Remote sensing of a levitated superconductor with a flux-tunable microwave cavity

We present a cavity-electromechanical system comprising a superconducting quantum interference device which is embedded in a microwave resonator and coupled via a pickup loop to a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mn>6</a:mn></a:math>-<d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mtext fontfamily="times">μ</d:mtext><d:mrow><d:mi mathvariant="normal">g</d:mi></d:mrow></d:math> magnetically levitated superconducting sphere. The motion of the sphere in the magnetic trap induces a frequency shift in the SQUID-cavity system. We use microwave spectroscopy to characterize the system, and we demonstrate that the electromechanical interaction is tunable. The measured displacement sensitivity of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><i:msup><i:mn>10</i:mn><i:mrow><i:mo>−</i:mo><i:mn>7</i:mn></i:mrow></i:msup><i:mspace width="0.1em"/><i:mrow><i:mrow><i:mi mathvariant="normal">m</i:mi></i:mrow></i:mrow><i:mo>/</i:mo><i:msqrt><i:mi>Hz</i:mi></i:msqrt></i:math> defines a path towards ground-state cooling of levitated particles with Planck-scale masses at millikelvin environment temperatures. Published by the American Physical Society 2024