Wideband Dual Sphere Detector of Gravitational Waves

We present the concept of a sensitive and broadband resonant mass gravitational wave detector. A massive sphere is suspended inside a second hollow one. Short, high-finesse Fabry-Perot optical cavities read out the differential displacements of the two spheres as their quadrupole modes are excited. At cryogenic temperatures, one approaches the standard quantum limit for broadband operation with reasonable choices for the cavity finesses and the intracavity light power. A molybdenum detector, of overall size of 2 m, would reach spectral strain sensitivities of $2\times {10}^{-23\mathrm{}}{\mathrm{Hz}}^{-1/2\mathrm{}}$ between 1000 and 3000 Hz.