Sound Propagation in a Bose-Fermi Mixture: From Weak to Strong Interactions.

Particlelike excitations, or quasiparticles, emerging from interacting fermionic and bosonic quantum fields underlie many intriguing quantum phenomena in high energy and condensed matter systems. Computation of the properties of these excitations is frequently intractable in the strong interaction regime. Quantum degenerate Bose-Fermi mixtures offer promising prospects to elucidate the physics of such quasiparticles. In this work, we investigate phonon propagation in an atomic Bose-Einstein condensate immersed in a degenerate Fermi gas with interspecies scattering length a_{BF} tuned by a Feshbach resonance. We observe sound mode softening with moderate attractive interactions. For even greater attraction, surprisingly, stable sound propagation reemerges and persists across the resonance. The stability of phonons with resonant interactions opens up opportunities to investigate novel Bose-Fermi liquids and fermionic pairing in the strong interaction regime.

A cavity loadlock apparatus for next-generation quantum optics experiments.

Cavity quantum electrodynamics (QED), the study of the interaction between quantized emitters and photons confined in an optical cavity, is an important tool for quantum science in computing, networking, and synthetic matter. In atomic cavity QED, this approach typically relies upon an ultrahigh vacuum chamber that hosts a cold trapped atomic ensemble and an optical cavity. Upgrading the cavity necessitates a months-long laborious process of removing external optics, venting, replacing the resonator, baking, and replacing optics, constituting a substantial bottleneck to innovation in resonator design. In this work, we demonstrate that the flexibility of optical cavities and the quick turnaround time in switching between them can be restored with the vacuum loadlock technique-reducing the cycle time to install a cavity, bake it, and transport it into the science chamber for days, achieving 3 × 10-10 Torr pressure in the science chamber. By reducing vacuum limitations, this approach is particularly powerful for labs interested in quickly exploring novel optic cavities or any other atomic physics relying on in-vacuum optics.