MHz gravitational wave constraints with decameter Michelson interferometers

A new detector, the Fermilab Holometer, consists of separate yet identical 39-meter Michelson interferometers. Strain sensitivity achieved is better than 10(-21) / root Hz between 1 to 13 MHz from a 130-h data set. This measurement exceeds the sensitivity and frequency range made from previous high frequency gravitational wave experiments by many orders of magnitude. Constraints are placed on a stochastic background at 382 Hz resolution. The 3 sigma upper limit on Omega(GW), the gravitational wave energy density normalized to the closure density, ranges from 5.6 x 10(12) at 1 MHz to 8.4 x 10(15) at 13 MHz. Another result from the same data set is a search for nearby primordial black hole binaries (PBHB). There are no detectable monochromatic PBHBs in the mass range 0.83-3.5 x 10(21) g between the Earth and the Moon. Projections for a chirp search with the same data set increase the mass range to 0.59 - 2.5 x 10(25) g and distances out to Jupiter. This result presents a new method for placing limits on a poorly constrained mass range of primordial black holes. Additionally, solar system searches for PBHBs place limits on their contribution to the total dark matter fraction.