Research

1. Nuclear magnetic resonance spectroscopy with diamond quantum sensors

Quantum sensing is the use of qubits (the logical 'bits' in a quantum computer) to measure properties of the environment. In this project, we use spin qubits in diamond as sensitive detectors of nuclear magnetic resonance (NMR) spectra. Unlike existing NMR spectrometers, these devices are capable of detecting picoliter sample volumes, at the scale of single cells.

We perform picoliter NMR spectrosopy by delivering analyte, via a microfluidic chip, to a sensor comprised of a diamond chip doped with nitrogen-vacancy (NV) spin qubits [1,2]. By applying quantum sensing pulse sequences of laser light and microwaves, the magnetic field from the analyte’s precessing magnetization becomes encoded in the NV fluorescence signal. Analysis of the fluorescence signal reveals the analyte's NMR spectrum, from which the chemical composition can be extracted from established libraries. This project is a collaboration with Andrey Jarmola (ODMR Technologies), Andrew McDowell (NuevoMR), and others.

[1] P. Kehayias*, A. Jarmola*, N. Mosavian, I. Fescenko, F. M. Benito, A. Laraoui, J. Smits, L. Bougas, D. Budker, A. Neumann, S. R. J. Brueck, V. M. Acosta, "Solution nuclear magnetic resonance spectroscopy on a nanostructured diamond chip." Nature Communications 8 188 (2017).

[2] J. Smits*, J. Damron*, P. Kehayias, A. F. McDowell, N. Mosavian, N. Ristoff, I. Fescenko. A. Laraoui, A. Jarmola, V. M. Acosta, "Two-dimensional nuclear magnetic resonance spectroscopy with a microfluidic diamond quantum sensor." Science Advances 5 eaaw7895 (2019). 

2. Femtotesla magnetometry and the sensitivity frontier of diamond quantum sensing

The world's most sensitive magnetometers can detect magnetic fields at the level of 10^(-15) T (i.e. 1 femtotesla). Naturally, we wondered whether sensors based on diamond NV centers could ever reach that limit. In our exploration of the sensitivity frontier, we have built diamond quantum sensors that can detect magnetic fields at the level of ~70 fT for one second integration [3]. This was enabled by the use of ferrite flux concentrators which collect magnetic flux from a larger area and concentrate it into a micrometer scale NV-doped diamond [4]. More recently, we have begun to investigate the fundamental limits of sensitivity and the role of microwave phase noise in electron-spin spectroscopy precision measurements. In parallel, we are working on implementing these devices for applications in navigation, nuclear quadrupole resonance spectroscopy [3], and magnetoenchephalography (imaging magnetic fields produced by the brain).   We collaborate with scientists at Los Alamos National Lab (Igor Savukov, Michael Malone), U Latvia (Ilja Fescenko), and ODMR Technologies (Andrey Jarmola).

[3] Y. Silani, J. Smits, I. Fescenko, M. W. Malone, A. F. McDowell, A. Jarmola, P. Kehayias, B. Richards, N. Mosavian, N. Ristoff, V. M. Acosta, "Nuclear quadrupole resonance spectroscopy with a femtotesla diamond magnetometer",  Science Advances 9 : eadh3189 (2023).

[4] I. Fescenko, A. Jarmola, I. Savukov, P. Kehayias, J. Smits, J. Damron, N. Ristoff, N. Mosavian, V. M. Acosta, "Diamond magnetometer enhanced by ferrite flux concentrators." Physical Review Research 2, 023394 (2020).

3. Imaging biomagnetism and nanomaterials with diamond magnetic microscopy

NV centers in diamond offer new possibilities for imaging nanoscale magnetic phenomena in biological and condensed-matter systems [5]. This is due to their unique combination of high sensitivity, nanoscale spatial resolution, and ability to operate in a wide range of temperatures and magnetic fields.

In our lab, we are developing new tools for high-throughput sorting and characterization of individual magnetic nanoparticles. We seek to label rare cell-bound biomarkers with magnetic nanoparticles and detect them noninvasively using ultrasensitive diamond magnetic microscopes. We also use diamond magnetic microscopy to study the paramagnetic nanocrystals produced by malaria parasites, called hemozoin [6].  We collaborate with scientists at Sandia National Lab (Andy Mounce, Dale Huber, Mike Lilly, Pauli Kehayias), U Nebraska (Abdelghani Laraoui) and ODMR Technologies (Andrey Jarmola). This project combines condensed-matter physics, quantum sensing, and biomedical imaging.

