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We show how to implement stationary one-way quantum steering with strong entanglement in a cavity magnonic system that consists of two magnon modes and a microwave cavity. The cavity is driven by a squeezed vacuum field generated by a flux-driven Josephson parameter amplifier and coupled to two Kittel modes via magnetic dipole interaction. We find that the steering directivity only depends on the ratio of two coupling rates (i.e., the ratio of coherent information exchange frequencies) and is barely affected by the dissipation of the system. Meanwhile, the entanglement and steering can be significantly enhanced due to the squeezed vacuum field and thus are more robust against thermal noises. This provides an active method to manipulate the steering directivity instead of adding asymmetric losses or noises to subsystems at the cost of reducing steerability.

Quantum conversion between microwave and optical photons is an important area of quantum information science and technology. Here we propose a one-step method to realize a coherent conversion between a microwave cavity and an optical cavity utilizing a nitrogen-vacancy center ensemble (NV ensemble). An NV ensemble considered here acts as a quantum transducer, dispersively coupled to the microwave and optical cavities, enabling transfer of the quantum state and generating entangled states between microwave and optical cavities. With state-of-the-art technology, the numerical simulation is performed to demonstrate that cat states and Fock states can be high-fidelity transferred and a maximally entangled state can be efficiently synthesized between microwave and optical cavities.

An accelerating photodetector is predicted to see photons in the electromagnetic vacuum. However, the extreme accelerations required have prevented the direct experimental verification of this quantum vacuum effect. In this work, we consider many accelerating photodetectors that are contained within an electromagnetic cavity. We show that the resulting photon production from the cavity vacuum can be collectively enhanced such as to be measurable. The combined cavity-photodetectors system maps onto a parametrically driven Dicke-type model; when the detector number exceeds a certain critical value, the vacuum photon production undergoes a phase transition from a normal phase to an enhanced superradiant-like, inverted lasing phase. Such a model may be realized as a mechanical membrane with a dense concentration of optically active defects undergoing gigahertz flexural motion within a superconducting microwave cavity. We provide estimates suggesting that recent related experimental devices are close to demonstrating this inverted, vacuum photon lasing phase., Comment: Published version with supplementary material added

Microwave assisted thermal sterilization (MATS) is a novel microwave technology currently used in the commercial production of ready-to-eat meals. It combines surface heating of high-temperature circulation water with internal microwave heating in cavities. The heating pattern inside the food packages in a MATS process depends heavily on the electric field distribution formed by microwaves from the top and bottom windows of the microwave heating cavities. The purpose of this research was to study the effect of the electric field on 922 MHz microwave heating of ready-to-eat meals as they moved through the microwave chamber of a pilot-scale MATS system using the finite-difference time-domain (FDTD) method. A three-dimensional numerical simulation model was developed as a digital twin of the MATS process of food moving through the microwave chamber. The simulation showed that the electric field intensity of the MATS microwave cavity was greatest on the surface and side edge of the cavity and of the food. There was a strong similarity of the experimental heating pattern with that of the electric field distribution simulated by a computer model. The digital twin modeling approach can be used to design options for improving the heating uniformity and throughput of ready-to-eat meals in MATS industrial systems.

The fields of cavity quantum electrodynamics and magnetism have recently merged into \textit{`cavity spintronics'}, investigating a quasiparticle that emerges from the strong coupling between standing electromagnetic waves confined in a microwave cavity resonator and the quanta of spin waves, magnons. This phenomenon is now expected to be employed in a variety of devices for applications ranging from quantum communication to dark matter detection. To be successful, most of these applications require a vast control of the coupling strength, resulting in intensive efforts to understanding coupling by a variety of different approaches. Here, the electromagnetic properties of both resonator and magnetic samples are investigated to provide a comprehensive understanding of the coupling between these two systems. Because the coupling is a consequence of the excitation vector fields, which directly interact with magnetisation dynamics, a highly-accurate electromagnetic perturbation theory is employed which allows for predicting the resonant hybrid mode frequencies for any field configuration within the cavity resonator, without any fitting parameters. The coupling is shown to be strongly dependent not only on the excitation vector fields and sample's magnetic properties but also on the sample's shape. These findings are illustrated by applying the theoretical framework to two distinct experiments: a magnetic sphere placed in a three-dimensional resonator, and a rectangular, magnetic prism placed on a two-dimensional resonator. The theory provides comprehensive understanding of the overall behaviour of strongly coupled systems and it can be easily modified for a variety of other systems.

