Quantum magnetometry of transient signals with a time resolution of 1.1 nanoseconds

At a Glance

Metadata	Details
Publication Date	2025-01-18
Journal	Nature Communications
Authors	Konstantin Herb, Laura A. Vӧlker, John M. Abendroth, Nicholas Meinhardt, Laura van Schie
Institutions	ETH Zurich
Citations	5
Analysis	Full AI Review Included

Executive Summary

This research demonstrates a significant breakthrough in quantum sensing by achieving nanosecond-scale time resolution for transient magnetic signals using a single Nitrogen-Vacancy (NV) center in diamond.

Core Achievement: Detection of transient magnetic fields with a best-effort time resolution of 1.1 ns, corresponding to an instantaneous bandwidth of 0.9 GHz.
Sensing Mechanism: A single NV center magnetometer operating at room temperature, utilizing a pump-probe scheme based on equivalent-time sampling and a speed-optimized Ramsey interferometry sequence.
Precision: The technique achieved a Time-of-Flight (ToF) precision better than 20 ps, enabling highly accurate timing of magnetic pulse events.
Technical Enablers: High-speed microwave pulse delivery via a broad-band coplanar waveguide (CPW) antenna, achieving Rabi frequencies up to 125 MHz.
Signal Processing: Temporal resolution is enhanced via post-processing using Wiener deconvolution, which accounts for pulse distortions and non-linear spin dynamics by simulating the spin evolution in the laboratory frame.
Future Potential: The achieved speeds make NV quantum magnetometers competitive with time-resolved synchrotron X-ray techniques, promoting single-spin probes for high-speed spintronics and nanoscale metrology.

Technical Specifications

Parameter	Value	Unit	Context
Best-Effort Time Resolution (t_min)	1.1	ns	Full Width at Half Maximum (FWHM) of kernel
Instantaneous Bandwidth (Ω_Bw)	0.9	GHz	Corresponding to 1.1 ns resolution
Time-of-Flight (ToF) Precision	< 20	ps	Absolute timing error limit
Maximum Rabi Frequency (Ω/2π)	125	MHz	Achieved using CPW antenna
Nominal Sensitivity (B_min)	35	µT/sqrt(Hz)	Calculated for t = 2 ns, α = π/2 rotation angle
Axial Bias Field (B₀)	36	mT	Used to isolate the ms=0 to ms=-1 transition
Microwave Antenna Bandwidth	ca. 7.5	GHz	3 dB bandwidth of Coplanar Waveguide (CPW)
NV Center Type	Single ¹⁵N	N/A	Located in diamond nanopillar waveguide
NV Creation Fluence	10⁹	cm^-2	¹⁵N⁺ ion implantation at 5 keV
Annealing Temperature/Time	1200 °C / 4	h	High vacuum annealing
Operating Temperature	Room	Temperature	Ambient conditions
Optical Spin Contrast (ε)	30-40	%	Measured NV contrast
CW Photon Count Rate (I₀)	1-2	Mcts/s	Continuous Wave illumination
Total Measurement Time (T)	1-10	s	Required to reach Co~0.1-1 Mcts

Key Methodologies

The time-resolved quantum sensing scheme relies on a combination of specialized hardware, a speed-optimized pulse sequence, and advanced post-processing:

NV Center Preparation: Single NV centers were created in electronic-grade diamond single crystals (Element6 Ltd.) via ¹⁵N⁺ ion implantation (5 keV, 10⁹ cm^-2 fluence), followed by high-vacuum annealing at 1200 °C. Nanopillar waveguide arrays were etched using electron-beam lithography to enhance photon yield.
Microwave Delivery System: Control pulses and test waveforms were generated using separate Arbitrary Waveform Generators (AWG1 and AWG2) and delivered via a broad-band (ca. 7.5 GHz) Coplanar Waveguide (CPW) antenna, narrowed to 20 µm in the core section to maximize Rabi frequency (up to 125 MHz).
Quantum Control Sequence: A pump-probe scheme was used, employing equivalent-time sampling. The core sensing step (Phase Measurement) utilized a composite sequence of two phase-shifted microwave pulses (P1-P2), equivalent to a zero-delay Ramsey interferometer, optimized to approach the quantum speed limit (QSL).
Time Synchronization: A picosecond digital delay line or AWG channel skew calibration (5-50 ps steps) was used to fine-adjust the relative timing between the electrical trigger (for the transient signal) and the spin manipulation pulses.
Time Resolution Optimization: Temporal resolution was optimized either by reducing the spin rotation angle (α) from 90° down to 45° (narrowing the kernel function) or by applying numerical post-processing.
Signal Deconvolution (Wiener Filtering): To correct for pulse distortions and non-linear spin driving effects, the measured output signal p(t) was deconvolved using Wiener filtering. The true convolution kernel k(t) was calculated by performing a density matrix simulation of the spin dynamics in the laboratory frame, using the actual measured microwave pulse shape as input.
Magnetic Signal Calibration: The measured photon counts were converted to transition probabilities p(t) and calibrated against magnetic field units by performing pulsed ODMR measurements with a constant test signal applied via a diplexer.

Commercial Applications

This technology is highly relevant for fields requiring high-speed, nanoscale magnetic characterization, bridging the gap between quantum sensing and ultrafast dynamics.

Spintronics and Memory:
- Time-resolved imaging of magnetization reversals in magnetic microdots (relevant for MRAM and non-volatile memories).
- Measurement of propagation velocity and dispersion of magnetic domain walls in racetrack memory devices.
- Studying current-induced spin-orbit torques and magnetic phase transitions on nanosecond timescales.
Nanoscale Device Metrology:
- Time-resolved imaging of current dynamics in integrated circuits (ICs), including in situ calibration of RF transmitters and analysis of signal dynamics in superconducting memory cells.
- Detection of transient photocurrents in light-sensitive electronic devices.
Quantum Sensing Hardware:
- Development of high-speed, broadband quantum magnetometers capable of detecting arbitrary waveforms, moving beyond static or narrow-band measurements.
Materials Science:
- Investigation of light-induced phase transitions in magnetic materials.
- Studying high-frequency ferromagnetic dynamics (e.g., multi-magnon relaxometry).

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-025-55956-1