arXiv subjects

Paul Kohl

Publications and source records attributed to Paul Kohl.

6 recordsLinked to original sources

arXiv2026

Modeling and Analysis of Phase Instability in Photonic Processor

Achieving both reconfigurability and stable output signals is a critical challenge in the development of integrated photonic circuits for large-scale optical quantum information processing. This has led to the creation of multimode photonic processors, also known as reconfigurable multimode interferometers, which have wide-ranging applications in quantum and classical information processing. However, maintaining phase stability in multi-port input signals remains a significant hurdle, particularly due to the phase instabilities introduced by active cooling systems and temperature drifts in the photonic processor. In this study, we propose theoretical models to simulate phase instability in photonic processors and validate them against experimental results. Two distinct modeling approaches were employed: a Brownian random walk and phase reconstruction based on experimentally observed oscillating harmonics. Additionally, we verified and applied our model to a specific application for input phase correction using self-feedback control within the photonic processor.

physics.optics↗

arXiv2025

Entangled Photon Pair Generator via Biexciton-Exciton Cascade in Semiconductor Quantum Dots and its Simulation

The generation of entangled photon pairs is highly useful for many types of quantum technologies. In this work an entangled photon pair generator that utilises the biexciton-exciton cascade in semiconductor quantum dots is described on a physical, mathematical, and software level. The system is implemented and simulated as a self-contained component in a framework for bigger quantum optical experiments. Thus, it is a description to further the holistic understanding of the system for interdisciplinary audiences in a hopefully simple yet sufficient manner. It is described from the condensed matter physics fundamentals, over the most important quantum optical properties, to a mathematical description of the used model, and finally a software description and simulation, making it an executable description of such a system. We provide a compact description in the Kraus operator formalism to seamlessly incorporate such an entangled photon pair generator simulation component into bigger simulations consisting of multiple components at a reasonable computational cost. The simulation accommodates a wide range of parameter regimes and makes it possible to simulate many different excitation strategies. This includes resonant two-photon excitation, adiabatic rapid passage chirped excitation, and dichromatic pulsed excitation.

quant-ph↗

arXiv2025

Integer Factoring with Unoperations

This work introduces the notion of unoperation $\mathfrak{Un}(\hat{O})$ of some operation $\hat{O}$. Given a valid output of $\hat{O}$, the corresponding unoperation produces a set of all valid inputs to $\hat{O}$ that produce the given output. Further, the working principle of unoperations is illustrated using the example of addition. A device providing that functionality is constructed utilising a quantum circuit performing the unoperation of addition - referred to as unaddition. To highlight the potential of the approach the unaddition quantum circuit is employed to construct a device for factoring integer numbers $N$, which is then called unmultiplier. This approach requires only a number of qubits $\in \mathcal{O}((\log{N})^2)$, rivalling the best known factoring algorithms to date.

quant-ph↗

arXiv2025

Photonic processor benchmarking for variational quantum process tomography

We present a quantum-analogous experimental demonstration of variational quantum process tomography using an optical processor. This approach leverages classical one-hot encoding and unitary decomposition to perform the variational quantum algorithm on a photonic platform. We create the first benchmark for variational quantum process tomography evaluating the performance of the quantum-analogous experiment on the optical processor against several publicly accessible quantum computing platforms, including IBM's 127-qubit Sherbrooke processor, QuTech's 5-qubit Tuna-5 processor, and Quandela's 12-mode Ascella quantum optical processor. We evaluate each method using process fidelity, cost function convergence, and processing time per iteration for variational quantum circuit depths of $d=3$ and $d=6$. Our results indicate that the optical processors outperform their superconducting counterparts in terms of fidelity and convergence behavior reaching fidelities of $0.8$ after $9$ iterations, particularly at higher depths, where the noise of decoherence and dephasing affect the superconducting processors significantly. We further investigate the influence of any additional quantum optical effects in our platform relative to the classical one-hot encoding. From the process fidelity results it shows that the (classical) thermal noise in the phase-shifters dominates over other optical imperfections, such as mode mismatch and dark counts from single-photon sources. The benchmarking framework and experimental results demonstrate that photonic processors are strong contenders for near-term quantum algorithm deployment, particularly in hybrid variational contexts. This analysis is valuable not only for state and process tomography but also for a wide range of applications involving variational quantum circuit based algorithms.

quant-ph↗

arXiv2015

Fluidic Integration of Nanophotonic Devices Using Decomposable Polymers

Polynorbornene-based decomposable polymer which can be patterned with ultraviolet or electron-beam radiation is used to create micrometer-scale fluidic channels. Silicon nitride substrates are used to fabricate nanophotonic wavegide and resonators operating in the visible range of the spectrum. Fluidic channels generated by thermally decomposing the polymer through the oxide cladding is used to deliver ultra-small amounts of florescent samples to the optical sensors.

physics.optics↗

arXiv2013

Giant Quasiparticle Bandgap Modulation in Graphene Nanoribbons Supported on Weakly Interacting Surfaces

In general, there are two major factors affecting bandgaps in nanostructures: (i) the enhanced electron-electron interactions due to confinement and (ii) the modified self-energy of electrons due to the dielectric screening. While recent theoretical studies on graphene nanoribbons (GNRs) report on the first effect, the effect of dielectric screening from the surrounding materials such as substrates has not been thoroughly investigated. Using large-scale electronic structure calculations based on the GW approach, we show that when GNRs are deposited on substrates, bandgaps get strongly suppressed (by as much as 1 eV) even though the GNR-substrate interaction is weak.

cond-mat.mtrl-sci↗