63 research outputs found
Three-dimensional nuclear spin positioning using coherent radio-frequency control
Distance measurements via the dipolar interaction are fundamental to the
application of nuclear magnetic resonance (NMR) to molecular structure
determination, but they only provide information on the absolute distance
and polar angle between spins. In this Letter, we present a protocol
to also retrieve the azimuth angle . Our method relies on measuring the
nuclear precession phase after application of a control pulse with a calibrated
external radio-frequency coil. We experimentally demonstrate three-dimensional
positioning of individual carbon-13 nuclear spins in a diamond host crystal
relative to the central electronic spin of a single nitrogen-vacancy center.
The ability to pinpoint three-dimensional nuclear locations is central for
realizing a nanoscale NMR technique that can image the structure of single
molecules with atomic resolution.Comment: 5 pages, 4 figure
High-bandwidth microcoil for fast nuclear spin control
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 microcoil transmitter system 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 Ohm transmission circuit with a broad excitation bandwidth of
approximately 20 MHz, and (iii) an optimized thermal management for removal of
Joule heating. Using individual 13C nuclear spins in the vicinity of a diamond
nitrogen-vacancy (NV) center as a test system, we demonstrate Rabi frequencies
exceeding 70 kHz and nuclear pi/2 rotations within 3.4 us. The extrapolated
values for 1H spins are about 240 kHz and 1 us, respectively. Beyond enabling
fast nuclear spin manipulations, our microcoil system is ideally suited for the
incorporation of advanced pulse sequences into micro- and nanoscale NMR
detectors operating at low (<1 T) magnetic field.Comment: 8 pages, 5 figures. Submitted to Rev. Sci. Inst
Quantum sensing with arbitrary frequency resolution
Quantum sensing takes advantage of well controlled quantum systems for
performing measurements with high sensitivity and precision. We have
implemented a concept for quantum sensing with arbitrary frequency resolution,
independent of the qubit probe and limited only by the stability of an external
synchronization clock. Our concept makes use of quantum lock-in detection to
continuously probe a signal of interest. Using the electronic spin of a single
nitrogen vacancy center in diamond, we demonstrate detection of oscillating
magnetic fields with a frequency resolution of 70 uHz over a MHz bandwidth. The
continuous sampling further guarantees an excellent sensitivity, reaching a
signal-to-noise ratio in excess of 10,000:1 for a 170 nT test signal measured
during a one-hour interval. Our technique has applications in magnetic
resonance spectroscopy, quantum simulation, and sensitive signal detection.Comment: Manuscript resubmitted to Science. Includes Supplementary Material
Multi-modal segmentation of 3D brain scans using neural networks
Purpose: To implement a brain segmentation pipeline based on convolutional
neural networks, which rapidly segments 3D volumes into 27 anatomical
structures. To provide an extensive, comparative study of segmentation
performance on various contrasts of magnetic resonance imaging (MRI) and
computed tomography (CT) scans. Methods: Deep convolutional neural networks are
trained to segment 3D MRI (MPRAGE, DWI, FLAIR) and CT scans. A large database
of in total 851 MRI/CT scans is used for neural network training. Training
labels are obtained on the MPRAGE contrast and coregistered to the other
imaging modalities. The segmentation quality is quantified using the Dice
metric for a total of 27 anatomical structures. Dropout sampling is implemented
to identify corrupted input scans or low-quality segmentations. Full
segmentation of 3D volumes with more than 2 million voxels is obtained in less
than 1s of processing time on a graphical processing unit. Results: The best
average Dice score is found on -weighted MPRAGE ().
However, for FLAIR (), DWI () and CT (), good-quality segmentation is feasible for most anatomical
structures. Corrupted input volumes or low-quality segmentations can be
detected using dropout sampling. Conclusion: The flexibility and performance of
deep convolutional neural networks enables the direct, real-time segmentation
of FLAIR, DWI and CT scans without requiring -weighted scans
High resolution quantum sensing with shaped control pulses
We investigate the application of amplitude-shaped control pulses for
enhancing the time and frequency resolution of multipulse quantum sensing
sequences. Using the electronic spin of a single nitrogen vacancy center in
diamond and up to 10,000 coherent microwave pulses with a cosine square
envelope, we demonstrate 0.6 ps timing resolution for the interpulse delay.
This represents a refinement by over 3 orders of magnitude compared to the 2 ns
hardware sampling. We apply the method for the detection of external AC
magnetic fields and nuclear magnetic resonance signals of carbon-13 spins with
high spectral resolution. Our method is simple to implement and especially
useful for quantum applications that require fast phase gates, many control
pulses, and high fidelity.Comment: 5 pages, 4 figures, plus supplemental materia
Tracking the precession of single nuclear spins by weak measurements
Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for
analyzing the structure and function of molecules, and for performing
three-dimensional imaging of the spin density. At the heart of NMR
spectrometers is the detection of electromagnetic radiation, in the form of a
free induction decay (FID) signal, generated by nuclei precessing around an
applied magnetic field. While conventional NMR requires signals from 1e12 or
more nuclei, recent advances in sensitive magnetometry have dramatically
lowered this number to a level where few or even individual nuclear spins can
be detected. It is natural to ask whether continuous FID detection can still be
applied at the single spin level, or whether quantum back-action modifies or
even suppresses the NMR response. Here we report on tracking of single nuclear
spin precession using periodic weak measurements. Our experimental system
consists of carbon-13 nuclear spins in diamond that are weakly interacting with
the electronic spin of a nearby nitrogen-vacancy center, acting as an optically
readable meter qubit. We observe and minimize two important effects of quantum
back-action: measurement-induced decoherence and frequency synchronization with
the sampling clock. We use periodic weak measurements to demonstrate sensitive,
high-resolution NMR spectroscopy of multiple nuclear spins with a priori
unknown frequencies. Our method may provide the optimum route for performing
single-molecule NMR at atomic resolution.Comment: 29 pages including methods and extended data figures; for
supplementary material, see v1 of this submissio
Three-dimensional localization spectroscopy of individual nuclear spins with sub-Angstrom resolution
We report on precise localization spectroscopy experiments of individual 13C
nuclear spins near a central electronic sensor spin in a diamond chip. By
detecting the nuclear free precession signals in rapidly switchable external
magnetic fields, we retrieve the three-dimensional spatial coordinates of the
nuclear spins with sub-Angstrom resolution and for distances beyond 10
Angstroms. We further show that the Fermi contact contribution can be
constrained by measuring the nuclear g-factor enhancement. The presented method
will be useful for mapping the atomic-scale structure of single molecules, an
ambitious yet important goal of nanoscale nuclear magnetic resonance
spectroscopy
Coherent control of solid state nuclear spin nano-ensembles
Detecting and controlling nuclear spin nano-ensembles is crucial for the
further development of nuclear magnetic resonance (NMR) spectroscopy and for
the emerging solid state quantum technology. Here we present the fabrication of
a 1 nanometre thick diamond layer consisting of C nuclear
spins doped with Nitrogen-Vacancy centres (NV) embedded in a spin-free C
crystal matrix. A single NV in the vicinity of the layer is used for
polarization of the C spins and the readout of their magnetization. We
demonstrate a method for coherent control of few tens of nuclear spins by using
radio frequency pulses and show the basic coherent control experiments - Rabi
oscillations, Ramsey spectroscopy and Hahn echo, though any NMR pulse sequence
can be implemented. The results shown present a first steps towards the
realization of a nuclear spin based quantum simulator
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