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Nikolay I. Zheludev

Publications and source records attributed to Nikolay I. Zheludev.

At least 37 records · Page 2Linked to original sources
arXiv2022

Ballistic Dynamics of Flexural Thermal Movements in a Nano-membrane Revealed with Subatomic Resolution

Flexural oscillations of free-standing films, nano-membranes and nano-wires are attracting growing attention for their importance to the thermal, electrical and mechanical properties of 2D materials. Here we report on the observation of short-timescale ballistic motion in the flexural mode of a nano-membrane cantilever, driven by thermal fluctuation of flexural phonons, including measurements of ballistic velocities and displacements performed with sub-atomic resolution, using a new free electron edge-scattering technique. Within intervals <10 μs, the membrane moves ballistically at a constant velocity, typically ~300 μm/s, while Brownian-like dynamics emerge for longer observation periods. Access to the ballistic regime provides verification of the equipartition theorem and Maxwell-Boltzmann statistics for flexural modes, and can be used in fast thermometry and mass sensing during atomic absorption/desorption processes on the membrane. We argue that the ballistic regime should be accounted for in understanding the electrical, optical, thermal and mechanical properties of 2D materials.

cond-mat.stat-mech↗
arXiv2022

Nondiffracting Supertoroidal Pulses: Optical "Kármán vortex streets"

Recently introduced supertoroidal light pulses [Nat. Commun. 15, 5891 (2021)] are a family of space-time nonseparable freespace electromagnetic excitations with unique topological properties including skyrmionic field configurations, fractal-like patterns of singularities, and extended areas of energy backflow. Here we report nondiffracting supertoroidal pulses (ND-STPs), propagation-robust skyrmionic and vortex-ring field that endure the singular configurations over arbitrary propagation distances. Intriguingly, the field structure in of ND-STPs has a strong similarity with a von Kármán vortex street, a pattern of swirling vortices observed in fluid and gas dynamics that is responsible for the "singing" of suspended telephone lines in wind. We argue that ND-STPs are of interest as directed energy channels for telecom applications.

physics.optics↗
arXiv2021

Volatile optical bistability enabled by mechanical nonlinearity

Optical devices with metastable states controlled with light (optical flip-flops) are needed in data storage, signal processing and displays. Although non-volatile optical memory relying on structural phase transitions in chalcogenide glasses has been widely used for optical data storage, beyond that, weak optical nonlinearities have hindered the development of low-power bistable devices. Here we report on a new type of volatile optical bistability in a resonant hybrid nano-optomechanical device, comprising of a pair of anchored nanowires decorated with plasmonic metamolecules. The nonlinearity resides in the mechanical properties of the nanowires and is transduced to its optical response by reconfiguring the plasmonic metamolecules. Such a system can be driven to a bistable response by acoustic signals modulated at the natural mechanical resonance of the nanowire. The memory of such a device is volatile and can be erased by removing the acoustic signal but in its presence, it can be switched between bistable optical states with microwatts of optical power. We argue that the demonstration of hybrid nano-optomechanical bistability opens new opportunities to develop practical low-power bistable devices.

physics.optics↗
arXiv2021

Modelling quantum photonics on a quantum computer

Modelling of photonic devices traditionally involves solving the equations of light-matter interaction and light propagation, and it is restrained by their applicability. Here we demonstrate an alternative modelling methodology by creating a "quantum copy" of the optical device in the quantum computer. As an illustration, we simulate quantum interference of light on a thin absorbing film. Such interference can lead to either perfect absorption or total transmission of light through the film, the phenomena attracting attention for data processing applications in classical and quantum information networks. We map behaviour of the photon in the quantum interference experiment to the evolution of a quantum state of transmon, a superconducting charge qubit of the IBM quantum computer. Details of the real optical experiment are flawlessly reproduced on the quantum computer. We argue that superiority of the "quantum copy" methodology shall be apparent in modelling complex multi-photon optical phenomena and devices.

quant-ph↗
arXiv2021

Supertoroidal light pulses: Propagating electromagnetic skyrmions in free space

Topological structures of electromagnetic fields could give access to nontrivial light-matter interactions and additional degrees of freedom for information and energy transfer. A characteristic example of such electromagnetic excitations are space-time non-separable single-cycle pulses, the exact solutions of Maxwell equation of toroidal topology predicted by Hellwarth and Nouchi in 1996 and recently observed experimentally. Here we introduce a new family of electromagnetic excitation of toroidal topology with increasing complexity in which the Hellwarth-Nouchi pulse is just the simplest member. The electromagnetic excitations of the new family can be parametrised by a single real number and exhibit skyrmionic structures of various orders. They feature multiple singularities in the electromagnetic and Poynting vector fields are accompanied by the fractal-like distributions of energy backflow. The generalized family of toroidal electromagnetic excitation with salient topologies are of interest for transient light-matter interactions, ultrafast optics, spectroscopy, and toroidal electrodynamics.

