Advanced Optical And Atom Interferometry For Research In QED And Relativity

Advanced optical and atom interferometry for research in QED and Relativity.

Holger Müller, Stanford

In the first part of this talk, we discuss tests of Lorentz symmetry that use ultrastable optical interferometers, cryogenic opti­cal reso­nators. Lorentz violation in electrodynamics (“photon sec­tor”) would shift the cavity reso­nan­ces; Lorentz violation in the motion of the elec­trons in the material (“matter sector”) would strain the cavity, also causing a measurable frequency change. We obtain several of our best tests of Lorentz invari­ance, surpassing predecessors by factors of up to 100. A recent analysis of data taken in Perth (Australia) and Berlin (Germany) simultaneously sets the most precise limits on Lorentz violation in the photon and matter sectors.

In the second part, we discuss atom interferometry. We describe the first competitive laboratory test of Einsteinian (post-Newtonian) gra­vity. It is based on the most precise cold-atom gravimeter thus far, a Mach-Zehnder atom interferometer with a pulse separation time of 400 ms. From 15 d of data, we obtain bounds on seven parameters that characterize preferred frame effects in gravity, with a sensitivity at the parts per billion (ppb) level. Comparison with the best astro­physics data (from 30 years of lunar laser ranging) fuels the hope that new insights might soon be gained from testing post-Newtonian physics in the laboratory.

Then, I present an atom interferometer that uses multi- (up to 24- ) photon Bragg diffraction as beam splitters, to increase the sensitivity even further. This is the largest momentum splitting in any light-pulse atom interferometer. It increases the phase shift, and thus the sensitivity, by 144 times rela­tive to established technology. Moreover, it allows for the cancel­lation of important syste­matic effects.

We furthermore realized the first simul­taneous conjugate Ramsey-Bordé-inter­fero­meters, to take out syste­matic influences such as gravity and vibrational noise.

The dramatic increase in sensitivity and precision this provides may be applied for, e.g., measurements of inertial forces, navigation, or tests of general relativity. Our near-term goal is measuring h/M, the ratio of the Planck constant to the mass of the cesium atom, and thereby the fine-structure constant, at the sub-ppb level. By comparison to the value derived from the electron's anomalous magnetic moment g-2, this would make the most precise test of the theory of quantum electrodynamics and may provide interesting bounds on supersymmetric theories, a possible internal structure of the electron, or low-energy dark matter candidates.

Finally, we will discuss the synthesis of atom interferometry and optical cavities: Cavity-assisted atomic fountain experiments. The cavity provides for mode-cleaning, resonant enhancement, and spatio-temporal modulation of the lasers, as well as single-atom detection. By envisioned special techniques, the versatility of free-beam experi­ments can be kept. Applications include precision atom inter­fero­metry, like for measuring h/M, short-range forces, the gravitational constant G, or gravi­ta­tio­nal frame-dragging. It can also realize a resonant cavity for matter waves, which would be useful in precision measurements as well as developing high-brightness atom sources or a new path towards quantum degeneracy and atom lasers. As a final example, the very clean, large, and versatile optical lattices that can be realized with this technology should prove to be valuable tools for quantum simulation and research on new quantum states of matter. Time per­mit­ting, an outlook on the development of other AMO physics technology will also be given.