The COMSOL Multiphysics software was used to perform numerical simulation analysis on the microwave drying process of pressurized sludge, and the influence of sludge thickness, moisture content, microwave power and sludge position on the electric field and sludge temperature field in the microwave cavity was studied. The results show that the microwave power has a great influence on the electric field and temperature field, while the sludge thickness, moisture content and position of the sludge does little. With the increase of the microwave power, the intensity of the electric field in the microwave cavity and the heating rate of the sludge increases. The optimal process conditions for the microwave drying of the pressurized sludge after numerical simulation are the microwave power of 1000 W, and the sludge is in the center of the cavity.

Nonlinear Josephson circuits play a crucial role in the growing landscape of quantum information and technologies. The typical circuits studied in this field consist of qubits, whose anharmonicity is much larger than their linewidth, and also of parametric amplifiers, which are engineered with linewidths of tens of MHz or more. The regime of small anharmonicity but also narrow linewidth, corresponding to the dynamics of a high-Q Duffing oscillator, has not been extensively explored using Josephson cavities. Here, we use two-tone spectroscopy to study the susceptibility of a strongly driven high-Q Josephson microwave cavity. Under blue-detuned driving, we observe a shift of the cavity susceptibility, analogous to the AC Stark effect in atomic physics. When applying a strong red-detuned drive, we observe the appearance of an additional idler mode above the bifurcation threshold with net external gain. Strong driving of the circuit leads to the appearance of two exceptional points and a level attraction between the quasimodes of the driven cavity. Our results provide insights on the physics of driven nonlinear Josephson resonators and form a starting point for exploring topological physics in strongly-driven Kerr oscillators.

The spin resonance of electrons can be coupled to a microwave cavity mode to obtain a photon-magnon hybrid system. These quantum systems are widely studied for both fundamental physics and technological quantum applications. In this paper, the behavior of a large number of ferrimagnetic spheres coupled to a single cavity is tested. We use second-quantization modeling of harmonic oscillators to theoretically describe our experimental setup and understand the influence of several parameters. The magnon-polariton dispersion relation is used to characterize the system, with a particular focus on the vacuum Rabi mode splitting due to multiple spheres. We combine the results obtained with simple hybrid systems to analyze the behavior of a more complex one and show that it can be devised in such a way to minimize the degrees of freedom needed to completely describe it. By studying single-sphere coupling two possible size effects related to the sample diameter have been identified, while multiple-sphere configurations reveal how to upscale the system. This characterization is useful for the implementation of an axion-to-electromagnetic field transducer in a ferromagnetic haloscope for dark matter searches. Our dedicated setup, consisting of ten 2-mm-diameter yttrium iron garnet spheres coupled to a copper microwave cavity, is used for this aim and studied at millikelvin temperatures. Moreover, we show that applications of optimally controlled hybrid systems can be foreseen for setups embedding a large number of samples.

Herein, the effects of polycrystalline germanium dioxide substrates on the structural, morphological, optical and electrical properties of zinc selenide thin films are reported. Thin films of ZnSe coated onto GeO2 are prepared by the thermal evaporation technique under vacuum pressure of 10–5 mbar. Compared to films grown onto glass substrates, ZnSe films deposited onto GeO2 exhibited narrower band gap and improved light absorbability. When ZnSe films are recoated onto gold substrates, the insertion of GeO2 layers between Au and ZnSe shifted the resonance peaks of the capacitance spectra from 527 to 711 MHz and formed new peak at 1000 MHz making the Au/ZnSe interfaces more appropriate for use as microwave cavities and as negative capacitance sources. Analysis of the conductivity spectra in the frequency domain of 10–1800 MHz revealed the domination of quantum mechanical tunneling and correlated barriers hoping of charge carriers in the samples. The fitting of the conductivity spectra assuming combined current conduction by these two mechanisms has shown that GeO2 layers increased the density of state near the Fermi level and shortened the scattering time of charge carriers. The designed Au/GeO2/ZnSe/C devices are also found to be suitable as band pass/stop filters. The notch frequency of these filters is shifted from 1420 MHz to 1050 MHz as a result of GeO2 participation in the structure of the Au/ZnSe devices.

