Quantum Optics Laboratory

Abstract: 

We theoretically study the quantum impurities immersed in atomic Fermi gases. 

First, we propose an ultracold atom setup, analogous to a spintronics device, to study non-equilibrium spin transport and statistics of fluctuations. This setup is a system of quantum impurities immersed into a two-component fermion gas with two antiparallel pseudospin species, which can be realized with currently available experiments on ultracold LiK mixtures. Manipulating quantum impurities controls spin transport between two species, which gives rise to non-equilibrium spin accumulation of atoms. Because ultracold systems preclude decoherence from extrinsic degrees of freedom, the nonequilibrium spin population can be measured even when the pumping is turned off. In contrast, in solid state-systems decoherence brings the accumulated spin population back to equilibrium. Repeating experiments allows one to investigate the full counting statistics in various regimes. Moreover, performing the Ramsey interferometry allows one to reach the dynamical response for full times, which exhibits a non-trivial exponential decay. This is different from the standard power-law decay of Anderson’s orthogonality catastrophe in the case of single host fermion. We also offer analytical expressions for the impurity response for long time dynamics. 

Furthermore, we can apply designed pulses to the impurity potential to create single particle excitations on top of one Fermi sea. Such excitations are called as levitons. In our protocol, one can obtain a source of clean single-particle transmission between two Fermi seas. The noise and the counting statistics of spin transport should be of single particle character.  Our study paves a way for controlling and harnessing fermionic many-body states in atomtronics.