We have demonstrated basic operations of a two-component superconducting gravity gradiometer (SGG) that is constructed with a pair of magnetically levitated test masses coupled to Superconducting Quantum Interference Devices (SQUIDs). An innovative design gives a potential sensitivity of 4 1 / 2

Laser interferometer gravitational-wave (GW) detectors are observing signals from merging black hole and neutron star binaries with a frequency window from 10[Formula: see text]Hz to several kHz. Future space-based laser interferometers will open a new window of 0.1[Formula: see text]mHz to 0.1[Formula: see text]Hz. In this paper, we discuss the possibility of constructing a terrestrial GW detector named Superconducting Omni-directional Gravitational Radiation Observatory (SOGRO), which can fill the missing frequency window, 0.1 to 10[Formula: see text]Hz, with astronomically interesting sensitivity. SOGRO measures all five tensor components of the spacetime metric, which results in uniform sensitivity for all-sky directions and enables identification of the source direction and wave polarization with a single detector. Seismic and Newtonian gravity noise pose the greatest challenges for constructing ground-based detectors below 10[Formula: see text]Hz. SOGRO utilizes enhanced mechanical and electrical stabilities of materials at cryogenic temperatures to reject common-mode seismic noise to a very high degree. Further, its full-tensor characteristic gives an advantage in the rejection of the Newtonian noise over conventional detectors.

State-of-the-art detectors are necessary to measure very tiny variations of gravity produced by spiraling neutron stars, merging black holes, moving tectonic plates. We are developing a superconducting gravity gradiometer and aim to achieve 0.1 mE Hz^{-1/2} in the frequency band of 0.1 mHz to 0.1 Hz. The superconducting test masses are levitated by a superconducting current-carrying monolayer pancake coil, which is one of the key components of the instrument. However, the nonlinear aspect of the magnetic field trapped between the test mass and the pancake coil imposes one of the main constraints to achieve that such low frequencies. In this paper, we investigated the causes of that nonlinearity by finite element method using COMSOL Multiphysics® simulation software. First, inductances were measured with an experimental setup where a gap spacing, created by a pancake coil and a niobium plate, could be adjustable. The inductances computed with a 2D axis-symmetric model satisfactorily agreed to the experimental data. Finally, we extensively studied several mechanisms for cancelling the nonlinearity of the inductance. A solenoid next to the pancake coil is the most effective and practical way to mitigate it. Furthermore, our approach can also be useful for those seeking a simple and effective model to study magnetostatic problems in a superconductor