arXiv subjects

Sebastian Steinlechner

Publications and source records attributed to Sebastian Steinlechner.

At least 19 recordsLinked to original sources

arXiv2025

Photodiode quantum efficiency for 2-{\mu}m light in the signal band of gravitational wave detectors

Quantum technologies with quantum correlated light require photodiodes with near-perfect `true' quantum efficiency, the definition of which adequately accounts for the photodiode dark noise. Future squeezed-light-enhanced gravitational wave detectors could in principle achieve higher sensitivities with a longer laser wavelength around 2 {\mu}m. Photodiodes made of extended InGaAs are available for this range, but the true quantum efficiency at room temperature and the low frequency band of gravitational waves is strongly reduced by dark noise. Here we characterize the change in performance of a commercial extended-InGaAs photodiode versus temperature. While the dark noise decreases as expected with decreasing temperature, the detection efficiency unfortunately also decreases monotonically. Our results indicate the need for a dedicated new design of photodiodes for gravitational wave detectors using 2-{\mu}m laser light.

quant-ph↗

arXiv2025

Mechanical Characterisation of Silicon for the ETpathfinder Test Masses

The next generation of gravitational-wave detectors, such as the Einstein Telescope, is designed to reduce noise in a wide band of frequencies compared to the current generation, through the use of new technologies. ETpathfinder, designed as an R&D facility for these technologies, is a prototype for which the mirrors were chosen to be made of crystalline silicon, produced by the Leibniz-Institut f\"ur Kristallz\"uchtung. This material choice was made to pave the way for a low thermal noise level at cryogenic temperatures in the Einstein Telescope. This paper shows the mechanical loss of silicon designated to become the test masses for ETpathfinder in the range between room temperature and 53K. In addition, the effect of the anisotropic nature of silicon on the measurement procedure is addressed. Predictions are made of the contribution of the mirror substrate material to the overall ETpathfinder noise budget.

physics.ins-det↗

arXiv2025

Challenges and Opportunities of Gravitational Wave Searches above 10 kHz

The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland).

gr-qc↗

arXiv2024

Observation of Noise Suppression during High-Efficiency Wavelength Doubling of Intense Quasi-Monochromatic Laser Light

Ultra-stable, quasi-monochromatic laser light forms the basis for high-precision interferometric measurements, e.g. for observing gravitational waves and for time keeping with optical clocks. Optical frequency conversion enables access to wavelengths at which optical materials have the lowest absorption and the lowest mechanical loss. Here we report a 25 % reduction in relative intensity noise (of technical origin) when converting 1064 nm to 2128 nm for powers far above parametric oscillation threshold. The new wavelength has high potential for improving gravitational wave detection and other ultra-high-precision experiments as well. Our results provide a better understanding of the dynamics of nonlinear optical processes and have great potential for the stabilisation of laser sources in optical sensing and metrology.

physics.optics↗

arXiv2023

30 W ultra-stable laser light at 2128 nm for future gravitational-wave observatories

Thermal noise of the dielectric mirror coatings can limit laser-optical high-precision measurements. Coatings made of amorphous silicon and silicon nitride could provide a remedy for both gravitational-wave detectors and optical clocks. However, the absorption spectra of these materials require laser wavelengths around 2 $μ$m. For GW detectors, ultra-stable laser light of tens or hundreds of watts is needed. Here, we report the production of nearly 30 W of ultra-stable laser light at 2128 nm by frequency conversion of 1064 nm light from a master oscillator power amplifier system. We achieve an external conversion efficiency of (67.5 $\pm$ 0.5) % via optical parametric oscillation and a relative power noise in the range of $10^{-6}$/$\sqrt{\text{Hz}}$ at 100 Hz, which is almost as low as that of the input light and underlines the potential of our approach.

physics.optics↗

arXiv2023

Fundamental sensitivity limit of lossy cavity-enhanced interferometers with external and internal squeezing

Quantum optical sensors are ubiquitous in various fields of research, from biological or medical sensors to large-scale experiments searching for dark matter or gravitational waves. Gravitational-wave detectors have been very successful in implementing cavities and quantum squeezed light for enhancing sensitivity to signals from black hole or neutron star mergers. However, the sensitivity to weak forces is limited by available energy and optical decoherence in the system. Here, we derive the fundamental sensitivity limit of cavity and squeezed-light enhanced interferometers with optical loss.This limit is attained by the optimal use of an additional internal squeeze operation, which allows to mitigate readout loss. We demonstrate the application of internal squeezing to various scenarios and confirm that it indeed allows to reach the best sensitivity in cavity and squeezed-light enhanced linear force sensors. Our work establishes the groundwork for the future development of optimal sensors in real-world scenarios where, up until now, the application of squeezed light was curtailed by various sources of decoherence.

quant-ph↗

arXiv2023

Science with the Einstein Telescope: a comparison of different designs

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where in each arm there is a `xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple `metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.

