Towards controlled interaction of Rydberg excitons in integrated and scalable solid state devices

• Applicant: Professor Dr. Harald Giessen
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Experimental Condensed Matter Physics
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316223591

We study Rydberg excitons in the semiconductor cuprite (Cu2O),which exhibit principal quantum numbers as high as n=25 andexcitonic Bohr radii in the micrometer range. These giant singlequantum objects in semiconductors have been discovered onlyrecently, and their potential as quantum devices has yet to berealized. Many properties of these systems are unknown and stillhave to be determined. We use artificially grown as well as naturalsingle Cu2O crystals of several mm² size and carry out AM/FMmodulation spectroscopy around the yellow p-, s-, and d-excitonseries at temperatures down to 1.5 K, using a tunable narrowbanddiode laser in the 570 nm wavelength range. Microlenses printed withfemtosecond direct laser writing on top of the semiconductors willallow for focusing down to micrometer sized focal spots, and by tiltingthe incidence angle, spatially resolved pump-probe experiments canbe carried out. This gives direct information on the Coulombinteraction distance and determines the Rydberg blockade radius.Both electric and magnetic fields cause a symmetry breaking andmodify the wavefunction nature, the optical transition selection rules,and hence the interaction. Using our spatially resolved pump-probescheme, we can investigate the influence of EIT-coupling schemesonto the Rydberg exciton interactions. 3D printed phaseplates andion-beam milled Fresnel-phaseplates will allow for generation oforbital angular momentum light directly in diffraction limited focalspots on the cuprite crystal. As the Rydberg excitons are several 100nm in size, their spatial overlap with the OAM light mode is ideal tostudy violation of dipolar selection rules upon additional angularmomentum of light. The fiber scheme in combination with multicoresingle mode fibers and near-diffraction limited imaging by printedlenses will allow for an integrated fiber-only scheme which canaddress a whole matrix of Rydberg excitons, being controllable andStark switchable through the transparent electrode grid. This will leadtowards a scalable, fiber-integrated device which can be measured incryostats with no optical windows even at sub-Kelvin temperatures,avoiding phonon scattering as much as possible. Within theSPP1929, we are going to benefit from interactions with the group ofManfred Bayer in Dortmund, who is also studying Rydberg excitons,as well as with the other atomic physics groups such as the one ofTilman Pfau and Robert Löw in Stuttgart, who deal with Rydberginteraction in atomic systems as well as EIT and cavity QED schemesfor nonlinear switching. Additionally, we experimentally collaboratewith Gerhard Birkl in Darmstadt, who uses our microlens arrays for hisatomic Rydberg atom arrays. We are going to collaborate with thetheory groups of Stefan Scheel in Rostock and HanspeterBüchler/Jörg Main in Stuttgart regarding the OAM selection rules and dipole matrix elements as well as the Rydberg quantum well excitonenergy calculations.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1929: Giant Interactions in Rydberg Systems (GiRyd)