Radiative loss of coherence in free electrons:a long-range quantum phenomenon

Quantum physics rules the dynamics of small objects as they interact over microscopic length scales.Nevertheless,quantum correlations involving macroscopic distances can be observed between entangled photons as well as in atomic gases and matter waves at low temperatures.The long-range nature of the electromagnetic coupling between charged particles and extended objects could also trigger quantum phenomena over large distances.Here,we reveal a manifestation of quantum mechanics that involves macroscopic distances and results in a nearly complete depletion of coherence associated with which-way free-electron interference produced by electron-radiation coupling in the presence of distant extended objects.This is a ubiquitous effect that we illustrate through a rigorous theoretical analysis of a two-path electron beam interacting with a semi-infinite metallic plate and find the inter-path coherence to vanish proportionally to the path separation at zero temperature and exponentially at finite temperature.The investigated regime of large distances originates in the coupling of the electron to radiative modes assisted by diffraction at material structures but without any involvement of material excitations.Besides the fundamental interest of this macroscopic quantum phenomenon,our results suggest an approach to measuring the vacuum temperature and nondestructively sensing the presence of distant objects.

High-Sensitivity Visualization of Ulitrafast Carrier Diffusion by Wide-Field Holographic Microscopy

Ultrafast transient microscopy is a key tool to study the photophysical properties of materials in space and time,but current implementations are limited to≈1-μm fields of view,offering no statistical information for heterogeneous samples.Recently,we demonstrated wide-field transient imaging based on multiplexed off-axis holography.Here,we perform ultrafast microscopy in parallel around a hundred diffraction-limited excitation spots over a≈60-μm field of view,which not only automatically samples the photophysical heterogeneity of the sample over a large area but can also be used to obtain a 10-fold increase in signal-tonoise ratio by computing an average spot.We apply our microscope to study the carrier diffusion processes in methylammonium lead bromide perovskites.We observe strong diffusion due to the presence of hot carriers during the first picosecond and slower diffusion afterward.We also describe how many-body kinetics can be misleadingly interpreted as strong diffusion at high excitation densities,while at weak excitation,real diffusion is observed.Therefore,the vast increase in sensitivity offered by this technique benefits the study of carrier transport not only by reducing data acquisition times but also by enabling the measurement of the much smaller signals generated at low carrier densities.

On the possibility that PbZrO_(3) not be antiferroelectric

Lead zirconate(PbZrO_(3))is considered the prototypical antiferroelectric material with an antipolar ground state.Yet,several experimental and theoretical works hint at a partially polar behaviour in this compound,indicating that the polarization may not be completely compensated.In this work,we propose a simple ferrielectric structure for lead zirconate.First-principles calculations reveal this state to be more stable than the commonly accepted antiferroelectric phase at low temperatures,possibly up to room temperature,suggesting that PbZrO_(3)may not be antiferroelectric at ambient conditions.We discuss the implications of our discovery,how it can be reconciled with experimental observations and how the ferrielectric phase could be obtained in practice.

Unraveling the optomechanical nature of plasmonic trapping

Noninvasive and ultra-accurate optical manipulation of nanometer objects has recently gained interest as a powerful tool in nanotechnology and biophysics.Self-induced back-action(SIBA)trapping in nano-optical cavities has the unique potential for trapping and manipulating nanometer-sized objects under low optical intensities.However,thus far,the existence of the SIBA effect has been shown only indirectly via its enhanced trapping performances.In this article,we present the first time direct experimental evidence of the self-reconfiguration of the optical potential that is experienced by a nanoparticle trapped in a plasmonic nanocavity.Our observations enable us to gain further understanding of the SIBA mechanism and to determine the optimal conditions for boosting the performances of SIBA-based nano-optical tweezers.

