ExpandQISE: Track 1: Bright, Highly Polarization-Squeezed Light Beam for Quantum Metrology

Non-technical Abstract: Squeezed light refers to quantum states of light in which the noise fluctuations in certain quadrature components of the electric field amplitude, or the polarization, are squeezed below the shot-noise limit. This enables better signal-to-noise in optical measurements than possible with perfectly coherent light emanating from the quietest lasers. Currently, there is great interest in exploiting this quantum advantage for precision measurement. Optical magnetometers are paradigmatic examples of high-performance magnetic field sensors that rely on the quantum advantage afforded by polarization-squeezed light. In this project, a new device, essentially a modified magnetometer, is built to generate a polarization-squeezed light beam with an unprecedentedly high degree of squeezing. The emerging beam is especially suited for transformatively advancing the field of quantum-enhanced optical magnetometry. The polarization-squeezed beam may also enable significant advancement in many other diverse fields, ranging from gravitational-wave detection to quantum-limited control of mechanical motion, where squeezed light affords quantum advantage. A close collaboration between Miami University, Ohio and the University of Wisconsin, Madison, leverages existing expertise in optical magnetometry at Wisconsin to synergistically engage Masters’ (MS) students and undergraduates at Miami and also students at high schools near Miami in intensive research and education at the forefront of quantum metrology. Concurrently, the project diversifies and expands student and faculty engagement at Miami in Quantum Information Science and Engineering (QISE) by a) developing two new QISE-centered physics courses, one at the freshman level, the other at the senior / first-year MS level, and b) incorporating key QISE concepts into multiple existing physics courses at all levels that impact several hundred science, technology, engineering, and math (STEM) majors per year. Technical Abstract: The goal of this project is to create a robust and efficient source of polarization-squeezed light to significantly enhance the performance of two widely-used state-of-the-art optical magnetometers, namely, spin-exchange-relaxation-free (SERF) magnetometers, which are currently the most sensitive magnetic sensors at extremely low magnetic fields (below one picoTesla), and Bell-Bloom magnetometers, which operate at earth-scale magnetic fields. The Miami-Wisconsin team’s method to create highly polarization-squeezed light relies on exploiting the physics of off-resonant Faraday rotation in dense atomic vapor. The key to this method is that the quantum polarization fluctuations in the light are mapped into effective magnetic field fluctuations via the AC Stark effect, which causes the atomic spins to alter the spin-dependent index of refraction in such a way as to cancel the original quantum polarization fluctuations. This yields highly polarization-squeezed light in a narrow frequency band from near-dc to about a kHz, where SERF magnetometers operate. Next, the Larmor frequency response of the atoms is engineered to produce squeezing centered at a desired radio frequency, which has vital import for Bell-Bloom magnetometers. The polarization squeezing process is modeled, and new theoretical approaches to squeezing in optical magnetometry are developed. 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.