Fragility of surface states in topological superfluid 3He

Abstract

Superfluid 3He, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust. Here we demonstrate that in topological superfluids and superconductors the surface Andreev bound states, which depend on the momentum space topology of the emergent order parameter, are fragile with respect to the details of surface scattering. We confine superfluid 3He within a cavity of height D comparable to the Cooper pair diameter ξ0. We precisely determine the superfluid transition temperature Tc and the suppression of the superfluid energy gap, for different scattering conditions tuned in situ, and compare to the predictions of quasiclassical theory. We discover that surface magnetic scattering leads to unexpectedly large suppression of Tc, corresponding to an increased density of low energy bound states.

Nonlinear two-level dynamics of quantum time crystals

“…These are important capabilities for realising magnon-based devices 27 – 32 . To access phenomena such as quantum entanglement, few-magnon operations can be implemented using nano-fluidic confinement and ultra-sensitive NMR techniques 33 , 34 . We emphasise that similar physical phenomena including quasiparticle Bose-Einstein condensation and the emergence of time crystals can be accessed in certain solid-state room-temperature systems, for example based on magnons in YIG films 35 – 42 .…”

Superfluid $^3$He in Planar Aerogel

“…It is worth noting that in the planar aerogel the anisotropy of scattering of 3 He quasiparticles is analogous to that in a narrow gap, and in the recent experiments with 3 He-A in a very thin gap [54] it was suggested that the suppression of the superfluid transition in the presence of solid paramagnetic 3 He on the walls is partially due to the magnetic scattering.…”

Superfluid Optomechanics With Phononic Nanostructures

“…In nanofluidic geometries, atomically smooth silicon surfaces can be used to reach a specularity close to its maximum value [93]. Additionally, the specularity of the walls in these geometries could be tuned in-situ with the amount of 4 He atoms covering the surface [40]. The maximum specularity (S = 0.98) was obtained with a coverage of 3-4 atomic layers of 4 He, which is enough to form a superfluid 4 He layer on the surface.…”

“…In the present work, we propose a novel architecture for superfluid optomechanics, based on engineered nanostructures allowing a better control over superfluid phonon propagation, preserving superfluid 4 He's exceptional intrinsic properties, and leading to enhanced quality factors and coupling strengths. Exploiting recent progress in quantum nanofluidics, concerning the confinement at the nanoscale of quantum fluids (liquid helium-4 [27][28][29][30][31][32][33][34] and liquid helium-3 [29,[35][36][37][38][39][40]), one can form a nanoscale cavity of typically hundreds of nm in height, and tens of µm in width defining the boundaries of a picogram or femtogram scale superfluid acoustic resonator [30][31][32]. Such superfluid acoustic resonator could be formed by means of a microsale hollow volume within a glass or silicon substrate.…”