arXiv subjects

Patrick Maier

Publications and source records attributed to Patrick Maier.

9 recordsLinked to original sources

arXiv2026

Integration of hBN Single-Photon Emitters into a Hybrid Optomechanical Membrane-in-the-Middle Fiber-Cavity

The integration of membranes into optical resonators plays a key role in a variety of applications, including optomechanics. Membranes hosting single photon emitters, ideally with access to spin states, open new avenues in optomechanics, spin-mechanics and spin-optomechanics. Hexagonal boron nitride is among the most promising two-dimensional materials, showing excellent optical and mechanical properties combined with the ability to host optically active (spin) defects. The deterministic creation of optically active defect centers in hexagonal boron nitride membranes and their coupling to optomechanical systems is an outstanding challenge. Here, we explore an alternative hybrid approach to establish coupling between a single photon emitter in commercially available hexagonal boron nitride flakes and a fiber cavity mode. We address technical challenges, such as scattering losses arising from uncontrolled flake topography, and establish deterministic hexagonal boron nitride positioning on the cavity mirror. For the coupled system, we observe cavity-induced spectral enhancement by a factor of up to 100 at room temperature. We extend our work by positioning single photon emitters in hexagonal boron nitride flakes on a highly strained silicon nitride membrane in a membrane-in-the-middle configuration. The mechanical vibrational modes of the silicon nitride membrane and cavity-coupled emission from the single photon emitter are simultaneously observed. Our work is a first step towards the realization of a cavity optomechanical platform with an incorporated single photon emitter and provides a starting point to explore hybrid spin-optomechanics.

physics.optics↗

arXiv2026

Investigating Spectral Dynamics and Spin Signatures of a Mechanically Isolated Quantum Emitter in hBN

Mechanically isolated defect centers in hexagonal boron nitride are promising coherent quantum emitters, yet spectral instabilities persist, and their spin-related nature remains unclear. Here we investigate a single mechanically isolated quantum emitter in hBN integrated onto a coplanar waveguide. The emitter exhibits exceptionally bright resonant fluorescence with saturation count rates exceeding $10\,\mathrm{Mc/s}$. High-resolution spectroscopy reveals two closely spaced zero-phonon-line transitions originating from the same defect complex. Time-resolved spectroscopy shows that these transitions exhibit markedly different spectral diffusion dynamics, consistent with distinct donor-acceptor-pair-like recombination pathways with different sensitivities to local electrostatic fluctuations. Off-resonant blue illumination redistributes emission between the two transitions and increases the emission duty cycle without significantly modifying the dominant spectral diffusion rates at low temperature, indicating repumping from long-lived shelving states. Magnetic-field-dependent photoluminescence, optically detected magnetic resonance, and pump-probe measurements reveal millisecond-scale relaxation dynamics and magnetic-field-dependent fluorescence contrast, demonstrating spin-dependent population dynamics in the metastable shelving state. These results clarify how charge-driven spectral fluctuations and spin-dependent shelving jointly shape the optical cycling dynamics.

quant-ph↗

arXiv2025

Extracting Membrane-like hexagonal Boron Nitride hosting single Defect Centers for Resonator Integration

The integration of membranes into optical resonators plays a key role in a variety of applications, including optomechanics. If such membranes host atom-like systems, ideally with access to spin states, new roads in quantum photonics and also in optomechanics can be taken. Layered, two-dimensional materials have emerged as candidates for membranes hosting atom-like quantum emitters. Hexagonal boron nitride (hBN) is among the most promising two-dimensional platforms showing good mechanical properties combined with the ability to host various kinds of optical active (spin-) defects. However, the determinisitc creation of optically active defect centers in hBN membranes is an outstanding challenge. Commercially available flakes of hBN host defect centers with promising optical properties, but the integration into optical resonators suffers from scattering losses due to the flakes topography and suitable transfer, handling and manipulation techniques need to be established. Here, we develope a toolset of nano-scaled manipulation techniques to extract membrane-like structures of commercially-available hBN containing spectrally narrow single photon emitters. We demonstrate the transfer and integration into photonic devices, by coupling a single photon emitter in membran-like hBN to the mode of an open Fabry-Perot fiber cavity (FPFC) and observe cavity induced spectral enhancement by a factor of up to 100 at room temperature. Overcoming hBN-induced scattering for extracted hBN membranes, which host single photon emitters, paves the way for future applications such as its use as an optomechanical system.

