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

Abstract

The physics of superconducting films, and especially the role of remanent 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 µm wide and 500 nm 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 remanent 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.

A scanning quantum cryogenic atom microscope at 6 K

“…However, combining atomic cooling and trapping techniques with the cryogenic cooling of nearby materials is technically challenging. Such systems have been built for the purpose of, e.g., trapping atoms with superconducting wires and/or near superconducting materials [6][7][8][9][10][11][12][13][14][15], increasing the lifetime of trapped ions [16,17], and creating hybrid quantum information devices by coupling atoms to superconducting qubits [18]. Scanning probe sensing with a BEC or ultracold thermal gas has been previously demonstrated [5,[19][20][21][22]; however, no other apparatus but the SQCRAMscope serves as a scanning probe for quantum materials with the capability of rapid sample exchange and BEC recovery, high-numerical-aperture imaging, and wide-area sample imaging [1,2].…”

Cooper pair trajectories in superconducting slab at self-field conditions

“…Transport current flow and self-generating magnetic field in superconducting slab have been under theoretical considerations since famous London brothers' paper [1] over decades [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The understanding of superconducting current flow in rectangular slab has direct impact on superconducting technology, because second generation high-temperature superconductors have a design in form of thin superconducting film deposited on a metallic substrate with shunting layers on both sides of the tape [20][21][22].…”

A scanning quantum cryogenic atom microscope at 6 K

“…However, combining atomic cooling and trapping techniques with the cryogenic cooling of nearby materials is technically challenging. Such systems have been built for the purpose of, e.g., trapping atoms with superconducting wires and/or near superconducting materials [6][7][8][9][10][11][12][13][14][15], increasing the lifetime of trapped ions [16,17], and creating hybrid quantum information devices by coupling atoms to superconducting qubits [18]. However, none but the SQCRAMscope serves as a scanning probe for quantum materials with the capability of rapid sample exchange and BEC recovery, high-numericalaperture imaging, and wide-area sample imaging [1,2].…”