arXiv subjects

Jeremy Bourhill

Publications and source records attributed to Jeremy Bourhill.

At least 19 recordsLinked to original sources

arXiv2026

Probing Light-Matter Interaction with Topological Data Analysis

We explore application of Topological Data Analysis to study light matter interaction through scattering response data in different dimensions. This method is robust against Fano resonance backgrounds in both strong and weak coupling regimes, maintaining accuracy even with reduced mode contrast, distorted lineshape, and the introduction of random trace noise. It scales to any number of interacting modes, reflecting the system's effective degrees of freedom. Crucially, TDA is not merely peak counting but reveals phase-encoded features in the scattering response and may be used even for a fully saturated amplitude response. The analysis is also applied to a three mode system with time reversal symmetry breaking, revealing change in apparent number of loops and voids in combined two way scattering data. This approach is demonstrated to differentiate the three Dyson ensembles through their topological complexity and probability density functions, enabling analysis of complex modal systems.

physics.app-ph↗

arXiv2026

Multi-mode input-output model for cavity magnonics: phase-resolved control of level repulsion, level attraction, and nonreciprocal transmission

We experimentally validate a unified input--output model that incorporates internal and external coupling phases across multiple cavity modes in a room-temperature cavity magnonic system. By explicitly accounting for both phase contributions, the model provides a clear interpretation of the transition from level repulsion to level attraction at an interference-induced antiresonance, and accurately reproduces nonreciprocal transmission arising from the internal phases of the contributing modes. Quantitative agreement between experiments and simulations is obtained across all coupling regimes, establishing a predictive framework for phase-controlled cavity--magnon devices including isolators, circulators, and quantum transducers.

quant-ph↗

arXiv2026

Inverse Design of Three-Dimensional Microwave Cavities for Optimizing Electromagnetic Helicity

We present a inverse-design framework framework for systematically engineering three-dimensional microwave cavity resonators that support modes with nonzero electromagnetic helicity. In contrast to heuristic approaches to cavity design, helicity maximisation is formulated as a boundary-shape optimisation problem, enabling systematic exploration of complex boundary-shape parameter spaces and the identification of high-helicity designs that are difficult to predict using heuristic design rules alone. We applied this framework to several cavity families composed of smooth, edge-free components, including globally twisted cavities with control-point-defined cross-sections realised in both linear and ring configurations, cavities defined by the intersection of orthogonal prisms, sphere-subtracted cylindrical cavities, and parametrised surface resonators. Two gradient-free optimisation strategies, a genetic algorithm and Bayesian optimisation, were independently employed to explore compact sets of design parameters for these geometries and to optimise a scaled-helicity figure of merit for the dominant helical mode, evaluated via finite-element eigenmode analysis. Robustness to manufacturing tolerances was quantified by applying Gaussian geometric perturbations to the optimised cavities and evaluating statistical robustness metrics that penalise sensitivity to geometric variation. The optimisation reveals clear physical design principles governing the generation of high electromagnetic helicity in three-dimensional microwave cavities.

physics.optics↗

arXiv2025

Coupling 4H-Silicon Carbide spins to a microwave resonator at milli-Kelvin temperature

Coupling microwave cavity modes with spin qubit transitions is crucial for enabling efficient qubit readout and control, long-distance qubit coupling, quantum memory implementation, and entanglement generation. We experimentally observe the coupling of different spin qubit transitions in Silicon Carbide (SiC) material to a 3D microwave (MW resonator mode around 12.6~GHz at a temperature of 10~mK. Tuning the spin resonances across the cavity resonance via magnetic-field sweeps, we perform MW cavity transmission measurements. We observe spin transitions of different spin defects that are detuned from each other by around 60-70~MHz. By optically exciting the SiC sample placed in the MW cavity with an 810~nm laser, we observe the coupling of an additional spin resonance to the MW cavity, also detuned by around 60-70 MHz from the centre resonance. We perform complementary confocal optical spectroscopy as a function of temperature from 4~K to 200~K. Combining the confocal spectroscopy results and a detailed analysis of the MW-resonator-based experiments, we attribute the spin resonances to three different paramagnetic defects: positively-charged carbon antisite vacancy pair (CAV$^+$), and the negatively-charged silicon vacancy spins located at two different lattice sites, namely V$_1$ and V$_2$ spins. The V$_1$ and V$_2$ lines in SiC are interesting qubit transitions since they are known to be robust to decoherence. Additionally, the CAV$^+$-transition is known to be a bright single-photon source. Consequently, the demonstration of the joint coupling of these spin qubits to a MW cavity mode could lead to interesting new modalities: The microwave cavity could act as an information bus and mediate long-range coupling between the spins, with potential applications in quantum computing and quantum communication, which is an attractive proposition in a CMOS-compatible material such as SiC.

