A digital feedback controller for stabilizing large electric currents to the ppm level for Feshbach resonance studies

Abstract

Magnetic Feshbach resonances are a key tool in the field of ultracold quantum gases, but their full exploitation requires the generation of large, stable magnetic fields up to 1000 G with fractional stabilities of better than 10 −4 . Design considerations for electromagnets producing these fields, such as optical access and fast dynamical response, mean that electric currents in excess of 100 A are often needed to obtain the requisite field strengths. We describe a simple digital proportional-integral-derivative current controller constructed using a field-programmable gate array and off-the-shelf evaluation boards which allows for timedependent control parameters, enabling optimal control of current sources with non-linear actuators. Our controller can stabilize an electric current of 340 A to the level of 2.4 × 10 −6 with a control bandwidth of 2 kHz.

Experimental observation of the avoided crossing of two S -matrix resonance poles in an ultracold atom collider

“…Once two separated clouds have been prepared, we apply a magnetic field along the collision axis using a pair of water-cooled coils in the Helmholtz configuration, which carries a current regulated to the sub-ppm level [36]. The field strength is selected to inspect the 930 G Feshbach resonance and the vertical trapping beams are steered to accelerate the atomic clouds towards each other as illustrated in Fig.…”

Microscopy of an ultranarrow Feshbach resonance using a laser-based atom collider: A quantum defect theory analysis

“…For higher collsion energies, we further separate the clouds allowing room for a 2 mm run-up to the collision. We tune the position of the Feshbach resonance by applying a magnetic field with a pair of Helmholtz coils carrying a current controlled at the ppm level [25], before accelerating the clouds towards each other by steering the vertical dipole beams. As the clouds reach the collision energy, all laser beams are turned off and the clouds collide in the absence of trapping.…”

Open-source electronics ecosystem for optical atomic clocks

“…In this paper, we present an electronic system aimed at supporting the operation of optical clocks. While the electronic components presented here are designed for optical atomic clocks, they are also suitable for many other types of ultracold atom experiments, such as Feshbach resonance spectroscopy [20], optically pumped magnetometers [21], cold atom gravimetry [22] and quantum computing [23]. The presented electronic devices are suitable for both present-generation passive optical lattice atomic clocks and future-generation continuous active optical clocks based on superradiance [24][25][26][27].…”