Light–electron interaction is the seminal ingredient in free-electron lasers and dynamical investigation of matter. Pushing the coherent control of electrons by light to the attosecond timescale and below would enable unprecedented applications in quantum circuits and exploration of electronic motions and nuclear phenomena. Here we demonstrate attosecond coherent manipulation of a free-electron wave function, and show that it can be pushed down to the zeptosecond regime. We make a relativistic single-electron wavepacket interact in free-space with a semi-infinite light field generated by two light pulses reflected from a mirror and delayed by fractions of the optical cycle. The amplitude and phase of the resulting electron–state coherent oscillations are mapped in energy-momentum space via momentum-resolved ultrafast electron spectroscopy. The experimental results are in full agreement with our analytical theory, which predicts access to the zeptosecond timescale by adopting semi-infinite X-ray pulses.

Introductory paragraph: Vortex-carrying matter waves, such as chiral electron beams, are of significant interest in both applied and fundamental science. Continuous wave electron vortex beams are commonly prepared via passive phase masks imprinting a transverse phase modulation on the electron's wave function. Here, we show that femtosecond chiral plasmonic near fields enable the generation and dynamic control on the ultrafast timescale of an electron vortex beam. The vortex structure of the resulting electron wavepacket is probed in both real and reciprocal space using ultrafast transmission electron microscopy. This method offers a high degree of scalability to small length scales and a highly efficient manipulation of the electron vorticity with attosecond precision. Besides the direct implications in the investigation of nanoscale ultrafast processes in which chirality plays a major role, we further discuss the perspectives of using this technique to shape the wave function of charged composite particles, such as protons, and how it can be used to probe their internal structure.Main Text: The quantum wave nature of both light and matter has enabled several tools to shape them into new wave structures defined by exotic non-trivial spatio-temporal properties (1). Among these techniques, the impartment of a vortex onto their transverse phase profile is showing a

We demonstrate that light-induced heat pulses of different duration and energy can write Skyrmions in a broad range of temperatures and magnetic field in FeGe. Using a combination of camera-rate and pump-probe cryo-Lorentz transmission electron microscopy, we directly resolve the spatiotemporal evolution of the magnetization ensuing optical excitation. The Skyrmion lattice was found to maintain its structural properties during the laser-induced demagnetization, and its recovery to the initial state happened in the sub-μs to μs range, depending on the cooling rate of the system.

In this paper we present a compact source of narrow-band energy-time entangled photon pairs in the telecom regime based on a Ti-indiffused Periodically Poled Lithium Niobate (PPLN) waveguide resonator, i.e. a waveguide with end-face dielectric multi-layer mirrors. This is a monolithic doubly resonant Optical Parametric Oscillator (OPO) far below threshold, which generates photon pairs by Spontaneous Parametric Down Conversion (SPDC) at around 1560 nm with a 117 MHz (0.91 pm)bandwidth. A coherence time of 2.7 ns is estimated by a time correlation measurement and a high quality of the entangled states is confirmed by a Bell-type experiment. Since highly coherent energy-time entangled photon pairs in the telecom regime are suitable for long distance transmission and manipulation, this source is well suited to the requirements of quantum communication.

We report on the experimental realization of a 4-qubit linear cluster state via two photons entangled both in polarization and linear momentum. This state was investigated by performing tomographic measurements and by evaluating an entanglement witness. By use of this state we carried out a novel nonlocality proof, the so-called "stronger two observer all versus nothing" test of quantum nonlocality.PACS numbers: 03.67. Mn,03.65.Ud,42.50.Xa Multipartite graph states and, in particular, cluster states, have been recently introduced by Briegel and Raussendorf as a fundamental resource aimed at the linear optics one way quantum computation [1,2], and at the realization of important quantum information tasks, such as quantum error correction and quantum communication protocols [3,4]. Recently, the experimental feasibility of one way quantum computation by four photon cluster states was demonstrated [5,6]. Besides the applications to quantum computation, cluster states are powerful tools for perfoming nonlocality tests [7,8]. It is well known that the adoption of an increasing number of internal qubits, i.e. in a higher dimensional Hilbert space, leads to a stronger violation of local realism [9]. Recently, a test demonstrating that nonlocality grows with the number of internal degrees of freedom of the system, was indeed successfully carried out by taking advantage of the peculiar properties of a 2-photon hyperentangled state [10]. It is worth noting that, at variance with the cluster states, hyperentangled, or double entangled states, are bi-separable and do not represent genuine four-qubit entangled states.In this letter we report the experimental realization of a high fidelity 2-photon 4-qubit linear cluster state by a linear optical technique consisting of the entanglement of the polarization (π) and momentum (k) degrees of freedom of one of the two photons belonging to an hyperentangled state. The cluster state was analyzed by quantum tomographic measurements and by an entanglement witness method [8,11]. By using this state, we performed a novel "All-Versus-Nothing" (AVN) test of nonlocality recently proposed by Cabello [12].As said, the starting point for the cluster state generation was the hyperentangled state |Ξ = |Φ − ⊗ |ψ + , where(|r A |ℓ B + |ℓ A |r B ). In the above equations H, V refer to the horizontal (H) and vertical (V ) polarizations and ℓ, r refer to the left (ℓ) or right (r) paths of the photon A (Alice) or B (Bob) (see Fig. 1). The state |Ξ is realized by a Spontaneous Parametric Down Conversion (SPDC) method already described in details in other papers [13,14]. A thin type I β-barium-borate BBO crystal slab operating under the double (back and forth) excitation of a cw Ar + laser (λ p = 364 nm) generated the π-entangled state |Φ − , obtained by the superposition of two perpendicularly polarized SPDC cones emerging from the crystal at the degenerate wavelength λ = 728 nm. The k-entangled state |ψ + was realized by selecting two pairs of correlated k-modes, r A -ℓ B and ℓ A -r B , belonging t...

