Quantum Sensing with Rydberg Excitons

Rydberg excitons are promising quasi-particles for quantum sensing applications due to their extended wavefunctions and strong dipolar interaction strengths at higher quantum states. Electromagnetic excitations surrounding the excitons can be accurately quantified and measured when pump-probe processes are performed on them. The transitions between high-lying Rydberg states are in the microwave to terahertz frequency range, thus the excitons can absorb resonant or nearly resonant electromagnetic fields and eventually get excited into a higher state. This will lead to characteristic photon emission when the excited state spontaneously decays to the ground state. Exciton-based sensors are stable and immune to manufacturing variations, aging, and calibration issues since atoms of the same isotopic species are the same everywhere.<br/><br/>To enable Rydberg sensing, a suitable material platform capable of hosting highly excited Rydberg excitons is crucial. Until now, cuprous oxide (Cu2O) is the only known semiconductor in which Rydberg excitons having principal quantum numbers as high as n = 25 have been observed. This is because of its high binding energy and symmetric lattice structure, which allow it to support many Rydberg exciton states without succumbing to thermal ionization. However, reaching a defect-free condition in naturally occurring bulk cuprous oxide remains a challenge, necessitating a more controlled manufacturing technique to produce high-purity, customized synthetic cuprous oxide. Thin-film cuprous oxide samples with thicknesses less than the blockade radius are especially appealing because they make the Rydberg blockade utilizable for nonlinear behavior in semiconductors.<br/><br/>Here, we present photoluminescence and absorption measurements performed on Cu2O grown on a Strontium Titanate (STO) substrate. The dielectric permittivity of STO shows a large temperature dependence and we probe this using Rydberg excitons in Cu2O. The large temperature-dependent change in refractive index at terahertz frequencies sensitizes the transition between Rydberg states to the temperature, which can then be measured through the dynamics of the quasi-particle. The Cu2O/STO also provides us with a platform to study the effects of dielectric screening and dipolar interactions on the exciton dynamics. In this manner, a CMOS-compatible, integrable, and scalable solid-state semiconductor sensing platform can be realized which can pave the way for microwave sensing technologies.