A superconductor can interact with magnets through the magnetic field which is induced by the supercurrent. However, this interaction is rather weak and requires relatively large magnets to reach a sizable hybridization of microwave electromagnetic modes with magnons. The size of the device can be drastically reduced by means of the large interfacial exchange interaction between spins in a magnet and a superconductor. In the spin-orbit coupled superconductor this interaction can be transmitted to the s-wave condensate through a mixing of triplet and singlet Cooper pairs. In this paper we theoretically consider thin antiferromagnetic films, which make a spin compensated contact to a superconducting wire, which forms a cavity for Mooij-Sch\"{o}n plasma waves. The effective Lagrangian is derived where the interaction of these waves with magnons is taken into account. Frequencies of hybrid magnon-plasmon modes are calculated. A system of two micromagnets placed far apart are also considered and their mutual coupling through the cavity mode is calculated., Comment: 9 pages, 1 figure

openaire: EC/H2020/670743/EU//QuDeT | openaire: EC/H2020/862644/EU//QUARTET Quantum correlations are an essential resource in advanced information processing based on quantum phenomena. Remarkably, the vacuum state of a quantum field may act as a key element for generation of strong quantum correlations. Besides, superconducting microwave cavities offer an excellent platform for experimental studies of such quantum effects. In this work, we numerically investigate vacuum correlations in a flux-tunable superconducting cavity under multiple pump tones. We consider double and triple pumping cases and explore pairwise correlations between three frequency bands specified within a single cavity resonance. Our work shows that three pumps produce more correlations than two pumps; thus, quantum resources facilitated by the triple pump scheme offers enhanced prospects for quantum data processing using parametric microwave cavities.

International audience; Silicon nitride (SiN) mechanical resonators with high quality mechanical properties are attractive for fundamental research and applications. However, it is challenging to maintain these mechanical properties while achieving strong coupling to an electrical circuit for efficient on-chip integration. Here, we present a SiN drum resonator covered with an aluminum thin film, enabling large capacitive coupling to a suspended top-gate. Implementing the full electrical measurement scheme, we demonstrate a high quality factor ~ 1E4 (comparable to that of bare drums at room temperature) and present our ability to detect ? 10 mechanical modes at low temperature. The drum resonator is also coupled to a microwave cavity, so that we can perform optomechanical sideband pumping with a fairly good coupling strength G and demonstrate mechanical parametric amplification. This SiN drum resonator design provides efficient electrical integration and exhibits promising features for exploring mode coupling and signal processing.

We demonstrate a sideband-resolved cavity electromechanical system operating at room temperature. It consists of a nanomechanical resonator, a strongly pre-stressed silicon nitride string, dielectrically coupled to a three-dimensional microwave cavity made of copper. The electromechanical coupling is characterized by two measurements, the cavity-induced eigenfrequency shift of the mechanical resonator and the optomechanically induced transparency. While the former is dominated by dielectric effects, the latter reveals a clear signature of the dynamical backaction of the cavity field on the resonator. This unlocks the field of cavity electromechanics for room temperature applications.

We study a cross-shaped cavity filled with superfluid $^4$He as a prototype resonant-mass gravitational wave detector. Using a membrane and a re-entrant microwave cavity as a sensitive optomechanical transducer, we were able to observe the thermally excited high-$Q$ acoustic modes of the helium at 20 mK temperature and achieved a strain sensitivity of $8 \times 10^{-19}$ Hz$^{-1/2}$ to gravitational waves. To facilitate the broadband detection of continuous gravitational waves, we tune the kilohertz-scale mechanical resonance frequencies up to 173 Hz/bar by pressurizing the helium. With reasonable improvements, this architecture will enable the search for GWs in the 1-30 kHz range, relevant for a number of astrophysical sources both within and beyond the Standard Model., Comment: 8 pages, 7 figures

