@article{21529, abstract = {A central challenge in the emerging field of free-electron quantum optics is to achieve strong quantum interaction and single-photon nonlinearity between a flying free electron and a photonic mode. Existing schemes are intrinsically limited by electron diffraction, which puts an upper bound on the interaction length and, therefore, on the strength of quantum coupling and nonlinearity. Here, we propose “free-electron fibers”: effectively one-dimensional photonic systems where free electrons copropagate with two guided modes. The first mode applies a ponderomotive trap to the free electron, removing the limitations due to electron diffraction. The second mode strongly couples to the guided free electron with an enhanced coupling that is orders of magnitude larger than previous designs. The extended interaction lengths enabled by our scheme allow for strong single-photon nonlinearities mediated by free electrons. We predict novel quantum effects in our system such as deterministic single-photon emission and nonlinear multimode dynamics. Our proposal paves the way toward the realization of heralded macroscopic nonclassical light generation, deterministic single-photon sources, and quantum gates controlled by free-electron–photon interactions.}, author = {Karnieli, Aviv and Roques-Carmes, Charles and Rivera, Nicholas and Fan, Shanhui}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {quantum optics, free electrons, single photon nonlinearity, electron-photon interaction}, number = {8}, pages = {3401--3411}, publisher = {American Chemical Society}, title = {{Strong coupling and single-photon nonlinearity in free-electron quantum optics}}, doi = {10.1021/acsphotonics.4c00908}, volume = {11}, year = {2024}, } @phdthesis{17164, abstract = {This thesis is structured into two parts. In the first part, we consider the random variable X := Tr(f1(W)A1 . . . fk(W)Ak) where W is an N × N Hermitian Wigner matrix, k ∈ N, and we choose (possibly N-dependent) regular functions f1, . . . , fk as well as bounded deterministic matrices A1, . . . , Ak. In this context, we prove a functional central limit theorem on macroscopic and mesoscopic scales, showing that the fluctuations of X around its expectation are Gaussian and that the limiting covariance structure is given by a deterministic recursion. We further give explicit error bounds in terms of the scaling of f1, . . . , fk and the number of traceless matrices among A1, . . . , Ak, thus extending the results of Cipolloni, Erdős and Schröder [40] to products of arbitrary length k ≥ 2. Analyzing the underlying combinatorics leads to a non-recursive formula for the variance of X as well as the covariance of X and Y := Tr(fk+1(W)Ak+1 . . . fk+ℓ(W)Ak+ℓ) of similar build. When restricted to polynomials, these formulas reproduce recent results of Male, Mingo, Peché, and Speicher [107], showing that the underlying combinatorics of noncrossing partitions and annular non-crossing permutations continue to stay valid beyond the setting of second-order free probability theory. As an application, we consider the fluctuation of Tr(eitW A1e −itW A2)/N around its thermal value Tr(A1) Tr(A2)/N2 when t is large and give an explicit formula for the variance. The second part of the thesis collects three smaller projects focusing on different random matrix models. In the first project, we show that a class of weakly perturbed Hamiltonians of the form Hλ = H0 + λW, where W is a Wigner matrix, exhibits prethermalization. That is, the time evolution generated by Hλ relaxes to its ultimate thermal state via an intermediate prethermal state with a lifetime of order λ −2 . As the main result, we obtain a general relaxation formula, expressing the perturbed dynamics via the unperturbed dynamics and the ultimate thermal state. The proof relies on a two-resolvent global law for the deformed Wigner matrix Hλ. The second project focuses on correlated random matrices, more precisely on a correlated N × N Hermitian random matrix with a polynomially decaying metric correlation structure. A trivial a priori bound shows that the operator norm of this model is stochastically dominated by √ N. However, by calculating the trace of the moments of the matrix and using the summable decay of the cumulants, the norm estimate can be improved to a bound of order one. In the third project, we consider a multiplicative perturbation of the form UA(t) where U is a unitary random matrix and A = diag(t, 1, ..., 1). This so-called UA model was first introduced by Fyodorov [73] for its applications in scattering theory. We give a general description of the eigenvalue trajectories obtained by varying the parameter t and introduce a flow of deterministic domains that separates the outlier resulting from the rank-one perturbation from the typical eigenvalues for all sub-critical timescales. The results are obtained under generic assumptions on U that hold for various unitary random matrices, including the circular unitary ensemble (CUE) in the original formulation of the model.