arXiv subjects

Daniel Friedrich

Publications and source records attributed to Daniel Friedrich.

At least 19 recordsLinked to original sources

arXiv2025

On chip plasmonic slit cavity platform for room temperature strong coupling with deterministically positioned colloidal quantum dots

Strong coupling between quantum emitters and optical cavities is essential for quantum information processing, high-purity single-photon sources, and nonlinear quantum devices. Achieving this regime at room temperature in a compact, deterministic on-chip platform-critical for integration with nanoelectronic circuitry and scalable device architectures-remains a major challenge, mainly due to the difficulty of fabricating cavities with ultra-small mode volumes and precisely positioning quantum emitters. Here, we demonstrate a robust quantum plasmonic device in which colloidal quantum dots (Qdots) are strongly coupled to plasmonic slit cavities using a dielectrophoresis-based positioning technique with real-time photoluminescence (PL) feedback, providing directly resolvable coupled structures that enable parallel device fabrication and straightforward integration with additional optical elements such as waveguides. Our measurements reveal clear PL resolved Rabi splitting at room temperature with pre characterized cavities, with variations across devices that scale with the average number of coupled Qdots. While electrical tuning via the quantum-confined Stark effect is enabled by integrated electrodes, its impact is largely overshadowed by room-temperature spectral diffusion. Our results pave the way for scalable, electrically tunable quantum plasmonic platforms, offering new opportunities for integrated quantum photonic circuits, active light-matter interactions, and room-temperature quantum technologies.

physics.optics↗

arXiv2025

Risk and Reward of Transitioning from a National to a Zonal Electricity Market in Great Britain

More spatially granular electricity wholesale markets promise more efficient operation and better asset siting in highly renewable power systems. Great Britain is considering moving from its current single-price national wholesale market to a zonal design. Existing studies reach varying and difficult-to-reconcile conclusions about the desirability of a zonal market in GB, partly because they rely on models that vary in their transparency and assumptions about future power systems. Using a novel open-source electricity market model, calibrated to match observed network behaviour, this article quantifies consumer savings, unit-level producer surplus impacts, and broader socioeconomic benefits that would have arisen had a six-zone market operated in Great Britain during 2022-2024. In the absence of mitigating policies, it is estimated that during those three years GB consumers would save approximately {\pounds}9.4/MWh (equalling an average of more than {\pounds}2.3B per year), but generators in northern regions would experience revenue reductions of 30-40\%. Policy interventions can restore these units' national market revenues to up to 97\% while still preserving around {\pounds}3.1/MWh in consumer savings (about {\pounds}750M per year). It is further estimated that the current system could achieve approximately {\pounds}380-{\pounds}770 million in annual welfare gain during 2022-2024 through improved operational efficiency alone. The drivers behind these benefits, notably wind curtailment volumes, are expected to become more pronounced towards 2030, suggesting that purely operationally achieved annual benefits of around {\pounds}1-2 billion beyond 2029 are likely. It is found that the scale of these benefits would outweigh the potential downsides related to increases in the cost of capital that have been estimated elsewhere.

econ.GN↗

arXiv2025

Market Integration Pathways for Enhanced Geothermal Systems in Europe

Enhanced Geothermal Systems (EGS) can provide constant, reliable electricity and heat with minimal emissions, but high drilling costs and uncertain cost reductions leave their future unclear. We explore scenarios for the future adoption of EGS in a carbon-neutral, multi-sector European energy system. We find that in a net-zero system, heat (co-)generating EGS at current cost can support 20--30 GWth of capacity in Europe, primarily driven by district heating demands. When drilling costs decrease by approximately 60%, EGS becomes competitive in electricity markets, expanding its market opportunity by one order of magnitude. However, the spatially dispersed rollout of district heating contrasts with the confined overlap of high geological potential and low potential for other renewables, which conditions the competitiveness of electricity-generating EGS. This results in a challenge where the majority of EGS market potential depends on pan-European technology learning for cost reductions, emphasising coordination is crucial in stakeholders' efforts to reduce EGS cost.

physics.soc-ph↗

arXiv2023

Anticrossing of a plasmonic nanoresonator mode and a single quantum dot at room temperature

