Quantum Coherent Applications of Superfluid 3He

Nontechnical Description:

There are two important challenges today where physics plays an essential role. The first is to develop a new generation of computers that can handle the complexity and vastness of the digital information age. These putative quantum computers take advantage of quantum states of matter which contain information that can be stored and manipulated at sufficiently low temperature that neither thermal fluctuations nor impurities destroy their coherence.

One important class of such quantum states is a robust form of superconductivity which does not have mirror symmetry and is called chirality, analogous to twisted strands of DNA. The paradigm quantum material having this property is superfluid 3He. Investigation in this project of quantum coherence in 3He tests a fundamental prediction that the anomalous thermal Hall can provide an unambiguous identification of chirality in any superconductor that is a candidate material for quantum computation.

There is a second challenge. Our universe appears to be missing 70% of its mass, so-called dark matter. Dark matter is unobserved except for its gravitational impact on star distributions in galaxies.

Its absence from all other observation is an existential problem. Many attempts have been launched to develop high resolution sensing tools to identify this missing mass as it floods throughout our environment. A possible detector is based on high coherence of i nuclear spin precession states in superfluid 3He.

Its known coherence makes it a very attractive choice for this purpose; yet the limits of coherence have not yet been fully explored. A second unique benefit of 3He spin precession for mass sensing, is its tunability allowing continuous measurements in situ to be made over a wide range of dark mass.

Technical Description:

Superfluid helium-three is a known topological quantum condensed system, a model for understanding complex quantum materials and in particular, odd-parity chiral superconductors; a subject of interest to researchers in the burgeoning field of quantum information science. The project Quantum Coherent Applications of Superfluid 3He, is a platform to improve and demonstrate quantum coherence among chiral quantum systems including superconducting quantum materials.

Additionally, these materials provide an opportunity for instrumentation development based on quantum sensing. One such important application addresses the existential problem, how to determine the nature of dark matter. For superfluid 3He, the paradigm system of choice, the quantum degrees of freedom are its nuclear spin and orbital angular momentum coherently manifest on a macroscopic scale.

Superfluid 3He imbibed into very high porosity (98%) uniformly anisotropic silica aerogel controls both the spin and orbital angular momentum quantization axes. Using nuclear magnetic resonance, the directions of these axes can be unambiguously determined. Recent theory predicts that observation of a non-zero thermal Hall effect in the superfluid in uniformly anisotropic silica aerogel defines the chiral axis perpendicular to a thermal gradient.

Confirmation of this theory provides a unique tool, measurement of the transverse thermal conductance, that can be used to determine chirality. The application extends to superconducting materials relevant to quantum information science. Quantum sensing is a second application in this project.

The long-lived, quantum-spin coherent state of superfluid 3He provides a promising detector for light dark matter. Importantly, in this case high sensing sensitivity is combined with the advantage of continuous tuning for the putative dark mass, thereby at the very least establishing limits on galactic axion production, an existential problem in modern physics.

Key to this project is its partnership with theoretical physicists in both the fields of superfluid 3He and dark matter, together with cryogenic and nuclear magnetic resonance spectroscopy expertise at Northwestern.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.