}, author = {Reker, Jana}, issn = {2663-337X}, keywords = {Random Matrices, Spectrum, Central Limit Theorem, Resolvent, Free Probability}, pages = {206}, publisher = {Institute of Science and Technology Austria}, title = {{Central limit theorems for random matrices: From resolvents to free probability}}, doi = {10.15479/at:ista:17164}, year = {2024}, } @article{9827, abstract = {The Nearest neighbour search (NNS) is a fundamental problem in many application domains dealing with multidimensional data. In a concurrent setting, where dynamic modifications are allowed, a linearizable implementation of the NNS is highly desirable.This paper introduces the LockFree-kD-tree (LFkD-tree ): a lock-free concurrent kD-tree, which implements an abstract data type (ADT) that provides the operations Add, Remove, Contains, and NNS. Our implementation is linearizable. The operations in the LFkD-tree use single-word read and compare-and-swap (Image 1 ) atomic primitives, which are readily supported on available multi-core processors. We experimentally evaluate the LFkD-tree using several benchmarks comprising real-world and synthetic datasets. The experiments show that the presented design is scalable and achieves significant speed-up compared to the implementations of an existing sequential kD-tree and a recently proposed multidimensional indexing structure, PH-tree.}, author = {Chatterjee, Bapi and Walulya, Ivan and Tsigas, Philippas}, issn = {0304-3975}, journal = {Theoretical Computer Science}, keywords = {Concurrent data structure, kD-tree, Nearest neighbor search, Similarity search, Lock-free, Linearizability}, pages = {27--48}, publisher = {Elsevier}, title = {{Concurrent linearizable nearest neighbour search in LockFree-kD-tree}}, doi = {10.1016/j.tcs.2021.06.041}, volume = {886}, year = {2021}, } @article{22570, abstract = {Atmospheric carbon dioxide concentration ([CO 2 ]) is increasing, which increases leaf-scalephotosynthesis and intrinsic water-use efficiency. These direct responses have the potential toincrease plant growth, vegetation biomass, and soil organic matter; transferring carbon from theatmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sinkwould slow the rate of [CO 2] increase and thus climate change. However, ecosystem CO2responses are complex or confounded by concurrent changes in multiple agents of global changeand evidence for a [CO 2]-driven terrestrial carbon sink can appear contradictory. Here wesynthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO 2](iCO 2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in globalphotosynthesis since pre-industrial times. Established theory, supported by experiments,indicates that iCO 2 is likely responsible for about half of the increase. Global carbon budgeting,atmospheric data, and forest inventories indicate a historical carbon sink, and these apparentiCO 2 responses are high in comparison to experiments and predictions from theory. Plantmortality and soil carbon iCO 2 responses are highly uncertain. In conclusion, a range of evidencesupports a positive terrestrial carbon sink in response to iCO2 , albeit with uncertain magnitudeand strong suggestion of a role for additional agents of global change.}, author = {Walker, Anthony P. and De Kauwe, Martin G. and Bastos, Ana and Belmecheri, Soumaya and Georgiou, Katerina and Keeling, Ralph F. and McMahon, Sean M. and Medlyn, Belinda E. and Moore, David J. P. and Norby, Richard J. and Zaehle, Sönke and Anderson‐Teixeira, Kristina J. and Battipaglia, Giovanna and Brienen, Roel J. W. and Cabugao, Kristine G. and Cailleret, Maxime and Campbell, Elliott and Canadell, Josep G. and Ciais, Philippe and Craig, Matthew E. and Ellsworth, David S. and Farquhar, Graham D. and Fatichi, Simone and Fisher, Joshua B. and Frank, David C. and Graven, Heather and Gu, Lianhong and Haverd, Vanessa and Heilman, Kelly and Heimann, Martin and Hungate, Bruce A. and Iversen, Colleen M. and Joos, Fortunat and Jiang, Mingkai and Keenan, Trevor F. and Knauer, Jürgen and Körner, Christian and Leshyk, Victor O. and Leuzinger, Sebastian and Liu, Yao and MacBean, Natasha and Malhi, Yadvinder and McVicar, Tim R. and Penuelas, Josep and Pongratz, Julia and Powell, A. Shafer and Riutta, Terhi and Sabot, Manon E. B. and Schleucher, Juergen and Sitch, Stephen and Smith, William K. and Sulman, Benjamin and Taylor, Benton and Terrer, César and Torn, Margaret S. and Treseder, Kathleen K. and Trugman, Anna T. and Trumbore, Susan E. and van Mantgem, Phillip J. and Voelker, Steve L. and Whelan, Mary E. and Zuidema, Pieter A.