Quantum optics and Quantum sensing in the Centre for Cold Matter
The Centre for Cold Matter has a major activity in quantum technology by using atom interferometry to sense small forces. These are (i) inertial sensing for navigation, and (ii) testing fundamental physics. These activities are funded by the MoD and by EPSRC.
Our atom interferometers use laser light to prepare the internal and motional states of a cloud of rubidium atoms. Next, the light splits the atomic wavefunction so that it propagates along two separated paths, before recombining these with a phase difference , much as light waves are split and recombined in a conventional Mach-Zehnder interferometer.
We use fluorescence detection to measure the final populations of two hyperfine ground states, which are given by and , as a result of quantum interference. If the atom is accelerated – for example by gravity or some other small force – this produces a shift of the phase . The conversion from phase shift to acceleration depends only on the wavelength of the laser light and on the timing of the light pulses. These are both very accurate and stable, so this device measures acceleration much more reliably than the best conventional accelerometers. It can also be extremely sensitive – for example the instrument in our laboratory can sense changes of a few billionths of the acceleration due to gravity.
Inertial sensing and navigation
One main line of this research is to apply that sensitivity and accuracy to enable navigation without the use of eternal signals such as Sonar or Satellite communications. To do this we need to very accurately measure accelerations. Then by integrating this signal twice we can determine our position with both high accuracy and precision.
This will enable vehicles to navigate without the need to communicate with external sources like GPS.
Testing fundamental physics
A second application of atom interferometry is to sense the very small force that is predicted by theories of dark energy. Cosmologists have observed that the expansion of the universe is accelerating and propose that this is due to a new scalar field, whose particles are very light. The energy density of this field drives the universal acceleration, but it is also expected to produce a small force between atoms and a test mass in vacuum. Our experiment uses atom interferometry to search for that force[1,2].
 Clare Burrage, Edmund J. Copeland, E. A. Hinds. JCAP 03 (2015) 042.
 Hamilton et al. Science, 349, 849-851 (2015).