[5] V. M. Acosta, L.-S. Bouchard, D. Budker, R. Folman, T. Lenz, P. Maletinsky, D. Rohner, Y. Schlussel, L. Thiel, "Color centers in diamond as novel probes of superconductivity." Journal of Supercond. and Novel Magnetism 32, 85 (2019).

[6] I. Fescenko, A. Laraoui, J. Smits, N. Mosavian, P. Kehayias, J. Seto, L. Bougas, A. Jarmola, V. M. Acosta, "Diamond magnetic microscopy of malarial hemozoin nanocrystals." Physical Review Applied 11, 034029 (2019). 

4. Search for new spin-dependent forces at the micrometer scale

For decades, searches for exotic spin-dependent interactions have used increasingly-precise laboratory measurements to exclude various theoretical models of particle physics. For example, spin-dependent interactions could be mediated by 'axions', hypothetical bosons which could explain the mysterious dark matter that allegedly comprises the majority of mass in the universe. Most searches have focused on interaction length scales greater than 1 mm, corresponding to hypothetical boson masses less than 0.2 meV. Recently, quantum sensors based on NV centers in diamond have emerged as a promising platform to probe spin-dependent interactions at the µm scale, opening the door to explore new physics at this length scale. 

We are starting up new experiments [7] to search for several hypothetical interactions between NV electron spins and moving masses. This is particularly important in light of a Nov. 2020 preprint that reports a surprising non-zero result on micron-scale spin-velocity interactions. This project combines NV quantum sensing, MEMS engineering, and particle physics. We collaborate with scientists at Los Alamos (Pinghan Chu, Young Jin Kim, Igor Savukov) and UNM Mechanical Engineering (Nathan Jackson). 

[7] P.-H. Chu*, N. Ristoff*, J. Smits, N. Jackson, Y. J. Kim, I. Savukov, V. M. Acosta, "Proposal for the search for new spin interactions at the micrometer scale using diamond quantum sensors." Physical Review Research 4, 023162 (2022).

5. Super-resolution diamond microscopy

We seek to push the frontier in spatial resolution and functional imaging in super-resolution microscopy (2014 Nobel Prize, Chemistry) using color centers in diamond [8]. Previously, we performed Stimulated Emission Depletion (STED) microscopy using Silicon-Vacancy (SiV) centers in diamond [9] , demonstratin that SiV centers have favorable properties for super-resolution microscopy, such as stable near-infrared emission and a large absorption cross section. More recently, we are using NV centers for super-resolution magnetic microscopy [10]. This project combines nonlinear optics, fluorescence microscopy, and magnetic nanoparticle imaging.

[8] J. M. Higbie, J. D. Perreault, V. M. Acosta, C. Belthangady, P. Lebel, M. H. Kim, K. Nguyen, V. Demas, V. Bajaj, C. Santori, "Multiphoton-Excited Fluorescence of Silicon-Vacancy Color Centers in Diamond." Physical Review Applied 7, 054010 (2017).

[9] Y. Silani*, F. Hubert*, V. M. Acosta, "Stimulated emission depletion microscopy with diamond silicon vacancy centers." ACS Photonics, 6 2577 (2019). 

[10] N. Mosavian, F. Hubert, J. Smits, P. Kehayias, Y. Silani, B. A. Richards, V. M. Acosta, "Super-resolution diamond magnetic microscopy of superparamagnetic nanoparticles. arXiv:2310.05436 (2023).

6. Nuclear spin polarization and readout for gyroscopes

In collaboration with Andrey Jarmola (UC Berkeley, ODMR Technologies) and scientists at Army Research Lab (Sean Lourette, Vladimir Malinovsky et al.), we are studying ways to  polarize, control, and detect nuclear spins in diamond and use them for precision rotation sensing (gyroscopy) [11-13].

[11] A. Jarmola, I. Fescenko, V. M. Acosta, M. W. Doherty, F. K. Fatemi, T. Ivanov, D. Budker, V. S. Malinovsky, "Robust optical readout and characterization of nuclear spin transitions in nitrogen-vacancy ensembles in diamond."   Physical Review Research 2, 023094 (2020).

[12] A. Jarmola, S. Lourette, V. M. Acosta, A. G. Birdwell, P. Blumler, D. Budker, T. Ivanov, V. S. Malinovsky, "Demonstration of diamond nuclear spin gyroscope." Science Advances 7 : eabl3840 (2021).

[13] S. Lourette, A. Jarmola, V. M Acosta, A. G. Birdwell, D. Budker, M. W. Doherty, T. Ivanov, V. S. Malinovsky, "Temperature Sensitivity of 14NV and 15NV Ground State Manifolds",  Physical Review Applied 19, 064084 (2023).