physics.optics↗
arXiv2021

Spatio-temporal characterization of ultrashort vector pulses

Ultrafast vectorially polarized pulses have found many applications in information and energy transfer owing mainly to the presence of strong longitudinal components and their space-polarization non-separability. Due to their broad spectrum, such pulses often exhibit space-time couplings, which significantly affect the pulse propagation dynamics leading to reduced energy density or utilized to create new effects like a rotating or sliding wavefront at focus. Here, we present a new method for the spatio-temporal characterization of ultrashort cylindrical vector pulses based on a combination of spatially resolved Fourier transform spectroscopy and Mach-Zehnder interferometry. The method provides access to spatially resolved spectral amplitudes and phases of all polarization components of the pulse. We demonstrate the capabilities of the method by completely characterizing a $10$~fs radially polarized pulse from a Ti:sapphire laser at $800$~nm.

physics.optics↗
arXiv2020

Topological Insulator Metamaterial with Giant Circular Photogalvanic Effect

One of the most striking manifestations of electronic properties of topological insulators is the dependence of the photocurrent direction on the helicity of circularly polarized optical excitation. The helicity dependent photocurrents, underpinned by spin-momentum locking of surface Dirac electrons, are weak and easily overshadowed by bulk contributions. Here we show that the chiral response can be enhanced by nanostructuring. The tight confinement of electromagnetic fields in the resonant nanostructure enhances the photoexcitation of spin-polarized surface states of topological insulator Bi1.5Sb0.5Te1.8Se1.2, leading to an 11-fold increase of the circular photogalvanic effect and an unprecedented photocurrent dichroism (\r{ho}circ=0.87) at room temperature. The control of spin-transport in topological materials by structural design is a previously unrecognised ability of metamaterials that bridges the gap between nanophotonics and spin-electronics, providing new opportunities for developing polarization sensitive photodetectors.

physics.app-ph↗
arXiv2020

Measures of space-time non-separability of electromagnetic pulses

Electromagnetic pulses are typically treated as space-time (or space-frequency) separable solutions of Maxwell's equations, where spatial and temporal (spectral) dependence can be treated separately. In contrast to this traditional viewpoint, recent advances in structured light and topological optics have highlighted the non-trivial wave-matter interactions of pulses with complex topology and space-time non-separable structure, as well as their potential for energy and information transfer. A characteristic example of such a pulse is the "Flying Doughnut" (FD), a space-time non-separable toroidal few-cycle pulse with links to toroidal and non-radiating (anapole) excitations in matter. Here, we propose a quantum-mechanics-inspired methodology for the characterization of space-time non-separability in structured pulses. In analogy to the non-separability of entangled quantum systems, we introduce the concept of space-spectrum entangled states to describe the space-time non-separability of classical electromagnetic pulses and develop a method to reconstruct the corresponding density matrix by state tomography. We apply our method to the FD pulse and obtain the corresponding fidelity, concurrence, and entanglement of formation. We demonstrate that such properties dug out from quantum mechanics quantitatively characterize the evolution of the general spatiotemporal structured pulse upon propagation.

physics.optics↗
arXiv2020

Hyperspectral Nanomotion Microscopy

We have developed a technique that extends static scanning electron microscopic imaging to include hyperspectral mapping of fast thermal and externally-driven movements at up to Megahertz frequencies. It is based on spectral analysis of the secondary electron flux generated by a focused electron beam incident on the moving object. We demonstrate detection of nanowire Brownian motion and hyperspectral mapping of stimulated oscillations of flea setae with deep sub-nanometer displacement sensitivity.

physics.app-ph↗
arXiv2020

Optical Metrology of Sub-Wavelength Objects Enabled by Artificial Intelligence

Microscopes and various forms of interferometers have been used for decades in optical metrology of objects that are typically larger than the wavelength of light λ. However, metrology of subwavelength objects was deemed impossible due to the diffraction limit. We report that measurement of the physical size of sub-wavelength objects with accuracy exceeding λ/800 by analyzing the diffraction pattern of coherent light scattered by the objects with deep learning enabled analysis. With a 633nm laser, we show that the width of sub-wavelength slits in opaque screen can be measured with accuracy of 0.77nm, challenging the accuracy of electron beam and ion beam lithographies. The technique is suitable for high-rate non-contact measurements of nanometric sizes in smart manufacturing applications with integrated metrology and processing tools.

physics.optics↗
arXiv2020

Deeply Subwavelength Optical Imaging

We report the experimental demonstration of deeply subwavelength far-field optical imaging of unlabelled samples with resolution better than $λ/20$. We beat the ~$λ$/2 diffraction limit of conventional optical microscopy several times over by recording the intensity pattern of coherent light scattered from the object into the far-field. We retrieve information about the object with a deep learning neural network trained on scattering events from a large set of known objects.