Herein, we report the design and experimental characterization of a broken gap heterojunction devices fabricated by vacuum evaporation of Yb/InSe/Sb2Te3/Au stacked layers. The structural characterizations of the stacked layers revealed an amorphous/polycrystalline heterojunction type. The measurements of capacitance-voltage characteristics in the frequency domain of 1.0-9.0 MHz displayed tunable metal-oxide-semiconductor (MOS) characteristics. The frequency dependent built-in voltage, depletion width, and free carrier density is also investigated. In addition, the analyses of current-voltage characteristics have shown that the device displays highly stable current rectification ratios of ~103 above 0.20 V. Moreover, the ac signal analyses in the frequency domain of 10-1800 MHz have shown the possible tunability of the conductance and capacitance over a wide range of frequency. Furthermore, the microwave cutoff frequency spectra indicated increasing cutoff frequency limits with increasing incident signal frequency. The microwave cutoff frequency reached 7.1 GHz for a propagating signal of frequency of 1800 MHz. WOS:000648288700002 Q4

Herein, metal-oxide-semiconductor fields effect transistors (MOSFET) are fabricated and characterized. p − type germanium dioxide coated onto Au/ n-CdSe substrates and top contacted with carbon point contacts is used to form the MOSFET devices. The structural investigations which were carried out with the help of X-ray diffraction technique revealed large lattice mismatched polycrystalline layers of CdSe and GeO2. The design of the energy band diagram has shown the formation of two Schottky arms (Au/ n − CdSe, C/GeO2) at the interfaces of the n − CdSe/ p − GeO2 layers. The capacitance-voltage characteristics which are recorded in the frequency domain of 1.0-50.0 MHz revealed the ability of formation of NMOS and PMOS layers. The signal frequency controlled built in potential is tunable in the range of 2.34 and 5.18 eV. In addition, the conductance and capacitance spectral analyses in the frequency domain of 10-1800 MHz revealed the domination of current conduction by tunneling and correlated barriers hoping below and above 760 MHz, respectively. In addition to its features as MOSFET devices, the Au/CdSe/GeO2/C hybrid devices are found to be appropriate for use as microwave cavities.

Using an operator scattering approach, we analyze the quantum dynamics of an ultrasensitive electrometer -- a Cooper pair transistor embedded in a quarter-wave microwave cavity (cCPT). While the cCPT is inherently a tunable, strongly nonlinear system affording a diverse range of functionalities, we restrict our present analysis to a necessary first investigation of its linear charge sensing capabilities, limiting to low pump powers corresponding to an average cavity photon number $\lesssim 1$. Assuming realizable cCPT parameters (B. L. Brock et al., Phys. Rev. Applied, 044009), and not including noise from the subsequent amplifier chain, we predict the fundamental, photon shot noise-limited charge sensitivity to be $0.12\, \mu{\mathrm{e}}/\sqrt{\mathrm{Hz}}$ when the pumped cavity has an average of one photon and the cCPT is operated close to charge degeneracy. This is to be compared with a first reported charge sensitivity value $14\, \mu{\mathrm{e}}/\sqrt{\mathrm{Hz}}$ in the single-photon regime (B. L. Brock et al., arXiv:2102.05362)., Comment: 15 pages, 4 figures

We explore the dissipative dynamics of nonlinearly driven oscillator systems tuned to resonances where multiple excitations are generated. Such systems are readily realised in circuit QED systems combining Josephson junctions with a microwave cavity and a drive achieved either through flux or voltage bias. For resonances involving 3 or more photons the system undergoes a sequence of two closely spaced dynamical transitions (the first one discontinuous and the second continuous) as the driving is increased leading to steady states that form complex periodic structures in phase space. In the vicinity of the transitions the system displays interesting bistable behaviour: we find that coherent effects can lead to surprising oscillations in the weight of the different dynamical states in the steady state of the system with increasing drive. We show that the dynamics is well-described by a simple effective rate model with transitions between states localised at different points in the phase space crystal. The oscillations in the weights of the dynamical states is reflected in corresponding oscillations in a time-scale that describes transitions between the states., 25 pages, 11 figures

The axion was first introduced as a consequence of the Peccei-Quinn mechanism to solve the CP problem in strong interactions of particle physics and is a well motivated cold dark matter candidate. This particle is expected to interact extremely weakly with matter and its mass is expected to lie in $\mu$eV range with the corresponding frequency roughly in GHz range. In 1983 P. Sikivie proposed a detection scheme, so called axion haloscope, where axions resonantly convert to photons in a tunable microwave cavity permeated by a strong magnetic field. A major source of the experimental noise is attributed to added noise by RF amplifiers, and thus precise understandings of amplifiers' noise is of importance. We present the measurements of noise temperatures of various low noise amplifiers broadly used for axion dark matter searches., Comment: 7 pages, 3 figures

