Abstract
Electron-phonon coupling is a major decoherence mechanism, which often causes scattering and energy dissipation in semiconductor electronic systems. However, this electron-phonon coupling may be used in a positive way for reaching the strong or ultra-strong coupling regime in an acoustic version of the cavity quantum electrodynamic system. Here we propose and demonstrate a phonon cavity for surface acoustic waves, which is made of periodic metal fingers that constitute Bragg reflectors on a GaAs/AlGaAs heterostructure. Phonon band gap and cavity phonon modes are identified by frequency, time and spatially resolved measurements of the piezoelectric potential. Tunneling spectroscopy on a double quantum dot indicates the enhancement of phonon assisted transitions in a charge qubit. This encourages studying of acoustic cavity quantum electrodynamics with surface phonons.
Highlights
1 μm frequency ω is bounded by electric dipole of the length lthanedfitnheeswtrauvcetluernegtchonλs5t,2a0n. tSiαn c~e 13g17e,oamsestereicncionntshtreaifnotrsmreωgqu=ire α V to l 2λ V be for an greater than l2λ, g is practically limited by α
The phonon cavity is attractive for overcoming this limitation ω by taking advantage of its small mode volume associated with the slow speed v compared with the light speed c
Considering the electromechanical coupling K2 (0.07% for GaAs SAW)[21,22], the normalized coupling for acoustic cavity quantum electrodynamic (cQED) is bounded by the effective fine structure constant αeff = αK2c/vεr
Summary
Periodic arrays serve as BRs for forming a phonon cavity and IDT for generating SAWs. Fine metal fingers in the middle of the cavity are used to define point contacts for the phase-sensitive local potential measurements or a DQD for studying phonon assisted tunneling. We show that GaAs SAW phonons are successfully confined in a cavity for enhancing the electron-phonon coupling. The SAW in the cavity mode induces phonon-assisted qubit transitions more efficiently than off-resonant SAW, which manifests the enhancement of electron-phonon coupling in the system
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