Optical Science Laboratory
Recently, atomic gases trapped in a vacuum chamber can be cooled down
to several nano-Kelvins regime, where the quantum effects govern physical
properties of the system. The high controllability of atoms provides us
with sophisticated tools for measuring the quantum phenomena. Thus, this
system can be regarded as a quantum simulator [1], which attracts much
interest of many researchers in various fields, such as condensed matter
physics, elementary particle physics, quantum chemistry, and so on. In
particular, the atoms trapped in an optical lattice, which is the artificially
created periodic potential by laser interference, are expected to make
great progress in condensed matter physics, because such fermionic atoms
mimic electrons in a metallic crystal [2]. We can explore the pure quantum
many-body effects by using this system without any lattice distortions
and impurities. Interestingly, this controllable system allows us to expand
the current knowledge in the electron systems.
Collaborating with the group at Kyoto University, we investigated the
Bose-Fermi mixtures trapped in an optical lattice both theoretically and
experimentally, and clarified appearance of novel quantum phases not observed
in condensed matters [3]. Here, we introduce a part of our results on the
attractively interacting Bose-Fermi mixtures. Kyoto University group measured
the pair occupancies with photo-association spectroscopy by changing the
number of fermionic atoms. We developed the numerical method for analyzing
this system and applied it to the experiments. We show our results in Fig.
1(a) and (b), and briefly explain the proceeding of the measurements in
Fig. 1(c). Our calculations show good quantitative agreements with experiments.
We further analyzed the quantities that are difficult to be directly measured
by the current experimental techniques. Based on these results, we clarified
that the nonmonotonic behavior of Bose-Bose pair occupancy seen in Fig.
1(b) results from the crossover among novel quantum phases. We also investigated
the repulsively interacting system and found a different type of crossover.
[1] I. Bloch, Nature Phys. 1 (2005) 23.
[2] M. Greiner and S. Fölling, Nature 453 (2008) 736.
[3] S. Sugawa, K. Inaba et al., Nature Phys. 7 (2011) 642.
 |
||
|