John Corson

Bose Polarons in the Strongly Interacting Regime

When an impurity is immersed in a Bose-Einstein condensate, impurity-boson interactions are expected to dress the impurity into a quasiparticle, the Bose polaron. We superimpose an ultracold atomic gas of ^{87}Rb with a much lower density gas of fermionic ^{40}K impurities. Through the use of a Feshbach resonance and radio-frequency spectroscopy, we characterize the energy, spectral width, and lifetime of the resultant polaron on both the attractive and the repulsive branches in the strongly interacting regime. The width of the polaron in the attractive branch is narrow compared to its binding energy, even as the two-body scattering length diverges.

Quenching to unitarity: Quantum dynamics in a three-dimensional Bose gas

We study the dynamics of a dilute Bose gas at zero temperature following a sudden quench of the scattering length from a noninteracting Bose condensate to unitarity (infinite scattering length). We apply three complementary approaches to understand the momentum distribution and loss rates. First, using a time-dependent variational ansatz for the many-body state, we calculate the dynamics of the momentum distribution. Second, we demonstrate that, at short times and large momenta compared to those set by the density, the physics can be well understood within a simple, analytic two-body model. We derive a quantitative prediction for the evolution of Tans contact, which increases linearly at short times. We also study the three-body losses at finite densities. Consistent with experiments, we observe lifetimes which are long compared to the dynamics of large momentum modes.

Bound-state signatures in quenched Bose-Einstein condensates

We investigate the dynamics of a homogenous Bose-Einstein condensate (BEC) following a sudden quench of the scattering length. Our focus is the time evolution of short-range correlations via the dynamical contact. We compute the dynamics using a combination of two- and many-body models, and we propose an intuitive connection between them that unifies their short-time, short-range predictions. Our two-body models are exactly solvable and, when properly calibrated, lead to analytic formulae for the contact dynamics. Immediately after the quench, the contact exhibits strong oscillations at the frequency of the two-body bound state. These oscillations are large in amplitude, and their time average is typically much larger than the unregularized Bogoliubov prediction. The condensate fraction shows similar oscillations, whose amplitude we are able to estimate. These results demonstrate the importance of including the bound state in descriptions of diabatically-quenched BEC experiments.

Ballistic quench-induced correlation waves in ultracold gases

We investigate the wave-packet dynamics of a pair of particles that undergoes a rapid change of scattering length. The short-range interactions are modeled in the zero-range limit, where the quench is accomplished by switching the boundary condition of the wave function at vanishing particle separation. This generates a correlation wave that propagates rapidly to nonzero particle separations. We have derived universal, analytic results for this process that lead to a simple phase-space picture of the quench-induced scattering. Intuitively, the strength of the correlation wave relates to the initial contact of the system. We find that, in one spatial dimension, the

Classical connection between near-field interactions and far-field radiation and the relevance to quantum photoemission

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Geometric stability spectra of dipolar Bose gases in tunable optical lattices

tail of the momentum distribution contains a ballistic contribution that does not originate from short-range pair correlations, and a similar conclusion can hold in other dimensionalities depending on the quench protocol. We examine the resultant quench-induced transport in an optical lattice in one dimension, and a semiclassical treatment is found to give quantitatively accurate estimates for the transport probabilities.

Stability spectroscopy of rotons in a dipolar Bose gas

Interference in the far-field radiation pattern emitted from a classical current distribution implies near-field work between different spatial portions of the distribution. We examine this relationship and the essential role of system geometry for the case of two oscillating dipoles and for a Gaussian current distribution. This analysis offers a compelling argument as to why the radiation from a large single-electron quantum wave packet should not exhibit the same destructive interference as that associated with a comparable classical charge density. Our discussion draws attention to the ad hoc heuristics motivating the original derivation of a quantum electrons radiation profile.

Scattering of a Strong Laser Field by an Electron Wave Packet

We examine the stability of quasi-two-dimensional dipolar Bose-Einstein condensates in the presence of weak optical lattices of various geometries. We find that when the condensate possesses a roton-maxon quasiparticle dispersion,theconditionsforstabilityexhibitastrongdependencebothonthelatticegeometryandthepolarization tilt. This results in rich structures in the system’s stability diagram akin to spectroscopic signatures. We show how these structures originate from the mode matching of rotons to the perturbing lattice. In the case of a one-dimensional lattice, some of the features emerge only when the polarization axis is tilted into the plane of the condensate. Our results suggest that the stability diagram may be used as a novel means to spectroscopically measure rotons in dipolar condensates.

Radiation Scattering by Localized Electron Wave Packets

JQI, NIST and Department of Physics, University of Maryland, Gaithersburg, Maryland 20899-8410, USA(Dated: January 11, 2013)We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate (dBEC) thatis perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate thatsystems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equalseither half the roton wavelength or a low roton subharmonic. We apply perturbation theory tothe Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the mechanisms behind theinstability threshhold. The features of our stability diagram may be used as a direct measurementof the roton wavelength for quasi-one-dimensional geometries.

Nodal Quasiparticle Lifetime in the Superconducting State of BSCCO(2212)

Quantum electrodynamics indicates that an electron scatters light independent of its wave-packet size, even when larger than the stimulating wavelength. We highlight this theoretical conclusion and give a progress report on experimental validation.