1,002 research outputs found
Metastable Quantum Phase Transitions in a One-Dimensional Bose Gas
This is a chapter for a book. The first paragraph of this chapter is as
follows: "Ultracold quantum gases offer a wonderful playground for quantum many
body physics, as experimental systems are widely controllable, both statically
and dynamically. One such system is the one-dimensional (1D) Bose gas on a
ring. In this system binary contact interactions between the constituent
bosonic atoms, usually alkali metals, can be controlled in both sign and
magnitude; a recent experiment has tuned interactions over seven orders of
magnitude, using an atom-molecule resonance called a Feshbach resonance. Thus
one can directly realize the Lieb-Liniger Hamiltonian, from the weakly- to the
strongly-interacting regime. At the same time there are a number of experiments
utilizing ring traps. The ring geometry affords us the opportunity to study
topological properties of this system as well; one of the main properties of a
superfluid is the quantized circulation in which the average angular momentum
per particle, L/N, is quantized under rotation. Thus we focus on a tunable 1D
Bose system for which the main control parameters are interaction and rotation.
We will show that there is a critical boundary in the interaction-rotation
control-parameter plane over which the topological properties of the system
change. This is the basis of our concept of \textit{metastable quantum phase
transitions} (QPTs). Moreover, we will show that the finite domain of the ring
is necessary for the QPT to occur at all because the zero-point kinetic
pressure can induce QPTs, i.e., the system must be finite; we thus seek to
generalize the concept of QPTs to inherently finite, mesoscopic or nanoscopic
systems."Comment: 29 pages, 12 figures, book will appear later this year; v2 is in
improved format and includes small corrections for final versio
Superpositions in Atomic Quantum Rings
Ultracold atoms are trapped circumferentially on a ring that is pierced at
its center by a flux tube arising from a light-induced gauge potential due to
applied Laguerre-Gaussian fields. We show that by using optical coherent state
superpositions to produce light-induced gauge potentials, we can create a
situation in which the trapped atoms are simultaneously exposed to two distinct
flux tubes, thereby creating superpositions in atomic quantum rings. We
consider the examples of both a ring geometry and harmonic trapping, and in
both cases the ground state of the quantum system is shown to be a
superposition of counter-rotating states of the atom trapped on the two
distinct flux tubes.Comment: 11 pages, 6 figure
Topological Winding and Unwinding in Metastable Bose-Einstein Condensates
Topological winding and unwinding in a quasi-one-dimensional metastable
Bose-Einstein condensate are shown to be manipulated by changing the strength
of interaction or the frequency of rotation. Exact diagonalization analysis
reveals that quasidegenerate states emerge spontaneously near the transition
point, allowing a smooth crossover between topologically distinct states. On a
mean-field level, the transition is accompanied by formation of grey solitons,
or density notches, which serve as an experimental signature of this
phenomenon.Comment: 4 pages, 3 figure
Symmetry Breaking in Bose-Einstein Condensates
A gaseous Bose-Einstein condensate (BEC) offers an ideal testing ground for
studying symmetry breaking, because a trapped BEC system is in a mesoscopic
regime, and situations exist under which symmetry breaking may or may not
occur. Investigating this problem can explain why mean-field theories have been
so successful in elucidating gaseous BEC systems and when many-body effects
play a significant role. We substantiate these ideas in four distinct
situations: namely, soliton formation in attractive BECs, vortex nucleation in
rotating BECs, spontaneous magnetization in spinor BECs, and spin texture
formation in dipolar BECs.Comment: Submitted to the proceedings of International Conference on Atomic
Physics 200
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