SOGRO: Superconducting Tensor Detector for Mid-Frequency Gravitational Waves*

Detection of gravitational waves (GWs) from binary black holes (BHs) and binary neutron stars by advanced laser interferometers has opened a new window of astronomical observation. Many conceivable sources such as intermediate-mass BH binaries and white dwarf binaries, as well as inspiraling stellar-mass BH binaries, would emit GWs below 10 Hz. It is highly desirable to open a new window in the infrasound frequency band below 10 Hz. We propose to construct a mid-frequency tensor detector by combining six magnetically levitated superconducting test masses. Seismic and Newtonian gravity noise are serious obstacles in constructing terrestrial GW detectors at sub-Hz frequencies. The proposed detector is capable of rejecting the seismic noise to one part in 10$^{\mathrm{9}}$ by its common-mode rejection characteristic, and can reject the near-field Newtonian gravity noise to a sufficient degree by its full-tensor nature. Such a detector is equally sensitive to GWs coming from anywhere in the sky, and is capable of resolving the source direction and wave polarization. I will present the design concept of a new mid-frequency detector, named SOGRO, which could reach a strain sensitivity of 10$^{\mathrm{-19}}$-10$^{\mathrm{-21}}$ Hz$^{\mathrm{-1/2}}$ at 0.1-10 Hz.