physics.optics↗

arXiv2025

Tunable cavity coupling of a single SnV$^{-}$ center in nanodiamond across bad-emitter and bad-cavity regimes

Efficient coupling between quantum emitters and optical cavities is essential for scalable quantum photonic technologies. Group IV vacancy centers in diamond, particularly the negatively charged tin-vacancy center, have emerged as promising candidates due to their spectral stability, high Debye-Waller factor and large orbital splitting in ground-states. Here, we demonstrate controlled couplinag of a single negatively charged tin vacancy center hosted in a nanodiamond to a fully tunable Fabry-Perot microcavity. At cryogenic temperatures, we access the weak coupling regime and observe a transition from the bad-emitter to the bad-cavity regime as the optical transition of the color center narrows. At 4 K, a Purcell factor exceeding 1.7 is measured, confirming cavity-enhanced emission. The obtained results demonstrate the potential of SnV$^{-}$ centers in nanodiamonds as a coherent single-photon source for quantum networks.

quant-ph↗

arXiv2025

Fabrication of Customized, Low-Loss Optical Resonators by Combination of FIB-Milling and CO$_2$ Laser Ablation

Fabry-Perot cavities are essential tools for applications like precision metrology, optomechanics and quantum technologies. A major challenge is the creation of microscopic spherical mirror structures which allow the precise matching with the wavefront of a Gaussian beam, while providing high surface quality. We present a novel fabrication technique, enabling the creation of customized microscopic cavity mirror structures over a wide range of geometrical parameters, by combining focused ion beam milling (FIB) and CO$_2$ laser smoothing. While FIB milling allows us to imprint features on the mirror substrate with a resolution on the nanometer scale, the application of defocused CO$_2$ laser pulses consistently reduces remaining surface deformations down to a roughness of $\sigma_\text{RMS}=0.2\,$nm. The average deviation of the profile from a spherical shape is kept below a few nanometres. This technique enables the customized and repeatable fabrication of low loss optics on a wide range of optical substrates, including optical fibres. Thus, Fabry-Perot cavities can be fabricated with pre-defined modal volume, high finesse and tailored ellipticity. Since the structural shape of the mirror is created by FIB milling, its pixel-by-pixel nature of the writing process can be used to create arbitrary structures with a resolution given by the FIB milling. At the same time, the surface quality is given by the CO$_2$ laser smoothing processes, without degrading the FIB milled shape.

physics.optics↗

arXiv2023

Enhanced Spectral Density of a Single Germanium Vacancy Center in a Nanodiamond by Cavity-Integration

Color centers in diamond, among them the negatively-charged germanium vacancy (GeV$^-$), are promising candidates for many applications of quantum optics such as a quantum network. For efficient implementation, the optical transitions need to be coupled to a single optical mode. Here, we demonstrate the transfer of a nanodiamond containing a single ingrown GeV- center with excellent optical properties to an open Fabry-P\'erot microcavity by nanomanipulation utilizing an atomic force microscope. Coupling of the GeV- defect to the cavity mode is achieved, while the optical resonator maintains a high finesse of F = 7,700 and a 48-fold spectral density enhancement is observed. This article demonstrates the integration of a GeV- defect with a Fabry-P\'erot microcavity under ambient conditions with the potential to extend the experiments to cryogenic temperatures towards an efficient spin-photon platform.

physics.optics↗

arXiv2022

A Quantum Repeater Platform based on Single SiV$^-$ Centers in Diamond with Cavity-Assisted, All-Optical Spin Access and Fast Coherent Driving

