Diamond NV centers for precision measurement and quantum control

Resonator SpinIndividual nitrogen vacancy (NV) defect center spins in diamond form a unique platform to study the quantum properties of matter because they are simple, they can be studied one at a time, and they have quantum coherence even under ambient conditions.  Because NV centers are point defects, they can be used to sense magnetic fields with high spatial resolution provided that they are close to the surface of the diamond host.  We are currently focused on developing effective methods of robust quantum control, making use of gigahertz frequency magnetic fields and gigahertz frequency lattice strain.  These studies shed light on fundamental interactions between spins, electromagnetic fields, and phonons, but also may find application in magnetometry, inertial sensing, and quantum information processing.

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Watch a video of Greg’s lecture III at ITAMP/B2 Institute Winter Graduate School on AMO Physics where he talks about our diamond spin-mechanics work.  You can also watch Greg give a seminar at Purdue from September 2016 on Nanohub.

Search for new quantum defects

Wide bandgap materials host a zoo of optically active point defectsWide bandgap materials host a zoo of optically active point defects.  Our group studies the solid-state and photo-physics of single defects as a basis for quantum optical information processing and metrology.  Alternatives to diamond may provide new avenues of growth, processing, and control over quantum states.  Interesting candidate materials that we are currently investigating include gallium nitride, silicon carbide, and hexagonal boron nitride.

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Quantum Magnonics

We are interested in understanding magnetic excitations in the quantum regime.  Traditionally, magnetic resonance phenomena – ferromagnetic resonance and spin waves – have been viewed as strictly classical.  However, by coupling ultra-low damping magnetic materials to other quantum structures, including spins and superconducting circuits, it is possible to investigate the quantum nature of single magnetic excitations: magnons.  Because magnetic materials break time-reversal symmetry, they potentially offer non-reciprocal (one-way) quantum interactions, which is attractive in both classical and quantum technologies.  Our work has focused on an unconventional magnetic material – the organic-based ferrimagnet vanadium tetracyanoethylene, or V[TCNE]x.  This work is a close collaboration with the group of Ezekiel Johnston-Halperin (OSU) and Michael Flatté (U. Iowa).

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Time-resolved magneto-thermal microscopy: a new spatiotemporal magnetic microscopy that we are pushing toward sub-100 nm spatial resolution

time-resolved thermal gradients as the basis for spatiotemporal magnetic microscopyWe use time-resolved thermal gradients as the basis for spatiotemporal magnetic microscopy.  Taking advantage of the magneto-thermoelectric interactions, such as the time-resolved anomalous Nernst effect (TRANE) and the time-resolved longitudinal spin Seebeck effect (TRLSSE), we use heat and light to transduce local magnetization into an electrical signal.  This enables new, quantitative imaging of magnetization dynamics on picosecond time-scales.  We are currently investigating magneto-thermal microscopy for applications in emerging material systems, including magnetic metals, magnetic insulators, materials with spin-orbit torques, antiferromagnetic materials, and chiral magnetic materials.

An exciting aspect of using heat rather than light for magnetic imaging is that there is no fundamental limit to the spatial resolution because it is determined by the generation and spatiotemporal evolution of a thermal gradient rather than on principles of optical diffraction.  Using this fact, we are developing a super-resolution magnetic microscope for imaging nanoscale magnetism and the dynamical properties of magnetic materials on 50-100 nm length scales.  This capability will enable studies of magnetic systems and devices on their fundamental scales: spatial scales comparable to domain wall widths and time scales smaller than the period of ferromagnetic resonance.

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You can watch Greg’s Online Spintronics Seminar from May 2020, where he talks about studying antiferromagnetic materials with magneto-thermal microscopy.

Chiral and topological magnetism

chiral magnetic materials, and their twisting magnetic statesWe grow and study chiral magnetic materials, and their twisting magnetic states.  A prime example is thin-film, B20 FeGe and related compounds grown on Si[111] via magnetron sputtering or molecular beam epitaxy (in collaboration with the Schlom group and PARADIM).  In these materials, the chirality is derived from the “handedness” of the crystal structure, which gives rise to chiral magnetic configurations including helical and conical magnetic states, and magnetic skyrmions. Skyrmions are magnetic quasiparticles with integer topological charge that are interesting for  information storage applications with very high density, operating with very low energy.  We seek to grow, characterize, understand, and control the magnetism in these materials, understand their interactions with a spin current, and ultimately harness these effects for applications in low-power memory technologies.


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