Quantum devices with superfluid helium

We pursue two primary research directions:

1. Superfluid Josephson Devices:
   We are developing Josephson junctions using superfluid 4He operating far below the transition temperature​, providing a robust framework for the development of novel quantum devices, such as ultra-sensitive inertial quantum sensors, quantum-limited acoustic amplifiers, and qubits. This is enabled by recent developments in the synthesis of 2D nanoporous polymer membranes, which have pore diameters on the order of the superfluid order parameter coherence length (~9 Å). These weak links span micron-scale apertures and are integrated into hydromechanical resonators monitored by SQUID-based displacement sensors. We expect this work to be a significant advancement compared to previous works, which successfully demonstrated Josephson effects in superfluid to only within 5mK [1, 2], where both the superfluid fraction approaches zero and the thermal noise would severely limit the sensitivity of any practical device. This work is part of a collaborative effort funded by the QuSeC-TAQS program, with Benjamin King (University of Nevada Reno), Keith Schwab (Caltech), Adrian Del Maestro (University of Tennessee), and Erik Henriksen (Washington University in St. Louis).‍
2. Acoustic Sagnac Gyroscopy:
   Additionally, we are developing a rotation sensor based on the Sagnac effect for first sound in superfluid helium. This approach bypasses the need for weak links, using the low-loss propagation of acoustic waves in closed superfluid loops to detect rotational phase shifts. By leveraging the frictionless nature of the superfluid and the high-Q nature of acoustic modes, this device architecture promises enhanced sensitivity for applications in geodesy, general relativity, and inertial navigation.

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