Dynamical Fluctuations of Random Walks in Higher-Order Networks.

Although higher-order interactions are known to affect the typical state of dynamical processes giving rise to new collective behavior, how they drive the emergence of rare events and fluctuations is still an open problem. We investigate how fluctuations of a dynamical quantity of a random walk exploring a higher-order network arise over time. In the quenched case, where the hypergraph structure is fixed, through large deviation theory we show that the appearance of rare events is hampered in nodes with many higher-order interactions, and promoted elsewhere.

A tunable clamshell cavity for wavelike dark matter searches.

Here, we present a frequency tuning mechanism for microwave cavities designed for axion dark matter searches and show that it provides a range of at least 200 MHz for the fundamental mode TM010 resonant at ∼10 GHz. The apparatus is based on a clamshell cavity, with the two semi-cells held together at a fixed joint while the other side opens to tune the frequency of the resonant modes. Measurements of the cavity frequencies and quality factor were taken at liquid helium temperature as the aperture was increased incrementally to ∼2°.

Electron thermalization length in solid para-hydrogen at low-temperature.

We report the first ever measurements of the thermalization length of low-energy electrons injected into solid para-hydrogen at a temperature T ≈ 2.8 K. The use of the pulsed Townsend photoinjection technique has allowed us to investigate the behavior of quasi-free electrons rather than of massive, slow negative charges, as reported in all previous literature.

Delocalization-localization dynamical phase transition of random walks on graphs.

We consider random walks evolving on two models of connected and undirected graphs and study the exact large deviations of a local dynamical observable. We prove, in the thermodynamic limit, that this observable undergoes a first-order dynamical phase transition (DPT). This is interpreted as a "coexistence" of paths in the fluctuations that visit the highly connected bulk of the graph (delocalization) and paths that visit the boundary (localization).

Instabilities of complex fluids with partially structured and partially random interactions.

We develop a theory for thermodynamic instabilities of complex fluids composed of many interacting chemical species organised in families. This model includes partially structured and partially random interactions and can be solved exactly using tools from random matrix theory. The model exhibits three kinds of fluid instabilities: one in which the species form a condensate with a local density that depends on their family (family condensation); one in which species demix in two phases depending on their family (family demixing); and one in which species demix in a random manner irrespective of their family (random demixing).

High quality factor photonic cavity for dark matter axion searches.

Searches for dark matter axions involve the use of microwave resonant cavities operating in a strong magnetic field. Detector sensitivity is directly related to the cavity quality factor, which is limited, until recently, to the use of non-superconducting metals by the presence of the external magnetic field. In this paper, we present a cavity of novel design whose quality factor is not affected by a magnetic field.

Comparison of the performance of a high voltage generator insulated by gas or liquid dielectric.

A module of a wireless high voltage generator was tested immersed in both gaseous and liquid environments providing electrical insulation. The overall performance of the module as well as a detailed performance of the key components are reported, and a comparison between the results in gas and liquid is given. The tests performed on the liquid dielectric show that it is a valid alternative to high pressure gas electrical insulation.

Axion Search with a Quantum-Limited Ferromagnetic Haloscope.

A ferromagnetic axion haloscope searches for dark matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier.

Experimental setup for the growth of solid crystals of inert gases for particle detection.

Low energy threshold detectors are necessary in many frontier fields of the experimental physics. In this work, we present a novel detection approach based on pure or doped matrices of inert gases solidified at cryogenic temperatures. The small energy release of the incident particle can be transferred directly (in pure crystals) or through a laser-driven ionization (in doped materials) to the electrons of the medium that are then converted into free electrons.

Axion dark matter detection by laser induced fluorescence in rare-earth doped materials.

We present a detection scheme to search for QCD axion dark matter, that is based on a direct interaction between axions and electrons explicitly predicted by DFSZ axion models. The local axion dark matter field shall drive transitions between Zeeman-split atomic levels separated by the axion rest mass energy m c . Axion-related excitations are then detected with an upconversion scheme involving a pump laser that converts the absorbed axion energy (~hundreds of μeV) to visible or infrared photons, where single photon detection is an established technique.

