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

TL;DR

This paper demonstrates how current-induced remnant magnetization in a superconducting niobium atomchip influences atom trapping, enabling control of magnetic traps via current history and the critical state model.

Contribution

It reveals the role of remnant magnetization in superconducting atomchips and validates the critical state model for predicting trapping behavior.

Findings

Remnant magnetization affects atom trap position.

Stable zero-current trap observed due to remnant magnetization.

Measurements align with the critical state model predictions.

Abstract

The physics of superconducting films, and especially the role of remnant magnetization has a defining influence on the magnetic fields used to hold and manipulate atoms on superconducting atomchips. We magnetically trap ultracold ^{87}Rb atoms on a 200{\mu}m wide and 500nm thick cryogenically cooled niobium Z wire structure. By measuring the distance of the atomcloud to the trapping wire for different transport currents and bias fields, we probe the trapping characteristics of the niobium superconducting structure. At distances closer than the trapping wire width, we observe a different behaviour than that of normal conducting wire traps. Furthermore, we measure a stable magnetic trap at zero transport current. These observations point to the presence of a remnant magnetization in our niobium film which is induced by a transport current. This current-induced magnetization defines the trap close to the chip surface. Our measurements agree very well with an analytic prediction based on the critical state model (CSM). Our results provide a new tool to control atom trapping on superconducting atomchips by designing the current distribution through its current history.