Three-axis measurement and cancellation of background magnetic fields to less than 50 µG in a cold atom experiment

Abstract

Many experiments involving cold and ultracold atomic gases require very precise control of magnetic fields that couple to and drive the atomic spins. Examples include quantum control of atomic spins, quantum control and quantum simulation in optical lattices, and studies of spinor Bose condensates. This makes accurate cancellation of the (generally time dependent) background magnetic field a critical factor in such experiments. We describe a technique that uses the atomic spins themselves to measure DC and AC components of the background field independently along three orthogonal axes, with a resolution of a few tens of µG in a bandwidth of ∼ 1 kHz. Once measured, the background field can be cancelled with three pairs of compensating coils driven by arbitrary waveform generators. In our laboratory, the magnetic field environment is sufficiently stable for the procedure to reduce the field along each axis to less than ∼50 µG rms, corresponding to a suppression of the AC part by about one order of magnitude. This suggests our approach can provide access to a new low-field regime in cold-atom experiments.

Real-time vector field tracking with a cold-atom magnetometer

“…Recent work with hotatom magnetometers has demonstrated three-axis sensing and control with nT precision at cm scales, 9,10 while a threeaxis modulated cold-atom magnetometer has shown nT sensitivity at 300 lm scales. 11,12 Here we demonstrate sub-nT sensitivity at 50 lm length-scale in a cold-atom magnetometer employing nearresonant Faraday rotation probing. 13 The instrument gives three-axis field information plus one gradient component, obtained by observation of free-induction decay (FID) after optical pumping.…”

Robust site-resolvable quantum gates in an optical lattice via inhomogeneous control

“…We use sideband cooling [28][29][30] to prepare atoms in the " j i state, with mean vibrational excitation " nE0.01 along x (excitation along y and z is unimportant). A bias magnetic field separates the qubit transition frequency from others in the ground manifold, and the combined bias, DC and AC background magnetic fields are stabilized to better than 20 mG using an approach similar to Smith et al 31 The resulting frequency variation in the qubit transition frequency is B50 Hz. The atomic qubits are driven with 9.2 GHz microwaves from two horn antennae adjusted to improve the field homogeneity across the atom cloud.…”

A simple geomagnetic field compensation system for uniform magnetic field applications

“…There are numerous applications in different study areas where the generation of homogeneous and controlled magnetic fields are required, one of these is the research in bioelectromagnetics [1][2][3]. Many of these studies ideally require devices capable of generating uniform magnetic fields and furthermore guaranteeing a controlled and repeatable exposure to different samples involved in the experiment [4,5]In this sense, the arrangements of aircore coils have been traditionally used for this purpose, particularly circular and square geometries [6][7][8].…”