Recent advancements in ultrafast electron microscopy have provided direct access to polariton dynamics, visualizing such dynamics in space and time. This work presents new experimental results revealing a myriad of phenomena involving interactions of vortex-anti-vortex pairs, their creation and annihilation. We show new behaviors that became accessible thanks to a new development in electron microscopy - Free-Electron Ramsey Imaging (FERI) - which enabled extracting both the sub-cycle and group dynamics of polariton wavepackets. Our demonstrations involve optical phonon-polaritons in hexagonal boron nitride (hBN) and Molybdenum oxide, renowned for their unique dispersion and novel wavepacket propagations behaviors. These discoveries not only enhance our understanding of vortex phenomena across various systems, but also offer promising avenues for accessing new kinds of light-matter interactions.
Until recently, work in quantum optics focused on light interacting with bound-electron systems such as atoms, quantum dots, and nonlinear optical crystals. In contrast, free-electron systems enable fundamentally different physical phenomena, as their energy distribution is continuous and not discrete, allowing for tunable transitions and selection rules.
Recent theoretical and experimental breakthroughs involving quantum interactions of free electrons spawned an exciting new field: free-electron quantum optics. We developed a platform for exploring free-electron quantum optics at the nanoscale, and used it to demonstrate the first coherent interaction of a free electron with a photonic cavity and with the quantum statistics of photons.
These capabilities open new paths toward using free electrons as carriers of quantum information. Free electrons emerge as quantum optical sources for desired photonics states used in fault-tolerant quantum computation and communication such as Schrodinger cat states and GKP states.
Concepts of quantum optics with free electrons also promote new modalities in electron microscopy. We demonstrated the first instance of coherent amplification in electron microscopy. Our vision is to develop a microscope that can image coherence, going beyond conventional imaging of matter to also image the coherent quantum state of matter and probe quantum correlations between individual quantum systems.
Effects of extreme nonlinear optics, such as high harmonic generation (HHG), are conventionally modeled with classical electromagnetic fields: both the driving and emitted fields are treated classically. We present the fully quantum electrodynamical theory of extreme nonlinear optics and use it to predict new quantum effects in HHG. The quantum description shows new effects in both the spectral and statistical properties of HHG. We also describe how the HHG process changes in the single-atom regime and discuss experiments that can test our various predictions. Revealing the quantum-optical nature of HHG could lead to novel sources of attosecond light having intrinsically quantum statistics, such as squeezing and entanglement.
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