Giant multiphononic effects in a perovskite oxide

Perovskite oxides offer tremendous potential for applications in information storage and energy conversion,owing to a subtle interplay between their spin,charge,orbital and lattice degrees of freedom.Here,we further expand the possible range of perovskite oxides operation towards the fields of thermal management and thermal computing by exploiting an exceptional synergy between different ferroic orders.We propose dynamical control of the heat flow in a distinctive family of perovskite oxides obtained via the application of small electric(~10 kV/cm)and/or magnetic(~1 T)fields.Based on first-principles simulations,we predict a relative heat conductivity variation of~100%in SrMnO_(3) thin films near room temperature resulting from a phase transition that involves huge changes in both the magnetization and electric polarization.The disclosed giant multiphononic effects are fundamentally caused by anharmonic spin-phonon couplings that strongly influence the mean lifetime of phonons.

Double-layer graphene for enhanced tunable infrared plasmonics

Graphene is emerging as a promising material for photonic applications owing to its unique optoelectronic properties.Graphene supports tunable,long-lived and extremely confined plasmons that have great potential for applications such as biosensing and optical communications.However,in order to excite plasmonic resonances in graphene,this material requires a high doping level,which is challenging to achieve without degrading carrier mobility and stability.Here,we demonstrate that the infrared plasmonic response of a graphene multilayer stack is analogous to that of a highly doped single layer of graphene,preserving mobility and supporting plasmonic resonances with higher oscillator strength than previously explored single-layer devices.Particularly,we find that the optically equivalent carrier density in multilayer graphene is larger than the sum of those in the individual layers.Furthermore,electrostatic biasing in multilayer graphene is enhanced with respect to single layer due to the redistribution of carriers over different layers,thus extending the spectral tuning range of the plasmonic structure.The superior effective doping and improved tunability of multilayer graphene stacks should enable a plethora of future infrared plasmonic devices with high optical performance and wide tunability.

Phase-sensitive plasmonic biosensor using a portable and large field-of-view interferometric microarray imager

Nanophotonics,and more specifically plasmonics,provides a rich toolbox for biomolecular sensing,since the engineered metasurfaces can enhance light–matter interactions to unprecedented levels.So far,biosensing associated with high-quality factor plasmonic resonances has almost exclusively relied on detection of spectral shifts and their associated intensity changes.However,the phase response of the plasmonic resonances have rarely been exploited,mainly because this requires a more sophisticated optical arrangement.Here we present a new phase-sensitive platform for high-throughput and label-free biosensing enhanced by plasmonics.It employs specifically designed Au nanohole arrays and a large field-of-view interferometric lens-free imaging reader operating in a collinear optical path configuration.This unique combination allows the detection of atomically thin(angstrom-level)topographical features over large areas,enabling simultaneous reading of thousands of microarray elements.As the plasmonic chips are fabricated using scalable techniques and the imaging reader is built with low-cost off-the-shelf consumer electronic and optical components,the proposed platform is ideal for point-of-care ultrasensitive biomarker detection from small sample volumes.Our research opens new horizons for on-site disease diagnostics and remote health monitoring.

Rapid and robust control of single quantum dots

The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules,quantum dots and plasmonic nanoparticles.Optimal control of the extremely short-lived coherences of these individual systems has so far remained elusive,yet its successful implementation would enable arbitrary external manipulation of otherwise inaccessible nanoscale dynamics.In ensemble measurements,such control is often achieved by resorting to a closed-loop optimization strategy,where the spectral phase of a broadband laser field is iteratively optimized.This scheme needs long measurement times and strong signals to converge to the optimal solution.This requirement is in conflict with the nature of single emitters whose signals are weak and unstable.Here we demonstrate an effective closed-loop optimization strategy capable of addressing single quantum dots at room temperature,using as feedback observable the two-photon photoluminescence induced by a phase-controlled broadband femtosecond laser.Crucial to the optimization loop is the use of a deterministic and robust-against-noise search algorithm converging to the theoretically predicted solution in a reduced amount of steps,even when operating at the few-photon level.Full optimization of the single dot luminescence is obtained within~100 trials,with a typical integration time of 100 ms per trial.These times are faster than the typical photobleaching times in single molecules at room temperature.Our results show the suitability of the novel approach to perform closed-loop optimizations on single molecules,thus extending the available experimental toolbox to the active control of nanoscale coherences.