Coherent coupling between multiple ferrimagnetic spheres and a microwave cavity in the quantum-limit

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 article, the behavior of a large number of ferrimagnetic spheres coupled to a single cavity is put under test. 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-spheres 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 in ten 2 mm-diameter YIG spheres coupled to a copper microwave cavity, is used for this aim and studied at mK temperatures. Moreover, we show that novel applications of optimally-controlled hybrid systems can be foreseen for setups embedding a large number of samples.Comment: 12 pages, 8 figure

The QUAX proposal: a search of galactic axion with magnetic materials

Aim of the QUAX (QUaerere AXion) proposal is to exploit the interaction of cosmological axions with the spin of electrons in a magnetized sample. Their effect is equivalent to the application of an oscillating rf field with frequency and amplitude which are fixed by axion mass and coupling constant, respectively. The rf receiver module of the QUAX detector consists of magnetized samples with the Larmor resonance frequency tuned to the axion mass by a polarizing static magnetic field. The interaction of electrons with the axion-equivalent rf field produces oscillations in the total magnetization of the samples. To amplify such a tiny field, a pump field at the same frequency is applied in a direction orthogonal to the polarizing field. The induced oscillatory magnetization along the polarizing field is measured by a SQUID amplifier operated at its quantum noise level.Comment: 5 pages, Contribution for the proceedings of the TAUP2015, International Conference on Topics in Astroparticle and Underground Physics, 7-11 September 2015, Torino, Ital

Resonance frequency shift in a cavity with a thin conducting film near a conducting wall

We show that a very thin conducting film (whose thickness can be much smaller than the skin depth), placed nearby a wall of an electromagnetic cavity, can produce the same shift of the resonance frequency as a bulk conducting slab, provided the displacement of the film from the wall is much bigger than the skin depth. We derive a simple analytical formula for the frequency shift and compare it with exact numerical calculations and experimental data

Laser system generating 250-mJ bunches of 5-GHz repetition rate, 12-ps pulses.

We report on a high-energy solid-state laser based on a master-oscillator power-amplifier system seeded by a 5-GHz repetition-rate mode-locked oscillator, aimed at the excitation of the dynamic Casimir effect by optically modulating a microwave resonator. Solid-state amplifiers provide up to 250 mJ at 1064 nm in a 500-ns (macro-)pulse envelope containing 12-ps (micro-)pulses, with a macro/micropulse format and energy resembling that of near-infrared free-electron lasers. Efficient second-harmonic conversion allowed synchronous pumping of an optical parametric oscillator, obtaining up to 40 mJ in the range 750-850 nm

Cascade Superfluorescence in Er:YLF

We report the analysis of paired photon pulses arising from two cascading transitions in continuously pumped Erbium-doped YLiF$_4$ 1% and 0.01% crystals at 1.6 K. The dependence of the pulse peak intensity on the squared number of involved Erbium ions, between 10$^{11}$ and 10$^{13}$, definitely identifies the cooperative nature of the two pulsed emissions, that are generated by the subsequent, spontaneous formation of coherent states. The observed fluctuations of the time interval between the paired pulses and, most importantly, its correlation with the second pulse duration, demonstrate that the Erbium ions coherence is indeed seeded by vacuum fluctuations

GaAs as a Bright Cryogenic Scintillator for the Detection of Low-Energy Electron Recoils From MeV/c 2 Dark Matter

This article presents the measurements of the luminescence and scintillation under X-ray of undoped, Si-doped, and Si, B codoped gallium-arsenide (GaAs) samples at cryogenic temperature over a wide infrared (IR) region using Si and InGaAs photodetectors. The undoped GaAs has a narrow emission band at 838 nm (1.48 eV) and a low light output of about 2 ph/keV. The GaAs:Si has three broad luminescence bands at 830 nm (1.49 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) and a light output of about 67 ph/keV. GaAs:(Si, B) has four luminescence bands at 860 nm (1.44 eV), 930 nm (1.33 eV), 1070 nm (1.16 eV), and 1335 nm (0.93 eV) with a light yield of approximately 119 ph/keV. With advances in photodetection, GaAs promises to be a useful cryogenic scintillator for the detection of electron recoils from MeV/c2 dark matter

The measurement of a single-mode thermal field with a microwave cavity parametric amplifier

In this paper, we present the experimental study of a single-mode thermal field carried out using a microwave parametric amplifier tuned at 1.5 GHz and working at room temperature. The parametric amplifier is based on a variable capacitance diode placed inside a microwave resonant cavity. The measured distribution of the thermal photons inside the resonator follows the expected Bose–Einstein distribution probability