Selenium oxide thin films are highly transparent optical layers proper for optoelectronic technology. However, SeO2 films are rarely studied and observed suffering from clustery surface morphology, low light absorbability and low dielectric constant. For this reason herein, in an attempt to enhance its properties, platinum nanosheets (10–50 nm) are used as plasmonic substrates to grow transparent selenium oxide thin films. The films are deposited onto glass and Pt substrates using thermal evaporation technique under a vacuum pressure of 10−5 mbar. Both films of the glass/SeO2 and Pt/SeO2 are characterized by the techniques of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, optical spectrophotometry and impedance spectroscopy. While no significant effect of Pt nanosheets on the amorphous nature of structure of SeO2 is observed, remarkable enhancements in the light absorbability by 50 times and in dielectric constant by three times are achieved. In addition, Pt nanosheets form plasmonic interfaces resulting in improving the plasmon frequency, drift mobility and free carrier density of the films. Pt/SeO2 films showed plasmon frequency larger than 6.0 GHz and free carrier density of 1018 cm−3. Moreover, analysis of the terahertz cutoff frequency and impedance spectra have shown that the Pt/SeO2 interfaces can also be employed as terahertz receivers and as low pass filters suitable for 5G/6G technologies.

Carbon fibre-reinforced polymer composites are widely used in modern aircraft structures for the high stiffness-to-weight ratio. An aircraft's exterior is commonly applied with coatings for minimisation of aerodynamic drag, resistance to chemicals, hydraulic fluid and ultraviolet exposure. The issues with the coatings are the possible high thickness variations due to the manual painting adopted. The existing thickness measurement methods are mostly suited to metals and cannot be well employed for in-field tests of composites. Here a new microwave cylindrical cavity resonator sensor is developed for the non-destructive thickness evaluation of coatings on composite substrates. The open cavity and conductive carbon fibre composite form a resonant system, where the presence of coating affects the surface impedance, causing changes in the resonance frequency. Applying the wall impedance perturbation and transmission line theories, an analytical model is proposed. From the measured data, a linear relationship is obtained between the resonance frequency shift and thickness change, thereby simplifying the prediction process. The insensitivity to the dielectric properties of the coating and anisotropy of the composite substrate offers convenient calibration and implementation. The new sensor can provide efficient on-site assessment of paint coatings on carbon fibre composite surfaces used in modern aircraft construction and other engineering applications.

Current systems for metal detection in dry food processing are limited by relatively large foreign objects and high-cost implementation. These issues are resolved here using a non-contact, cylindrical microwave cavity resonator sensor where food passes through the cavity and metallic objects are detected by a shift in the resonant frequency. Classic perturbation theory is applied to the basic set-up and numerical simulations are used to verify the design of the sensor. A cavity sensor was fabricated with a quartz tube symmetrically located for dry food flow and metal detection. Good performance is demonstrated for a range of foods such as spaghetti, noodles, rice, wheat flour and soy milk powder. It is shown that the resonance frequency shift becomes larger when the foreign body gets closer to the cavity centre. The frequency variation is directly related to the volume of the object, and it is estimated that the minimum diameter of a detectable ball can be lower than 2 mm. For completeness it is also observed that the set-up can be used to detect dielectric objects. A graphical user interface is developed for practical applications. The method proposed is low-cost, convenient, scalable and complementary to other metallic contaminant detection approaches.

Microwave Pressing is a promising way to reduce microwave sintering temperatures and stabilize microwave powder materials processing. A multi-physics simulation was conducted of the regulated pressure-assisted microwave cavity. This simulation took into consideration resonance phenomena and the nonlinear temperature-dependent material parameters of zirconia. The intrinsic behaviors of microwave systems and zirconia make the regulation of the microwave pressing difficult. However, the same phenomena can be used to activate flash sintering. Flash microwave sintering uses high electric fields of the resonant microwave profile, the Negative Temperature Behavior (NTC) of zirconia resistivity, and the mechanical pressure applied to the powder via a die compaction configuration. The resulting flash microwave pressing still needs improvement in terms of the processed material structure homogeneity, but it has the capacity to become the fastest sintering treatment as it allows room temperature activation where the total process time only takes a few seconds. In addition, this 10-20s processing technique has shown good potential for improving the transparency of alumina pre-sintered specimens.

