2009 Cs Experiment


Tunable Atomic and Molecular Quantum Gases in Optical Lattices

2009 - In situ Observation of incompressible Mott-insulating domains in ultracold atomic gases

 N. Gemelke, X. Zhang, C.-L. Hung, C. Chin Nature 460, 995 (2009)


Near absolute zero temperature, quantum fluctuations can drive a phase transition in the many-body ground state of the system. A prominent example of such a quantum phase transition is the change from a superfluid (SF) to a Mott-insulating (MI) phase in a system of repulsively interacting bosons in a lattice potential.


Competing orders in the quantum many-body ground state: 


Superfluid at low lattice depth: delocalized atomic wavefunction (Kinetic energy dominates)

Mott Insulator at high lattice depth: integer number of atoms per site (Interaction energy dominates)

In this paper, we prepare a sample of N=7500 BEC atoms at scattering length a=310a0. When the lattice depth is gradually ramped up, we observe the following regimes:
A: Superfluid
B: Phase transition regime
C: Mott insulator
Density plateau identify the emergence of a Mott-insulting domain


How to realize it?


We use a pair of laser beams to form a deep vertical lattice potential and freeze the atomic motion in the vertical direction into the harmonic ground state of one single lattice site, making the sample effectively two-dimensional. Then we use two pairs of laser beams to form standing waves in the horizontal plane which create a two dimensional suqare lattice potential. By increasing the depth of this square lattice potential beyond a critical value, we induce the superfluid to Mott insulator transition. We then use absorption imaging and high resolution microscope objective to probe the in situ atomic density.


More fun images...


The apparatus: