Picometer Metrology for Fundamental Science: The Equivalence Principle and Exoplanets

The Standard Model unifies electricity and magnetism and the weak and strong nuclear forces. Theories that unify gravity with the Standard Model frequently violate the weak equivalence principle (WEP). The WEP states that under the influence of identical gravitational fields, bodies fall identically, independent of their composition. Testing the WEP provides one of the few experimental probes of these unifying theories. The Ground-based Principle Of Equivalence Measurement (G-POEM) will be sensitive to WEP violations of 5 parts in 10^14 in a run of one day. In G-POEM, we will drop test masses made of disparate materials repeatedly and observe their fall with a picometer laser distance gauge, the Tracking Frequency Gauge (TFG). There is a well-developed concept for a sounding-rocket version that would improve the precision to 1 part in 10^17.

We now know that many stars have planets. A key step in studying these planets further is to observe directly light reflecting from them. This requires suppressing the light from the nearby host star by up to 10 orders of magnitude. This suppression requires a space-based telescope with extreme dimensional stability. The TFG can provide the measurements needed for achieving that stability actively.

Phillips developed the TFG and G-POEM at the Smithsonian Astrophysical Observatory. SAO has now donated the equipment to IIT, and Phillips is working with a group here at IIT to develop them further. We are improving the TFG performance in preparation for these and other experiments.