Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2019)

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.

    Cover page: Quantum light-matter interactions in metasurface and two-dimensional materials
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2022)
    Quantum fluids exhibit quantum mechanical effects at the macroscopic level, which contrast strongly with classical fluids. Gain-dissipative solid-state exciton-polaritons systems are promising emulation platforms for complex quantum fluid studies at elevated temperatures. Recently, halide perovskite polariton systems have emerged as materials with distinctive advantages over other room-temperature systems for future studies of topological physics, non-Abelian gauge fields, and spin-orbit interactions. However, the demonstration of nonlinear quantum hydrodynamics, such as superfluidity and Čerenkov flow, which is a consequence of the renormalized elementary excitation spectrum, remains elusive in halide perovskites. Here, using homogenous halide perovskites single crystals, we report, in both one- and two-dimensional cases, the complete set of quantum fluid phase transitions from normal classical fluids to scatterless polariton superfluids and supersonic fluids-all at room temperature, clear consequences of the Landau criterion. Specifically, the supersonic Čerenkov wave pattern was observed at room temperature. The experimental results are also in quantitative agreement with theoretical predictions from the dissipative Gross-Pitaevskii equation. Our results set the stage for exploring the rich non-equilibrium quantum fluid many-body physics at room temperature and also pave the way for important polaritonic device applications.
      Cover page: Room-temperature polariton quantum fluids in halide perovskites
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2023)
      Photosynthesis is generally assumed to be initiated by a single photon1-3 from the Sun, which, as a weak light source, delivers at most a few tens of photons per nanometre squared per second within a chlorophyll absorption band1. Yet much experimental and theoretical work over the past 40 years has explored the events during photosynthesis subsequent to absorption of light from intense, ultrashort laser pulses2-15. Here, we use single photons to excite under ambient conditions the light-harvesting 2 (LH2) complex of the purple bacterium Rhodobacter sphaeroides, comprising B800 and B850 rings that contain 9 and 18 bacteriochlorophyll molecules, respectively. Excitation of the B800 ring leads to electronic energy transfer to the B850 ring in approximately 0.7 ps, followed by rapid B850-to-B850 energy transfer on an approximately 100-fs timescale and light emission at 850-875 nm (refs. 16-19). Using a heralded single-photon source20,21 along with coincidence counting, we establish time correlation functions for B800 excitation and B850 fluorescence emission and demonstrate that both events involve single photons. We also find that the probability distribution of the number of heralds per detected fluorescence photon supports the view that a single photon can upon absorption drive the subsequent energy transfer and fluorescence emission and hence, by extension, the primary charge separation of photosynthesis. An analytical stochastic model and a Monte Carlo numerical model capture the data, further confirming that absorption of single photons is correlated with emission of single photons in a natural light-harvesting complex.
        Cover page: Single-photon absorption and emission from a natural photosynthetic complex
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2023)
        The recently emerged ferromagnetic two-dimensional (2D) materials provide unique platforms for compact spintronic devices down to the atomic-thin regime; however, the prospect is hindered by the limited number  of ferromagnetic 2D materials discovered with limited choices of magnetic properties. If 2D antiferromagnetism could be converted to 2D ferromagnetism, the range of 2D magnets and their potential applications would be significantly broadened. Here, we discovered emergent ferromagnetism by interfacing non-magnetic WS2 layers with the antiferromagnetic FePS3. The WS2 exhibits an order of magnitude enhanced Zeeman effect with a saturated interfacial exchange field ~38 Tesla. Given the pristine FePS3 is an intralayer antiferromagnet, the prominent interfacial exchange field suggests the formation of ferromagnetic FePS3 at interface. Furthermore, the enhanced Zeeman effect in WS2 is found to exhibit a strong WS2-thickness dependence, highlighting the layer-tailorable interfacial exchange coupling in WS2-FePS3 heterostructures, which is potentially attributed to the thickness-dependent interfacial hybridization.
          Cover page: Ferromagnetism emerged from non-ferromagnetic atomic crystals.
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2019)
          The condensation of half-light half-matter exciton polaritons in semiconductor optical cavities is a striking example of macroscopic quantum coherence in a solid-state platform. Quantum coherence is possible only when there are strong interactions between the exciton polaritons provided by their excitonic constituents. Rydberg excitons with high principal value exhibit strong dipole-dipole interactions in cold atoms. However, polaritons with the excitonic constituent that is an excited state, namely Rydberg exciton polaritons (REPs), have not yet been experimentally observed. Here, we observe the formation of REPs in a single crystal CsPbBr3 perovskite cavity without any external fields. These polaritons exhibit strong nonlinear behavior that leads to a coherent polariton condensate with a prominent blue shift. Furthermore, the REPs in CsPbBr3 are highly anisotropic and have a large extinction ratio, arising from the perovskite's orthorhombic crystal structure. Our observation not only sheds light on the importance of many-body physics in coherent polariton systems involving higher-order excited states, but also paves the way for exploring these coherent interactions for solid-state quantum optical information processing.
            Cover page: Observation of Rydberg exciton polaritons and their condensate in a perovskite cavity.
            Top