arXiv subjects

Aldo Ejlli

Publications and source records attributed to Aldo Ejlli.

14 recordsLinked to original sources

arXiv2026

Axion Polarimetric Experiment (APE)

We present the Axion Polarimetric Experiment (APE), a cavity-enhanced polarimeter designed to search for ultralight axion and axion-like-particle dark matter through a time-dependent rotation of the linear polarization of laser light. In cavity-based schemes, intracavity quarter-wave plates can restore coherent buildup of the axion-induced orthogonal polarization, but their transmissive loss limits the achievable finesse. To avoid transmissive intracavity optics, we propose a folded Fabry-Perot cavity that employs dielectric phase-shifting mirrors. At an incidence angle near $45^\circ$, these mirrors provide a reflection-phase difference $\Delta\phi \equiv \phi_s-\phi_p \simeq \pi/2$ between $s$ and $p$ polarizations and therefore act as reflective quarter-wave plates. We present the coating design, thickness optimization, and measurements of the phase shift and optical loss of the phase-shifting mirrors. Using a heterodyne polarimetric readout and an explicitly stated noise model, we derive design-level sensitivity projections for the axion-photon coupling $g_{a\gamma\gamma}$. These projections should be interpreted as target sensitivities for the proposed cavity configuration, since the full-system birefringence noise and angular-jitter coupling remain to be measured.

physics.optics↗

arXiv2026

The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

hep-ph↗

arXiv2026

Any Light Particle Searches with ALPS II: Description of the first science campaign

From February to May of 2024 the Any Light Particle Search II (ALPS II) conducted its first science campaign using the `light-shining-through-a-wall' technique to search for pseudo-Goldstone bosons that lie beyond the Standard Model of particle physics and which are inaccessible by accelerator-based experiments. The experimental setup consists of two strings of superconducting dipole magnets, each more than 100 m long, that are separated by a wall. Laser light is directed through the first magnet string and a heterodyne detection system is used to measure the electromagnetic power that traverses a wall via the conversion to and then from a bosonic field. After the wall, a high-finesse optical cavity resonantly enhances the signal power. Two searches were carried out, one with the laser polarized perpendicular to the magnetic field direction and another with its polarization state aligned parallel to the magnetic field. No evidence for the existence of new bosons was found. In its first science campaign, ALPS II reached photon-boson conversion probability sensitivities of a few $10^{-13}$. The ongoing upgrade of the optical system aims to increase this sensitivity by about four orders of magnitude.

hep-ex↗

arXiv2025

Any Light Particle Searches with ALPS II: first science results

The light-shining-through-a-wall experiment ALPS II at DESY in Hamburg searched for axions and similar lightweight particles in its first science campaign from February to May 2024. No evidence for the existence of such particles was found. For pseudoscalar bosons like the axion, with masses below about 0.1 meV, we achieved a limit for the di-photon coupling strength of 1.5e-9 1/GeV at a 95% confidence level. This is more than a factor of 20 improvement compared to all previous similar experiments. We also provide limits on photon interactions for scalar, vector and tensor bosons. An achievement of this first science campaign is the demonstration of stable operation and robust calibration of the complex experiment. Currently, the optical system of ALPS II is being upgraded aiming for another two orders of magnitude sensitivity increase.

hep-ex↗

arXiv2024

Broadband limits on stochastic length fluctuations from a pair of table-top interferometers

The Quantum-Enhanced Space-Time (QUEST) experiment consists of a pair of co-located Power Recycled Michelson Interferometers, each designed to have a broadband, shot-noise limited displacement sensitivity of $2\times10^{-19}$ $\mathrm{m/\sqrt{Hz}}$ from 1 to 200 MHz. Here we present the first results of QUEST that set new upper limits on correlated length fluctuations from 13 to 80 MHz, constituting the first broadband constraints for a stochastic gravitational wave background at these frequencies. In a coincident observing run of $10^{4}$ s the averaging of the cross-correlation spectra between the two interferometer signals resulted in a strain sensitivity of $3\times10^{-20}$ $\mathrm{1/\sqrt{Hz}}$ at 40 MHz, making QUEST the most sensitive table-top interferometric system to date.