}, issn = {1469-8137}, journal = {New Phytologist}, keywords = {Beta factor, Carbon dioxide, CO2 fertilization, CO2-fertilization hypothesis, Free-air CO2 enrichment (FACE), Global carbon cycle, Land–atmosphere feedback, Terrestrial ecosystems}, number = {5}, pages = {2413--2445}, publisher = {Wiley}, title = {{Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2}}, doi = {10.1111/nph.16866}, volume = {229}, year = {2021}, } @article{21525, abstract = {We present a novel design for an ultracompact, passive light source capable of generating ultraviolet and X-ray radiation, based on the interaction of free electrons with the magnetic near-field of a ferromagnet. Our design is motivated by recent advances in the fabrication of nanostructures, which allow the confinement of large magnetic fields at the surface of ferromagnetic nanogratings. Using ab initio simulations and a complementary analytical theory, we show that highly directional, tunable, monochromatic radiation at high frequencies could be produced from relatively low-energy electrons within a tabletop design. The output frequency is tunable in the extreme ultraviolet to hard X-ray range via electron kinetic energies from 1 keV to 5 MeV and nanograting periods from 1 μm to 5 nm. The proposed radiation source can achieve the tunability and monochromaticity of current free-electron-driven sources (free-electron lasers, synchrotrons, and laser-driven undulators), yet with a significantly reduced scale, cost, and complexity. Our design could help realize the next generation of tabletop or on-chip X-ray sources.}, author = {Fisher, Sophie and Roques-Carmes, Charles and Rivera, Nicholas and Wong, Liang Jie and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {X-ray sources, free electrons, nanostructure, undulator, synchrotron, free-electron laser}, number = {5}, pages = {1096--1103}, publisher = {American Chemical Society }, title = {{Monochromatic X-ray source based on scattering from a magnetic nanoundulator}}, doi = {10.1021/acsphotonics.0c00121}, volume = {7}, year = {2020}, } @article{21533, abstract = {Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer new prospects for generating visible light emission from low-energy electrons. Here we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith–Purcell (SP) effect. We demonstrate SP light emission from nanoscale gratings with periodicity as small as 50 nm, enabling the observation of tunable visible radiation from low-energy electrons (1.5 to 6 keV), an order of magnitude lower in energy than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Our results open the way to the production of SP-based nanophotonics integrated devices. Built inside electron microscopes, SP sources could enable the development of novel electron–optical correlated spectroscopic techniques and facilitate the observation of new quantum effects in light sources.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Yang, Yujia and Kooi, Steven E. and Yang, Yi and Murdia, Chitraang and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {light−matter interactions, periodic structures, nanophotonics, free-electron light sources}, number = {9}, pages = {3513--3518}, publisher = {American Chemical Society }, title = {{Smith–Purcell radiation from low-energy electrons}}, doi = {10.1021/acsphotonics.8b00743}, volume = {5}, year = {2018}, } @article{1317, abstract = {We analyze the behaviour of free boundaries in thin-film flow in the regime of strong slippage n∈[1,2) and in the regime of very weak slippage n∈,3) qualitatively and quantitatively. In the regime of strong slippage, we construct initial data which are bounded from above by the steady state but for which nevertheless instantaneous forward motion of the free boundary occurs. This shows that the initial behaviour of the free boundary is not determined just by the growth of the initial data at the free boundary. Note that this is a new phenomenon for degenerate parabolic equations which is specific for higher-order equations. Furthermore, this result resolves a controversy in the literature over optimality of sufficient conditions for the occurrence of a waiting time phenomenon. In contrast, in the regime of very weak slippage we derive lower bounds on free boundary propagation which are optimal in the sense that they coincide up to a constant factor with the known upper bounds. In particular, in this regime the growth of the initial data at the free boundary fully determines the initial behaviour of the interface.}, author = {Fischer, Julian L}, issn = {1873-1430}, journal = {Annales de l'Institut Henri Poincare (C) Non Linear Analysis}, keywords = {Thin-film equation, Free boundary, Waiting time, Qualitative behaviour, Higher-order parabolic equation, Degenerate parabolic equation}, number = {5}, pages = {1301 -- 1327}, publisher = {EMS Press}, title = {{Behaviour of free boundaries in thin-film flow: The regime of strong slippage and the regime of very weak slippage}}, doi = {10.1016/j.anihpc.2015.05.001}, volume = {33}, year = {2016}, } @article{10396, abstract = {Stimfit is a free cross-platform software package for viewing and analyzing electrophysiological data. It supports most standard file types for cellular neurophysiology and other biomedical formats. Its analysis algorithms have been used and validated in several experimental laboratories. Its embedded Python scripting interface makes Stimfit highly extensible and customizable.}, author = {Schlögl, Alois and Jonas, Peter M and Schmidt-Hieber, C. and Guzman, S. J.}, issn = {1862-278X}, journal = {Biomedical Engineering / Biomedizinische Technik}, keywords = {biomedical engineering, data analysis, free software}, location = {Graz, Austria}, number = {SI-1-Track-G}, publisher = {De Gruyter}, title = {{Stimfit: A fast visualization and analysis environment for cellular neurophysiology}}, doi = {10.1515/bmt-2013-4181}, volume = {58}, year = {2013}, }