Leonardo Uhthoff-Rodríguez

Cold atom experiments utilize magnetic fields, commonly generated by coils, as an essential tool to control and manipulate atomic samples. In these experiments, it is often necessary to rapidly switch the magnetic field between two values. However, typical power supplies have a limited switching time for the current flowing through the coil. We present a control scheme implemented as an electronic circuit that overcomes this limitation. A faster control is achieved by momentarily applying an on-demand high voltage when the control signal variation surpasses the limits that the conventional power supply can follow, allowing a faster current flow into the magnetic coil. In our specific application, a coil with an inductance of 491 μH and a resistance of 0.26 Ω, corresponding to a time constant of ∼1.9 ms, is driven so that its current faithfully follows the control signals from −1 to 1 A. It is capable of completing a full-scale transition in just ∼31 μs, with an effective bandwidth of 15.2 kHz. This corresponds to an improvement by a factor of more than 20 in both bandwidth and switching speed over a conventional power supply. By appropriately selecting the components of the circuit, both the bandwidth and switching time can be tuned to match specific needs within a wide range of inductive and power requirements.

A fundamental parameter to determine how electromagnetic waves interfere is their relative phase, and achieving a fine control over it enables a wide range of interferometric applications. Existing phase control methods rely on modifying the optical path length either by changing the path followed by the light or by altering the thickness or index of refraction of an optical element in the setup. In this Letter, we present a novel, to the best of our knowledge, method, based on acousto-optic modulators (AOMs), which allows adjusting the phase by shifting the frequency of the light in a segment of its path. Since the amount of phase shift depends on the length of the segment, an optical fiber is used to realize a 2π shift. Two experimental implementations are described which deal with different sources of phase fluctuations. The first addresses fluctuations resulting from the optical fiber, while the second tackles unwanted variations originating from the AOMs.