arXiv subjects

Jovana Petrovic

Publications and source records attributed to Jovana Petrovic.

12 recordsLinked to original sources

arXiv2024

Controlled molecule injector for cold, dense, and pure molecular beams at the European x-ray free-electron laser

A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A $b$-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold ($T\approx1$~K) and dense ($ρ\approx10^8$~cm$^{-3}$) molecular beam with pulse durations up to 100~\us generated by a new version of the Even-Lavie valve. Here, a performance overview of the COMO setup is presented along with characterization experiments performed both, with an optical laser at the Center for Free-Electron-Laser Science and with x-rays at EuXFEL under burst-mode operation. COMO was designed to be attached to different instruments at the EuXFEL, in particular at the small quantum systems (SQS) and single particles, clusters, and biomolecules (SPB) instruments. This advanced controlled-molecules injection setup enables XFEL studies using highly defined samples with soft and hard x-ray FEL radiation for applications ranging from atomic, molecular, and cluster physics to elementary processes in chemistry and biology.

physics.chem-ph↗

arXiv2024

Observation of topologically protected compact edge states in flux-dressed graphene photonic lattices

Systems with engineered flatband spectra are a postulate of high-capacity transmission links and a candidate for high-temperature superconductivity. However, their operation relies on the edge or surface modes susceptible to fluctuations and fabrication errors. While the mode robustness can be enhanced by a combination of Aharonov-Bohm caging and topological insulation, the design of the corresponding flatbands requires approaches beyond the standard $k$-vector-based methods. Here, we propose a synthetic-flux probe as a solution to this problem and a route to the realization of ultra-stable modes. We prove the concept in a laser-fabricated graphene-like ribbon photonic lattice with the band-flattening flux induced by "P" waveguide coupling. The topological non-triviality is witnessed by an integer Zak phase derived from the mean chiral displacement. Mode stability is evidenced by excellent mode localization and the robustness to fabrication tolerances and variations of the input phase. Our results can serve as a basis for the development of multi-flat-band materials for low-energy electronics.

cond-mat.mes-hall↗

arXiv2022

Bend-Free Multiarm Interferometers on Optical Chips

Multiarm interferometers can enhance measurement precision and provide multiparameter capability to the measurement. Their realisation requires multiport beam splitters, which has been a long-standing challenge in free-space and integrated optics. Here, we propose a new type of multiport interferometers suitable for implementation on optical chips. Their prospective advantages over the standard directional-coupler architectures: an arbitrary number of arms, planar architecture and two orders of magnitude reduction in footprint, are achieved by the layout based exclusively on the finite modulated photonic lattices. The inverse design of photonic lattices is facilitated by restricting the light propagation to periodic patterns. The corresponding interferometer model predicts the maximum $1/\sqrt{N}$ sensitivity scaling with the number of arms $N$. While the presented design solutions are ubiquitous to all implementations, the advantages are discussed in both the low and high refractive-index contrast platforms. Finally, we provide an outlook on the possibilities for the interferometer applications in distributed classical and quantum measurements.

physics.optics↗

arXiv2021

A new concept for design of photonic integrated circuits with the ultimate density and low loss

We challenge the current thinking and approach to the design of photonic integrated circuits (PICs) for applications in communications, quantum information and sensing. The standard PICs are based on directional couplers, that provide a wide range of functionalities but do not fully respond to the major technological challenges: massive parallelisation of transmission channels, low-energy dissipation and small footprint. We propose a new concept for design of PICs with the ultimate downscaling capability, the absence of geometric loss and a high-fidelity throughput. This is achieved by a periodic continuous-time quantum walk of photons through waveguide arrays that leverages on the simple and effective algebraic approach to engineering waveguide couplings. We demonstrate the potential of the new concept by reconsidering the design of basic building blocks of the information and sensing systems: interconnects, multiport couplers, entanglement generators and interferometers. An extensive feasibility check in dielectric and semiconductor fabrication platforms confirmed this potential.

physics.optics↗

arXiv2020

Spatial separation of 2-propanol monomer and its ionization-fragmentation pathways

The spatial separation of 2-propanol monomer from its clusters in a molecular beam by an electrostatic deflector was demonstrated. Samples of 2-propanol monomer with a purity of 90 % and a beam density of $7\times10^6~\text{cm}^{-3}$ were obtained. These samples were utilized to study the femtosecond-laser-induced strong-field multi-photon ionization and fragmentation of 2-propanol using non-resonant 800 nm light with peak intensities of $3-7\times10^{13}~W/cm^{2}$.

physics.chem-ph↗

arXiv2018

Millisecond pulsar origin of the Galactic center excess and extended gamma-ray emission from Andromeda - a closer look

A new measurement of a spatially extended gamma-ray signal from the center of the Andromeda galaxy (M31) has been recently published by the Fermi-LAT collaboration, reporting that the emission broadly resembles the so-called Galactic center excess (GCE) of the Milky Way (MW). At the same time, evidence is accumulating on a millisecond pulsar (MSPs) origin for the GCE. These elements prompt us to compare the mentioned observations with what is, perhaps, the simplest model for an MSP population, solely obtained by rescaling of the MSP luminosity function determined in the local MW disk via the respective stellar mass of the systems. It is remarkable that without free fitting parameters, this model can account for both the energetics and the morphology of the GCE within uncertainties. For M31, the estimated luminosity due to primordial MSPs is expected to contribute only about a quarter of the detected emission, although a dominant contribution cannot be excluded given the large uncertainties. If correct, the model predicts that the M31 disk emission due to MSP is not far below the present upper bound. We also discuss a few refinements of this simple model. In particular, we use the correlation between globular cluster gamma-ray luminosity and stellar encounter rate to gauge the dynamical MSP formation in the bulge. This component is expected to contribute to the GCE only at a level $\lesssim 5\%$, but it may be of some importance in explaining the signal's morphology in the inner region of the Galaxy. We also comment on some effects which may lead to violations of the simple scaling used, on alternative models, and on future perspectives for improved diagnostics.

