Hybrid superconducting-photonic microresonators are a promising platform for realizing microwave-to-optical transduction. However, the absorption of scattered photons by the superconductors leads to unintended microwave resonance-frequency variation and line-width broadening. Here, we experimentally study the dynamics of this effect and its impact on microwave-to-optics conversion in an integrated lithium niobate--superconductor hybrid-resonator platform. We unveil an adiabatic frequency shifting of the intracavity microwave photons induced by the fast photoresponses of the thin-film superconducting resonator. As a result, the temporal and spectral responses of electro-optics transduction are modified and well described by our theoretical model. This work provides insights into the light-induced conversion dynamics that must be considered in future designs of hybrid superconducting-photonic system.
Electro-optic transduction can bypass the loss and noise of electronic frequency conversion at millimeter-wave frequencies by parametrically converting signals onto low-loss, low-noise optical carriers, with coupling rates that grow with frequency. Exploiting this growth, however, requires shrinking both the millimeter-wave and optical resonators while preserving their quality factors and spatial overlap, which has not yet been achieved. Here, we demonstrate a triply resonant transducer whose optical and millimeter-wave resonators have comparable dimensions and minimal mode volumes. Coupled lithium niobate Fabry-Pérot cavities, with free spectral ranges above 650 GHz and quality factors up to
106, form a photonic molecule integrated with a quarter-wave gold resonator at 263 GHz. The device reaches a vacuum electro-optic coupling rate
g0/2π≈60 kHz, six times larger than previous millimeter-wave transducers and sixty times larger than at microwave frequencies. The device optically detects room-temperature thermal millimeter-wave photons at effective occupancies below one, which also serve as a calibration tone for transduction efficiency. Coherent transduction reaches cooperativities approaching 0.3, corresponding to internal efficiencies around 67%, accompanied by electro-optic dynamical back-action that broadens or narrows the optical resonances. These results demonstrate the advantage and feasibility of the frequency scaling of electro-optic coupling, establishing an architecture for weak-signal sensing and quantum and classical networking.
The quantum dynamics of the coupling between a cavity optical field and a resonator microwave field via the electro-optic effect is studied. This coupling has the same form as the optomechanical coupling via radiation pressure, so all previously considered optomechanical effects can in principle be observed in electro-optic systems as well. In particular, I point out the possibilities of laser cooling of the microwave mode, entanglement between the optical mode and the microwave mode via electro-optic parametric amplification, and back-action-evading optical measurements of a microwave quadrature.