Progress Towards a Low Temperature Superfluid 4He Josephson Junction using 2D Nanoporous Materials

We outline our progress in creating a superfluid 4He Josephson junction that will function far below the superfluid transition temperature T_λ , providing a robust framework for the development of novel quantum devices, such as ultra-sensitive inertial quantum sensors, quantum-limited acoustic amplifiers, and qubits. Our approach is to utilize recent developments in the synthesis of 2D nanoporous polymers with a pore size of 9Å,, which is on the order of the coherence length in the superfluid, ξ ~3Å. These polymer films are covalently bonded and are able to span micron size apertures. We discuss the design and operation of our experimental cell used to detect Josephson physics in superfluid 4He using these materials, which employs a SQUID-based position sensor to detect driven superfluid motion in a hydromechanical resonator. We expect this work to be a significant advancement compared to previous works, which successfully demonstrated Josephson effects in superfluid 4He to only within ~5 mK of T_ λ, where both the superfluid fraction approaches zero and the thermal noise would severely limit the sensitivity of any practical device.