physics.optics↗
arXiv2019

Building blocks for space-time non-separable pulses

Space-time non-separable pulses hold promise for topological information transfer, probing ultra-fast light-matter interactions and engaging toroidal excitations in matter. Spurred by recent advances in ultra-fast and topological optics, these exotic electromagnetic excitations are now becoming the focus of growing experimental efforts. Many practical questions are yet to be answered regarding their generation, detection and light matter interactions. In particular, can these pulses be constructed from plane waves or other simple but experimentally accessible waves? Here we demonstrate that they can and as an example we provide analytical expressions for the characteristic case of the flying doughnut pulse which allows the expansion and synthesis of the pulse from sets of monochromatic beams, single-cycle pulses, and plane waves.

physics.optics↗
arXiv2019

Phase stabilization of a coherent fibre network by single-photon counting

Coherent optical fibre networks are extremely sensitive to thermal, mechanical and acoustic noise, which requires elaborate schemes of phase stabilization with dedicated auxiliary lasers, multiplexers and photodetectors. This is particularly demanding in quantum networks operating at the single-photon level. Here we propose a simple method of phase stabilization based on single-photon counting and apply it to quantum fibre networks implementing single-photon interference on a lossless beamsplitter and coherent perfect absorption on a metamaterial absorber. As a proof of principle, we show dissipative single-photon switching with visibility close to 80%. This method can be employed in quantum networks of greater complexity without classical stabilization rigs, potentially increasing efficiency of the quantum channels.

quant-ph↗
arXiv2019

Coupling of atomic quadrupole transitions with resonant surface plasmons

We report on the coupling of an electric quadrupole transition in atom with plasmonic excitation in a nanostructured metallic metamaterial. The quadrupole transition at 685 nm in the gas of Cesium atoms is optically pumped, while the induced ground state population depletion is probed with light tuned on the strong electric dipole transition at 852 nm. We use selective reflection to resolve the Doppler-free hyperfine structure of Cesium atoms. We observed a strong modification of the reflection spectra at the presence of metamaterial and discuss the role of the spatial variation of the surface plasmon polariton on the quadrupole coupling.

physics.atom-ph↗
arXiv2019

Cooperative field localization and excitation eigenmodes in disordered metamaterials

We investigate numerically and experimentally the near-field response of disordered arrays comprising asymmetrically split ring resonators that exhibit strong cooperative response. Our simulations treat the unit cell split ring resonators as discrete pointlike oscillators with associated electric and magnetic point dipole radiation, while the strong cooperative radiative coupling between the different split rings is fully included at all orders. The methods allow to calculate local field and Purcell factor enhancement arising from the collective electric and magnetic excitations. We find substantially increased standard deviation of the Purcell-enhancement with disorder, making it increasingly likely to find collective excitation eigenmodes with very high Purcell factors that are also stronger for magnetic than electric excitations. We show that disorder can dramatically modify the cooperative response of the metamaterial even in the presence of strong dissipation losses as is the case for plasmonic systems. Our analysis in terms of collective eigenmodes paves a way for controlled engineering of electromagnetic device functionalities based on strongly interacting metamaterial arrays.

physics.optics↗
arXiv2018

Strong radiative interactions and subradiance in disordered metamaterials

We provide detailed comparisons between experimental findings and numerical simulations of large cooperatively interacting, spatially disordered metamaterial arrays, consisting of asymmetrically split rings. Simulation methods fully incorporate strong field-mediated inter-meta-atom interactions between discrete resonators and statistical properties of disorder, while approximating the resonators' internal structure. Despite the large system size, we find a qualitative agreement between the simulations and experiments, and characterize the microscopic origins of the observed disorder response. Our microscopic description of macroscopic electrodynamics reveals how the response of disordered arrays with strong field-mediated interactions is inherently linked to their cooperative response to electromagnetic waves where the multiple scattering induces strong correlations between the excitations of individual resonators. Whereas for a regular array the response can be overwhelmingly dominated by a spatially-extended collective eigenmode with subradiant characteristics, a gradual increase of the positional disorder rapidly leads to a spatial localization of both the electric and magnetic dipolar excitation profile of this eigenmode. We show how the effects of disorder and cooperative interactions are mapped onto the transmission resonance in the far field spectrum and measure the "cooperative Lamb shift" of the resonance that is shifting toward the red as the disorder increases. The interplay between the disorder and interactions generally is most dramatic in the microwave arrays, but we find that in suitable regimes the strong disorder effects can be achieved also for plasmonic optical systems.

physics.optics↗
arXiv2018

All-dielectric free-electron-driven holographic light sources

It has recently been shown that holographically nanostructured surfaces can be employed to control the wavefront of (predominantly plasmonic) optical-frequency light emission generated by the injection of medium-energy electrons into a gold surface. Here we apply the concept to manipulation of the spatial distribution of transition radiation emission from high-refractive-index dielectric/semiconductor target materials, finding that concomitant incoherent luminescent emission at the same wavelength is unperturbed by holographic surface-relief structures, and thereby deriving a means of discriminating between the two emission components.

physics.optics↗