Brian E. Granger

Python: An Ecosystem for Scientific Computing

As the relationship between research and computing evolves, new tools are required to not only treat numerical problems, but also to solve various problems that involve large datasets in different formats, new algorithms, and computational systems such as databases and Internet servers. Python can help develop these computational research tools by providing a balance of clarity and flexibility without sacrificing performance.

Jupyter Notebooks—a publishing format for reproducible computational workflows

It is increasingly necessary for researchers in all fields to write computer code, and in order to reproduce research results, it is important that this code is published. We present Jupyter notebooks, a document format for publishing code, results and explanations in a form that is both readable and executable. We discuss various tools and use cases for notebook documents.

Tuning the Interactions of Spin-Polarized Fermions Using Quasi-One-Dimensional Confinement

We develop a multichannel scattering theory for atom-atom collisions in quasi-1D geometries. We apply our general framework to the low energy scattering of two spin-polarized fermions and show that tightly confined fermions have infinitely strong interactions at a particular value of the 3D, free-space p-wave scattering volume. Moreover, we describe a mapping of this strongly interacting system of two quasi-1D fermions to a weakly interacting system of two 1D bosons.

GPULib: GPU Computing in High-Level Languages

GPULib helps scientists and engineers take advantage of GPUs from within high-level programming environments without requiring any detailed knowledge of the GPU architecture.

Quasi-One-Dimensional Bose Gases with a Large Scattering Length

Bose gases confined in highly elongated harmonic traps are investigated over a wide range of interaction strengths using quantum Monte Carlo techniques. We find that the properties of a Bose gas under tight transverse confinement are well reproduced by a 1D model Hamiltonian with contact interactions. We point out the existence of a unitary regime, where the properties of the quasi-1D Bose gas become independent of the actual value of the 3D scattering length a(3D). In this unitary regime, the energy of the system is well described by a hard-rod equation of state. We investigate the stability of quasi-1D Bose gases with positive and negative a(3D).

Feshbach resonance cooling of trapped atom pairs

Spectroscopic studies of few-body systems at ultracold temperatures provide valuable information that often cannot be extracted in a hot environment. Considering a pair of atoms, we propose a cooling mechanism that makes use of a scattering Feshbach resonance. Application of a series of time-dependent magnetic field ramps results in either zero, one, or two atoms remaining trapped. If two atoms remain in the trap after the field ramps are completed, then they have been cooled. Application of the proposed cooling mechanism to optical traps or lattices is considered.

Exponentially decaying correlations in a gas of strongly interacting spin-polarized 1D fermions with zero-range interactions.

We consider the single-particle correlations and momentum distributions in a gas of strongly interacting, spinless 1D fermions with zero-range interactions. This system represents a fermionic version of the Tonks-Girardeau gas of impenetrable bosons as it can be mapped to a system of noninteracting 1D bosons. We use this duality to show that the T = 0, single-particle correlations exhibit an exponential decay with distance. This strongly interacting system is experimentally accessible using ultracold atoms and has a Lorentzian momentum distribution at large momenta whose width is given by the linear density.

Nonclassical Paths in the Recurrence Spectrum of Diamagnetic Atoms

Using time-independent scattering matrices, we study how the effects of nonclassical paths on the recurrence spectra of diamagnetic atoms can be extracted from purely quantal calculations. This study reveals an intimate relationship between two types of nonclassical paths: exotic ghost orbits and diffractive orbits. This relationship proves to be a previously unrecognized reason for the success of semiclassical theories, such as closed-orbit theory, and permits a comprehensive reformulation of the semiclassical theory that elucidates its convergence properties.

Bands of Image States in Nanowire Lattices and Infrared‐Control of Proteins on Nanotube Ropes

Abstract We show that suspended arrarys of parallel nanowires support bound electron image states with rich band structures. These states could be controlled by electric and magnetic fields and used in building of waveguides, mirrors, and storage places for Rydberg‐like electrons. We also exploit the possibility of controlling proteins attached to hybrid nanotube ropes. Near infrared excitation of such ropes causes their depolarization, leading to the change of proteins conformation.

Tubular Image States and Light‐Driven Molecular Switches

We introduce new tubular image states (TIS) that can be formed around linear conductors and dielectrics, like metallic carbon nanotubes. These Rydberg‐like molecular states have a very large extent and possess peculiar physical properties. We also present a two‐step light‐driven enantiomeric switch, which within 100 ns can turn a mixture of left and right chiral molecules into a pure enantiomeric form. Molecular switches with more quasi‐stable states can be used as dynamic memories or motors.