quant-ph↗

arXiv2024

Sharp electromagnetically induced absorption via balanced interferometric excitation in a microwave resonator

A cylindrical TM$_{0,1,0}$ mode microwave cavity resonator was excited using a balanced interferometric configuration that allowed manipulation of the electric field and potential within the resonator by adjusting the phase and amplitude of the interferometer arms driving the resonator. With precise tuning of the phase and amplitude, 25 dB suppression of the electric field at the resonance frequency was achieved while simultaneously resonantly enhancing the time-varying electric-scalar potential. Under these conditions, the system demonstrated electromagnetically induced absorption in the cavity response due to the annulment of the electric field at the resonance frequency. This phenomena can be regarded as a form of extreme dispersion, and led to a sharp increase in the cavity phase versus frequency response by an order of magnitude when compared to the cavity Q-factor. This work presents an experimental setup that will allow the electric-scalar Aharonov-Bohm effect to be tested under conditions involving a time-varying electric-scalar potential, without the presence of an electric field or magnetic vector potential, an experiment that has not yet been realised.

physics.ins-det↗

arXiv2024

Level attraction in a quasi-closed cavity

We provide a comprehensive analytical description of the effective coupling associated with an antiresonance within a hybrid system comprised of a quasi-closed photonic cavity and a ferrimagnetic material. Whilst so-called level attraction between a resonant system inside an open cavity is well understood, the physical underpinnings of this phenomena within quasi-closed cavities have remained elusive. Leveraging the input-output theory, we successfully differentiate between the repulsive and attractive aspects of this coupling. Our proposed model demonstrates that by understanding the phase-jump at the resonances and the studied antiresonance, we can predict the nature of the effective coupling of the antiresonance for a given position of the ferrimagnet in the cavity.

quant-ph↗

arXiv2023

Precision Multi-Mode Microwave Spectroscopy of Paramagnetic and Rare-Earth Ion Spin Defects in Single Crystal Calcium Tungstate

We present experimental observations of dilute ion spin ensemble defects in a low-loss single crystal cylindrical sample of CaWO$_4$ cooled to $30$ mK in temperature. Crystal field perturbations were elucidated by constructing a dielectrically loaded microwave cavity resonator from the crystal. The resonator exhibited numerous whispering gallery modes with high $Q$-factors of up to $3\times 10^7$, equivalent to a loss tangent of $\sim 3\times 10^{-8}$. The low loss allowed precision multi-mode spectroscopy of numerous high $Q$-factor photon-spin interactions. Measurements between 7 to 22 GHz revealed the presence of Gd$^{3+}$, Fe$^{3+}$, and another trace species, inferred to be rare-earth, at concentrations on the order of parts per billion. These findings motivate further exploration of prospective uses of this low-loss dielectric material for applications regarding precision and quantum metrology, as well as tests for beyond standard model physics.

quant-ph↗

arXiv2023

Engineering synthetic gauge fields through the coupling phases in cavity magnonics

Cavity magnonics, which studies the interaction of light with magnetic systems in a cavity, is a promising platform for quantum transducers and quantum memories. At microwave frequencies, the coupling between a cavity photon and a magnon, the quasi-particle of a spin wave excitation, is a consequence of the Zeeman interaction between the cavity's magnetic field and the magnet's macroscopic spin. For each photon/magnon interaction, a coupling phase factor exists, but is often neglected in simple systems. However, in "loop-coupled" systems, where there are at least as many couplings as modes, the coupling phases become relevant for the physics and lead to synthetic gauge fields. We present experimental evidence of the existence of such coupling phases by considering two spheres made of Yttrium-Iron-Garnet and two different re-entrant cavities. We predict numerically the values of the coupling phases, and we find good agreement between theory and the experimental data. These results show that in cavity magnonics, one can engineer synthetic gauge fields, which can be useful for cavity-mediated coupling and engineering dark mode physics.

quant-ph↗

arXiv2023

Metallised 3D printed plastic resonator demonstrates superconductivity below 4 K

We report the first observation of a superconducting transition in a 3D printed, metallised-plastic device. A cylindrical cavity is 3D printed from a photosensitive polymer resin and then a 20 $\mu$m layer of tin deposited. A resonant TE microwave mode at 13.41 GHz is observed to reduce its losses by an order of magnitude once it is cooled below 3.72 K; the superconducting transition temperature of tin, with the mode's $Q$ factor increasing from $2.7\times10^4$ to $4.0\times10^5$.

