Abstract
We report exciton-mediated coupling between microwave and optical fields in cuprous oxide (Cu$_2$O) at low temperatures. Rydberg excitonic states with principal quantum number up to $n=12$ were observed at 4~K using both one-photon (absorption) and two-photon (second harmonic generation) spectroscopy. Near resonance with an excitonic state, the addition of a microwave field significantly changed the absorption lineshape, and added sidebands at the microwave frequency to the coherent second harmonic. Both effects showed a complex dependence on $n$ and angular momentum, $l$. All of these features are in semi-quantitative agreement with a model based on intraband electric dipole transitions between Rydberg exciton states. With a simple microwave antenna we already reach a regime where the microwave coupling (Rabi frequency) is comparable to the nonradiatively broadened linewidth of the Rydberg excitons. The results provide a new way to manipulate excitonic states, and open up the possibility of a cryogenic microwave to optical transducer based on Rydberg excitons.
Highlights
Improved coupling between microwave and optical frequencies would enhance classical telecommunications as well as finding applications in distributed quantum networks and quantum communication
These strong electric dipole transitions are responsible for the long-range van der Waals interactions and Rydberg blockade observed in Cu2O [29,47,48], with potential applications in creating quantum states of light [49–51]
In this paper we study optical transitions between the upper level of the valence band ( 7+ symmetry) and excitonic states associated with the lowest level of the conduction band ( 6+ symmetry), referred to as the yellow exciton series (570–610 nm)
Summary
Improved coupling between microwave and optical frequencies would enhance classical telecommunications as well as finding applications in distributed quantum networks and quantum communication. Combined with the reduced Rydberg constant of excitonic states, this scaling means that for the “yellow” series in Cu2O, electric dipole transitions accessible to microwave frequencies on the order of a few tens of GHz occur for states as low as n = 8. These strong electric dipole transitions are responsible for the long-range van der Waals interactions and Rydberg blockade observed in Cu2O [29,47,48], with potential applications in creating quantum states of light [49–51]. These results provide a tool for manipulating Rydberg states of excitons, and the first step to building a microwave to optical transducer based on Rydberg excitons
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