DAC-board based X-band EPR spectrometer with arbitrary waveform control

Abstract

We present arbitrary control over a homogenous spin system, demonstrated on a simple, home-built, electron paramagnetic resonance (EPR) spectrometer operating at 8–10 GHz (X-band) and controlled by a 1 GHz arbitrary waveform generator (AWG) with 42 dB (i.e. 14-bit) of dynamic range. Such a spectrometer can be relatively easily built from a single DAC (digital to analog converter) board with a modest number of stock components and offers powerful capabilities for automated digital calibration and correction routines that allow it to generate shaped X-band pulses with precise amplitude and phase control. It can precisely tailor the excitation profiles “seen” by the spins in the microwave resonator, based on feedback calibration with experimental input. We demonstrate the capability to generate a variety of pulse shapes, including rectangular, triangular, Gaussian, sinc, and adiabatic rapid passage waveforms. We then show how one can precisely compensate for the distortion and broadening caused by transmission into the microwave cavity in order to optimize corrected waveforms that are distinctly different from the initial, uncorrected waveforms. Specifically, we exploit a narrow EPR signal whose width is finer than the features of any distortions in order to map out the response to a short pulse, which, in turn, yields the precise transfer function of the spectrometer system. This transfer function is found to be consistent for all pulse shapes in the linear response regime. In addition to allowing precise waveform shaping capabilities, the spectrometer presented here offers complete digital control and calibration of the spectrometer that allows one to phase cycle the pulse phase with 0.007° resolution and to specify the inter-pulse delays and pulse durations to ≤250 ps resolution. The implications and potential applications of these capabilities will be discussed.

Training Schrödinger’s cat: quantum optimal control

“…The huge range of practical applications has generated a multi-billion dollar branch of the instrument manufacturing industry (Bruker, Siemens, Phillips, General Electric, JEOL, etc.). This in turn has resulted in the continuous development of more and more sophisticated instruments with superb flexibility in terms of the available control schemes: for example, arbitrary waveform generators and linear amplifies have been standard NMR and MRI equipment for more than three decades (and have more recently also become available with sub-nanosecond time resolution for ESR applications [108,288]). With their help, even very complex pulse shapes can routinely be implemented with high fidelity [289].…”

“…In ESR spectroscopy, the first broadband optimal-control pulses have recently been developed and experimentally implemented [108,288]. In this context, the efficiency of novel approaches to take into account transient effects due to transfer line effects and limited resonator bandwidth was both numerically and experimentally demonstrated [108].…”

Frequency swept microwaves for hyperfine decoupling and time domain dynamic nuclear polarization

“…5d and 8a [72]. Following Han and colleagues [73], we expect to correct for deviations from this linear response by altering the controlling voltage waveform. Fig.…”

Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals

“…X-band pulsed EPR has recently been performed using microwaves generated with an AWG [13, 25]. One other lab, in parallel with our efforts, has digitally generated the incident RF and directly digitized the CW EPR signal at 300 MHz [26, 27].…”