A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized state of water protons can be achieved by flowing aqueous liquid through a microwave resonator placed directly in the bore of a 1.5 T MRI magnet. Here we describe a new open Fabry–Pérot resonator as DNP polarizer, which exhibits a larger microwave exposure volume for the flowing liquid in comparison with a cylindrical TE013 microwave cavity. The Fabry–Pérot resonator geometry was designed using quasi-optical theory and simulated by CST software. Performance of the new polarizer was tested by MRI DNP experiments on a TEMPOL aqueous solution using a blood-vessel phantom. The Fabry–Pérot resonator revealed a 2-fold larger DNP enhancement with a 4-fold increased flow rate compared to the cylindrical microwave resonator. This increased yield of hyperpolarized liquid allows MRI applications on larger target objects.

Multimode cavity quantum electrodynamics ---where a two-level system interacts simultaneously with many cavity modes---provides a versatile framework for quantum information processing and quantum optics. Due to the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of $2$ ms and cooperativities of $0.5-1.5\times10^9$ across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.

The dissipative squeezing mechanism is an effective method to generate the strong squeezing, which is important in the precision metrology. Here, we propose a practical method to achieve arbitrary bosonic squeezing via introducing frequency modulation into the coupled harmonic resonator model. We analyze the effect of frequency modulation and give the analytical and numerical squeezing results, respectively. To measure the accurate dynamic squeezing in our proposal, we give a more general defination of the relative squeezing degree. Finally, the proposed method is extended to generate the strong mechanical squeezing (>3 dB) in a practical optomechanical system consisting of a graphene mechanical oscillator coupled to a superconducting microwave cavity. The result indicates that the strong mechanical squeezing can be effectively achieved even when the mechanical oscillator is not initially in its ground state. The proposed method expands the study on nonclassical state and does not need the bichromatic microwave driving technology.

Braking conditions are a fundamental issue for the railway and have been a limiting factor in network capacity and timetabling. Leaf fall, especially during the autumn season, creates low-adhesion problems on railways, causing braking problems for trains. To address the requirements of the novel plasma industrial applications towards environmental applications, this work developed and tested a 2.45 GHz microwave atmospheric pressure plasma system for in situ removal of the third body layer deposited onto the railway so as to improve braking. The plasma reactor consisted of a 15 kW, 2.45 GHz magnetron-based microwave generator and a plasma reactor (dielectric tube placed in a TE01 monomode microwave cavity), the atmospheric plasma ignited and sustained at different power levels (2&ndash, 15 kW) in different gases (nitrogen, argon) as well as mixtures of these gases with reactive molecules (water, oxygen) was jetted directly onto the railhead as to change the conditions for the wheel&ndash, rail interface. This technology is hoped to be a game-changer in enabling predictable and optimized braking on the railway network. Challenges encountered during the demonstration phase are discussed. Subsequent work should validate the results on a working railway line during the autumn season.

We propose to realize the ground state cooling of magnomechanical resonator in a parity-time ( $${\cal P}{\cal T}$$ )-symmetric cavity magnomechanical system composed of a loss ferromagnetic sphere and a gain microwave cavity. In the scheme, the magnomechanical resonator can be cooled close to its ground state via the magnomechanical interaction, and it is found that the cooling effect in $${\cal P}{\cal T}$$ -symmetric system is much higher than that in non- $${\cal P}{\cal T}$$ -symmetric system. Resorting to the magnetic force noise spectrum, we investigate the final mean phonon number with experimentally feasible parameters and find surprisingly that the ground state cooling of magnomechanical resonator can be directly achieved at room temperature. Furthermore, we also illustrate that the ground state cooling can be flexibly controlled via the external magnetic field.