astro-ph.HE↗

arXiv2015

Millisecond pulsars and the Galactic Center gamma-ray excess: the importance of luminosity function and secondary emission

Several groups of authors have analyzed Fermi LAT data in a region around the Galactic Center finding an unaccounted gamma-ray excess over diffuse backgrounds in the GeV energy range. It has been argued that it is difficult or even impossible to explain this diffuse emission by the leading astrophysical candidates - millisecond pulsars (MSPs). Here we provide a new estimate of the contribution to the excess by a population of yet unresolved MSP located in the bulge of the Milky Way. We simulate this population with the GALPLOT package by adopting a parametric approach, with the range of free parameters gauged on the MSP characteristics reported by the second pulsar catalogue (2PC). We find that the conclusions strongly depend on the details of the MSP luminosity function (in particular, its high luminosity end) and other explicit or tacit assumptions on the MSP statistical properties, which we discuss. Notably, for the first time we study the importance of the possible secondary emission of the MSPs in the Galactic Center, {i.e. the emission via inverse Compton losses of electrons injected in the interstellar medium. Differently from a majority of other authors, we find that within current uncertainties a large if not dominant contribution of MSPs to the excess cannot be excluded. We also show that the sensitivities of future instruments or possibly already of the latest LAT data analysis (Pass 8) provide good perspectives to test this scenario by resolving a significant number of MSPs.

astro-ph.HE↗

arXiv2015

Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?

Several groups have recently claimed evidence for an unaccounted gamma-ray excess over {the} diffuse backgrounds at few GeV in {the} Fermi-LAT data in a region around the Galactic Center, consistent with a dark matter annihilation origin. We demonstrate that the main spectral and angular features of this excess can be reproduced if they are mostly due to inverse Compton emission from high-energy electrons injected in a burst event of ~10^52 - 10^53erg roughly O(10^6) years ago. We consider this example as a proof of principle that time-dependent phenomena need to be understood and accounted for - together with detailed diffuse foregrounds and unaccounted "steady state" astrophysical sources - before any robust inference can be made about dark matter signals at the Galactic Center. In addition, we point out that the timescale suggested by our study, which controls both the energy cutoff and the angular extension of the signal, intriguingly matches (together with the energy budget) what is indirectly inferred by other evidences suggesting a very active Galactic Center in the past, for instance related to intense star formation and accretion phenomena.

astro-ph.HE↗

arXiv2015

Composite localized modes in discretized spin-orbit-coupled Bose-Einstein condensates

We introduce a discrete model for binary spin-orbit-coupled (SOC) Bose-Einstein condensates (BEC) trapped in a deep one-dimensional optical lattice. Two different types of the couplings are considered, with spatial derivatives acting inside each species, or between the species. The discrete system with inter-site couplings dominated by the SOC, while the usual hopping is negligible, \textit{emulates} condensates composed of extremely heavy atoms, as well as those with opposite signs of the effective atomic masses in the two components.\ Stable localized composite states of miscible and immiscible types are constructed. The effect of the SOC on the immiscibility-miscibility transition in the localized complexes, which emulates the phase transition between insulating and conducting states in semiconductors, is studied.

cond-mat.quant-gas↗

arXiv2011

A Multi-Path Interferometer on an Atom Chip

Cold-atom interferometry is a powerful tool for high-precision measurements of the quantum properties of atoms, many-body interactions and gravity. Further enhancement of sensitivity and reduction of complexity of these devices are crucial conditions for success of their applications. Here we introduce a multi-path interferometric scheme that offers advances in both these aspects. It uses coherent coupling between Bose-Einstein condensates in different Zeeman states to generate an interferometric signal with sharp fringes. We realise such an interferometer as a compact easy-to-use atom-chip device and thus provide an alternative method for measurement of the light-atom and surface-atom interactions.

physics.atom-ph↗

arXiv2009

Demonstrating coherent control in 85Rb2 using ultrafast laser pulses: a theoretical outline of two experiments

Calculations relating to two experiments that demonstrate coherent control of preformed rubidium-85 molecules in a magneto-optical trap using ultrafast laser pulses are presented. In the first experiment, it is shown that pre-associated molecules in an incoherent mixture of states can be made to oscillate coherently using a single ultrafast pulse. A mechanism that can transfer molecular population to more deeply bound vibrational levels is used in the second. Optimal parameters of the control pulse are presented for the application of the mechanism to molecules in a magneto-optical trap. The calculations make use of an experimental determination of the initial state of molecules photoassociated by the trapping lasers in the magneto-optical trap and use shaped pulses consistent with a standard ultrafast laser system.

physics.atom-ph↗

arXiv2009

A pump-probe study of the formation of rubidium molecules by ultrafast photoassociation of ultracold atoms

An experimental pump-probe study of the photoassociative creation of translationally ultracold rubidium molecules is presented together with numerical simulations of the process. The formation of loosely bound excited-state dimers is observed as a first step towards a fully coherent pump-dump approach to the stabilization of Rb$_2$ into its lowest ground vibrational states. The population that contributes to the pump-probe process is characterized and found to be distinct from a background population of pre-associated molecules.

physics.chem-ph↗