Room-temperature strong coupling of a single quantum emitter and a single resonant plasmonic mode is a key resource for quantum information processing and quantum sensing at ambient conditions. To beat dephasing, ultrafast energy transfer is achieved by coupling single emitters to a plasmonic nanoresonator with an extremely small mode volume and optimal spectral overlap. Typically, normal mode splittings in luminescence spectra of single-emitter strongly-coupled systems are provided as evidence for strong coupling and to obtain rough estimates of the light-matter coupling strength g. However, a complete anticrossing of a single emitter and a cavity mode as well as the characterization of the uncoupled constituents is usually hard to achieve. Here, we exploit the light-induced oxygen-dependent blue-shift of individual CdSe/ZnS semiconductor quantum dots to tune their transition energy across the resonance of a scanning plasmonic slit resonator after characterizing both single emitter and nano resonator in their uncoupled states. Our results provide clear proof of single-emitter strong light-matter coupling at ambient condition as well as a value for the Rabi splitting at zero detuning 100 meV, consistent with modeling, thereby opening the path towards plexitonic devices that exploit single-photon nonlinearities at ambient conditions.

physics.optics↗

arXiv2021

Reducing energy system model distortions from unintended storage cycling through variable costs

Energy model distortions may unknowingly appear and represent unrealistic and non-physical effects that can mislead optimal model decisions. A prominent misleading effect is unintended storage cycling that was observed in previous literature by simultaneous charging and discharging of the same storage in 12 of 18 energy models. Especially for popular net-zero energy model scenarios, unintended storage cycling can cause high distortions and, hence, urges for its removal. Methods to remove such misleading effects exist, but are not computational efficient and sometimes not effective such as MILP formulations. Other techniques are successful, but only if renewable energy target constraints exist. This paper explores how to eradicate unintended storage cycling for models without renewable target constraints by correctly setting variable costs of relevant system components. We find through 124 simulations that determining appropriate levels of variable costs depends on the solver accuracy used for the optimization. If set too loose, the solver prevents the removal of unintended storage cycling. We further find that reliable data for variable costs in energy modelling needs to be improved and provide a list of recommended model inputs as well as a minimum variable cost threshold that can significantly reduce the magnitude and likeliness of unintended storage cycling. Finally, our results suggest that variable cost additives may remove other known unintended energy cycling effects, such as unintended line cycling or sector cycling.

physics.soc-ph↗

arXiv2021

Beyond cost reduction: Improving the value of energy storage in electricity systems

An energy storage technology is valuable if it makes energy systems cheaper. Traditional ways to improve storage technologies are to reduce their costs; however, the cheapest energy storage is not always the most valuable in energy systems. Modern techno-economical evaluation methods try to address the cost and value situation but do not judge the competitiveness of multiple technologies simultaneously. This paper introduces the market potential method as a new complementary valuation method guiding innovation of multiple energy storage. The market potential method derives the value of technologies by examining common deployment signals from energy system model outputs in a structured way. We apply and compare this method to cost evaluation approaches in a renewables-based European power system model, covering diverse energy storage technologies. We find that characteristics of high-cost hydrogen storage can be more valuable than low-cost hydrogen storage. Additionally, we show that modifying the freedom of storage sizing and component interactions can make the energy system 10% cheaper and impact the value of technologies. The results suggest looking beyond the pure cost reduction paradigm and focus on developing technologies with suitable value approaches that can lead to cheaper electricity systems in future.

eess.SY↗

arXiv2020

Single Quantum Emitter Dicke Enhancement

Coupling $N$ identical emitters to the same field mode is well-established method to enhance light matter interaction. However, the resulting $\sqrt{N}$ boost of the coupling strength comes at the cost of a "linearized" (effectively semi-classical) dynamics. Here, we instead demonstrate a new approach for enhancing the coupling constant of a \textit{single} quantum emitter, while retaining the nonlinear character of the light-matter interaction. We consider a single quantum emitter with $N$ nearly degenerate transitions that are collectively coupled to the same field mode. We show that in such conditions an effective Jaynes-Cummings model emerges, with a boosted coupling constant of order $\sqrt{N}$. The validity and consequences of our general conclusions are analytically demonstrated for the instructive case $N=2$. We further observe that our system can closely match the spectral line shapes and photon autocorrelation functions typical of Jaynes-Cummings physics, hence proving that quantum optical nonlinearities are retained. Our findings match up very well with recent broadband plasmonic nanoresonator strong-coupling experiments and will therefore facilitate the control and detection of single-photon nonlinearities at ambient conditions.