Recently, a laboratory setup for microwave-based characterization of powder samples at elevated temperatures and different gas atmospheres was presented. The setup is particularly interesting for operando investigations on typical materials for exhaust gas aftertreatment. By using the microwave cavity perturbation method, where the powder is placed inside a cavity resonator, the change of the resonant properties provides information about changes in the dielectric properties of the sample. However, determining the exact complex permittivity of the powder samples is not simple. Up to now, a simplified microwave cavity perturbation theory had been applied to estimate the bulk properties of the powders. In this study, an extended approach is presented which allows to determine the dielectric properties of the powder materials more correctly. It accounts for the electric field distribution in the resonator, the depolarization of the sample and the effect of the powder filling. The individual method combines findings from simulations and recognized analytical approaches and can be used for investigations on a wide range of materials and sample geometries. This work provides a more accurate evaluation of the dielectric powder properties and has the potential to enhance the understanding of the microwave behavior of storage materials for exhaust gas aftertreatment, especially with regard to the application of microwave-based catalyst state diagnosis.

We use a quantum path integral approach to describe the behavior of a microwave cavity coupled to a dissipative mesoscopic circuit. We integrate out the mesoscopic electronic degrees of freedom to obtain a cavity effective action at fourth order in the light/matter coupling. By studying the structure of this action, we establish sufficient conditions in which the cavity dynamics can be described with a Lindblad equation. This equation depends on effective parameters set by electronic correlation functions. It reveals that the mesoscopic circuit induces an effective Kerr interaction and two-photon dissipative processes. We use our method to study the effective dynamics of a cavity coupled to a double quantum dot with normal metal reservoirs. If the cavity is driven at twice its frequency, the double dot circuit generates photonic squeezing and non-classicalities visible in the cavity Wigner function. In particular, we find a counterintuitive situation where mesoscopic dissipation enables the production of photonic Schr\"odinger cats. These effects can occur for realistic circuit parameters. Our method can be generalized straightforwardly to more complex circuit geometries with, for instance, multiple quantum dots, and other types of fermionic reservoirs such as superconductors and ferromagnets., Comment: 23 pages, 12 figures, submitted

In this thesis, we have studied an ultrahigh quality factor mechanical oscillator coupled to a microwave cavity. We will present an original technique to probe the losses of planar microwave cavities, as well as a resolved sideband cooling technique to actively cool this mechanical oscillator using the microwave cavity. Finally, we will present some optimizations of this experiment which open the path towards the ground state cooling of the mechanical oscillator. Such a hybrid quantum system could be used as an on-chip quantum memory, able to store fragile quantum states generated by superconducting quantum circuits for coherence times approaching a second.; Dans cette thèse, nous avons étudié un système mécanique de très haut facteur de qualité couplé à une cavité micro-onde supraconductrice. Nous présenterons une technique originale de caractérisation des pertes des cavités micro-ondes planaires, ainsi qu’une technique de refroidissement par bande latérale résolue utilisée pour refroidir activement cet oscillateur mécanique à l’aide de la cavité micro-onde. Enfin, nous présenterons des optimisations de cette expérience qui ouvrent la voie au refroidissement de l'oscillateur mécanique dans son état quantique fondamental. Un tel système hybride pourrait jouer le rôle de mémoire quantique sur puce, permettant de stocker les états quantiques non-gaussiens générés par des circuits quantiques supraconducteurs dans des vibrations mécaniques avec des temps de cohérence approchant la seconde.

In this thesis, we have studied an ultrahigh quality factor mechanical oscillator coupled to a microwave cavity. We will present an original technique to probe the losses of planar microwave cavities, as well as a resolved sideband cooling technique to actively cool this mechanical oscillator using the microwave cavity. Finally, we will present some optimizations of this experiment which open the path towards the ground state cooling of the mechanical oscillator. Such a hybrid quantum system could be used as an on-chip quantum memory, able to store fragile quantum states generated by superconducting quantum circuits for coherence times approaching a second.; Dans cette thèse, nous avons étudié un système mécanique de très haut facteur de qualité couplé à une cavité micro-onde supraconductrice. Nous présenterons une technique originale de caractérisation des pertes des cavités micro-ondes planaires, ainsi qu’une technique de refroidissement par bande latérale résolue utilisée pour refroidir activement cet oscillateur mécanique à l’aide de la cavité micro-onde. Enfin, nous présenterons des optimisations de cette expérience qui ouvrent la voie au refroidissement de l'oscillateur mécanique dans son état quantique fondamental. Un tel système hybride pourrait jouer le rôle de mémoire quantique sur puce, permettant de stocker les états quantiques non-gaussiens générés par des circuits quantiques supraconducteurs dans des vibrations mécaniques avec des temps de cohérence approchant la seconde.

