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Thomas Gerrits

Publications and source records attributed to Thomas Gerrits.

At least 19 recordsLinked to original sources
arXiv2026

A Measurement Plane for Quantum Networking

Quantum networking testbeds lack a distinct plane for coordinating distributed measurements and collecting experimental data across heterogeneous devices. To address this gap, we present the Measurement Plane, a dedicated plane that complements the data, control, and management planes rather than replacing or extending their pipelines. The contribution is presented as a distributed framework that organizes measurement functions into four layers: application, experiment coordination, capability, and resource agents. Our design separates user workflows from device-specific control. We implemented the framework as containerized microservices connected through publish--subscribe messaging, and validated it on a two-node quantum networking setup connected by an optical network. The framework successfully coordinated remote nodes to execute coincidence measurement and polarization entanglement distribution experiments with visibility interference of up to 98 percent. This evaluation demonstrated the effectiveness of the framework for supporting complex, distributed quantum experiments, enabling online measurement and feedback, and significantly reducing manual configuration and execution effort.

quant-ph↗
arXiv2026

Entanglement Distribution over a Polarization-Stabilized Aerial Fiber

We experimentally demonstrate the distribution of polarization-entangled photons across a 62-km, partially-aerial fiber. With polarization stabilization applied to the fiber link, we achieve a photon pair rate of approximately 1500 per second and observe a CHSH inequality violation with S=2.34.

quant-ph↗
arXiv2025

Scalable Time-Tagged Data Acquisition for Entanglement Distribution in Quantum Networks

In distributed quantum applications such as entanglement distribution, precise time synchronization and efficient time-tagged data handling are essential. Traditional systems often suffer from overflow, synchronization drift, and storage inefficiencies. We propose a modular Time Tagging (TT) agent that uses a 1 pulse per second (PPS) signal from White Rabbit (WR) devices to achieve network-wide synchronization, while applying real-time calibration, overflow mitigation, and compression. A live two-lab entanglement distribution experiment validated the system's performance, achieving synchronized coincidence detection at 25,000 counts/sec.

cs.SE↗
arXiv2025

Picosecond synchronization of mode-locked lasers for metropolitan-scale quantum networks

We demonstrate picosecond-level synchronization of two actively mode-locked Ti:Sapphire lasers via the White Rabbit Precision Time Protocol (WR-PTP), tested over 120 km of deployed optical fiber. This synchronization capability, in combination with the highly single-mode, transform-limited pulses produced by each laser, enables their use as pump lasers for indistinguishable photon sources at remote locations in a quantum network. Here, the WR-PTP serves as a scalable network synchronization protocol, and its performance is compared to traditional methods of local synchronization. We demonstrate pulse-to-pulse synchronization better than 3 ps and time deviation (TDEV) values below 4 ps for all averaging times up to 10 s. With a designed coherence time of 35 ps for single photon sources utilizing these lasers, the achievable temporal overlap corresponds to 98 % Hong-Ou-Mandel (HOM) interference visibility between independent sources.

quant-ph↗
arXiv2025

Crosstalk Analysis in Quantum Networks: Detection and Localization Insights with photon counting OTDR

Optical crosstalk from sub-milliwatt classical-channel power into quantum channels presents a significant challenge in quantum network development, introducing substantial noise that limits the network's performance, scalability, and fidelity. Here we report a demonstration using photon counting optical time-domain reflectometry ({\nu}-OTDR) to precisely identify and localize crosstalk between separate channels within the same fiber and between separate fibers. The coexistence of classical and quantum signals in the same network necessitates the use of optical switches for efficient routing and control. Crosstalk characterization of an optical switch reveals that crosstalk depends strongly on cross connect configuration, with higher levels observed when connections are presumed to be physically closer and lower levels when further apart. Additionally, we found that crosstalk exhibits a pronounced wavelength dependence, increasing over tenfold at longer wavelengths. These findings demonstrate the value of {\nu}-OTDR in diagnosing and mitigating crosstalk in quantum networks. They highlight the importance of optimizing optical switch configurations and wavelength management to minimize noise, ultimately enhancing the scalability, fidelity, and overall performance of quantum networks. This work establishes a foundational approach to addressing crosstalk, paving the way for more robust and efficient quantum network designs.

quant-ph↗
arXiv2024

Accurate Unsupervised Photon Counting from Transition Edge Sensor Signals

We compare methods for signal classification applied to voltage traces from transition-edge sensors (TES) which are photon-number resolving detectors fundamental for accessing quantum advantages in information processing, communication and metrology. We quantify the impact of numerical analysis on the distinction of such signals. Furthermore, we explore dimensionality reduction techniques to create interpretable and precise photon-number embeddings. We demonstrate that the preservation of local data structures of some nonlinear methods is an accurate way to achieve unsupervised classification of TES traces. We do so by considering a confidence metric that quantifies the overlap of the photon-number clusters inside a latent space. Furthermore, we demonstrate that for our dataset previous methods such as the signal's area and principal component analysis can resolve up to 16 photons with confidence above $90\%$ while nonlinear techniques can resolve up to 21 with the same confidence threshold. Also, we showcase implementations of neural networks to leverage information within local structures, aiming to increase confidence in assigning photon numbers. Finally, we demonstrate the advantage of some nonlinear methods to detect and remove outlier signals.

