arXiv subjects

Shai Tsesses

Publications and source records attributed to Shai Tsesses.

23 records · Page 2Linked to original sources

arXiv2022

Observation of 2D Cherenkov radiation

For over 80 years of research, the conventional description of free-electron radiation phenomena, such as Cherenkov radiation, has remained unchanged: classical three-dimensional electromagnetic waves. Interestingly, in reduced dimensionality, the properties of free-electron radiation are predicted to fundamentally change. Here, we present the first observation of Cherenkov surface waves, wherein free electrons emit narrow-bandwidth photonic quasiparticles propagating in two-dimensions. The low dimensionality and narrow bandwidth of the effect enable to identify quantized emission events through electron energy loss spectroscopy. Our results support the recent theoretical prediction that free electrons do not always emit classical light and can instead become entangled with the photons they emit. The two-dimensional Cherenkov interaction achieves quantum coupling strengths over two orders of magnitude larger than ever reported, reaching the single-electron-single-photon interaction regime for the first time with free electrons. Our findings pave the way to previously unexplored phenomena in free-electron quantum optics, facilitating bright, free-electron-based quantum emitters of heralded Fock states.

quant-ph↗

arXiv2021

Light Emission by Free Electrons in Photonic Time-Crystals

Photonic time-crystals (PTCs) are spatially-homogeneous media whose electromagnetic (EM) susceptibility varies periodically in time, causing temporal reflections and refractions for any wave propagating within the medium. The time-reflected and time-refracted waves interfere, giving rise to Floquet modes with momentum bands separated by gaps (rather than energy bands and gaps, as in photonic crystals). Here, we show that a free electron moving in a PTC spontaneously emits radiation, and, when associated with momentum-gap modes, the radiation of the electron is exponentially amplified by the modulation of the refractive index. Moreover, under strong electron-photon coupling, the quantum formulation reveals that the spontaneous emission into the PTC bandgap experiences destructive quantum interference with the emission of the electron into the PTC band modes, leading to suppression of the interdependent emission. Free-electron physics in PTCs offers a new platform for studying a plethora of exciting phenomena such as radiating dipoles moving at relativistic speeds and highly efficient quantum interactions with free electrons. Radiation emission in PTCs and its non-resonant nature hold the promise for constructing new particle detectors with adjustable sensitivity and highly tunable laser sources, ranging from terahertz to the x-ray regime, drawing their power from the modulation.

physics.optics↗

arXiv2020

Coherent interaction between free electrons and a photonic cavity

Since its inception, research of cavity quantum electrodynamics (CQED) has extended our understanding of light-matter interactions and our ability to utilize them. Thus far, all the work in this field has been focused on light interacting with bound electron systems - such as atoms, molecules, quantum dots, and quantum circuits. In contrast, markedly different physical phenomena are found in free-electron systems, the energy distribution of which is continuous and not discrete, implying tunable transitions and selection rules. In addition to their uses for electron microscopy, the interaction of free electrons with light enables important phenomena such as Cherenkov radiation, Compton scattering, and free-electron lasing. However, no experiment has shown the integration of free electrons into the framework of CQED, because the fundamental electron-light interaction is limited in strength and lifetime. This limit explains why many phenomena have remained out of reach for experiments with free electrons. In this work, we developed the platform for studying CQED at the nanoscale with free electrons and demonstrated it by observing their coherent interaction with cavity photons for the first time. We also directly measure the cavity photon lifetime via a free electron probe and show more than an order of magnitude enhancement in the electron-photon interaction strength. These capabilities may open new paths toward using free electrons as carriers of quantum information, even more so after strong coupling between free electrons and cavity photons will have been demonstrated. Efficient electron-cavity photon coupling could also allow new nonlinear phenomena of cavity opto-electro-mechanics and the ultrafast exploration of soft matter or other beam-sensitive materials using low electron current and low laser exposure.

physics.optics↗

arXiv2020

Sub-wavelength spin excitations in ultracold gases created by stimulated Raman transitions

Raman transitions are used in quantum simulations with ultracold atoms for cooling, spectroscopy and creation of artificial gauge fields. Spatial shaping of the Raman fields allows local control of the effective Rabi frequency, which can be mapped to the atomic spin. Evanescent Raman fields are of special interest as they can provide a new degree of control emanating from their rapidly decaying profile and for their ability to generate features below the diffraction limit. This opens the door to the formation of sub-wavelength spin textures. In this work, we present a theoretical and numerical study of Raman Rabi frequency in the presence of evanescent driving fields. We show how spin textures can be created by spatially varying driving fields and demonstrate a skyrmionium lattice - a periodic array of topological spin excitations, each of which is composed of two skyrmions with opposite topological charges. Our results pave the way to quantum simulation of spin excitation dynamics in magnetic materials, especially of itinerant spin models.

cond-mat.quant-gas↗

arXiv2019

Enhanced sensitivity of silicon-photonics-based ultrasound detection via BCB coating

Ultrasound detection via silicon waveguides relies on the ability of acoustic waves to modulate the effective refractive index of the guided modes. However, the low photo-elastic response of silicon and silica limits the sensitivity of conventional silicon-on-insulator (SOI) sensors, in which the silicon core is surrounded by a silica cladding. In this paper, we demonstrate that the sensitivity of silicon waveguides to ultrasound may be significantly enhanced by replacing the silica over-cladding with bisbenzocyclobutene (BCB) - a transparent polymer with a high photo-elastic coefficient. In our experimental study, the response to ultrasound, in terms of the induced modulation in the effective refractive index, achieved for a BCB-coated silicon waveguide with TM polarization was comparable to values previously reported for polymer waveguides and an order of magnitude higher than the response achieved by an optical fiber. In addition, in our study the susceptibility of the sensors to surface acoustic waves and reverberations was reduced for both TE and TM modes when the BCB over-cladding was used.

physics.optics↗