cond-mat.supr-con↗

arXiv2023

Strong to ultra-strong coherent coupling measurements in a YIG/cavity system at room temperature

We present an experimental study of the strong to ultra-strong coupling regimes at room temperature in frequency-reconfigurable 3D re-entrant cavities coupled with a YIG slab. The observed coupling rate, defined as the ratio of the coupling strength to the cavity frequency of interest, ranges from 12% to 59%. We show that certain considerations must be taken into account when analyzing the polaritonic branches of a cavity spintronic device where the RF field is highly focused in the magnetic material. Our observations are in excellent agreement with electromagnetic finite element simulations in the frequency domain.

quant-ph↗

arXiv2022

Manifestation of the coupling phase in microwave cavity magnonics

The interaction between microwave photons and magnons is well understood and originates from the Zeeman coupling between spins and a magnetic field. Interestingly, the magnon/photon interaction is accompanied by a phase factor which can usually be neglected. However, under the rotating wave approximation, if two magnon modes simultaneously couple with two cavity resonances, this phase cannot be ignored as it changes the physics of the system. We consider two such systems, each differing by the sign of one of the magnon/photon coupling strengths. This simple difference, originating from the various coupling phases in the system, is shown to preserve, or destroy, two potential applications of hybrid photon/magnon systems, namely dark mode memories and cavity-mediated coupling. The observable consequences of the coupling phase in this system is akin to the manifestation of a discrete Pancharatnam-Berry phase, which may be useful for quantum information processing.

quant-ph↗

arXiv2022

Experimental generation of circulating cavity magnon polaritons

We experimentally realize circularly polarised unidirectional cavity magnon polaritons in a torus-shaped microwave cavity loaded by a small magnetic sphere. At special positions the clockwise and counterclockwise modes are circularly polarized, such that only one of them couples to the magnet, which breaks the mode degeneracy. We reveal the chiral nature of the spectral energy and angular momentum flow by observing and modelling non-reciprocities of the microwave scattering matrix.

cond-mat.mtrl-sci↗

arXiv2020

Universal Characterisation of Cavity--Magnon Polariton Coupling Strength Verified in Modifiable Microwave Cavity

A comprehensive study of the frequency dependence of the photon-magnon coupling for different magnetic samples is made possible with a tuneable 3D--printed re--entrant cavity. Strong coupling is achieved, with values ranging between 20--140 MHz. The reworked theory, experimentally verified for the first time here, enables coupling values to be calculated from simulations alone, enabling future experiments with exotic cavity designs to be precisely engineered, with no limitations on sample and cavity geometry. Finally, the requirements of the deep strong coupling regime are shown to be achievable in such experiments.

physics.app-ph↗

arXiv2020

Generation of Coherent Phonons via a Cavity Enhanced Photonic Lambda Scheme

We demonstrate the generation of coherent phonons in a quartz Bulk Acoustic Wave (BAW) resonator through the photoelastic properties of the crystal, via the coupling to a microwave cavity enhanced by a photonic lambda scheme. This is achieved by imbedding a single crystal BAW resonator between the post and the adjacent wall of a microwave reentrant cavity resonator. This 3D photonic lumped LC resonator at the same time acts as the electrodes of a BAW phonon resonator, and allows the direct readout of coherent phonons via the linear piezoelectric response of the quartz. A microwave pump, $\omega_p$ is tuned to the cavity resonance $\omega_0$, while a probe frequency, $\omega_{probe}$, is detuned and varied around the red and blue detuned values with respect to the BAW phonon frequency, $\Omega_m$. The pump and probe power dependence of the generated phonons unequivocally determines the process to be electrostrictive, with the phonons produced at the difference frequency between pump and probe, with no back action effects involved. Thus, the phonons are created without threshold and can be considered analogous to a Coherent Population Trapped (CPT) maser scheme.

physics.app-ph↗

arXiv2020

Characterisation of Cryogenic Material Properties of 3D-Printed Superconducting Niobium using a 3D Lumped Element Microwave Cavity

We present an experimental characterisation of the electrical properties of 3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant microwave cavity resonator. The resonator was cooled to temperatures below the critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while measuring the quality factors of the electromagnetic resonances. This was then compared with finite element analysis of the cavity and a measurement of the same cavity with an Aluminium post of similar dimensions and frequency, to extract the surface resistance of the Niobium post. The 3D-printed Niobium exhibited a transition to the superconducting state at a similar temperature to the regular Niobium, as well as a surface resistance of $3.1\times10^{-4}$ $Ω$. This value was comparable to many samples of traditionally machined Niobium previously studied without specialised surface treatment. Furthermore, this study demonstrates a simple new method for characterizing the material properties of a relatively small and geometrically simple sample of superconductor, which could be easily applied to other materials, particularly 3D-printed materials. Further research and development in additive manufacturing may see the application of 3D-printed Niobium in not only superconducting cavity designs, but in the innovative technology of the future.