physics.ins-det↗
arXiv2022

Precision Bounds on Continuous-Variable State Tomography using Classical Shadows

Shadow tomography is a framework for constructing succinct descriptions of quantum states using randomized measurement bases, called classical shadows, with powerful methods to bound the estimators used. We recast existing experimental protocols for continuous-variable quantum state tomography in the classical-shadow framework, obtaining rigorous bounds on the number of independent measurements needed for estimating density matrices from these protocols. We analyze the efficiency of homodyne, heterodyne, photon number resolving (PNR), and photon-parity protocols. To reach a desired precision on the classical shadow of an $N$-photon density matrix with a high probability, we show that homodyne detection requires an order $\mathcal{O}(N^{4+1/3})$ measurements in the worst case, whereas PNR and photon-parity detection require $\mathcal{O}(N^4)$ measurements in the worst case (both up to logarithmic corrections). We benchmark these results against numerical simulation as well as experimental data from optical homodyne experiments. We find that numerical and experimental homodyne tomography significantly outperforms our bounds, exhibiting a more typical scaling of the number of measurements that is close to linear in $N$. We extend our single-mode results to an efficient construction of multimode shadows based on local measurements.

quant-ph↗
arXiv2021

Scalable multiphoton quantum metrology with neither pre- nor post-selected measurements

The quantum statistical fluctuations of the electromagnetic field establish a limit, known as the shot-noise limit, on the sensitivity of optical measurements performed with classical technologies. However, quantum technologies are not constrained by this shot-noise limit. In this regard, the possibility of using every photon produced by quantum sources of light to estimate small physical parameters, beyond the shot-noise limit, constitutes one of the main goals of quantum optics. Here we experimentally demonstrate a scalable protocol for quantum-enhanced optical phase estimation across a broad range of phases, with neither pre- nor post-selected measurements. This is achieved through the efficient design of a source of spontaneous parametric down-conversion in combination with photon-number-resolving detection. The robustness of two-mode squeezed vacuum states against loss allows us to outperform schemes based on N00N states, in which the loss of a single photon is enough to remove all phase information from a quantum state. In contrast to other schemes that rely on N00N states or conditional measurements, the sensitivity of our technique could be improved through the generation and detection of high-order photon pairs. This unique feature of our protocol makes it scalable. Our work is important for quantum technologies that rely on multiphoton interference such as quantum imaging, boson sampling and quantum networks.

quant-ph↗
arXiv2021

Witnessing the survival of time-energy entanglement through biological tissue and scattering media

We demonstrate the preservation of time-energy entanglement of near-IR photons through thick biological media ($\leq$1.55 mm) and tissue ($\leq$ 235 $μ$m) at room temperature. Using a Franson-type interferometer, we demonstrate interferometric contrast of over 0.9 in skim milk, 2% milk, and chicken tissue. This work supports the many proposed opportunities for nonclassical light in biological imaging and analyses from sub-shot noise measurements to entanglement-enhanced fluorescence imaging, clearly indicating that the entanglement characteristics of photons can be maintained even after propagation through thick, turbid biological samples.

quant-ph↗
arXiv2021

Setting bounds on two-photon absorption cross-sections in common fluorophores with entangled photon pair excitation

Excitation with entangled photon pairs may lead to an increase in the efficiency of two-photon absorption at low photon flux. The corresponding process, entangled two-photon absorption (E2PA), has been investigated in numerous theoretical and experimental studies. However, significant ambiguity and inconsistency remain in the literature about the absolute values of E2PA cross-sections. Here, we use a fluorescence-based registration scheme to experimentally determine upper bounds on the cross-sections for six fluorophores. These bounds are up to four orders of magnitude lower than the smallest published cross-section. For two samples that have been studied by others, Rhodamine 6G and 9R-S, we measure upper bounds four and five orders of magnitude lower than the previously reported cross-sections.

