UC Berkeley

Light-matter interactions critically exist in our life, ranging from photosynthesis to the optical high-speed Internet and datacenters. The quantum nature of light and its interactions with matter not only provide us the fundamental understanding of the subject but also enable the revolutionary fields of quantum information science and technologies. In this dissertation, I present our study of quantum light-matter interactions in emergent two-dimensional platforms such as van der Waals materials and nano-structured metasurface. The demonstrated novel physics and unprecedented control capability expand our knowledge on light-matter interactions and promise future applications in quantum communication and quantum computation.

The dissertation consists of three parts. The first part investigates quantum single-photon emission from color centers in van der Waals hexagonal boron nitride. We characterize those superb single-photon emitters and demonstrate the giant Stark effect of photon energy at room temperature. The surprisingly large 31 meV Stark shift is achieved by applying huge in-plane electric fields on scale of 0.1 V/nm. Moreover, we report, for the first time, the angle-resolved Stark effect in solid-state single-photon emitters by rotating the field direction. A permanent electric dipole is uncovered, which unveils that both inversion and three-fold rotation symmetries are broken at the color center. The remarkable giant Stark effect and the significant structural information of the color center pave a way towards the scalable solid-state quantum technologies at room temperature.

The second part focuses on nonlinear optics at excited states of exciton polaritons, the partial-light partial-matter quantum quasiparticles, in microcavity containing monolayer WS2. We directly probe the excited states of exciton polaritons by utilizing valley sensitive nonlinear selection rules. Specifically, we unravel the valley-dependent dark 2p excited states by resonant two-photon luminescence excitation spectroscopy. Moreover, we look into the dynamically unstable upper polariton band by the instantaneous second harmonic generation spectroscopy. Our study of the excited states of exciton polaritons in two dimensional materials clears the way for room-temperature valley polariton condensation and full control of these polaritons for quantum applications.

The third part is on steering quantum photon-photon interaction mediated by two-dimensional metasurface. We, for the first time, propose and experimentally demonstrate that the rotation of metasurface enables a new degree of freedom in optical quantum interference through its unique anisotropic phase responses. Specifically, we show that the output of two-photon interference can be dynamically tuned to be bunching state, split state, or their arbitrary intermediate state, by simply rotating the metasurface. Consequently, the effective photon-photon interaction at metasurface beam-splitter can be manipulated continuously from attractive to repulsive. Our metasurface opens a door for both fundamental quantum photon-photon interaction and the development of innovative quantum gates, algorithms and computing models.