Scanning magnetoresistance microscopy of atom chips

Abstract

Surface based geometries of microfabricated wires or patterned magnetic films can be used to magnetically trap and manipulate ultracold neutral atoms or Bose-Einstein condensates. We investigate the magnetic properties of such atom chips using a scanning magnetoresistive (MR) microscope with high spatial resolution and high field sensitivity. By comparing MR scans of a permanent magnetic atom chip to field profiles obtained using ultracold atoms, we show that MR sensors are ideally suited to observe small variations of the magnetic field caused by imperfections in the wires or magnetic materials which ultimately lead to fragmentation of ultracold atom clouds. Measurements are also provided for the magnetic field produced by a thin current-carrying wire with small geometric modulations along the edge. Comparisons of our measurements with a full numeric calculation of the current flow in the wire and the subsequent magnetic field show excellent agreement. Our results highlight the use of scanning MR microscopy as a convenient and powerful technique for precisely characterizing the magnetic fields produced near the surface of atom chips.

Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

“…Here we describe the development of a new scanning magnetic microscope based on commercial MTJ sensors optimized for high spatial resolution measurements of room-temperature samples. Our improvements represent a 10-30 fold increase in magnetic field sensitivity compared to that of similar instruments previously reported [1,20].…”

Fabricating atom chips with femtosecond laser ablation

“…Ultracold atoms have recently been demonstrated as highly sensitive field probes perhaps heralding a new form of cold-atom microscopy [8]. A complementary solid-state technique that can quickly be performed in atmosphere was recently demonstrated in our laboratory based on a microscopic (5 × 5 μm 2 active area) magnetic tunnelling junction sensor (MicroMagnetics STJ-020), which measures the out-of-plane B y magnetic field component above either microwires or permanent magnetic media [25]. Briefly, the microscope consists of the MR sensor probe, preamplification electronics, a lock-in amplifier (LIA), UTM150PP.1 translation stages for x and z positioning and a computer control.…”

A Magnetic Field Camera for Real-Time Subsurface Imaging Applications

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