arXiv subjects

Yushan Zeng

Publications and source records attributed to Yushan Zeng.

3 recordsLinked to original sources

arXiv2026

Programming Coherent and Quantum Light with a Free-Electron Wavepacket

The pursuit of compact, programmable light sources with high coherence and spectral purity hinges on establishing a precise set of phase relationships in light-matter interactions. Here, we demonstrate that the quadratic dispersion of freely propagating electron wavepacket serves as a programmable quantum medium. Prepared in a coherent momentum-state ladder via a single laser interaction, the electron subsequently undergoes deterministic phase evolution during free propagation-an intrinsic process that compiles its quantum state into two distinct emission channels. This mechanism, quantified by a quantum bunching factor, enables: (i) Talbot-resonant bunching, where the electron density self-structures into sub-cycle combs with tunable harmonic selectivity, and (ii) coherent phase transfer of the programmed quadratic phase to light, generating nonclassical photon states such as multi-component Schrodinger cat states via measurement-conditioned interaction. This quadratic-phase programming establishes a versatile platform for on-demand quantum state synthesis, bridging beam engineering with electron wavefunction shaping for compact quantum light sources, coherent radiation control, and scalable quantum information processing.

physics.optics↗

arXiv2025

Direct Reconstruction of Terahertz-driven Subcycle Electron Emission Dynamics

While field-driven electron emission is theoretically understood down to the subcycle regime, its direct experimental temporal characterization using long-wavelength terahertz (THz) fields remains elusive. Here, by driving a graphite tip with phase-stable quasi-single-cycle THz pulses, we reveal distinct subcycle electron emission dynamics including: (1) At a carrier-envelope phase (CEP) zero, spectral peaks scale linearly with THz field strength, characteristic of subcycle emission; (2) At nearly opposite CEP, dominant deceleration fields generate stationary low-energy peaks. Crucially, we develop a pump-probe-free, direct reconstruction method extracting electron pulse profiles solely from measured energy spectra, obtaining durations from 73.0 to 81.0 fs as the field increases (191-290 kV/cm). Phase-resolved simulations further reveal a 72.8% modulation in the cutoff energy and a near-total (99.7%) suppression of the emission current. This work not only validates the field-emisssion theory under THz excitation but also establishes a general framework for the direct temporal characterization of subcycle electron emission, opening pathways for precise electron control in ultrafast electron sources and lightwave nanoelectronics.

physics.optics↗

arXiv2024

Auger photoemission as a laser-like coherent cathode

In pursuit of quantum advancements across disciplines, a bright and coherent electron source is expected to be a cornerstone of diverse applications including electron microscopy, laser accelerators, and free electron lasers. Current cathodes, such as cold field and photoemission, can generate high-quality electron beams with different cathode materials, geometric configurations, and laser excitation profiles, but their maintenance of both quantum coherence and high beam brightness suffers from the space-charge repulsion of many electrons. Here, we propose a new mechanism to provide collective emission of coherent electrons based on Auger photoemission. Our approach leverages a photon-induced four-level Auger process that necessitates a combination of photoemission and Auger recombination. The Auger electrons, energized through a recycling process of photoelectrons, emit collectively into the vacuum as secondary electrons. We compare coherent and incoherent Auger photoemission, identifying that the working condition of the coherent photoemission requires population inversion, akin to the four-level laser system. Our work provides insights for experimental realization and nanofabrication of Auger photocathodes, addressing a critical need in advancing quantum technologies relating to correlated coherent sources.

quant-ph↗