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Parametric x-ray radiation (PXR) is a prospective mechanism for producing directional, tunable, and quasi-coherent x-rays in laboratory-scale dimensions, yet it is limited by heat dissipation and self-absorption. Resolving these limits, we show the PXR source flux is suitable for medical imaging and x-ray spectroscopy. We discuss the experimental feasibility of these findings for a compact commercial PXR source. [ABSTRACT FROM AUTHOR]

In strong-field physics and attosecond science, intense light induces ultrafast electron dynamics. Such ultrafast dynamics of electrons in matter is at the core of phenomena such as high-harmonic generation, where these dynamics lead to the emission of extreme-ultraviolet bursts with attosecond duration. So far, all ultrafast dynamics of matter were understood to purely originate from the classical vector potential of the driving light, disregarding the influence of the quantum nature of light. Here we show theoretically that the dynamics of matter driven by bright (intense) light significantly depend on the quantum state of the driving light through its quantum noise, which induces an effective photon-statistics force. To provide a unified framework for the analysis and control over such a force, we extend the strong-field approximation theory to account for non-classical driving light. Our quantum strong-field approximation theory shows that in high-harmonic generation, experimentally feasible squeezing of the driving light can shift and shape electronic trajectories and attosecond pulses at the scale of hundreds of attoseconds. Our work presents a new degree of freedom for attosecond spectroscopy, by relying on non-classical electromagnetic fields, and more generally, introduces a direct connection between attosecond science and quantum optics. Strong-field approximation theory is extended to account for non-classical driving light. This extended theory predicts that ultrafast dynamics of strongly light-driven matter significantly depends on the quantum state of the driving light, particularly on its photon statistics. [ABSTRACT FROM AUTHOR]

Tunable x-ray radiation sources are of wide importance for imaging and spectroscopy in fundamental science, medicine, and industry. The growing demand for highly tunable, high-brightness lab-scale x-ray sources motivates research of new mechanisms of x-ray generation. Parametric x-ray radiation (PXR) is a mechanism for tunable x-ray radiation from free electrons traversing crystalline materials. Although PXR has been investigated over decades, it remained limited in usages due to the low flux and strict dependence on fixed crystal properties. Here, we find new effects hiding in the PXR mechanisms, which provide control over the radiation polarization and spatial and temporal distribution. The radiation can form ultrashort pulses and delta-pulse trains, which makes the new effects fundamentally different from all conventional mechanisms of x-ray generation. We show how these new effects can be created from free-electron interactions with van der Waals materials. Furthermore, we consider free electrons traversing near material edges, which provides an additional degree of tunability in angular distribution and polarization of PXR. Our findings enable us to utilize recent breakthroughs in the atomic-scale design of 2D material heterostructures to provide platforms for creating tunable x-ray pulses. [ABSTRACT FROM AUTHOR]

The article offers insight to a study imprinting the quantum statistics of photons on free electrons. It mentions that a silicon-photonics device integrated in an electron microscope provides efficient electron interactions with continuous-wave light, enabling the detection of the quantum photon statistics. It also mentions about highly efficient electron-light interaction facilitated by an inverse-designed silicon-photonic nanostructure scanning electron microscope image.

Free electrons provide a powerful tool for probing material properties at atomic resolution. Recent advances in ultrafast electron microscopy enable the manipulation of free-electron wave functions using laser pulses. It would be of great importance if one could combine the spatial resolution of electron microscopes with the ability of laser pulses to probe coherent phenomena in quantum systems. To this end, we propose a novel concept that leverages free electrons that are coherently shaped by laser pulses to measure quantum coherence in materials. We develop the quantum theory of interactions between shaped electrons and arbitrary qubit states in materials, and show how the postinteraction electron energy spectrum enables measuring the qubit state (on the Bloch sphere) and the decoherence or relaxation times (T2/T1). Finally, we describe how such electrons can detect and quantify superradiance from multiple qubits. Our scheme can be implemented in ultrafast transmission electron microscopes (UTEM), opening the way toward the full characterization of the state of quantum systems at atomic resolution. [ABSTRACT FROM AUTHOR]