We consider a collection of two level systems, such as qubits, embedded into a microwave cavity as a promising candidate for the realization of high power quantum batteries. In this perspective, the possibility to design devices where the conventional single-photon coupling is suppressed and the dominant interaction is mediated by two-photon processes is investigated, opening the way to an even further enhancement of the charging performance. By solving a Dicke model with both single- and two-photon coupling we determine the range of parameters where the latter unconventional interaction dominates the dynamics of the system leading to better performances both in the charging times and average charging power of the QB compared to the single-photon case. In addition, the scaling of the maximum stored energy, fluctuations and charging power with the finite number of qubits N is inspected. While the energy and fluctuations scale linearly with N, the quadratic growth of the average power leads to a relevant improvement of the charging performance of quantum batteries based on this scheme with respect to the purely single-photon coupling case. Moreover, it is shown that the charging process is progressively faster by increasing the coupling from the weak to the ultra-strong regime., 13 pages, 9 figures

A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized state of water protons can be achieved by flowing aqueous liquid through a microwave resonator placed directly in the bore of a 1.5 T MRI magnet. Here we describe a new open Fabry-Pérot resonator as DNP polarizer, which exhibits a larger microwave exposure volume for the flowing liquid in comparison with a cylindrical TE013 microwave cavity. The Fabry-Pérot resonator geometry was designed using quasi-optical theory and simulated by CST software. Performance of the new polarizer was tested by MRI DNP experiments on a TEMPOL aqueous solution using a blood-vessel phantom. The Fabry-Pérot resonator revealed a 2-fold larger DNP enhancement with a 4-fold increased flow rate compared to the cylindrical microwave resonator. This increased yield of hyperpolarized liquid allows MRI applications on larger target objects.

A new approach for an in-line beam monitor for ionizing radiation was introduced in a recent publication (Beckers, J., et al. "Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy." Journal of Physics D: Applied Physics 52.3 (2018): 034004.). Due to the recent detection and investigation of an additional third decay regime of the afterglow of an extreme ultraviolet photon-induced plasma described in a later article (Platier, B., et al. "Transition of ambipolar-to-free diffusion in the decay of an extreme ultraviolet photon-induced low-pressure argon plasma." Applied Physics Letters 116.10 (2020), 103703.) there is an additional reason for a minimum number of photons for this approach to work. Near or below this threshold, we explain that the response time of the diagnostic method is a limiting factor. Further, a second limit for the number of photons within a pulse is formalized related to the trapping of highly energetic free electrons.

We propose a quantum state readout mechanism of a weakly coupled qubit in a dispersive regime. The hybrid system consists of a ferromagnetic insulator and a weakly coupled quantum system, e.g., single electron spin, in a microwave cavity. The enhancement of the measurement sensitivity is achieved by exerting torque on the ferromagnetic insulator magnetization, which compensates the damping of the system leading to an exceptional point. The proposed mechanism allows us to measure the qubit state either via the transmission of the cavity or the FMR signal of the magnetic material.

Coherent conversion from microwave to optical wave opens new research avenues towards a long distance quantum network covering quantum communication, computing, and sensing out of the laboratory. Especially a multimode enabled system is essential for practical applications. Here we experimentally demonstrate coherent multimode conversion from the microwave to optical wave via collective spin excitation in a single crystal yttrium iron garnet (YIG, ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$) which is strongly coupled to a microwave cavity mode in a three-dimensional rectangular cavity. Expanding a collective spin excitation mode of our magnon-cavity hybrid system from Kittel to multimagnetostatic modes, we verify that the size of the YIG sphere predominantly plays a crucial role for the microwave-to-optical multimode conversion efficiency at resonant conditions. We also find that the coupling strength between multimagnetostatic modes and a cavity mode is manipulated by the position of a YIG inside the cavity. It is expected to be valuable for designing a magnon-hybrid system that can be used for coherent conversion between microwave and optical photons.