1,324 research outputs found
Critical temperature of trapped interacting bosons from large-N based theories
Ultracold atoms provide clues to an important many-body problem regarding the
dependence of Bose-Einstein condensation (BEC) transition temperature on
interactions. However, cold atoms are trapped in harmonic potentials and
theoretical evaluations of the shift of trapped interacting Bose gases
are challenging. While previous predictions of the leading-order shift have
been confirmed, more recent experiments exhibit higher-order corrections beyond
available mean-field theories. By implementing two large-N based theories with
the local density approximation (LDA), we extract next-order corrections of the
shift. The leading-order large-N theory produces results quantitatively
different from the latest experimental data. The leading-order auxiliary field
(LOAF) theory containing both normal and anomalous density fields captures the
shift accurately in the weak interaction regime. However, the LOAF theory
shows incompatible behavior with the LDA and forcing the LDA leads to density
discontinuities in the trap profiles. We present a phenomenological model based
on the LOAF theory, which repairs the incompatibility and provides a prediction
of the shift in stronger interaction regime.Comment: 11 pages, 3 figure
Site-wise manipulations and Mott insulator-superfluid transition of interacting photons using superconducting circuit simulators
The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a
paradigm in many-body physics, and it exhibits a Mott insulator (MI)-superfluid
(SF) transition at integer filling. Here a quantum simulator of the BHM using a
superconducting circuit is proposed. Specifically, a superconducting
transmission line resonator supporting microwave photons is coupled to a charge
qubit to form one site of the BHM, and adjacent sites are connected by a
tunable coupler. To obtain a mapping from the superconducting circuit to the
BHM, we focus on the dispersive regime where the excitations remain
photon-like. Standard perturbation theory is implemented to locate the
parameter range where the MI-SF transition may be simulated. This simulator
allows single-site manipulations and we illustrate this feature by considering
two scenarios where a single-site manipulation can drive a MI-SF transition.
The transition can be analyzed by mean-field analyses, and the exact
diagonalization was implemented to provide accurate results. The variance of
the photon density and the fidelity metric clearly show signatures of the
transition. Experimental realizations and other possible applications of this
simulator are also discussed.Comment: 13 pages, 9 figure
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