gr-qc↗

arXiv2024

Design and Performance of the ALPS II Regeneration Cavity

The Regeneration Cavity (RC) is a critical component of the Any Light Particle Search II (ALPS II) experiment. It increases the signal from possible axions and axion-like particles in the experiment by nearly four orders of magnitude. The total round-trip optical losses of the power circulating in the cavity must be minimized in order to maximize the resonant enhancement of the cavity, which is an important figure of merit for ALPS II. Lower optical losses also increase the cavity storage time and with the 123 meter long ALPS II RC we have demonstrated the longest storage time of a two-mirror optical cavity. We measured a storage time of $7.17 \pm 0.01$ ms, equivalent to a linewidth of 44.4 Hz and a finesse of 27,500 at a wavelength of 1064 nm.

physics.optics↗

arXiv2024

Squeezing the quantum noise of a gravitational-wave detector below the standard quantum limit

Precision measurements of space and time, like those made by the detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), are often confronted with fundamental limitations imposed by quantum mechanics. The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot both be precisely measured, giving rise to an apparent limitation called the Standard Quantum Limit (SQL). Reducing quantum noise below the SQL in gravitational-wave detectors, where photons are used to continuously measure the positions of freely falling mirrors, has been an active area of research for decades. Here we show how the LIGO A+ upgrade reduced the detectors' quantum noise below the SQL by up to 3 dB while achieving a broadband sensitivity improvement, more than two decades after this possibility was first presented.

gr-qc↗

arXiv2024

Searching for scalar field dark matter with LIGO

We report on a direct search for scalar field dark matter using data from LIGO's third observing run. We analyse the coupling of size oscillations of the interferometer's beamsplitter and arm test masses that may be caused by scalar field dark matter. Using new efficient search methods to maximise sensitivity for signatures of such oscillations, we set new upper limits for the coupling constants of scalar field dark matter as a function of its mass, which improve upon bounds from previous direct searches by several orders of magnitude in a frequency band from 10 Hz to 180 Hz.

astro-ph.CO↗

arXiv2024

DarkGEO: A Large-Scale Laser-Interferometric Axion Detector

Axions and axion-like particles (ALPs) are leading candidates for dark matter. They are well motivated in many extensions of the Standard Model and supported by astronomical observations. We propose an iterative transformation of the existing facilities of the gravitational-wave detector and technology testbed GEO600, located near Ruthe in Germany, into a kilometre-scale upgrade of the laser-interferometric axion detector LIDA. The final DarkGEO detector could search for coincident signatures of axions and ALPs and significantly surpass the current constraints of both direct searches and astrophysical observations in the measurement band from $10^{-16}$ to $10^{-8}$ $\text{eV}$. We discuss realistic parameters and design sensitivities for the configurations of the different iteration steps as well as technical challenges known from the first LIDA results. The proposed DarkGEO detector will be well suited to probe the parameter space associated with predictions from theoretical models, like grand-unified theories, as well as from astrophysical evidence, like the cosmic infrared background.

astro-ph.CO↗

arXiv2023

Probing dark matter with polarimetry techniques

In this work, we propose polarimetry experiments to search for low-mass (sub-eV) bosonic field dark matter, including axions and axion-like particles. We show that a polarimetry configuration consisting of a thick birefringent solid inside a Fabry-Pérot cavity is exceptionally sensitive to scalar field dark matter, which may cause oscillatory variations in the solid's thickness and refractive index. In addition, we show that a reconfiguration of this polarimetry experiment, in which two quarter-wave plates are placed inside the Fabry-Pérot cavity instead of a thick birefringent solid, is very sensitive to axion-like particles. We investigate the possibility of using cross-correlation of twin polarimeters to increase the sensitivity of the experiment, which in turn could allow us to explore unexplored parts of the parameter space and potentially detect a signal in either dark matter scenario.