gr-qc↗

arXiv2023

Mitigating quantum decoherence in force sensors by internal squeezing

The most efficient approach to laser interferometric force sensing to date uses monochromatic carrier light with its signal sideband spectrum in a squeezed vacuum state. Quantum decoherence, i.e. mixing with an ordinary vacuum state due to optical losses, is the main sensitivity limit. In this work, we present both theoretical and experimental evidence that quantum decoherence in high-precision laser interferometric force sensors enhanced with optical cavities and squeezed light injection can be mitigated by a quantum squeeze operation inside the sensor's cavity. Our experiment shows an enhanced measurement sensitivity that is independent of the optical readout loss in a wide range. Our results pave the way for quantum improvements in scenarios where high decoherence previously precluded the use of squeezed light. Our results hold significant potential for advancing the field of quantum sensors and enabling new experimental approaches in high-precision measurement technology.

quant-ph↗

arXiv2021

NQontrol: An open-source platform for digital control-loops in quantum-optical experiments

Experiments in quantum optics often require a large number of control loops, e.g. for length-stabilization of optical cavities and control of phase gates. These control loops are generally implemented using one of three approaches: commercial (digital) controllers, self-built analog circuitry, or custom solutions based on Field Programmable Gate Arrays (FPGAs) and microcontrollers. Each of these approaches has individual drawbacks, such as high cost, lack of scalability and flexibility, or high maintenance effort. Here we present NQontrol, a solution based on the ADwin digital control platform that delivers eight simultaneous locking loops running with 200 kHz sampling frequency, and offers five second-order filtering sections per channel for optimal control performance. A comprehensive software package written in Python, together with a web-based graphical user interface (GUI), makes the system as easy to use as commercial products, while giving the full flexibility of open-source platforms.

physics.ins-det↗

arXiv2021

Squeezed light at 2128 nm for future gravitational-wave observatories

All gravitational-wave observatories (GWOs) have been using the laser wavelength of 1064 nm. Ultra-stable laser devices are at the sites of GEO 600, Kagra, LIGO and Virgo. Since 2019, not only GEO 600 but also LIGO and Virgo have been using separate devices for squeezing the uncertainty of the light, so-called squeeze lasers. The sensitivities of future GWOs will strongly gain from reducing the thermal noise of the suspended mirrors, which involves shifting the wavelength into the 2 $μ$m region. Our work aims for reusing the existing high-performance lasers at 1064 nm. Here, we report the realisation of a squeeze laser at 2128 nm that uses ultra-stable pump light at 1064 nm. We achieve the direct observation of 7.2 dB of squeezing, as the first step, at MHz sideband frequencies. The squeeze factor achieved is mainly limited by the photodiode's quantum efficiency, which we estimated to (92$\pm$3)%. Reaching larger squeeze factors seems feasible, also in the required audio and sub-audio sideband, provided photo diodes with sufficiently low dark noise will be available. Our result promotes 2128 nm as the new, cost-efficient wavelength of GWOs.

physics.optics↗

arXiv2020

Highly-efficient generation of coherent light at 2128 nm via degenerate optical-parametric oscillation

Cryogenic operation in conjunction with new test-mass materials promises to reduce the sensitivity limitations from thermal noise in gravitational-wave detectors. The currently most advanced materials under discussion are crystalline silicon as a substrate with amorphous silicon-based coatings. They require, however, operational wavelengths around 2 $\mathrmμ$m to avoid laser absorption. Here, we present a light source at 2128 nm based on a degenerate optical parametric oscillator (DOPO) to convert light from a 1064 nm non-planar ring-oscillator (NPRO). We achieve an external conversion efficiency of $(88.3\,\pm\,1.4)\,\%$ at a pump power of 52 mW in PPKTP (periodically-poled potassium titanyl phosphate, internal efficiency was 94 %), from which we infer an effective non-linearity of $(4.75\,\pm\,0.18)\,\mathrm{pm/V}$. With our approach, light from the established and existing laser sources can be efficiently converted to the 2 $\mathrmμ$m regime, while retaining the excellent stability properties.

physics.optics↗

arXiv2019

Demonstration of interferometer enhancement through EPR entanglement

The sensitivity of laser interferometers used for the detection of gravitational waves (GWs) is limited by quantum noise of light. An improvement is given by light with squeezed quantum uncertainties, as employed in the GW detector GEO600 since 2010. To achieve simultaneous noise reduction at all signal frequencies, however, the spectrum of squeezed states needs to be processed by 100m-scale low-loss optical filter cavities in vacuum. Here, we report on the proof-of-principle of an interferometer setup that achieves the required processed squeezed spectrum by employing Einstein-Podolsky-Rosen (EPR) entangled states. Applied to GW detectors, the cost-intensive cavities would become obsolete, while the price to pay is a 3dB quantum penalty.

quant-ph↗

arXiv2018

Mitigating mode-matching loss in nonclassical laser interferometry

Strongly squeezed states of light are a key technology in boosting the sensitivity of interferometric setups, such as in gravitational-wave detectors. However, the practical use of squeezed states is limited by optical loss, which reduces the observable squeeze factor. Here we experimentally demonstrate that introducing squeezed states in additional, higher-order spatial modes can significantly improve the observed nonclassical sensitivity improvement when the loss is due to mode-matching deficiencies. Our results could be directly applied to gravitational-wave detectors, where this type of loss is a major contribution.

