoms in a particular state of the trap (ground state in our case). The starting point is to load a Bose Einstein Condensate into a 1D box with very tight confinement in the transverse direction which is created using the Hermite Gaussian TEM01 mode of the laser beam. Under these circumstances the interparticle interactions are dominant and there exists a high correlation between the height of the box and the number of atoms that it can hold. By reducing the size of the box the final atom number can be changed. The large enegy splitting ensures high fidelity of the final Fock state. The final number, down to even a single atom, can be detected with a high accuracy using fluorescence detection.
2. Quantum Transport of a Bose Einstein Condensate in a periodic potential.
The main goal of this experiment was to study the effect of interactions on quantum transport in a periodic potential. The initial condition for the experiment is a Bose Einstein Condensate (BEC). The BEC is released in a 1D magnetic waveguide superposed with a periodic potential created by an optical lattice. The BEC is allowed to expand in this external potential and its rate of expansion is measured for different heights of the optical potential. We then compare this behaviour with that of thermal atoms which do not possess any mean field energy. We identify a regime of well depths where the rate of expansion is reduced due to interactions. The results of this experiment are published in Phys. Rev. Lett. 96 150401 (2006).
The image shows the expansion of thermal atoms (a) and a Bose Einstein Condensate (b). The dotted lines are theoretical density profiles based on single particle band structure calculation.
3. Bose Einstein Condensate driven by a kicked rotor while being confined in a finite box.
The goal of this experiment was to study the behaviour of a BEC confined in a quasi 1D box while it is kicked periodically with a spatially periodic potential. We first load a BEC in a finite size box created by a magnetic waveguide providing transverse confinement and two Gaussian beam of far detuned light creating the axial walls of the box. The typical length of the box is 120 μm. The kicking is done by an array of 5 Gaussian laser beam spots with a periodicity of 20 μm that fill up the box. We measure the heating rate and phase space density of the atoms as a function of number of kicks. To observe the effect of interactions it was necessary that we have along time between kicks (order of 10's of milli seconds). Due to the finite height of our box the dynamics was quickly dominated by the hot atoms leaving the box. The behaviour could thus be explained based on just this classical effect. The results of this experiment are published in Europhys. Lett. 75 392 (2006).
4. An optical lattice with realtime tunability of its periodicity
The goal of this experiment was to device a setup that can create an optical lattice whose periodicity can be changed in real time by over an order of magnitude in a very stable and robust way. The basic idea of the setup is to have two collimated laser beams that are parallel to each other and spatially seperated by some distance. These beams fall on a single focussing lens causing them to intersect at the focal point of the lens. This creates an interference pattern at the focal plane whose spacing depends on the distance between the incoming beams. We use a mechanical translation stage to change this distance which changes the periodicity of the lattice at the focal plane. The details of this setup are published in Optics Express 16 5465 (2008).
The image shows the experimental setup and CCD images of the tunable lattice. The image of the expanding fringes is created using a number of vertical strips taken at different times.