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E 5

A Tunable Optical Kagome Lattice

B171 Birge - (510) 643-0543

Overview and Motivation

In a material system, electronic and optical properties arise due to the organization of the atoms in a crystal lattice structure. In E5 we artificially create a crystal lattice structure using interfering laser light. We then expose a Bose-Einstein Condensate to this periodic potential, and watch as the BEC behaves in ways similar to electrons in a solid crystal. This is a tunable and defect-free means of exploring how physical properties arise from crystal lattice structure.

We study a two-dimensional tunable optical superlattice with Rb-87 atoms. Our lattice can take on a variety of potential geometries, but the most significant is the kagome structure. This lattice geometry gives rise interesting electronic and magnetic properties, but materials with this structure are very difficult to study in the solid state. Materials with this structure have been studied extensively in solid-state physics, but kagome magnets suffer from disorder that complicates the interpretation of experimental results. Our cold atom lattice provides new opportunities to explore the properties of this interesting lattice geometry in a highly controlled environment.

The kagome lattice has three sites per unit cell. We create this optical potential landscape by overlaying two commensurate lattices: an attractive 532 nm triangular lattice and a repulsive 1064 nm triangular lattice. We then load a BEC of Rb-87 atoms into the structure that we have created. We can then dynamically control the relative phase of the lattices, leading to a variety of accessible lattice geometries.

Current Work

The second excited energy band of the kagome lattice, which is dispersionless and highly degenerate, may support various exotic many-body quantum states in the cold atom system. We have explored two experimental approaches of populating atoms in higher bands of the kagome superlattice. In the first, we prepare the atoms in a lattice where all atoms occupy a single site within a unit cell, and then dynamically change the geometry so that the occupied site corresponds to a higher energy level within the s-orbital. The populated atoms in higher orbitals can be selectively resolved in band mapping. In the second approach, we modulate the phases of the lattice beams to invert the tunneling energy and thus the band structure.

Previous Work

Spin texture dynamics in a BEC

Ultracold atomic and molecular systems offer a high-fidelity physical realization of many-body quantum Hamiltonians which exhibit a rich array of interesting physics. One can study these atomic or molecular systems far from equilibrium and undergoing long-term coherent dynamics, in contrast with other condensed matter systems whose characteristic timescales are far shorter. This poster describes present activities by our group focused on developing novel tools toward studying quantum magnetism.

Quantum Quench of a Spinor Condensate

In E5 we developed an in-situ probe of the vector magnetization profile of an optically-trapped spinor condensate with spatial and temporal resolution. We have studied spontaneously modulated spin textures, symmetry breaking, a quantum phase transition, and the dipolar interactions in this magnetic superfluid. Long-term goals of this work are to advance the understanding of quantum phase transitions, and the role of dipolar interactions, and ultimately move onto studying spinors in optical lattices.

Experimental setup

Our team is exploring a novel magnetic quantum gas - the degenerate spinor Bose-Einstein condensate - in which the phenomena of quantum magnetism and superfluidity are intertwined. A spinor condensate is one which possesses a spin degree of freedom with full rotational symmetry. We use an optically trapped gas of atoms in the F=1 hyperfine level of ^{87}Rb. A far-detuned optical trap provides equal confinement for the three spin states. When a condensate is formed from atoms distributed among the various spin states, the result is three separate but coupled condensates, or equivalently a single multicomponent "spinor" condensate. The new vacuum chamber replaced the old E1 setup in January 2009 and first BECs in the optical trap were achieved in April 2009.

Schematic of cooling elements. Ultimately atoms are transported into the glass cell detailed in (b)

Thermal Equilibrium Spin Texture in a degenerate spinor BEC

Magnetic phases of Rb F=1 spinor gases can be studied for different quadratic zeeman shift. For this, thermal spin mixtures are slowly cooled down to T_c in the presence of a microwave dressing m_F=0 atomic state.

(Preliminary data)Spin Mixing in time-of-flight absorption imaging
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