Design of magnetic traps for neutral atoms with vortices in type-II superconducting microstructures

Abstract

We design magnetic traps for atoms based on the average magnetic field of vortices induced in a type-II superconducting thin film. This magnetic field is the critical ingredient of the demonstrated vortex-based atom traps, which operate without transport current. We use Bean's critical-state method to model the vortex field through mesoscopic supercurrents induced in the thin strip. The resulting inhomogeneous magnetic fields are studied in detail and compared to those generated by multiple normally-conducting wires with transport currents. Various vortex patterns can be obtained by programming different loading-field and transport current sequences. These variable magnetic fields are employed to make versatile trapping potentials.

Magnetic confinement of neutral atoms based on patterned vortex distributions in superconducting disks and rings

“…Solid line: sheet current density obtained by Eq. (3); dashed line: sheet current density in our former results[22].…”

“…After we obtain J (x i ,t n ), we compute the B field outside of the superconducting film (z > 0) using the Biot-Savart law. In order to validate our numerical model, we consider the case of vortices induced in a superconducting strip, for which an analytical solution exists [22]. Applying a magnetic-field pulse with a magnitude of B ext perpendicular to the strip surface, the magnetic flux penetrates the strip.…”

“…Previously we reported on the design and realization of several types of magnetic traps involving linear type II superconducting microstructures [22][23][24]. These traps are formed by the magnetic field carried by vortices imprinted in the superconductor to confine ultracold atoms.…”

“…Section II describes the equations of motion for the sheet current density J in a type II superconducting strip, disk, and ring in an external magnetic field. To validate our numerical approach, we compute the supercurrents in a superconducting strip and compare them with analytical results [22]. For the two-dimensional structures considered in this paper, no explicit analytical solution is known.…”

Current-induced magnetization hysteresis defines atom trapping in a superconducting atomchip

“…Applying magnetic fields to type-II superconductors induces a remanent magnetization created by permanent super-currents across the wire cross-section [43][44][45], and, with it, modifies the trapping. Experiments performed with YBCO superconducting atomchips focused on inducing a remanent magnetization with an external magnetic field [21][22][23][24]. The study in [8] looked at the remanent magnetization effects of a 200 µm wide niobium film for various magnetic field histories during the experimental cycle.…”