Magnetometry based on electron spin defects

Abstract

A magnetometer includes: a substrate; a diamond layer on the substrate, in which the diamond layer includes a defect sub-layer including multiple lattice point defects; a microwave field transmitter; an optical source configured to emit light including a first wavelength that excites the multiple lattice point defects from a ground state to an excited state; a photodetector arranged to detect photoluminescence including a second wavelength emitted from the defect sub-layer, in which the first wavelength is different from the second wavelength; and a magnet arranged adjacent to the defect sub-layer.

What is claimed is: 
     
         1 . A method of performing magnetocardiography using a magnetometer, wherein the magnetometer comprises an electron spin defect layer comprising a plurality of lattice point defects, a microwave field transmitter, an optical source, a photodetector, and a magnet, the method comprising:
 rotating the magnetometer around a rotation axis and relative to a first time-varying magnetic field of a first frequency so that the magnetometer experiences a second time-varying magnetic field of a second frequency that is greater than the first frequency, wherein the first time-varying magnetic field is emitted from a heart;   directing, during the rotation of the magnetometer, light from the optical source toward the electron spin defect layer, wherein the light comprises a first wavelength that excites the plurality of lattice point defects from a ground state to an excited state;   detecting, during the rotation of the magnetometer, a photoluminescence from the electron spin defect layer using the photodetector to provide a measurement signal, wherein the photoluminescence comprises a second wavelength that is different from the first wavelength; and   determining, from the measurement signal, information about the first time-varying magnetic field.   
     
     
         2 . The method of  claim 1 , wherein rotating the magnetometer comprises oscillating the magnetometer around the rotation axis at a rotation angle of less than 360 degrees. 
     
     
         3 . The method of  claim 1 , comprising applying a microwave signal to the electron spin defect layer, wherein applying the microwave signal comprises applying a series of microwave pulses, wherein the series of microwave pulses comprises a first pi/2 pulse, one or more pi pulses subsequent to the first pi/2 pulse, and a second pi/2 pulse subsequent to the first pi pulse, and wherein the one or more pi pulses are applied at a same time as a zero-crossing of the second time-varying magnetic field. 
     
     
         4 . The method of  claim 1 , wherein the magnetometer comprises a microwave field control circuit to generate a microwave source signal, and wherein the method comprises:
 prior to rotating the magnetometer, sweeping a frequency of the microwave source signal over a predetermined range; and   identifying a reduction in photoluminescence from the photodetector at a first microwave frequency within the predetermined range to locate an electron spin resonance frequency.   
     
     
         5 . The method of  claim 1 , wherein determining information about the first time-varying magnetic field comprises:
 extracting a quantum phase accumulation from the measurement signal; and   determining a vector of the first time-varying magnetic field, a magnitude of the first time-varying magnetic field, a phase of the first time-varying magnetic field or both the magnitude and the phase of the first time-varying magnetic field from the quantum phase accumulation.   
     
     
         6 . The method of  claim 1 , wherein directing the light from the optical source toward the electron spin defect layer comprises directing the light from the optical source through the electron spin defect layer so that the light impinges on an interface of the electron spin defect layer at an angle greater than a total internal reflection critical angle of the interface. 
     
     
         7 . The method of  claim 1 , wherein one or surfaces of the electron spin defect layer include mirrors configured to reflect the light from the optical source within the electron spin defect layer. 
     
     
         8 . The method of  claim 1 , wherein directing the light from the optical source toward the electron spin defect layer comprises recycling the light in an optical resonator cavity defined by at least three surfaces, on at least three sides of the optical resonator cavity, that are arranged to reflect the light within the optical resonator cavity,
 wherein the light from the optical source is transmitted into the optical resonator cavity through a first surface of the at least three surfaces, and   wherein at least a portion of the electron spin defect layer constitutes one or more of the at least three surfaces of the optical resonator cavity.   
     
     
         9 . The method of  claim 1 , wherein the electron spin defect layer, the microwave field transmitter, the optical source, the photodetector, and the magnet are arranged on a single chip, the single chip secured to a platform, and
 wherein rotating the magnetometer comprises rotating the platform.   
     
     
         10 . The method of  claim 1 , wherein the electron spin defect layer is seated within a recess of a substrate, and
 wherein the recess comprises at least one reflective sidewall facing the electron spin defect layer to reflect the light from the optical source towards the electron spin defect layer or to redirect the light from the optical source that has been reflected from the electron spin defect layer.   
     
     
         11 . The method of  claim 1 , wherein rotating the magnetometer comprises rotating the magnetometer with a frequency of rotation that is greater than the first frequency. 
     
     
         12 . The method of  claim 1 , wherein rotating the magnetometer comprises rotating the magnetometer such that an axis of rotation of the magnetometer is substantially perpendicular to a magnetic field vector of the first time-varying magnetic field. 
     
     
         13 . The method of  claim 1 , comprising attaching an enclosure comprising the magnetometer to an article of clothing. 
     
     
         14 . The method of  claim 1 , comprising adhering an enclosure comprising the magnetometer to skin.