Atomic magnetometers

Our group has been developing several types of atomic magnetometers using laser-pumped alkali-metal atoms. Such atoms (K, Rb, or Cs) can be contained in a small glass cell that is simply heated to achieve high atom density. We developed spin-exchange relaxation free (SERF) and radio-frequency (RF) atomic magnetometers that are being used for detection of weak signals of practical significance, such as magnetic signals from the heart and the brain. Our goal is to achieve the highest possible magnetic field sensitivity, often setting world records for sensitivity in a given sensor volume. Our current focus is on the development of vector magnetic field sensors that can simultaneously detect the three vector field components with quantum-limited sensitivity.

Nuclear spin co-magnetometers

Another long-standing focus of our group is the development of co-magnetometers that use two different spin species to measure magnetic field in the same volume. The goal of these sensors is to search for new physics that couples to spins while excluding the effects of ordinary magnetic fields. With such sensors we set the best limits of violation of local Lorentz invariance, long-range spin-dependent forces and possible axion-like dark matter. In general, most new physics effects that couple to particle spin can be searched for using co-magnetometers. In the past we focused on alkali-metal  nuclear-spin co-magnetometers that can achieve the highest energy resolution. Our recent focus is on the development of noble gas co-magnetometers containing two noble gas species with nuclear spins (for example He-3 and Xe-129 or  Ne-21). Such systems have particularly long spin coherence times and strong signals, so can eventually achieve even higher energy resolution. Spin co-magnetometers also can be used as inertial rotation sensors with competitive sensitivity, so they have a practical application as well.

Rydberg atom microwave detectors

Our recent new project is the development of detectors for microwave signals in the GHz range using alkali-metal atoms excited to Rydberg states. Such atoms can still be  contained in a glass cell at room temperature, making it a very practical sensor. Estimates of sensitivity indicate that Rydberg atom detectors can exceed the sensitivity of room temperature microwave antennas. We are making progress toward realizing such a quantum-limited antenna. We use multi-pass optical cells that allow one to control the optical path length separately for the two laser beams participating in the interrogation of Rydberg atoms. 

Portable operation of atomic sensors

Another direction of our research is in the development of portable magnetic field sensors. Here we collaborate closely with a small company Twinleaf  started by former group members. We investigate fundamental limitations of portable self-contained magnetic field sensors and help develop their applications, for example in measurements of magnetoencephalography (MEG) signals generated by electrical currents in the human brain. Such signals are a billion times smaller than Earth's magnetic field and could only be studied for many years using liquid-helium cooled SQUID magnetometers inside heavily shielded rooms. We have previously demonstrated detection of MEG signals using SERF atomic magnetometers inside a magnetic shield, but  now we can detect such signals with a portable system without a magnetic shield by making use of the high dynamic range of our recent scalar atomic magnetometers.