Research Interests

Free-Electron Optics explores how free electrons interact with classical electromagnetic fields and quantum vacuum fluctuations, connecting advanced nanophotonics, electron physics, and quantum optics. In these interactions, free electrons act as versatile nonlinear quantum media, enabling frequency conversion and the tailoring of tunable radiation spectra. Furthermore, free-electron–light interactions can serve as quantum gates: free electrons can become entangled with the photons they emit, allowing precise manipulation of light at the quantum wave packet level and the creation of non-classical light states.

Our research deepens the fundamental understanding of quantum electron–light–matter interactions and aims to achieve precise control of radiation at both the nanoscale and the quantum level. By harnessing the quantum properties of free electrons, we strive to develop compact, ultrashort-wavelength light sources and generate quantum light states beyond what conventional approaches can achieve.

Quantum Free-electron Radiation

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Free electrons have quantum structures that go beyond the simple point-charge model. Since Nobel Laureate Ahmed Zewail’s pioneering work in 2009 on free-electron interaction with light near-fields, these quantum properties have been widely studied, especially in electron microscopy. Today, researchers are exploring how to use these quantum features; for example, ultrashort electron pulses enable attosecond electron microscopy to capture ultrafast optical dynamics. Here, we investigate how these quantum structures affect free-electron radiation . This is crucial when low-energy electrons interact with nanostructures, where the quantum wavepacket nature can introduce a paradigm shift in radiation behavior. For instance, we find that entanglement between free electrons and emitted photons can shift and split radiation spectra compared to classical predictions. Even more intriguing, the quantum structure offers new degrees of freedom to control radiation, especially in challenging regimes like X-rays, beyond the reach of traditional optical methods.

Free-electron X-ray Optics

Control of X-rays is not as advanced as that of visible and infrared light, primarily due to the intrinsically weak interaction between X-rays and conventional optical materials. In contrast, novel beam shaping techniques in the optical regime, such as Airy beams and other structured light fields, have unlocked new capabilities in imaging and microscopy. Motivated by these advances, we aim to directly generate shaped X-rays by harnessing free-electron interactions with engineered nanostructures. Recent demonstrations include X-ray focused beams and X-ray Airy beams using van der Waals heterostructures. Looking ahead, we plan to develop innovative approaches that minimize reliance on bulky X-ray optical components and enable sophisticated control over X-ray beams within a compact platform, opening up new possibilities for high-resolution imaging and advanced spectroscopy.
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Electron-Heralded Quantum X-ray Source

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The current technology for generating quantum light mainly relies on the nonlinearity of materials, which limits the available spectrum of quantum light states. Free electrons can also act as nonlinear media during their interaction with light, such as in Compton scattering and free-electron radiation. Recent investigations of free-electron radiation treat this process as the scattering of entangled electron-photon pairs, giving rise to a new field called free-electron quantum optics. In this field, quantum light can be heralded by post-selecting the electron, for example, in energy space. One significant advantage of this approach is the ability to generate quantum light in regimes, such as the X-ray regime, that are inaccessible or challenging for traditional methods.