Massachusetts Institute of Technology

Linh M Pham

John Francis Barry

Danielle Ann Braje

Kerry Alexander Johnson

Michael F O'Keeffe

Christopher Michael McNally

Erik R Eisenach

Hannah Anne Clevenson

Erik M Thompson

Carson Arthur Teale

Jonah A Majumder

Christopher Louis Panuski

Isaac Chuang

Matthew Steinecker

Jessica Kedziora

Jennifer Schloss

Peter Moulton

Xingyu Zhang

We have developed a high-performance, low-volume, low-weight, and low-power sensor based on a self-sustaining oscillator. The techniques described here may be used for sensing various fields; we demonstrate magnetic sensing. The oscillator is based on a dielectric resonator that contains paramagnetic defects and is connected to a sustaining amplifier in a feedback loop. The resonance frequency of the dielectric resonator shifts in response to changes in the magnetic field, resulting in a shift in the frequency of the self-sustaining oscillator. The value of the magnetic field is thereby encoded in the shift or modulation output of the self-sustaining oscillator. The sensor as demonstrated uses no optics, no input microwaves, and, not including digitization electronics, consumes less than 300 mW of power and exhibits a sensitivity at or below tens of pT/√{square root over (Hz)}. In some implementations, the sensor is less than 1 mL in volume.

Oscillator-based solid-state spin sensor

A magnetometer containing a crystal sensor with solid-state defects senses the magnitude and direction of a magnetic field. The solid-state defects in the crystal sensor absorb microwave and optical energy to transition between several energy states while emitting light intensity indicative of their spin states. The magnetic field alters the spin-state transitions of the solid-state defects by amounts depending on the solid-state defects' orientations with respect to the magnetic field. The optical read out, reporting the spin state of an ensemble of solid-state defects from one particular orientation class, can be used to lock microwave signals to the resonances associated with the spin-state transitions. The frequencies of the locked microwave signals can be used to reconstruct the magnetic field vector.

Methods and apparatus for optically detecting magnetic resonance

Applying a bias magnetic field to a solid-state spin sensor enables vector magnetic field measurements with the solid-state spin sensor. Unfortunately, if the bias magnetic field drifts slowly, it creates noise that confounds low-frequency field measurements. Fortunately, the undesired slow drift of the magnitude of the bias magnetic field can be removed, nullified, or cancelled by reversing the direction (polarity) of the bias magnetic field at known intervals. This makes the resulting solid-state spin sensor system suitable for detecting low-frequency (mHz, for example) changes in magnetic field or other physical parameters.

Chopped bias magnetic field solid-state spin sensor for low frequency measurements of physical quantities

Microwave resonator readout of the cavity-spin interaction between a spin defect center ensemble and a microwave resonator yields fidelities that are orders of magnitude higher than is possible with optical readouts. In microwave resonator readout, microwave photons probe a microwave resonator coupled to a spin defect center ensemble subjected to a physical parameter to be measured. The physical parameter shifts the spin defect centers' resonances, which in turn change the dispersion and/or absorption of the microwave resonator. The microwave photons probe these dispersion and/or absorption changes, yielding a measurement with higher visibility, lower shot noise, better sensitivity, and higher signal-to-noise ratio than a comparable fluorescence measurement. In addition, microwave resonator readout enables coherent averaging of spin defect center ensembles and is compatible with spin systems other than nitrogen vacancies in diamond.

Microwave resonator readout of an ensemble solid state spin sensor

Here we present a solid-state spin sensor with enhanced sensitivity. The enhanced sensitivity is achieved by increasing the T* dephasing time of the color center defects within the solid-state spin sensor. The T* dephasing time extension is achieved by mitigating dipolar coupling between paramagnetic defects within the solid-state spin sensor. The mitigation of the dipolar coupling is achieved by applying a magic-angle-spinning magnetic field to the color center defects. This field is generated by driving a magnetic field generator (e.g., Helmholtz coils) with phase-shifted sinusoidal waveforms from current source impedance-matched to the magnetic field generator. The waveforms may oscillate (and the field may rotate) at a frequency based on the precession period of the color center defects to reduce color center defect dephasing and further enhance measurement sensitivity.

Stationary magic angle spinning enhanced solid state spin sensor

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Arlington, MA, United States of America

Linh M Pham