arXiv subjects

Christopher Ticknor

Publications and source records attributed to Christopher Ticknor.

27 records · Page 2Linked to original sources

arXiv2010

Anisotropic superfluidity in a dipolar Bose gas

We study the superfluid character of a dipolar Bose-Einstein condensate (DBEC) in a quasi-two dimensional (q2D) geometry. In particular, we allow for the dipole polarization to have some non-zero projection into the plane of the condensate so that the effective interaction is anisotropic in this plane, yielding an anisotropic dispersion for propagation of quasiparticles. By performing direct numerical simulations of a probe moving through the DBEC, we observe the sudden onset of drag or creation of vortex-antivortex pairs at critical velocities that depend strongly on the direction of the probe's motion. This anisotropy emerges because of the anisotropic manifestation of a roton-like mode in the system.

cond-mat.quant-gas↗

arXiv2010

Quasi-two dimensional dipolar scattering

We study two body dipolar scattering with one dimension of confinement. We include the effects of confinement by expanding this degree of freedom in harmonic oscillator states. We then study the properties of the resulting multi-channel system. We study the adiabatic curves as a function of D/l, the ratio of the dipolar and confinement length scales. There is no dipolar barrier for this system when D/l < 0.34. We also study the WKB tunneling probability as a function of D/l and scattering energy. This can be used to estimate the character of the scattering.

physics.atom-ph↗

arXiv2009

2-Dimensional Dipolar Scattering

We characterize the long range dipolar scattering in 2-dimensions. We use the analytic zero energy wavefunction including the dipolar interaction; this solution yields universal dipolar scattering properties in the threshold regime. We also study the semi-classical dipolar scattering and find universal dipolar scattering for this energy regime. For both energy regimes, we discuss the validity of the universality and give physical examples of the scattering.

physics.atom-ph↗

arXiv2007

Collisional Control of Ground State Polar Molecules and Universal Dipolar Scattering

We explore the impact of the short range interaction on the scattering of ground state polar molecules, and study the transition from a weak to strong dipolar scattering over an experimentally reasonable range of energies and electric field values. In the strong dipolar limit, the scattering scales with respect to a dimensionless quantity defined by mass, induced dipole moment, and collision energy. The scaling has implications for all quantum mechanical dipolar scattering, and therefore this universal dipolar scaling provides estimates of scattering cross sections for any dipolar system.

physics.atom-ph↗

arXiv2007

Energy Dependence of Scattering Ground State Polar Molecules

We explore the total cross section of ground state polar molecules in an electric field at various energies, focusing on RbCs and RbK. An external electric field polarizes the molecules and induces strong dipolar interactions leading to non-zero partial waves contributing to the scattering even as the collision energy goes to zero. This results in the need to compute scattering problems with many different values of total M to converge the total cross section. An accurate and efficient approximate total cross section is introduced and used to study the low field temperature dependence. To understand the scattering of the polar molecules we compare a semi-classical cross section with quantum unitarity limit. This comparison leads to the ability to characterize the scattering based on the value of the electric field and the collision energy.

physics.atom-ph↗

arXiv2005

Bose-Fermi Mixtures Near an Interspecies Feshbach Resonance: Testing a Non Equilibrium Approach

We test a non equilibrium approach to study the behavior of a Bose-Fermi mixture of alkali atoms in the presence of a Feshbach resonance between bosons and fermions. To this end we derive the Hartree-Fock-Bogoliubov (HFB) equations of motion for, the interacting system. This approach has proven very successful in the study of resonant systems composed of Bose particles and Fermi particles. However, when applied to a Bose-Fermi mixture, the HFB theory fails to identify even the correct binding energy of molecules in the appropriate limit. Through a more rigorous analysis we are able to ascribe this difference to the peculiar role that bosonic depletion plays in the Bose-Fermi pair correlation, which is the mechanism through which molecules are formed. We therefore conclude that molecular formation in Bose-Fermi mixtures is driven by three point and higher order correlations in the gas, unlike any other resonant system studied in the context of ultra-cold atomic physics.

cond-mat.stat-mech↗

arXiv2005

Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H$_{2}$CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of the H$_{2}$CO molecule. We have decelerated a molecular beam of H$_{2}$CO essentially to rest, producing cold molecule packets at a temperature of 100 mK with a few million molecules in the packet at a density of $\sim10^{6}$ cm$^{-3}$.

physics.atom-ph↗

arXiv2005

Long range scattering resonances in strong-field seeking states of polar molecules

We present first steps toward understanding the ultracold scattering properties of polar molecules in strong electric field-seeking states. We have found that the elastic cross section displays a quasi-regular set of potential resonances as a function of the electric field, which potentially offers intimate details about the inter-molecular interaction. We illustrate these resonances in a ``toy'' model composed of pure dipoles, and in more physically realistic systems. To analyze these resonances, we use a simple WKB approximation to the eigenphase, which proves both reasonably accurate and meaningful. A general treatment of the Stark effect and dipolar interactions is also presented.

physics.atom-ph↗

arXiv2004

Influence of magnetic fields on cold collisions of polar molecules

We consider cold collisions of OH molecules in the $^2Π_{3/2}$ grounds state, under the influnce of a magnetic field. We find that modest fields of several thousand gauss can act to suppress inelastic collisions of weak-field seeking states by two orders of magnitude. We attribute this suppression to two factors: (i) An indirect coupling of the entrance and the exit channel, in contrast to the effect of an applied electric field; and (ii) the realtive motion of the entrance and exit scattering thresholds. In view of these results, magnetic trapping of OH may prove feasible.

physics.atom-ph↗