quant-ph↗

arXiv2020

Performance-based screening of porous materials for carbon capture

Computational screening methods have been accelerating discovery of new materials and deployment of technologies based on them in many areas from batteries and alloys to photovoltaics and separation processes. In this review, we focus on post-combustion carbon capture using adsorption in porous materials. Prompted by unprecedented developments in material science, researchers in material engineering, molecular simulations, and process modelling have been interested in finding the best materials for carbon capture using energy efficient pressure-swing adsorption processes. Recent efforts have been directed towards development of new multiscale and performance-based screening workflows where we are able to go from the atomistic structure of an adsorbent to its equilibrium and transport properties for gas adsorption, and eventually to its separation performance in the actual process. The objective of this article is to review the current status of these emerging approaches, explain their significance for materials screening, while at the same time highlighting the existing pitfalls and challenges that limit their application in practice and industry. It is also the intention of this review to encourage cross-disciplinary collaborations for the development of more advanced screening methodologies. For this specific reason, we undertake an additional task of compiling and introducing all the elements that are needed for the development and operation of the performance-based screening workflows, including information about available materials databases, state-of-the-art molecular simulation and process modelling tools and methods, and the full list of data and parameters required for each stage.

cond-mat.mtrl-sci↗

arXiv2019

Nonclassical optical properties of mesoscopic gold

Gold nanostructures have important applications in nanoelectronics, nano-optics as well as in precision metrology due to their intriguing opto-electronic properties. These properties are governed by the bulk band structure but to some extend are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.

physics.optics↗

arXiv2018

Possible Experimental Realization of a Basic Z2 Topological Semimetal

We report experimental and theoretical evidence that GaGeTe is a basic $Z_2$ topological semimetal with three types of charge carriers: bulk-originated electrons and holes as well as surface state electrons. This electronic situation is qualitatively similar to the primer 3D topological insulator Bi2Se3, but important differences account for an unprecedented transport scenario in GaGeTe. High-resolution angle-resolved photoemission spectroscopy combined with advanced band structure calculations show a small indirect energy gap caused by a peculiar band inversion in the \textit{T}-point of the Brillouin zone in GaGeTe. An energy overlap of the valence and conduction bands brings both electron- and hole-like carriers to the Fermi level, while the momentum gap between the corresponding dispersions remains finite. We argue that peculiarities of the electronic spectrum of GaGeTe have a fundamental importance for the physics of topological matter and may boost the material's application potential.

cond-mat.mtrl-sci↗

arXiv2014

Method to reduce excess noise of a detuned cavity for application in KAGRA

Ground-based gravitational-wave detectors are based on high precision laser interferometry. One promising technique to improve the detector's sensitivity is the detuning of an optical cavity, which enhances the signal at around certain frequencies for target astronomical sources. The detuning, however, involves technical noise due to an asymmetry of the control sidebands, which includes photo-detector noise and oscillator-phase noise. Here, we introduce a solution to reduce the two kinds of excess noise using an amplitude-modulation sideband that compensates the asymmetry. The solution is planned to be implemented in the Japanese second-generation gravitational-wave detector KAGRA.

gr-qc↗

arXiv2014

Precise Measurement of Laser Power using an Optomechanical System

This paper shows a novel method to precisely measure the laser power using an optomechanical system. By measuring a mirror displacement caused by the reflection of an amplitude modulated laser beam, the number of photons in the incident continuous-wave laser can be precisely measured. We have demonstrated this principle by means of a prototype experiment uses a suspended 25 mg mirror as an mechanical oscillator coupled with the radiation pressure and a Michelson interferometer as the displacement sensor. A measurement of the laser power with an uncertainty of less than one percent (1 sigma) is achievable.

physics.ins-det↗

arXiv2013

Calculation of thermal noise in grating reflectors

Grating reflectors have been repeatedly discussed to improve the noise performance of metrological applications due to the reduction or absence of any coating material. So far, however, no quantitative estimate on the thermal noise of these reflective structures exists. In this work we present a theoretical calculation of a grating reflector's noise. We further apply it to a proposed 3rd generation gravitational wave detector. Depending on the grating geometry, the grating material and the temperature we obtain a thermal noise decrease by up to a factor of ten compared to conventional dielectric mirrors. Thus the use of grating reflectors can substantially improve the noise performance in metrological applications.

gr-qc↗

arXiv2013

Invariance of waveguide grating mirrors to lateral displacement phase shifts

We present a method to analyse the coupling of lateral displacements in nanoscale structures, in particular waveguide grating mirrors (WGM), into the phase of a reflected Gaussian beam using a finite-difference time-domain simulation. Such phase noise is of interest for using WGMs in high-precision interferometry. We show that WGMs do not couple lateral displacements into the phase of a reflected beam to a precision of 10^{-7} rad and that WGMs are therefore not subject to the same stringent alignment requirements as previously proposed layouts using diffraction gratings.

