An optical lattice with sound

Quantised sound waves -- phonons -- govern the elastic response of crystalline materials, and also play an integral part in determining their thermodynamic properties and electrical response (e.g., by binding electrons into superconducting Cooper pairs). The physics of lattice phonons and elasticity...

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Bibliographic Details
Published in:arXiv.org 2022-05
Main Authors: Guo, Yudan, Kroeze, Ronen M, Marsh, Brendan P, Gopalakrishnan, Sarang, Keeling, Jonathan, Lev, Benjamin L
Format: Article
Language:English
Subjects:
Bose-Einstein condensates
Cooper pairs
Crystal defects
Crystal lattices
Crystallization
Elasticity
Electrons
Lattice vibration
Low temperature
Neutral atoms
Optical lattices
Optical properties
Optical resonators
Phonons
Photons
Quantum electrodynamics
Simulators
Sound waves
Thermodynamic properties
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Summary:Quantised sound waves -- phonons -- govern the elastic response of crystalline materials, and also play an integral part in determining their thermodynamic properties and electrical response (e.g., by binding electrons into superconducting Cooper pairs). The physics of lattice phonons and elasticity is absent in simulators of quantum solids constructed of neutral atoms in periodic light potentials: unlike real solids, traditional optical lattices are silent because they are infinitely stiff. Optical-lattice realisations of crystals therefore lack some of the central dynamical degrees of freedom that determine the low-temperature properties of real materials. Here, we create an optical lattice with phonon modes using a Bose-Einstein condensate (BEC) coupled to a confocal optical resonator. Playing the role of an active quantum gas microscope, the multimode cavity QED system both images the phonons and induces the crystallisation that supports phonons via short-range, photon-mediated atom-atom interactions. Dynamical susceptibility measurements reveal the phonon dispersion relation, showing that these collective excitations exhibit a sound speed dependent on the BEC-photon coupling strength. Our results pave the way for exploring the rich physics of elasticity in quantum solids, ranging from quantum melting transitions to exotic ``fractonic'' topological defects in the quantum regime.
ISSN:2331-8422
DOI:10.48550/arxiv.2104.13922