arXiv subjects

Julian Gurs

Publications and source records attributed to Julian Gurs.

6 recordsLinked to original sources

arXiv2026

Hyperloss from coherent spatial-mode mixing in quantum-correlated networks

Quantum-correlated networks distribute quantum resources such as squeezed and entangled states. These states are central to modern quantum technology, including photonic quantum computing, quantum communications, non-destructive biological sensing and gravitational-wave detection. Even for squeezed states of light - the most robust quantum-correlated resource - loss-induced decoherence remains the dominant obstacle to strong quantum advantage in in large-scale interferometric and networked quantum systems. Common design assumption in these applications is treating mismatches between spatial modes as a small, incoherent loss. Here we show that this picture can fail: coherent spatial-mode mixing with higher-order spatial modes can produce an apparent loss exceeding 100% relative to the initial squeezing, a regime we term hyperloss. We experimentally demonstrate hyperloss in a minimal two-node quantum network: with only 8% mode mismatch, a 5.8dB squeezed state is converted into an effectively thermal state with no quadrature squeezing, eliminating the quantum advantage. Because the effect is coherent, it is controllable: lost correlations can be recovered by tuning differential spatial-mode phases (e.g., Gouy-/propagation-phase). We demonstrate this recovery experimentally, not only eliminating the hyperloss, but even significantly suppressing the mode mismatch loss, with 15% geometric mismatch acting like only ~2.8% effective loss. Hyperloss is a design-limiting mechanism for all quantum networks with squeezed light, from from photonic quantum processors to large-scale interferometers and distributed quantum-sensing networks. Our results provide a practical route to avoid hyperloss and turn mode mismatch into an explicit, phase-aware design parameter for future quantum technologies.

quant-ph↗

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↗

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↗

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↗