Superfluid helium-4 is a remarkable state of matter: a stable quantum condensate, available in liter quantities, which demonstrates frictionless motion, quantum coherence over macroscopic distances, and quantum interference. It is chemically perfectly pure, isotopically ultra-pure, and is routable in both macro and micro-fluidic circuits. Some of these properties provide important advantages over other quantum condensates such as atomic Bose-Einstein condensate: BEC's are small, need to be recreated every few seconds, and is difficult to route in circuits. It is now becoming clear that superfluid helium could be very useful for ultra-sensitive experiments which address fundamental questions spanning geodesy, astrophysics, general relativity, and particle physics. Superfluid acoustic resonators with very large quality factors (Q ≈ 10^8), coupled to very low dissipation superconducting resonators has been demonstrated, with quality factors of 10^11 possible for temperatures < 10mK . Estimates suggest this system has the potential, limited by thermal noise at milli-kelvin temperatures, to sense the gravitational waves expected from the nearest pulsars with initial experiments under-development. Superfluid optomechanics has been demonstrated over very large range of sample size, from cm-scale, to micron size, spanning 10^3 to nearly 10^9Hz resonances[2, 5, 6]. It is now been shown that superfluid acoustic resonators can provide new bounds on the phase-space for dark-matter candidates[7, 8], with initial experiments very recently reported.
Beyond the very sensitive detection possible with extremely low loss acoustic resonators, is the
opportunity to utilize the quantum phase coherence to form ultra-sensitive matter-wave interfer-
ence devices. It has been demonstrated that superfluid helium interferometers with sensing loops
exceeding 1 meter in length can sense the earth’s rotation[10, 11]. Much more sensitive quantum
interference gyroscopes appear possible with the realization of a Josephson junction using new 2D
materials, which may put the sensing of the fluctuations in the rotation of the earth’s rotation and
general relativistic effects such as the Lense-Thirring effect within reach. These devices may
find use in precision pointing of telescope. It is also possible that superfluid interferometers may place bounds on dark-matter candidates in similar ways which atomic interferometers can.
Finally, with a superfluid Josephson junctions comes the possibility for engineered two-level
systems, a superfluid qubit. This has obvious possible applications to quantum information, but
more broadly, it may form the mechanism for the detection and manipulation of single acoustic
quanta in the superfluid, and the engineering of quantized fluid circuits, similar to what has been
demonstrated in superconductivity. All of these possibilities are waiting to be explored once a
proper Josephson junction structure has been demonstrated, which is the current research focus in
a recent NSF QuSeC-TAQS award (to Schwab and collaborators.)
The main focus of a thesis project will be the development of a superﬂuid Josephson junction using new 2D nanoporous materials which is provide by chemists and material science groups. Techniques which will be used are cryogenics, sensitive electronic detection (RF to microwave frequencies,) vacuum systems, and novel apparatus development. No previous experience with these technicques is required. An interest in current questions in fundamental physics is also important.
 L.A. De Lorenzo and K.C. Schwab, ”Ultra-High Q Acoustic Resonance in Superﬂuid He4,”
Journal of Low Temperature Physics, 186, 233–240, (2017).
 L.A. De Lorenzo and K.C. Schwab, ”Superﬂuid optomechanics: coupling of a superﬂuid to a
superconducting condensate.” New Journal of Physics 16.11 (2014): 113020.
 S. Singh, L.A. De Lorenzo, I. Pikovski, and K.C. Schwab, ”Detecting continuous gravitational
waves with superﬂuid 4He,” New Journal of Physics 19, 073023 (2017).
 Vadakkumbatt, V and Hirschel, M and Manley, J and Clark, TJ and Singh, S and Davis, JP,
”Prototype superﬂuid gravitational wave detector,” Physical Review D, 104, 082001 (2021).
 Harris, GI and McAuslan, DL and Sheridan, E and Sachkou, Y and Baker, C and Bowen, WP, ”Laser cooling and control of excitations in superﬂuid helium, ” Nature Physics, 12, 788-793,(2016.)
 Shkarin, AB and Kashkanova, AD and Brown, CD and Garcia, S and Ott, K and Reichel, J and Harris, JGE, ”Quantum optomechanics in a liquid,” Physical review letters, 122, 153601,(2019.)
 Schutz, Katelin and Zurek, Kathryn M, ”Detectability of light dark matter with superﬂuid
helium,” Physical review letters, 117, 121302 (2016).
 Manley, Jack and Wilson, Dalziel J and Stump, Russell and Grin, Daniel and Singh, Swati, ”Searching for scalar dark matter with compact mechanical resonators,” Physical review letters, 124, 151301 (2020.)
 Hirschel, M and Vadakkumbatt, V and Baker, NP and Schweizer, FM and Sankey, JC and Singh, S and Davis, JP, ”HeLIOS: The Superﬂuid Helium Ultralight Dark Matter Detector,” arXiv preprint arXiv:2309.07995, 2023.
 K.C. Schwab and N. Bruckner and R.E. Packard, ”Detection of the Earth’s rotation using
superﬂuid phase coherence,” Nature, 386, 585-587 (1997).
 Bruckner, Niels and Packard, Richard, ”Large area multiturn superﬂuid phase slip gyroscope,” Journal of applied physics, 93, 1798–1805 (2003.)
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Kenneth G., Gendreau, Keith C., Karovska, Margarita Kaaret, Philip E., Reasenberg, Robert D., SPIE 5491 (2004), 320.
 Du, Yufeng and Murgui, Clara and Pardo, Kris and Wang, Yikun and Zurek, Kathryn M, ”Atom interferometer tests of dark matter,” Physical Review D, 106, 095041 (2022).