Optical Manipulation of a Magnon-Photon Hybrid System.

We demonstrate an all-optical method for manipulating the magnetization in a 1-mm yttrium-iron-garnet (YIG) sphere placed in a ∼0.17  T uniform magnetic field. A harmonic of the frequency comb delivered by a multi-GHz infrared laser source is tuned to the Larmor frequency of the YIG sphere to drive magnetization oscillations, which in turn give rise to a radiation field used to thoroughly investigate the phenomenon.

Realization of a high voltage generator by series connection of floating modules.

A high voltage generator built by a series connection of 100 kV modules was produced. The series connection feasibility is ensured by the inherent floating character of each module which is wireless powered by high efficiency photovoltaic cells illuminated by a laser system. Each module is equipped with a control and monitoring board allowing excellent stabilization of the high voltage output.

Optomechanical Rydberg-atom excitation via dynamic Casimir-Polder coupling.

We study the optomechanical coupling of a oscillating effective mirror with a Rydberg atomic gas, mediated by the dynamical atom-mirror Casimir-Polder force. This coupling may produce a near-field resonant atomic excitation whose probability scales as ∝(d(2)an(4)t)(2)/z(0)(8), where z(0) is the average atom-surface distance, d the atomic dipole moment, a the mirror's effective oscillation amplitude, n the initial principal quantum number, and t the time. We propose an experimental configuration to realize this system with a cold atom gas trapped at a distance ∼2×10  μm from a semiconductor substrate whose dielectric constant is periodically driven by an external laser pulse, hence realizing an effective mechanical mirror motion due to the periodic change of the substrate from transparent to reflecting.

Generation of microwave radiation by nonlinear interaction of a high-power, high-repetition rate, 1064 nm laser in KTiOPO4 crystals.

We report measurements of microwave (RF) generation in the centimeter band accomplished by irradiating a nonlinear KTiOPO4 crystal with a home-made, infrared laser at 1064 nm as a result of optical rectification. The laser delivers pulse trains of duration up to 1 μs. Each train consists of several high-intensity pulses at an adjustable repetition rate of approximately 4.

A modular optically powered floating high voltage generator.

The feasibility of fully floating high voltage (HV) generation was demonstrated producing a prototype of a modular HV system. The primary power source is provided by a high efficiency semiconductor power cell illuminated by a laser system ensuring the floating nature of each module. The HV is then generated by dc-dc conversion and a HV multiplier.

A laser system for the parametric amplification of electromagnetic fields in a microwave cavity.

We describe recent improvements in the development of the high power laser system used in the motion induced radiation (MIR) experiment to amplify electromagnetic fields inside a microwave cavity. The improvements made on the oscillator stabilization, the pulse train shaping device, and the spatial beam uniformity are reported.

A battery-operated, stabilized, high-energy pulsed electron gun for the production of rare gas excimers.

We report on the design of a new type of hot-filament electron gun delivering fairly high current (a few hundreds of μ A) at high voltage (up to 100 kV) in continuous or pulsed mode. Its novel features are that the filament is heated by means of a pack of rechargeable batteries floated atop the high-voltage power supply in order to get rid of bulky isolation transformers, and that the filament current and, hence, the electron gun current, is controlled by a feedback circuit including a superluminescent diode decoupled from the high voltage by means of an optical fiber. This electron gun is intended for general purposes, although we have especially developed it to meet the needs of our experiment on the infrared emission spectroscopy of rare gas excimers.

Measurement of the Casimir force between parallel metallic surfaces.

We report on the measurement of the Casimir force between conducting surfaces in a parallel configuration. The force is exerted between a silicon cantilever coated with chromium and a similar rigid surface and is detected by looking at the shifts induced in the cantilever frequency when the latter is approached. The scaling of the force with the distance between the surfaces was tested in the 0.