Ultrafast generation of hidden phases via energy-tuned electronic photoexcitation in magnetite.

Phase transitions occurring in nonequilibrium conditions can evolve through high-energy intermediate states inaccessible via equilibrium adiabatic conditions. Because of the subtle nature of such hidden phases, their direct observation is extremely challenging and requires simultaneous visualization of matter at subpicoseconds and subpicometer scales. Here, we show that a magnetite crystal in the vicinity of its metal-to-insulator transition evolves through different hidden states when controlled via energy-tuned ultrashort laser pulses. By directly monitoring magnetite's crystal structure with ultrafast electron diffraction, we found that upon near-infrared (800 nm) excitation, the trimeron charge/orbital ordering pattern is destroyed in favor of a phase-separated state made of cubic-metallic and monoclinic-insulating regions. On the contrary, visible light (400 nm) activates a photodoping charge transfer process that further promotes the long-range order of the trimerons by stabilizing the charge density wave fluctuations, leading to the reinforcement of the monoclinic insulating phase. Our results demonstrate that magnetite's structure can evolve through completely different metastable hidden phases that can be reached long after the initial excitation has relaxed, breaking ground for a protocol to control emergent properties of matter.

Ultrafast generation and control of an electron vortex beam via chiral plasmonic near fields.

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 wavefunction. 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 wavefunction of charged composite particles, such as protons, and how it can be used to probe their internal structure.

Holographic imaging of electromagnetic fields via electron-light quantum interference.

Holography relies on the interference between a known reference and a signal of interest to reconstruct both the amplitude and the phase of that signal. With electrons, the extension of holography to the ultrafast time domain remains a challenge, although it would yield the highest possible combined spatiotemporal resolution. Here, we show that holograms of local electromagnetic fields can be obtained with combined attosecond/nanometer resolution in an ultrafast transmission electron microscope (UEM). Unlike conventional holography, where signal and reference are spatially separated and then recombined to interfere, our method relies on electromagnetic fields to split an electron wave function in a quantum coherent superposition of different energy states. In the image plane, spatial modulation of the electron energy distribution reflects the phase relation between reference and signal fields. Beyond imaging applications, this approach allows implementing quantum measurements in parallel, providing an efficient and versatile tool for electron quantum optics.

Author Correction: Attosecond coherent control of free-electron wave functions using semi-infinite light fields.

The authors became aware of a mistake in the original version of this Article. Specifically, an extra factor γ was incorrectly included in a number of mathematical equations and expressions. As a result of this, a number of changes have been made to both the PDF and the HTML versions of the Article. A full list of these changes is available online.

Attosecond coherent control of free-electron wave functions using semi-infinite light fields.

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.

Laser-Induced Skyrmion Writing and Erasing in an Ultrafast Cryo-Lorentz Transmission Electron Microscope.

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.

Quality control for estrogen and progesterone receptor assay in human breast cancer: the influence of computation methods on intra and interlaboratory variability.

The importance of evaluating receptors for estrogen and progestin in human breast cancer has been pointed out by many authors. In the absence of a reference standard, receptor assays must be controlled by intra and interlaboratory quality control programs. Much interlaboratory variability exists due to non-uniform analytical protocols, non-uniform ligands, intrinsic errors and also errors in computation methods. The goals of our Italian Quality Control Program on Multicenter Trials are to standardize the analytical procedures and computation methods. Twenty Italian laboratories participated in the Quality Control Program. Each specimen was assayed for steroid receptor content according to the standardized dextran-coated-charcoal method. Data were subjected to computerized analyses by 5 different methods of calculation (Scatchard plot, direct plot, Lineweaver-Burk method, Brunauer-Emmet-Teller analysis, single-point approach). The results were than evaluated to identify intra- and inter-assay variation coefficients and to define other statistical parameters. The authors suggest different calculation methods depending on the specific experimental and/or physiopathological conditions.

T-cell subsets in melanoma patients evaluated by anti-T-cell monoclonal antibodies.

Functional T-cell subpopulations have been evaluated in the peripheral blood of 124 melanoma patients (71 non-metastatic and 53 metastatic) using monoclonal antibodies: OKT3, OKT4, OKT8, every 2 months for 1 year. The levels of OKT3+ cells were significantly lower in metastatic patients than in normal controls and they decreased in the advanced phases of the disease. Percentages and absolute OKT4+ cell values were reduced in metastatic patients only, while a significant reduction in OKT8+ cells was noted in both long-surviving, non-metastatic and metastatic patients. The ratio of OKT4+/OKT8+ cells was increased in non-metastatic patients and in patients remaining metastasis-free for 4 years after resection of their metastases. Patients with prolonged survival show normal T-helper cells and low T-suppressor cells with a significant increased ratio OKT4/OKT8. In the patients who developed visceral metastases and in those who died the progressive reduction in total T cells is mainly due to the decrease in OKT4+ cells.

Relationship between mutagenic effect and toxic effect in the Ames test.

This study concerns the relationship between spontaneous revertants and number of bacterial cells plated in the Ames test. These two parameters do not appear to bear a direct relationship: marked variations in cell input are attended by negligible variations in spontaneous revertants. However, a relationship, described by a quadratic equation that approximates a hyperbole, exists between the spontaneous revertants and the number of total cellular divisions permitted by the histidine concentration in the medium. Furthermore a direct linear relationship has been observed between cell input and diameter of the plate background microcolonies. The problem of the toxic effect in the Ames test performed with drugs or substances having high bactericidal activity is discussed.

Results of the Italian interlaboratory quality control program for estradiol receptor assay.

This article presents results of the first Italian quality control program for determining the estradiol receptor on lypophilized guinea pig and calf uteri. Despite considerable variability in quantitative terms, the results concur in ability to define samples as positive or negative for receptor content. One of the parameters that most strongly influences accuracy of determination of receptor concentration is protein assay. The evaluation of several lyophilized preparations at scalar concentrations permitted identification, by linear regression, for each laboratory of the systematic and non-systematic variables. More comparable results will be forthcoming when a standardized methodology program has been fully adopted.