We report the fabrication, characterization, and use of rubidium vapor dispensers based on highly oriented pyrolytic graphite (HOPG) intercalated with metallic rubidium. Compared to commercial chromate salt dispensers, these intercalated HOPG (IHOPG) dispensers hold an order of magnitude more rubidium in a similar volume, require less than one-fourth the heating power, and emit less than one-half as many impurities. Appropriate processing permits exposure of the IHOPG to atmosphere for over ninety minutes without any adverse effects. Intercalation of cesium, potassium, and lithium into HOPG has also been demonstrated in the literature, which suggests that IHOPG dispensers may also be made for those metals.

We present a method for generating precise magnetic potentials that can be described by a polynomial series along the axis of a cold atom waveguide near the surface of an atom chip. With a single chip design consisting of several wire pairs, various axial potentials can be created by varying the ratio of the currents in the wires, including double wells, triple wells, and pure harmonic traps with suppression of higher order terms. We use this method to design and fabricate a chip with modest experimental requirements. Finally, we use the chip to demonstrate a double well potential.

We demonstrate a two-dimensional (2D) grating magneto-optical trap (GMOT) with a single input cooling laser beam and a planar diffraction grating using 87Rb. This configuration increases experimental access when compared with a traditional 2D magneto-optical trap (MOT). As described in the paper, the output flux is several hundred million rubidium atoms/s at a mean velocity of 16.5(9) m/s and a velocity distribution of 4(3) m/s standard deviation. We use the atomic beam from the 2D GMOT to demonstrate loading of a three-dimensional (3D) GMOT with 2.46(7) x 10(8) atoms. Methods to improve output flux are discussed.

Received 2 October 2017DOI:https://doi.org/10.1103/PhysRevA.96.049902©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtom interferometryAtom lasersAtom opticsBose-Einstein condensatesCold atoms & matter wavesCooling & trappingAtomic, Molecular & Optical

Ex vacuo atom chips, used in conjunction with a custom thin walled vacuum chamber, have enabled the rapid replacement of atom chips for magnetically trapped cold atom experiments. Atoms were trapped in >2 kHz magnetic traps created using high power atom chips. A thin walled vacuum chamber allowed the atoms to be trapped ≲1 mm from the atom chip conductors which were located outside of the vacuum system. Placing the atom chip outside of the vacuum simplified the electrical connections and improved the thermal management. Using a multi-lead Z-wire chip design, a Bose-Einstein condensate was produced with an external atom chip. Vacuum and optical conditions were maintained while replacing the Z-wire chip with an atom chip with a cross-wire design. The atom chips were exchanged and an initial magnetic trap was achieved in less than 3 h.

We calculate the sensitivity to changes in temperature and current for a resonant atom interferometer device based on oscillations of a cold, magnetically trapped cloud in a two wire harmonic trap. The sensitivity of the trap frequency and area enclosed are estimated for typical trap parame- ters. Based on this analysis, the frequency and area enclosed are both more sensitive to the stability of the current creating the magnetic eld than the thermal expansion of the substrate. Current experimental progress measuring the frequency stability of current atom chip devices is outlined.

We study steady-state evaporation in an atom guide via Monte Carlo simulations. The evaporation surface follows a specific profile as a function of longitudinal guide location. We demonstrate that the choice of evaporation profile significantly impacts the performance of the evaporation. Our simulations also demonstrate a significant performance boost in the evaporation when using a longitudinally compressed guide. We show that for a purely pressure-driven atom beam, it should be possible to reach degeneracy within a 0.5 m guide for experimentally feasible, albeit challenging, loading conditions.

We have observed time-varying spin relaxation of trapped cold atoms due to photon scattering in blue-detuned, crossed, hollow Laguerre-Gaussian beams. These beams are formed by imparting an azimuthal phase of l phi to a Gaussian beam, where l is an integer, and have an intensity distribution that scales with r(2l) to the lowest order. For all degrees of anharmonicity, we observe a time-varying spin-relaxation rate due to energy-dependent photon scattering. For l = 8, we directly measure temperature-dependent scattering rates and show that by removing the most energetic atoms from the trap, a more purely spin-polarized sample remains. The results agree well with Monte Carlo simulations, and we present a simple functional form for the spin-relaxation curves.

Parallel code presents a non-trivial problem of load balancing computational workload throughout a system of hardware and software resources. The task of load balancing is further complicated when the number of allowable processors changes through time. This paper presents a two-component load-balancing mechanism using optimal initial workload distribution and dynamic load maintenance. The initial guess is provided by inversion of the workload distribution function. Workload distribution inversion enables efficient domain decomposition for arbitrary workloads and easily compensates for changes in system resources. Dynamic load balancing is provided by process feedback control as used, for example, in control mechanisms of physical processes. Proportional, integral, and differential (PID) feedback readily allows controls to compensate for runtime-changes of the workload distribution function. This paper demonstrates a one-dimensional realization of the ideas presented here. We apply this load-balancing technique to our gridless direct simulation Monte Carlo algorithm. We demonstrate that the method does indeed maintain uniform workload distribution across available resources as the workload and usable system resources undergo change through time.

This work concerns the development of a gridless method for modeling the inter-particle collisions of a gas. Conventional fixed-grid algorithms are susceptible to grid-mismatch to the physical system, resulting in erroneous solutions. On the contrary, a gridless algorithm can be used to simulate various physical systems without the need to perform grid-mesh optimization. An octree algorithm provides the gridless character to a direct simulation Monte Carlo (DSMC) code by automatically sorting nearest-neighbor gas particles into local clusters. Automatic clustering allows abstraction of the DSMC algorithm from the physical system of the problem in question. This abstraction provides flexibility for domains with complex geometries as well as a decreased code development time for a given physical problem. To evaluate the practicality of this code, the time required to perform the gridless overhead from the octree sort is investigated. This investigation shows that the gridless method can indeed be practical and compete with other DSMC codes. To validate gridless DSMC, results of several benchmark simulations are compared to results from a fixed-grid code. The benchmark simulations include several Couette flows of differing Knudsen number, low-velocity flow past a thin plate, and two hypersonic flows past embedded objects at a Mach number of 10. The results of this comparison to traditional DSMC are favorable. This work is intended to become part of a larger gridless simulation tool for collisional plasmas. Corresponding work includes a gridless field solver using an octree for the evaluation of long range electrostatic forces. We plan to merge the two methods creating a gridless framework for simulating collisional-plasmas.

We observe velocity-selective two-photon resonances in a cold atom cloud in the presence of a magnetic field. We use these resonances to demonstrate a simple magnetometer with sub-mG resolution. The technique is particularly useful for zeroing the magnetic field and does not require any additional laser frequencies than are already used for standard magneto-optical traps. We verify the effects using Faraday rotation spectroscopy.

We explore a cooling mechanism that results from a two-photon Raman process resonant with a particular velocity class of atoms. We have seen evidence for cooling with both red and blue detuned light.