hep-ph↗

arXiv2021

Optimisation of table-top 3D interferometers for Observational Quantum Gravity

With the use of twin, co-located, 3D interferometers, Cardiff University's Gravity Exploration Institute aims to observe quantum fluctuations of space-time as predicted by some theories of quantum gravity. Our design displacement sensitivity exceeds that of previous similar experiments, which have constrained the magnitudes of the fluctuations in the 1-25 MHz band. The increased sensitivity comes in large part from the comparably higher circulating power we aim to achieve, which reduces the overall shot noise. One complication of higher circulating power is an increase in contrast defect light, which includes higher-order modes. We will use the DC-readout scheme, whose dark-fringe offset must sufficiently dominate the contrast defect in order to detect faint signals. However, too much total output power risks saturating the high-bandwidth photodetectors. Suppressing the higher-order mode content of the contrast defect is a key strategy to realising the high circulating power and eliminating non-signal-carrying power that contributes to shot noise. For this, the inclusion of an output mode cleaner, whose design is described, is required.

astro-ph.IM↗

arXiv2021

An Experiment for Observing Quantum Gravity Phenomena using Twin Table-Top 3D Interferometers

Theories of quantum gravity based on the holographic principle predict the existence of quantum fluctuations of distance measurements that accumulate and exhibit correlations over macroscopic distances. This paper models an expected signal due to this phenomenology, and details the design and estimated sensitivity of co-located twin table-top 3D interferometers being built to measure or constrain it. The experiment is estimated to be sensitive to displacements $\sim10^{-19}\,\rm{m}/\sqrt{\rm{Hz}}$ in a frequency band between 1 and 250 MHz, surpassing previous experiments and enabling the possible observation of quantum gravity phenomena. The experiment will also be sensitive to MHz gravitational waves and various dark matter candidates.

gr-qc↗

arXiv2020

Upper limits on the amplitude of ultra-high-frequency gravitational waves from graviton-photon mixing

In this work, we present the first experimental upper limits on the presence of stochastic ultra-high-frequency gravitational waves. We exclude gravitational waves in the frequency bands from $(2.7 - 14)\times10^{14}~$Hz and $(5 - 12)\times10^{18}~$Hz down to a characteristic amplitude of $h_c^{\rm min}\approx6\times 10^{-26}$ and $h_c^{\rm min}\approx 5\times 10^{-28}$ at $95~$% confidence level, respectively. To obtain these results, we used data from existing facilities that have been constructed and operated with the aim of detecting WISPs (Weakly Interacting Slim Particles), pointing out that these facilities are also sensitive to gravitational waves by graviton to photon conversion in the presence of a magnetic field. The principle applies to all experiments of this kind, with prospects of constraining (or detecting), for example, gravitational waves from light primordial black hole evaporation in the early universe.

gr-qc↗

arXiv2017

Polarisation dynamics of a birefringent Fabry-Perot cavity

Optical Fabry-Perot cavities always show a non-degeneracy of two orthogonal polarisation states. This is due to the unavoidable birefringence of dielectric mirrors whose effects are extremely important in Fabry-Perot based high-accuracy polarimeters. We have developed and present here a theory of the polarisation state dynamics in a birefringent Fabry-Perot resonator, and we validate it through measurements performed with the polarimeter of the PVLAS experiment. The measurements are performed while a laser is frequency-locked to the cavity, and provide values for the finesse of the cavity and for the phase difference between the two orthogonal polarisation components introduced by the combination of the two cavity mirrors (equivalent wave-plate). The theoretical formulas and the experimental data agree well showing that the consequences of the mirror birefringence must be taken into account in this and in any other similar experiment.

physics.optics↗