Active cancellation – A means to zero dead-time pulse EPR

Abstract

The necessary resonator employed in pulse electron paramagnetic resonance (EPR) rings after the excitation pulse and creates a finite detector dead-time that ultimately prevents the detection of signal from fast relaxing spin systems, hindering the application of pulse EPR to room temperature measurements of interesting chemical or biological systems. We employ a recently available high bandwidth arbitrary waveform generator (AWG) to produce a cancellation pulse that precisely destructively interferes with the resonant cavity ring-down. We find that we can faithfully detect EPR signal at all times immediately after, as well as during, the excitation pulse. This is a proof of concept study showcasing the capability of AWG pulses to precisely cancel out the resonator ring-down, and allow for the detection of EPR signal during the pulse itself, as well as the dead-time of the resonator. However, the applicability of this approach to conventional EPR experiments is not immediate, as it hinges on either (1) the availability of low-noise microwave sources and amplifiers to produce the necessary power for pulse EPR experiment or (2) the availability of very high conversion factor micro coil resonators that allow for pulse EPR experiments at modest microwave power.

Storing quantum information in spins and high-sensitivity ESR

“…In such cases, the resonators could be over-coupled, or other resonators used, bearing in mind a 1000-fold reduction in the Q-factor would reduce the per-echo sensitivity by a factor of about 30, but the per-root-Hz sensitivity by 1000. The possibility of Q-switched resonators, or shaped microwave pulses to obtain short drive pulses in high-Q cavities [95], could have useful applications in such situations.…”

“…In such cases, the resonators could be over-coupled, or other resonators used, bearing in mind a 1000-fold reduction in the Q-factor would reduce the per-echo sensitivity by a factor of about 30, but the per-root-Hz sensitivity by 1000. The possibility of Q-switched resonators, or shaped microwave pulses to obtain short drive pulses in high-Q cavities [95], could have useful applications in such situations. Second, when performing magnetic field sweeps, as is typical in ESR, it is important to consider the shift in the resonator frequency (and, potentially Q-factor) which may remain even if the field is well aligned with the plane of the resonator (see Section III C).…”

Milliwatt three- and four-pulse double electron electron resonance for protein structure determination

“…45 Another remarkable approach is based on the use of an arbitrary waveform generator (AWG) to synthesize active cancellation pulses that destructively interfere with the resonator ringdown. 49,50 Apart from experimental approaches, computational methods, such as linear prediction (LP) 51 can be used to reconstruct signals backwards in time, based on the frequency content present in the recorded data, as it is common in NMR. 52,53 In addition to the discussed detector dead time, another type of signal distortion arises if two pulses are placed too close to each other in time, since the Q-value of the resonator leads to a delay in the build-up and in the the dissipation of the energy stored in the resonator with respect to the applied incident power.…”

Randomized benchmarking of quantum gates implemented by electron spin resonance

“…Moreover, in other spectroscopic techniques such as double electron-electron resonance (DEER) [24,25] and solution-state 2D electron-electron double resonance (2D-ELDOR) [1,26,27], arbitrary waveform generation is beneficial for creating desired excitation profiles [28][29][30][31]. Integrating an arbitrary waveform generator (AWG) into pulsed ESR spectrometers has been reported in several previous works [8,9,[28][29][30][31][32][33]. In order to achieve precise coherent control, efforts have also been made to overcome pulse distortions due to limited bandwidth of the resonator and amplifier nonlinearity [9,[28][29][30][31]34].…”