SearcharxivSearch

arXiv subjects

C. S. Chisholm

Publications and source records attributed to C. S. Chisholm.

4 recordsLinked to original sources

Probing supersolidity through excitations in a spin-orbit-coupled Bose-Einstein condensate

Spin-orbit-coupled Bose-Einstein condensates are a flexible experimental platform to engineer synthetic quantum many-body systems. In particular, they host the so-called stripe phase, an instance of a supersolid state of matter. The peculiar excitation spectrum of the stripe phase, a definite footprint of its supersolidity, has been difficult to measure experimentally. Here, we perform in situ imaging of the stripes and directly observe both superfluid and crystal excitations. We investigate superfluid hydrodynamics and reveal a stripe compression mode, thus demonstrating that the system possesses a compressible crystalline structure. Through the frequency softening of this mode, we locate the supersolid transition point. Our results establish spin-orbit-coupled supersolids as ideal systems to investigate supersolidity and its rich dynamics.

cond-mat.quant-gas

Deuterium-Tritium Levitated Dipole Fusion Power Plants

Levitated dipole reactors offer an attractive path towards economic fusion power generation. The intrinsic decoupling of the confining magnetic field-generating REBCO magnets and the vacuum vessel offer unparalleled accessibility and maintainability, allowing for high plant duty factors and theoretically low electricity prices. In order to achieve rapid deployment of fusion power to the grid, the use of the Deuterium-Tritium (DT) fuel cycle is required due to its lower required plasma triple products. Historically, designs of levitated dipole fusion power plants have targeted advanced fuels as a DT device was seen to be infeasible due to the high fluxes of 14.1 MeV neutrons on the superconducting core magnet. This study presents high level designs for two feasible first-of-a-kind (FOAK) DT levitated dipole fusion power plants, the larger of which produces 667 MW of fusion power and is predicted to produce 208 MW of net electric power. Both designs consist of a heavily neutron-shielded, high-field REBCO core magnet capable of producing peak magnetic field strengths of 23 T while keeping peak mechanical strains below 0.4%. The neutron shielding is comprised of a layered structure of tungsten and boron carbide, which allows for 92% of the heat deposited in the neutron shield to be radiated out to the first wall while still providing sufficient neutron attenuation to give adequate REBCO conductor lifetimes. The core magnet REBCO coil is comprised of a small "sacrificial" section and a larger semi-permanent section. The sacrificial section, comprising ~20% of the coil, will have a neutron damage limited lifetime of ~1 year, after which the core magnet will be quickly removed from the vacuum vessel and replaced. This allows the damaged core magnet to be refurbished and reused, reducing cost and allowing for economic fusion power generation from a DT levitated dipole reactor.

physics.plasm-ph

Interaction control and bright solitons in coherently-coupled Bose-Einstein condensates

We demonstrate fast control of the interatomic interactions in a Bose-Einstein condensate by coherently coupling two atomic states with intra- and inter-state scattering lengths of opposite signs. We measure the elastic and inelastic scattering properties of the system and find good agreement with a theoretical model describing the interactions between dressed states. In the attractive regime, we observe the formation of bright solitons formed by dressed-state atoms. Finally, we study the response of the system to an interaction quench from repulsive to attractive values, and observe how the resulting modulational instability develops into a bright soliton train.

cond-mat.quant-gas

A three-dimensional steerable optical tweezer system for ultracold atoms

We present a three-dimensional steerable optical tweezer system based on two pairs of acousto-optic deflectors. Radio frequencies used to steer the optical tweezers are generated by direct digital synthesis and multiple cross beam dipole traps can be produced through rapid frequency toggling and time averaging. We demonstrate production of arrays of ultracold atomic clouds in both horizontal and vertical planes and use this as an indicator for the three-dimensional nature of this optical tweezer system.

cond-mat.quant-gas