Magnetometry through direct phase measurement with correlated frequency combs

The PIs propose the development of a generic sensor with enhanced resolution arising from measuring signal phase rather than amplitude, and enhanced sensitivity that comes from the implementation of the sensor in an integrated photonics platform. The team will demonstrate the enhanced resolution and sensitivity through sensing of magnetic field gradients. Gradient magnetic field detection is only one application, with a huge impact on magnetic imaging applied to the heart, brain, and magnetic nanoparticles for tracing cancer cells. The integrated optics devices being inherently lightweight and compact, this sensor will have the capability of leading to wearable and portable sensors. Additionally, this sensor technology can be applied to rotation sensing, measuring acceleration or displacement, and index of refraction measurements, which makes it useful for a large number of navigational and manufacturing processes. TECHNICAL DESCRIPTION Most sensors are based on measuring a phase by detecting the amplitude of interfering beams. The PIs propose instead a different approach to sensing, in which they exploit frequency comb techniques to make direct phase detection rather than signal amplitude. This project encompasses a theoretical study of quantum mechanics applied to sensing, (“exceptional points” and squeezing), verification of the theory with a discrete components laser, and application to a chip magnetometer. This work builds on successful tabletop experiments demonstrating sub-nanoradian resolution using frequency comb mode-locked lasers and Optical Parametric Oscillators. Use of dual-propagating frequency combs of the same repetition rate facilitates both large signal to noise beat and common mode cancellation of 1/f noise. By miniaturizing this setup using on-chip waveguide resonators, the investigators will be able to improve the sensitivity, which scales as the inverse of the cavity dimensions. Dispersion manipulation will be used to enhance the signal with no noise penalty. Once the noise has reached the classical limit, quantum mechanical squeezing will be devised to further enhance the signal to noise ratio. As an example of practical application, the team will concentrate their efforts on a demonstration of chip (gradient) magnetometry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.