quant-ph↗

arXiv2017

Demonstration of a switchable damping system to allow low-noise operation of high-Q low-mass suspension systems

Low mass suspension systems with high-Q pendulum stages are used to enable quantum radiation pressure noise limited experiments. Utilising multiple pendulum stages with vertical blade springs and materials with high quality factors provides attenuation of seismic and thermal noise, however damping of these high-Q pendulum systems in multiple degrees of freedom is essential for practical implementation. Viscous damping such as eddy-current damping can be employed but introduces displacement noise from force noise due to thermal fluctuations in the damping system. In this paper we demonstrate a passive damping system with adjustable damping strength as a solution for this problem that can be used for low mass suspension systems without adding additional displacement noise in science mode. We show a reduction of the damping factor by a factor of 8 on a test suspension and provide a general optimisation for this system.

physics.ins-det↗

arXiv2017

A new type of quantum speed meter interferometer: measuring speed to search for intermediate mass black holes

The recent discovery of gravitational waves (GW) by LIGO has impressively launched the novel field of gravitational astronomy and it allowed us to glimpse at exciting objects we could so far only speculate about. Further sensitivity improvements at the low frequency end of the detection band of future GW observatories rely on quantum non-demolition (QND) methods to suppress fundamental quantum fluctuations of the light fields used to readout the GW signal. Here we invent a novel concept of how to turn a conventional Michelson interferometer into a QND speed meter interferometer with coherently suppressed quantum back-action noise by using two orthogonal polarisations of light and an optical circulator to couple them. We carry out a detailed analysis of how imperfections and optical loss influence the achievable sensitivity and find that the configuration proposed here would significantly enhance the low frequency sensitivity and increase the observable event rate of binary black hole coalescences in the range of $10^2-10^3 M_\odot$ by a factor of up to $\sim300$.

gr-qc↗

arXiv2017

Effects of static and dynamic higher-order optical modes in balanced homodyne readout for future gravitational waves detectors

With the recent discovery of Gravitational waves, marking the start of the new field of GW astronomy, the push for building more sensitive laser-interferometric gravitational wave detectors (GWD) has never been stronger. Balanced homodyne detection (BHD) allows for a quantum noise limited readout of arbitrary light field quadratures, and has therefore been suggested as a vital building block for upgrades to Advanced LIGO and third generation observatories. In terms of the practical implementation of BHD, we develop a full framework for analyzing the static optical high order modes (HOMs) occurring in the BHD paths related to the misalignment or mode matching at the input and output ports of the laser interferometer. We find the effects of HOMs on the quantum noise limited sensitivity is independent of the actual interferometer configuration, e.g. Michelson and Sagnac interferometers are effected in the same way. We show that output misalignment only effects the high frequency part of the quantum noise limited sensitivity. However, at low frequencies, HOMs reduce the interferometer response and the radiation pressure noise by the same amount and hence the quantum noise limited sensitivity is not negatively effected. We show that the input misalignment to the interferometer produces the same effect as output misalignment and additionally decreases the power inside the interferometer. We also analyze dynamic HOM effects, such as beam jitter created by the suspended mirrors of the BHD. Our analyses can be directly applied to any BHD implementation in a future GWD. Moreover, we apply our analytical techniques to the example of the speed meter proof of concept experiment under construction in Glasgow. We find that for our experimental parameters, the performance of our seismic isolation system in the BHD paths is compatible with the design sensitivity of the experiment.

gr-qc↗

arXiv2016

Reduction of Classical Measurement Noise via Quantum-Dense Metrology

Quantum-dense metrology (QDM) constitutes a special case of quantum metrology in which two orthogonal phase space projections of a signal are simultaneously sensed beyond the shot noise limit. Previously it was shown that the additional sensing channel that is provided by QDM contains information that can be used to identify and to discard corrupted segments from the measurement data. Here, we demonstrate a proof-of-principle experiment in which this information is used for improving the sensitivity without discarding any measurement segments. Our measurement reached sub-shot-noise performance although initially strong classical noise polluted the data.

quant-ph↗

arXiv2015

Local-Oscillator Noise Coupling in Balanced Homodyne Readout for Advanced Gravitational Wave Detectors

The second generation of interferometric gravitational wave detectors are quickly approaching their design sensitivity. For the first time these detectors will become limited by quantum back-action noise. Several back-action evasion techniques have been proposed to further increase the detector sensitivity. Since most proposals rely on a flexible readout of the full amplitude- and phase-quadrature space of the output light field, balanced homodyne detection is generally expected to replace the currently used DC readout. Up to now, little investigation has been undertaken into how balanced homodyne detection can be successfully transferred from its ubiquitous application in table-top quantum optics experiments to large-scale interferometers with suspended optics. Here we derive implementation requirements with respect to local oscillator noise couplings and highlight potential issues with the example of the Glasgow Sagnac Speed Meter experiment, as well as for a future upgrade to the Advanced LIGO detectors.

physics.optics↗