Guided atom clock interferometry is a new paradigm in atom interferometry. This is so for two reasons. 1) the interferometer arms are not determined by the free-fall of the atomic clouds, but by a matter-wave-guide, and 2) the beam splitter is either a π/2 pulse of the Bragg scheme (which splits the wavepacket in momentum components via laser radiation) or a π/2 pulse of the Ramsey scheme (which splits the wavepacket in spin components via, usually, microwave radiation). π-pulses can be used analogously to mirrors in both cases. Figure 1 shows a sketch of how this would work
We have developed fundamental tools to get, in particular, the atom interferometry Ramsey scheme to measure the Sagnac phase (briefly: this is the phase that two waves travelling along opposite paths along a closed loop develop if this loop is placed in a rotating frame). The first of this tools is state-dependent manipulation of two spin states: under the same experimental sequence, each spin state travels along the ring in an opposite direction (we did this together with T. Fernholz at Nottingham). Figure 2 shows both a simulation and experimental images of state-dependent manipulation in the ring waveguide.
But this is not enough! A Ramsey interferometer relies on the preservation of the superposition state created after the first pulse for as long as the duration of the free-evolution time (which, in this case, consists of, at least, one round trip along the ring waveguide). In Rubidium 87 atoms, two spin-states, the hyperfine Zeeman sub-levels and are well regarded for this job, because of their “magic field” (no, really, this link). At this magic field, a superposition state is robust against magnetic field fluctuations.
However, things get complicated when these spin states enter the ring potential. The reason is that the trapping is based in Radio-Frequeny (RF) dressing. RF-dressing results in non-trivial spectra when driving transitions between the two hyperfine manifolds F=1 and F=2, and it also ends up broadening the magic transition, which shortens the dephasing time of the superposition state.
We have worked, together with our colleages at Nottingham and Sussex to understand microwave transitions between RF-dressed states.
We have narrowed down the not-anymore-a-clock-transition in an RF-dressed potential by one order of magnitude and interferometry will be coming soon!