We have observed Fermi polarons in a highly imbalanced mixture of fermionic
atoms using tomographic RF spectroscopy. Feshbach resonances allow to freely
tune the interactions between the two spin states involved. A single spin
down atom immersed in a Fermi sea of spin up atoms can do one of two things:
For strong attraction, it can form a molecule with exactly one spin up
partner, but for weaker interaction it will spread its attraction and
surround itself with a collection of majority atoms. This spin down atom
"dressed" with a spin up cloud constitutes the Fermi polaron. We
have observed a striking spectroscopic signature of this quasi-particle for
various interaction strengths, which allows us to directly measure the
polaron energy and infer the quasi-particle residue Z.
The polarons are weakly interacting, and can thus be identified with the
quasi-particles of Landau's Fermi liquid theory.
At a critical interaction strength, we observe a transition from
polarons to molecules. At this point the Fermi liquid of polarons undergoes
a phase transition into a superfluid Bose liquid.
10 Minute Talk: Photonic Phase Gate via an Exchange of Fermionic Spin Waves in a Spin Chain
We propose a new protocol for implementing the two-qubit photonic phase gate. In our approach, the pi phase is acquired by mapping two single photons into atomic excitations with fermionic character and exchanging their positions. The fermionic excitations are realized as spin waves in a spin chain, while photon storage techniques provide the interface between the photons and the spin waves. Possible imperfections and experimental systems suitable for implementing the gate are discussed. Reference: arXiv:1001.0968.