Superconducting thin film spiral coils as low-noise cryogenic actuators

We present results on actuator development for a cryogenic superconducting inertial sensor with a displacement sensitivity of a few fm/√Hz at 0.5 Hz. The first version will use niobium as sensor mechanics material. Niobium is sufficiently superconducting below 5 K allowing superconducting coils to form low-noise actuators as part of a force feedback sensing scheme. Future improvements include the use of silicon in combination with high temperature superconductors for even lower frequency fm/√Hz performance. This device will be the world's most sensitive low-frequency inertial sensor. Here, we focus on its actuator, which ensures low-noise performance below 5 Hz by decreasing the mechanical loss and therefore thermal noise.