Ultra-low noise and high bandwidth bipolar current driver for precise magnetic field control

Abstract

Current sources with extremely low noise are significant for many branches of scientific research, such as experiments of ultra-cold atoms, superconducting quantum computing, and precision measurements. Here we construct and characterize an analog-controlled bipolar current source with high bandwidth and ultra-low noise. A precise and stable resistor is connected in series with the output for current sensing. After being amplified with an instrumentation amplifier, the current sensing signal is compared with an ultra-low noise reference, and proportional-integral (PI) calculations are performed via a zero-drift low-noise operational amplifier. The result of the PI calculation is sent to the output power operational amplifier for closed-loop control of the output current. In this way, a current of up to 16 A can be sourced to or sunk from a load with a compliance voltage of greater than ±12 V. The broadband current noise of our bipolar current source is about 0.5 μA/Hz and 1/f corner frequency is less than 1 Hz. Applications of this current source in a cold atom interferometer, as well as active compensation of a stray magnetic field, are presented. A method for measuring high-frequency current noise in a 10 A DC current with a sensitivity down to a level of 10 μA is also described.

Functional building blocks for scalable multipartite entanglement in optical lattices

“…As shown in Fig. 2D, the extracted oscillation amplitudes exhibit the exponential decay with a time constant of τ = 2.20±0.13 s [30][31][32]. This long coherence time guarantees scaling up the entanglement of atoms.…”

Bidirectional, Analog Current Source Benchmarked with Gray Molasses-Assisted Stray Magnetic Field Compensation

“…It is then sent to the source part closing the feedback loop. There are several common circuits for bipolar current sources, such as Howland pumps, current-in/current-out amplifiers, and push-pull setups (based on transistors or operational amplifiers) [11][12][13][14][15]. We choose the latter solution to obtain high-output currents and smooth, linear zero-current crossing.…”

“…Such a feature is useful, for example, when, during an experimental sequence, the magnetic field direction needs to be adiabatically changed to orient the quantization axis differently than during the optical pumping stage. Bidirectional current sources, on the other hand, enable both the direction and the amplitude control of the current and, if properly designed, offer a smooth zero-current crossing [11][12][13][14][15]. With such sources, running current through each pair of three mutually orthogonal pairs of coils in a near-Helmholtz configuration provides the ability to create uniform magnetic field waveforms.…”

“…Of the two frequently used approaches, digital and analog, we choose the latter one. Digital circuits, although offering better independence of nonlinearities, thermal drifts, and repeatability [16], often rely on expensive, complex, high-resolution digital-to analog (DAC) and analog-to-digital (ADC) converters [12,13]. Moreover, switching of digital signals is a well known noise source for the analog part of the circuit.…”

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

“…A typical solution is to build an analog proportional-integral-derivative (PID) feedback loop that stabilizes the current produced from a voltage-controlled power-supply using external regulating transistors to control the current. While some of these solutions have been very successful, with reported stabilities of better than 10 ppm 23,[26][27][28][29][30] , designing and implementing a high-precision, low-noise, and robust analog PID controller from discrete, linear components is a non-trivial task because the transistors used to regulate the current are inherently non-linear.…”