quant-ph↗
arXiv2020

Precisely determining photon-number in real-time

Superconducting transition-edge sensors (TES) are extremely sensitive microcalorimeters used as photon detectors with unparalleled energy resolution. They have found application from measuring astronomical spectra through to determining the quantum property of photon-number, $\hat{n} {=} \hat{a}^{\dag} \hat{a}$, for energies from 0.6-2.33eV. However, achieving optimal energy resolution requires considerable data acquisition -- on the order of 1GB/min -- followed by post-processing, which does not allow access to energy information in real time. Here we use a custom hardware processor to process TES pulses while new detections are still being registered, allowing photon-number to be measured in real time as well as reducing data requirements by orders-of-magnitude. We resolve photon number up to n=16 -- achieving up to parts-per-billion discrimination for low photon numbers on the fly -- providing transformational capacity for applications of TES detectors from astronomy through to quantum technology.

physics.ins-det↗
arXiv2020

Generalized overlap quantum state tomography

We propose and experimentally demonstrate a quantum state tomography protocol that generalizes the Wallentowitz-Vogel-Banaszek-Wódkiewicz point-by-point Wigner function reconstruction. The full density operator of an arbitrary quantum state is efficiently reconstructed in the Fock basis, using semidefinite programming, after interference with a small set of calibrated coherent states. This new protocol is resource- and computationally efficient, is robust against noise, does not rely on approximate state displacements, and ensures the physicality of results.

quant-ph↗
arXiv2019

Calibration of free-space and fiber-coupled single-photon detectors

We measure the detection efficiency of single-photon detectors at wavelengths near 851 nm and 1533.6 nm. We investigate the spatial uniformity of one free-space-coupled single-photon avalanche diode and present a comparison between fusion-spliced and connectorized fiber-coupled single-photon detectors. We find that our expanded relative uncertainty for a single measurement of the detection efficiency is as low as 0.70 % for fiber-coupled measurements at 1533.6 nm and as high as 1.78 % for our free-space characterization at 851.7 nm. The detection-efficiency determination includes corrections for afterpulsing, dark count, and count-rate effects of the single-photon detector with the detection efficiency interpolated to operation at a specified detected count rate.

quant-ph↗
arXiv2019

State-independent quantum tomography of a single-photon state by photon-number-resolving measurements

The Wigner quasiprobability distribution of a narrowband single-photon state was reconstructed by quantum state tomography using photon-number-resolving measurements with transition-edge sensors (TES) at system efficiency 58(2)%. This method makes no assumptions on the nature of the measured state, save for the limitation on photon flux imposed by the TES. Negativity of the Wigner function was observed in the raw data without any inference or correction for decoherence.

quant-ph↗
arXiv2019

On the scalability of parametric down-conversion for generating higher-order Fock states

Spontaneous parametric down-conversion (SPDC) is the most widely-used method to generate higher-order Fock states ($n\geq 2$). Yet, a consistent performance analysis from fundamental principles is missing. Here we address this problem by introducing a framework for state fidelity and generation probability under the consideration of losses and multimode emission. With this analysis we show the fundamental limitations of this process as well as a trade-off between state fidelity and generation rate intrinsic to the probabilistic nature of the process. This identifies the parameter space for which SPDC is useful when generating higher-order Fock states for quantum applications. We experimentally investigate the strong pump regime of SPDC and demonstrate heralded Fock states up to $\lvert n\rangle =4$.

quant-ph↗
arXiv2019

Multiphoton Quantum-State Engineering using Conditional Measurements

The quantum theory of electromagnetic radiation predicts characteristic statistical fluctuations for light sources as diverse as sunlight, laser radiation and molecule fluorescence. Indeed, these underlying statistical fluctuations of light are associated with the fundamental physical processes behind their generation. In this contribution, we demonstrate that the manipulation of the quantum electromagnetic fluctuations of a pair of vacuum states leads to a novel family of quantum-correlated multiphoton states with tunable mean photon numbers and degree of correlation. Our technique relies on the use of conditional measurements to engineer the excitation mode of the field through the simultaneous subtraction of photons from two-mode squeezed vacuum states. The experimental generation of multiphoton states with quantum correlations by means of photon subtraction unveils novel mechanisms to control fundamental properties of light. As a remarkable example, we demonstrate the engineering of a quantum correlated state of light, with nearly Poissonian photon statistics, that constitutes the first step towards the generation of entangled lasers. Our technique enables a robust protocol to prepare quantum states with multiple photons in high-dimensional spaces and, as such, it constitutes a novel platform for exploring quantum phenomena in mesoscopic systems.

quant-ph↗
arXiv2018

Integrated transition edge sensors on lithium niobate waveguides

We show the proof-of-principle detection of light at 1550 nm coupled evanescently from a titanium in-diffused lithium niobate waveguide to a superconducting transition edge sensor. The coupling efficiency strongly depends on the polarization, the overlap between the evanescent field, and the detector structure. We experimentally demonstrate polarization sensitivity of this coupling as well as photon-number resolution of the integrated detector. The combination of transition edge sensors and lithium niobate waveguides can open the field for a variety of new quantum optics experiments.

physics.ins-det↗