physics.optics↗

arXiv2012

Michelson interferometer with diffractively-coupled arm resonators in second-order Littrow configuration

Michelson-type laser-interferometric gravitational-wave (GW) observatories employ very high light powers as well as transmissively- coupled Fabry-Perot arm resonators in order to realize high measurement sensitivities. Due to the absorption in the transmissive optics, high powers lead to thermal lensing and hence to thermal distortions of the laser beam profile, which sets a limit on the maximal light power employable in GW observatories. Here, we propose and realize a Michelson-type laser interferometer with arm resonators whose coupling components are all-reflective second-order Littrow gratings. In principle such gratings allow high finesse values of the resonators but avoid bulk transmission of the laser light and thus the corresponding thermal beam distortion. The gratings used have three diffraction orders, which leads to the creation of a second signal port. We theoretically analyze the signal response of the proposed topology and show that it is equivalent to a conventional Michelson-type interferometer. In our proof-of-principle experiment we generated phase-modulation signals inside the arm resonators and detected them simultaneously at the two signal ports. The sum signal was shown to be equivalent to a single-output-port Michelson interferometer with transmissively-coupled arm cavities, taking into account optical loss. The proposed and demonstrated topology is a possible approach for future all-reflective GW observatory designs.

physics.optics↗

arXiv2012

Tomographic readout of an opto-mechanical interferometer

The quantum state of light changes its nature when being reflected off a mechanical oscillator due to the latter's susceptibility to radiation pressure. As a result, a coherent state can transform into a squeezed state and can get entangled with the motion of the oscillator. The complete tomographic reconstruction of the state of light requires the ability to readout arbitrary quadratures. Here we demonstrate such a readout by applying a balanced homodyne detector to an interferometric position measurement of a thermally excited high-Q silicon nitride membrane in a Michelson-Sagnac interferometer. A readout noise of $\unit{1.9 \cdot 10^{-16}}{\metre/\sqrt{\hertz}}$ around the membrane's fundamental oscillation mode at $\unit{133}{\kilo\hertz}$ has been achieved, going below the peak value of the standard quantum limit by a factor of 8.2 (9 dB). The readout noise was entirely dominated by shot noise in a rather broad frequency range around the mechanical resonance.

quant-ph↗

arXiv2011

Diffractively coupled Fabry-Perot resonator with power-recycling

We demonstrate the optical coupling of two cavities without light transmission through a substrate. Compared to a conventional coupling component, that is a partially transmissive mirror, an all-reflective coupler avoids light absorption in the substrate and therefore associated thermal problems, and even allows the use of opaque materials with possibly favourable mechanical and thermal properties. Recently, the all-reflective coupling of two cavities with a low-efficiency 3-port diffraction grating was theoretically investigated. Such a grating has an additional (a third) port. However, it was shown that the additional port does not necessarily decrease the bandwidth of the coupled cavities. Such an all-reflective scheme for cavity coupling is of interest in the field of gravitational wave detection. In such detectors light that is resonantly enhanced inside the so-called power-recycling cavity is coupled to (kilometre-scale) Fabry-Perot resonators representing the arms of a Michelson interferometer. In order to achieve a high sensitivity over a broad spectrum, the Fabry-Perot resonators need to have a high bandwidth for a given (high) power build-up. We realized such an all-reflective coupling in a table-top experiment. Our findings are in full agreement with the theoretical model incorporating the characteristics of the 3-port grating used, and therefore encourage the application of all-reflective cavity couplers in future gravitational wave detectors.

physics.optics↗

arXiv2011

Waveguide grating mirror in a fully suspended 10 meter Fabry-Perot cavity

We report on the first demonstration of a fully suspended 10m Fabry-Perot cavity incorporating a waveguide grating as the coupling mirror. The cavity was kept on resonance by reading out the length fluctuations via the Pound-Drever-Hall method and employing feedback to the laser frequency. From the achieved finesse of 790 the grating reflectivity was determined to exceed 99.2% at the laser wavelength of 1064\,nm, which is in good agreement with rigorous simulations. Our waveguide grating design was based on tantala and fused silica and included a ~20nm thin etch stop layer made of Al2O3 that allowed us to define the grating depth accurately during the fabrication process. Demonstrating stable operation of a waveguide grating featuring high reflectivity in a suspended low-noise cavity, our work paves the way for the potential application of waveguide gratings as mirrors in high-precision interferometry, for instance in future gravitational wave observatories.

physics.optics↗