Quantum key distribution enables secure communication based on the principles of quantum mechanics. The distance in fiber-based quantum communication is limited to about a hundred kilometers due to signal attenuation. Thus, quantum repeaters are required to establish large-scale quantum networks. Ideal quantum repeater nodes possess a quantum memory which is efficiently connected to photons, the carrier of quantum information. Color centers in diamond and, in particular, the negatively-charged silicon-vacancy centers are promising candidates to establish such nodes. The major obstacle is an inefficient connection between the color centers spin to the Gaussian optics of fiber networks. Here, we present an efficient spin-photon interface. Individual silicon-vacancy centers coupled to the mode of a hemispherical Fabry-P\'erot microcavity show Purcell-factors larger than 1 when operated in a bath of liquid Helium. We demonstrate coherent optical driving with a Rabi frequency of $290\,\mathrm{MHz}$ and all-optical access to the electron spin in strong magnetic fields of up to $3.2\,\mathrm{T}$. Spin initialization within $67\,\mathrm{ns}$ with a fidelity of $80\,\%$ and a lifetime of $350\,\mathrm{ns}$ are reached inside the cavity. The spin-photon interface is passively stable, enabled by placing a color center containing nanodiamond in the hemispherical Fabry-P\'erot mirror structure and by choosing short cavity lengths. Therefore, our demonstration opens the way to realize quantum repeater applications.

quant-ph↗

arXiv2017

Replicable Parallel Branch and Bound Search

Combinatorial branch and bound searches are a common technique for solving global optimisation and decision problems. Their performance often depends on good search order heuristics, refined over decades of algorithms research. Parallel search necessarily deviates from the sequential search order, sometimes dramatically and unpredictably, e.g. by distributing work at random. This can disrupt effective search order heuristics and lead to unexpected and highly variable parallel performance. The variability makes it hard to reason about the parallel performance of combinatorial searches. This paper presents a generic parallel branch and bound skeleton, implemented in Haskell, with replicable parallel performance. The skeleton aims to preserve the search order heuristic by distributing work in an ordered fashion, closely following the sequential search order. We demonstrate the generality of the approach by applying the skeleton to 40 instances of three combinatorial problems: Maximum Clique, 0/1 Knapsack and Travelling Salesperson. The overheads of our Haskell skeleton are reasonable: giving slowdown factors of between 1.9 and 6.2 compared with a class-leading, dedicated, and highly optimised C++ Maximum Clique solver. We demonstrate scaling up to 200 cores of a Beowulf cluster, achieving speedups of 100x for several Maximum Clique instances. We demonstrate low variance of parallel performance across all instances of the three combinatorial problems and at all scales up to 200 cores, with median Relative Standard Deviation (RSD) below 2%. Parallel solvers that do not follow the sequential search order exhibit far higher variance, with median RSD exceeding 85% for Knapsack.

cs.DC↗

arXiv2017

Gate-tunable, normally-on to normally-off memristance transition in patterned LaAlO3/SrTiO3 interfaces

We report gate-tunable memristive switching in patterned LaAlO3/SrTiO3 interfaces at cryogenic temperatures. The application of voltages in the order of a few volts to the back gate of the device allows controlling and switching-on and -off the inherent memory functionality (memristance). For large and small gate voltages a simple non-linear resistance characteristic is observed while a pinched hysteresis loop and memristive switching occurs in an intermediate voltage range. The memristance is further controlled by the density of oxygen vacancies, which is tuned by annealing the sample at 300 °C in nitrogen atmosphere. Depending on the annealing time the memristance at zero gate voltage can be switched on and off leading to normally-on and normally-off memristors. The presented device offers reversible and irreversible control of memristive characteristics by gate voltages and annealing, respectively, which may allow to compensate fabrication variabilities of memristors that complicate the realization of large memristor-based neural networks.

cond-mat.mes-hall↗