physics.app-ph↗

arXiv2019

Experimental Implementations of Cavity-Magnon Systems: from Ultra Strong Coupling to Applications in Precision Measurement

Several experimental implementations of cavity-magnon systems are presented. First an Yttrium Iron Garnet (YIG) block is placed inside a re-entrant cavity where the resulting hybrid mode is measured to be in the ultra strong coupling regime. When fully hybridised the ratio between the coupling rate and uncoupled mode frequencies is determined to be $g/ω=0.46$. Next a thin YIG cylinder is placed inside a loop gap cavity. The bright mode of this cavity couples to the YIG sample and is similarly measured to be in the ultra strong coupling regime with ratio of coupling rate to uncoupled mode frequencies as $g/ω=0.34$. A larger spin density medium such as lithium ferrite (LiFe) is expected to improve couplings by a factor of 1.46 in both systems as coupling strength is shown to be proportional to the square root of spin density and magnetic moment. Such strongly coupled systems are potentially useful for cavity QED, hybrid quantum systems and precision dark matter detection experiments. The YIG disc in the loop gap cavity, is, in particular, shown to be a strong candidate for dark matter detection. Finally, a LiFe sphere inside a two post re-entrant cavity is considered. In past work it was shown that the magnon mode in the sample has a turnover point in frequency. Additionally, it was predicted that if the system was engineered such that it fully hybridised at this turnover point the cavity-magnon polariton (CMP) transition frequency would become insensitive to both first and second order magnetic bias field fluctuations, a result useful for precision frequency applications. This work implements such a system by engineering the cavity mode frequency to near this turnover point, with suppression in sensitivity to second order bias magnetic field fluctuations shown.

quant-ph↗

arXiv2019

Electrodynamic improvements to the theory of magnetostatic modes in ferrimagnetic spheres and their applications to saturation magnetization measurements

Electrodynamic theory applied to the analysis of TEn0p mode resonances in ferromagnetic spheres placed either in metallic cavities or in the free space is compared with Walker-Fletcher's theory of so-called magnetostatic modes. The influence of the diameter of the sample, its permittivity and the permittivity of the surrounding media on the resonance frequencies of a few modes is analyzed. It is shown that the dominant resonances are essentially related either to negative values of the diagonal component of the permeability tensor or, for clockwise circularly polarized magnetic fields, to negative effective permeability. The electrodynamic theory is used to determine the saturation magnetization (Ms) from measured TEn01 frequency differences. Measurements on different samples confirmed that Ms can be determined using an electrodynamic approach with uncertainties of the order of 2% regardless of sample sizes, metal enclosures or static magnetic field values.

physics.app-ph↗

arXiv2019

Broadening Frequency Range of a Ferromagnetic Axion Haloscope with Strongly Coupled Cavity-Magnon Polaritons

With the axion being a prime candidate for dark matter, there has been some recent interest in direct detection through a so called `Ferromagnetic haloscope.' Such devices exploit the coupling between axions and electrons in the form of collective spin excitations of magnetic materials with the readout through a microwave cavity. Here, we present a new, general, theoretical treatment of such experiments in a Hamiltonian formulation for strongly coupled magnons and photons, which hybridise as cavity-magnon polaritons. Such strongly coupled systems have an extended measurable dispersive regime. Thus, we extend the analysis and operation of such experiments into the dispersive regime, which allows any ferromagnetic haloscope to achieve improved bandwidth with respect to the axion mass parameter space. This experiment was implemented in a cryogenic setup, and initial search results are presented setting laboratory limits on the axion-electron coupling strength of $g_{aee}>3.7\times10^{-9}$ in the range $33.79~μ$eV$< m_a<33.94~μ$eV with $95\%$ confidence. The potential bandwidth of the Ferromagnetic haloscope was calculated to be in two bands, the first of about $1$GHz around $8.24$GHz (or $4.1~μ$eV mass range around $34.1~μ$eV) and the second of about $1.6$GHz around $10$GHz ($6.6~μ$eV mass range around $41.4~μ$eV). Frequency tuning may also be easily achieved via an external magnetic field which changes the ferromagnetic resonant frequency with respect to the cavity frequency. The requirements necessary for future improvements to reach the DFSZ axion model band are discussed in the paper.

physics.ins-det↗