Session B6: Quantum Simulation and Quantum Information Theory in Cold Atoms

Cold atoms in 1D

Ultracold atoms in optical lattices present a wealth of phenomena in one-dimensional geometries. In this talk, I will focus on specifically one-dimensional phenomena such as spin-charge separation in fermionic systems and the bosonic counterpart, as well as models of collective magnetism realized in ultracold atom systems. Special emphasis will be given to the observation of coherent quantum dynamics far from equilibrium which we can now simulate using the time-dependent density-matrix renormalization group method, in order to use cold atoms to address questions of relaxation to steady states in interacting quantum systems.   

Probing Phase Transitions in Cold Atoms

In this talk I will describe various interferometric probes, which can be used to study correlation functions of low-dimensional cold atom systems. These probes allow one to analyze both properties of phases with long or quasi-long range order and phase transitions. I will suggest the way of detecting fermionic superfluidity and the symmetry of the pairing gap. I will also discuss connections between interferometry in 1D bosonic systems with partition functions of some condensed matter models and with extreme value statistics. Finally I will describe the shot noise and argue how one can suppress it both for bosons and fermions using optical lattices.   

Quantum Control with Ultracold Atoms

Ultracold atoms have long been considered as a platform for quantum information processing. Of critical importance is the ability to coherently control both internal degrees of freedom such as spin and also interactions between atoms that depend on ``external'' motional degrees of freedom. In this talk I will review a variety of advances, including the ability to perform qudit operations such as state preparation and unitary gates, quantum-state reconstruction via continuous measurement, and cooling of atomic motion without decohering spin qubits. Two different platforms will be presented -- alkali atoms transported in a lattice with microwave-induced spin-flips, and alkaline-earth atoms in which quantum information is stored in nuclear spins. Microwave-induced spin flips provide a robust mechanism for inducing cold collisions between atoms that can form the basis of a quantum logic gate. As an alternative, cold alkaline-earth atoms are attractive since the ground state is a closed shell, with zero electron angular momentum. The nuclear spin is thus decoupled from the system and can acts as robust decoherence-free qubit.   

Imaging single atoms in a three dimensional array

We have demonstrated trapping and imaging of 250 single atoms in a 3D optical lattice. The 5 micron lattice spacing is large enough that individual atoms can be addressed using lasers and microwaves in a way that does not affect the quantum coherence of other atoms. Our goal is to use these trapped atoms as qubits. So far, we fill a random half of the lattice sites, but a combination of site-selective state changes and state-selective lattice translations should allow us to verifiably fill all vacancies. We will describe our experiments to date and our plans for entangling atoms and implementing a neutral atom quantum computer. Our lattice can readily be scaled to include thousands of trapped atoms. This work was performed in collaboration with Karl Nelson and Xiao Li.   

Atomtronics

We explore the analogy between ultracold atoms in optical lattices and electrons in crystal lattices. Of particular interest is atomtronics, where the analogy is extended to include electrical circuits and doped semiconductor materials. Lattice ``defects'' achieve behaviors similar to P-type and N-type semiconductor materials. Naturally the interest is to adjoin P-type and N-type atoms lattices to produce an atom diode, and then an NPN or PNP lattice ``sandwich" to achieve bipolar transistor-like behavior for ultracold atoms.