Optical and acoustic tractor beams are currently the focus of intense research due to their counterintuitive property of exerting a pulling force on small scattering objects. In this Letter we propose a matter-wave tractor beam and utilize the de Broglie waves of nonrelativistic matter particles in analogy to "classical" tractor beams. We reveal the presence of the quantum-mechanical pulling force for the variety of quantum mechanical potentials observing the resonant enhancement of the pulling effect under the conditions of the suppressed scattering known as the Ramsauer-Townsend effect. We also derive the sufficient conditions on the scattering potential for the emergence of the pulling force and show that, in particular, a Coulomb scatterer is always shoved, while a Yukawa (screened Coulomb) scatterer can be drawn. Pulling forces in optics, acoustics, quantum mechanics, and classical mechanics are compared, and the matter-wave pulling force is found to have exclusive properties of dragging slow particles in short-range potentials. We envisage that the use of tractor beams could lead to the unprecedented precision in manipulation with atomic-scale quantum objects. [ABSTRACT FROM AUTHOR]

The manipulation of quantum many-body systems is a crucial goal in quantum science. Entangled quantum states that are symmetric under qubits permutation are of growing interest. Yet, the creation and control of symmetric states has remained a challenge. Here, we introduce a method to universally control symmetric states, proposing a scheme that relies solely on coherent rotations and spin squeezing. We present protocols for the creation of different symmetric states including Schrödinger's cat and Gottesman-Kitaev-Preskill states. The obtained symmetric states can be transferred to traveling photonic states via spontaneous emission, providing a powerful approach for engineering desired quantum photonic states.

The ability to form monoenergetic electron beams is vital for high-resolution electron spectroscopy and imaging. Such capabilities are commonly achieved using an electron monochromator, which energy filters a dispersed electron beam, thus reducing the electron flux to yield down to meV energy resolution. This reduction in flux hinders the use of monochromators in many applications, such as ultrafast transmission electron microscopes (UTEMs). Here, we develop and demonstrate a mechanism for electron energy monochromation that does not reduce the flux-a lossless monochromator. The mechanism is based on the interaction of free-electron pulses with single-cycle THz near fields, created by nonlinear conversion of an optical laser pulse near the electron beam path inside a UTEM. Our experiment reduces the electron energy spread by a factor of up to 2.9 without compromising the beam flux. Moreover, as the electron-THz interaction takes place over an extended region of many tens of microns in free space, the realized technique is highly robust-granting uniform monochromation over a wide area, larger than the electron beam diameter. We further demonstrate the wide tunability of our method by monochromating the electron beam at multiple primary electron energies from 60 to 200 keV, studying the effect of various electron and THz parameters on its performance. Our findings have direct applications in the fast-growing field of ultrafast electron microscopy, allowing time- and energy-resolved studies of exciton physics, phononic vibrational resonances, charge transport effects, and optical excitations in the mid IR to the far IR.

The ultrafast dynamics of charge carriers in solids plays a pivotal role in emerging optoelectronics, photonics, energy harvesting, and quantum technology applications. However, the investigation and direct visualization of such nonequilibrium phenomena remains as a long-standing challenge, owing to the nanometer-femtosecond spatiotemporal scales at which the charge carriers evolve. Here, we propose and demonstrate an interaction mechanism enabling nanoscale imaging of the femtosecond dynamics of charge carriers in solids. This imaging modality, which we name charge dynamics electron microscopy (CDEM), exploits the strong interaction of free-electron pulses with terahertz (THz) near fields produced by the moving charges in an ultrafast scanning transmission electron microscope. The measured free-electron energy at different spatiotemporal coordinates allows us to directly retrieve the THz near-field amplitude and phase, from which we reconstruct movies of the generated charges by comparison to microscopic theory. The CDEM technique thus allows us to investigate previously inaccessible spatiotemporal regimes of charge dynamics in solids, providing insight into the photo-Dember effect and showing oscillations of photogenerated electron-hole distributions inside a semiconductor. Our work facilitates the exploration of a wide range of previously inaccessible charge-transport phenomena in condensed matter using ultrafast electron microscopy.