By using 2-photon 4-qubit cluster states we demonstrate deterministic one-way quantum computation in a single qubit rotation algorithm. In this operation feed-forward measurements are automatically implemented by properly choosing the measurement basis of the qubits, while Pauli error corrections are realized by using two fast driven Pockels cells. We realized also a C-NOT gate for equatorial qubits and a C-PHASE gate for a generic target qubit. Our results demonstrate that 2-photon cluster states can be used for rapid and efficient deterministic one-way quantum computing.

The electronic, optical, and magnetic properties of quantum solids are determined by their low--energy (< 100 meV) many--body excitations. Dynamical characterization and manipulation of such excitations relies on tools that combine nm--spatial, fs--temporal, and meV--spectral resolution. Currently, phonons and collective plasmon resonances can be imaged in nanostructures with sub--nm and 10s meV space/energy resolution using state--of--the--art energy--filtered transmission electron microscopy (TEM), but only under static conditions, while fs--resolved measurements are common but lack spatial or energy resolution. Here, we demonstrate a new method of spectrally--resolved photon--induced near--field electron microscopy (SRPINEM) that allows us to obtain nm--fs--resolved maps of nanoparticle plasmons with an energy resolution determined by the laser linewidth (20 meV in this work), and not limited by electron beam and spectrometer energy spreading. This technique can be extended to any optically--accessible low--energy mode, thus pushing TEM to a previously inaccessible spectral domain with an unprecedented combination of space, energy, and temporal resolution.

The recent identification of strongly bound excitons in room temperature anatase TiO 2 single crystals and nanoparticles underscores the importance of bulk many-body effects in samples used for applications. Here, for the first time, we unravel the interplay between many-body interactions and correlations in highly-excited anatase TiO 2 nanoparticles using ultrafast two-dimensional deepultraviolet spectroscopy. With this approach, under non-resonant excitation, we disentangle the optical nonlinearities contributing to the bleach of the lowest direct exciton peak. This allows us to clock the ultrafast timescale of the hot electron thermalization in the conduction band with unprecedented temporal resolution, which we determine to be < 50 fs, due to the strong electronphonon coupling in the material. Our findings call for the design of alternative resonant excitation schemes in photonics and nanotechnology.1 arXiv:1703.07818v2 [cond-mat.mes-hall] 13 Jan 2018In the last decades, anatase TiO 2 has attracted huge interest as one of the most promising materials for a variety of challenging applications, ranging from photocatalysis [1,2] and photovoltaics [3] to sensors [4,5]. Since these technologies involve charge transport, thermalization and localization, they call for studies of the fast electron and hole dynamics, which provide a deep knowledge of the nature of the photogenerated/injected charge carriers and of the energy balance therein. These processes intimately depend on the details of the electronic structure and the presence of many body-effects in the material. Since anatase TiO 2 is a d 0 transition metal oxide, strong electron-electron correlations do not play a substantial role in the electronic structure [6]. Hence, this solid can be classified within the simple band insulator scheme, in which the forbidden energy gap arises as a result of band theory and is not a consequence of the strong on-site Coulomb interaction. However, different to conventional band insulators, anatase TiO 2 represents a peculiar example in which electron-phonon interaction and electron-hole correlation become relatively strong and influence the optical spectra. On the one hand, the presence of a moderately large electron-phonon coupling in anatase TiO 2 has often been invoked to interpret experimental results naturally pointing to the polaronic (self-trapped) picture [7][8][9][10][11][12][13]. Notable examples include the low temperature green photoluminescence (PL) due to self-trapped excitons [14][15][16][17][18][19][20] and the room temperature electron mobilities whose values are limited by strong scattering with phonons [10]. On the other hand, many-body correlations have been thought to be negligible in this material and, as such, they remained widely unexplored. Recently, by employing state-of-the-art experimental [21] and computational techniques [21][22][23][24][25], the substantial role of electron-hole Coulomb correlations was unravelled in the anatase polymorph of TiO 2 . Strongly bound direct excitons were...