arXiv subjects

Franz Roeder

Publications and source records attributed to Franz Roeder.

7 recordsLinked to original sources

arXiv2026

High-gain effects in broadband continuous-wave parametric down conversion sources and measurements with undetected photons

We study theoretically how high-gain effects affect the measurement outcome of visible signal spectra in undetected photon measurement schemes. We consider two interferometric configurations: firstly, the SU(1,1) interferometer where the idler incurs loss and additional dispersion in between two identical, lossless, squeezers; secondly, the induced coherence interferometer where the idler incurs loss and additional dispersion in between two identical, lossless, squeezers and where the second squeezer is seeded by the idler and a vacuum ancilla mode. Furthermore, we consider a distributed loss configuration where the idler incurs loss as it propagates in the nonlinear medium. Motivated by experimental evidence and due to the fact that broadband sources are ideal for these measurement schemes, we use the dispersive data of a third-order dispersion engineered integrated waveguide parametric down conversion (PDC) source presented in New Journal of Physics 26, 123025 (2024) to model the PDC spectra in the three configurations. For each configuration we consider the case of idler-only (i) absorption, (ii) additional dispersion, and (iii) the combined effects. We obtain results which outline the strength and weaknesses of the different configurations at different operation points.

quant-ph↗

arXiv2026

Quantum Fisher information analysis for absorption measurements with undetected photons

We theoretically compare the quantum Fisher information (QFI) for three configurations of absorption spectroscopy with undetected idler photons: an SU(1,1) interferometer with inter-source idler loss, an induced-coherence (IC) setup in which the idler partially seeds a second squeezer together with a vacuum ancilla, and a distributed-loss (DL) scheme with in-medium attenuation. We calculate the QFI as a function of parametric gain for both full and signal-only detection access. For losses below 99% and low to moderate gain, the SU(1,1) configuration provides the largest QFI. At high gain and intermediate loss, the IC scheme performs best, while under extreme attenuation (transmission $<$ 1%) the DL model becomes optimal. These results delineate the measurement regimes in which each architecture is optimal in terms of information theory.

quant-ph↗

arXiv2025

Limitations of Entangled Two-Photon Absorption detection

We introduce a method for determining the sensitivity of any given Entangled Two-Photon Absorption (ETPA) measurement. By modeling all signal and noise contributions to the measurement, we derive a single numerical value that describes the sensitivity of the ETPA measurement in G\"oppert-Mayer units. This allows us to directly compare vastly different experimental approaches and, determine whether ETPA will be detectable under the given conditions. Therefore, we can quantify the effect of any change to a given experimental apparatus and identify the ideal optimization pathway.

quant-ph↗

arXiv2025

Towards integrated sensors for optimized OCT with undetected photons

The development of practical sensors for optical coherence tomography (OCT) with undetected photons requires miniaturization via integration. To be practical, these sensors must exhibit a large spectral bandwidth and a high brightness, which are linked to a high axial resolution and a sufficient signal to noise ratio, respectively. Here, we combine these requirements in a scheme for OCT-measurements with undetected photons based on nonlinear Ti:LiNbO$_3$ waveguides. We investigate the performance benchmarks of the commonly used SU(1,1) scheme in comparison to an induced coherence scheme and find that the latter is actually better suited when implementing measurements with undetected photons in integrated systems. In both schemes, we perform pump gain optimization and OCT measurements with undetected photons with an axial resolution as low as 28 $\mathrm{\mu}$m.

quant-ph↗

arXiv2025

A ultrabright, two-colour photon pair source based on thin-film lithium niobate for bridging visible and telecom wavelengths

We present the design and characterisation of a guided-wave, bright and highly frequency non-degenerate parametric down-conversion source in thin-film lithium niobate. The source generates photon pairs with wavelengths of 815$\,\mathrm{nm}$ and 1550$\,\mathrm{nm}$ linking the visible wavelength regime with telecommunication wavelengths. We confirm the high quality of the generated single photons by determining a value for the heralded second-order correlation function as low as $g^{(2)}_h(0) = (6.7\pm1.1)\cdot10^{-3}$. Furthermore, we achieve a high spectral brightness of 0.44$\cdot$10$^{7}$$\frac{\text{pairs}}{\text{s} \cdot \text{mW} \cdot \text{GHz}}$ which is two orders of magnitude higher than sources based on weakly guiding waveguides. The almost perfect sinc-shape and the strong agreement between the effective and nominal bandwidth highlights the success of our integrated workflow, which begins with device design and continues through precise fabrication to detailed quantum-state characterization. This comprehensive approach enables targeted optimization of the source, resulting in excellent quantum state generation. Our results set a new standard for on-chip, non-degenerate photon-pair sources and represent a crucial step towards practical, scalable quantum communication networks and photonic quantum computing.

quant-ph↗

arXiv2024

Ultra-broadband non-degenerate guided-wave bi-photon source in the near and mid-infrared

The latest applications in ultrafast quantum metrology require bright, broadband bi-photon sources with one of the photons in the mid-infrared and the other in the visible to near infrared. However, existing sources based on bulk crystals are limited in brightness due to the short interaction length and only allow for limited dispersion engineering. Here, we present an integrated PDC source based on a Ti:LiNbO$_3$ waveguide that generates broadband bi-photons with central wavelengths at $860\,\mathrm{nm}$ and $2800\,\mathrm{nm}$. Their spectral bandwidth exceeds $25\,\mathrm{THz}$ and is achieved by simultaneous matching of the group velocities and cancellation of group velocity dispersion for the signal and idler field. We provide an intuitive understanding of the process by studying our source's behaviour at different temperatures and pump wavelengths, which agrees well with simulations.

quant-ph↗

arXiv2024

Integrated, bright, broadband parametric down-conversion source for quantum metrology and spectroscopy

Broadband quantum light is a vital resource for quantum metrology and spectroscopy applications such as quantum optical coherence tomography or entangled two photon absorption. For entangled two photon absorption in particular, very high photon flux combined with high time-frequency entanglement is crucial for observing a signal. So far these conditions could be met by using high power lasers driving degenerate, type 0 bulk-crystal spontaneous parametric down conversion (SPDC) sources. This naturally limits the available wavelength ranges and precludes deterministic splitting of the generated output photons. In this work we demonstrate an integrated two-colour SPDC source utilising a group-velocity matched lithium niobate waveguide, reaching both exceptional brightness $1.52\cdot10^6\frac{\mathrm{pairs}}{\mathrm{s\,mW\,GHz}}$ and large bandwidth ($7.8\,$THz FWHM) while pumped with a few mW of continuous wave (CW) laser light. By converting a narrow band pump to broadband pulses the created photon pairs show correlation times of $\Delta \tau \approx 120\,\text{fs}$ while maintaining the narrow bandwidth $\Delta \omega_p \ll 1\,\text{MHz}$ of the CW pump light, yielding strong time-frequency entanglement. Furthermore our process can be adapted to a wide range of central wavelengths.

quant-ph↗