Broadband radio-frequency transmitter for fast nuclear spin control

Abstract

The active manipulation of nuclear spins with radio-frequency (RF) coils is at the heart of nuclear magnetic resonance (NMR) spectroscopy and spin-based quantum devices. Here, we present a miniature RF transmitter designed to generate strong RF pulses over a broad bandwidth, allowing for fast spin rotations on arbitrary nuclear species. Our design incorporates (i) a planar multilayer geometry that generates a large field of 4.35 mT per unit current, (ii) a 50 Ω transmission circuit with a broad excitation bandwidth of ∼20 MHz, and (iii) an optimized thermal management leading to minimal heating at the sample location. Using individual 13 C nuclear spins in the vicinity of a diamond nitrogen-vacancy center as a test system, we demonstrate Rabi frequencies exceeding 70 kHz and nuclear π/2 rotations within 3.4 μs. The extrapolated values for 1 H spins are about 240 kHz and 1 μs, respectively. Beyond enabling fast nuclear spin manipulations, our transmitter system is ideally suited for the incorporation of advanced pulse sequences into micro-and nanoscale NMR detectors operating at a low (<1 T) magnetic field.

Coherent manipulation of nuclear spins in the strong driving regime

“…We demonstrate the antenna's function by driving Rabi oscillations in a proton spin ensemble of an organic sample on the diamond's surface. As a preliminary experiment, we detect proton NMR with an XY8-N dynamical decoupling sequence [22], employing phase randomization to exclude spurious harmonics of 13 C spins [27]. Figure 4(b) features an XY8-10 trace with a dip at the expected position of the proton Larmor frequency (B 0 ≈ 652 G, ω1 H ≈ 2.78 MHz), indicating that the NV senses the proton's oscillating magnetization.…”

“…Fast manipulation of nuclear spins by strong RF driving fields can better utilize the limited sensing time of NV center sensors, generate broadband excitation of the nuclear spin resonance, and enable novel sensing protocols [11]. Previous works demonstrated strong driving for the NV center electron spin at a rate of ∼1 GHz [12], and 13 C spins in diamond at ∼70 kHz [13]. The highest reported driving rates for protons in NV-based NMR are 50-80 kHz [1,3].…”

Parallel detection and spatial mapping of large nuclear spin clusters

“…Weak-measurement protocol for detecting the free precession signal from many nuclei in parallel. We polarize the nuclear spins by a repeated NOVEL sequence (gray, inset a) [49,50], initiate simultaneous precession of all nuclei by applying a π/2 pulse with an external RF coil (blue) [51], and detect the precession by repeated sampling of the transverse nuclear magnetization (purple) [12,13,52]. t pol is the polarization time, ts is the sampling time and K is the number of samples.…”

“…We probe the NV centers at room temperature using non-resonant optical excitation and a single-photon counting module [56]. Electronic and nuclear spins are manipulated via two arbitrary waveform generators connected to separate microwave transmission line and RF micro-coil circuits, respectively [16,51]. Experiments use a bias field B 0 ∼ 200 mT aligned to within 1 • of the NV symmetry axis (Fig.…”

Pulsed Electron‐Nuclear Double Resonance in the Fourier Regime

“…Moreover, it is questionable whether a small sample that can fit inside such an ESR setup and into such an NMR microcoil is able to provide large enough ESR signals to facilitate an efficient ENDOR detection scheme. One recent example of a successful combination of NMR microcoils with ESR is found in the field of optically‐detected ESR, where the sample can be very small (even a single spin) and therefore it is fairly straightforward to implement a miniature NMR coil near it [16] . However, even in this very specialized case, due to heat dissipation, the setup (which has been used only for 13 C ENDOR) shows the equivalent of 1 H π pulses of no less than ∼1 μs, which corresponds to an overall instantaneous RF frequency coverage of not more than ∼1 MHz.…”