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

Evidence of dual Shapiro steps in a Josephson junctions array

The modern primary voltage standard is based on the AC Josephson effect and the ensuing Shapiro steps, where a microwave tone applied to a Josephson junction yields a constant voltage $hf/2e$ ($h$ is Planck's constant and $e$ the electron charge) determined by only the microwave frequency $f$ and fundamental constants. Duality arguments for current and voltage have long suggested the possibility of dual Shapiro steps -- that a Josephson junction device could produce current steps with heights determined only on the applied frequency. In this report, we embed an ultrasmall Josephson junction in a high impedance array of larger junctions to reveal dual Shapiro steps. For multiple frequencies, we detect that the AC response of the circuit is synchronised with the microwave tone at frequency $f$, and the corresponding emergence of flat steps in the DC response with current $2ef$, equal to the tunnelling of a Cooper pair per tone period. This work sheds new light on phase-charge duality, omnipresent in condensed matter physics, and extends it to Josephson circuits. Looking forward, it opens a broad range of possibilities for new experiments in the field of circuit quantum electrodynamics and is an important step towards the long-sought closure of the quantum metrology electrical triangle.Comment: 14 pages, 11 figure

Studio computazionale dell’effetto del flusso sulla resa di una reazione bimolecolare in circuiti microfluidici

Questo elaborato presenta un'analisi effettuata, mediante metodi di simulazione numerica degli effetti di variazione di geometria, costante di reazione e campo di velocità sulla resa di un processo chimico elementare bimolecolare all'interno di un microreattore a T

Towards the development of the ferromagnetic axion haloscope

The axion is an hypothetical beyond the Standard Model particle, first introduced in the seventies as a consequence of the strong CP problem of QCD. Axions can be the main constituents of the galactic Dark Matter halos. Their experimental search can be carried out with Earth-based instruments immersed in the Milky Way’s halo, which are therefore called “haloscopes”. Nowadays haloscopes rely on the inverse Primakoff effect to detect axioninduced excesses of photons in a microwave cavity under a static magnetic field. This thesis describes the process leading to the successful peration of a ferromagnetic axion haloscope, which does not exploit the axion-to-photon conversion but its interaction with the electron spin. The study of the axionspin interaction and of the Dark Matter halo properties yields the features of the axionic signal, and is fundamental to devise a proper detector. A scheme of a realistic ferromagnetic haloscope is drawn to realize the challenges of its development. It emerges that there are a number of requirements for a this setup to get to the sensitivity needed for a QCD-axion search. These are kept in mind when designing the prototypes, to overcome the problems without compromising other requirements. A state-of-the-art sensitivity to rf signals allows for the detection of extremely weak signals as the axionic one. The number of monitored spins is necessarily large to increase the exposure of the setup, thus its scalability is a key part of the design process. A ferromagnetic haloscope consists in a transducer of the axionic signal, which is then measured by a suitable detector. The transducer is a hybrid system formed by a magnetic material coupled to a microwave cavity through a static magnetic field. Its two parts are separately studied to find the materials which match the detection conditions imposed by the axionsignal. The detector is an amplifier, an HEMT or a JPA, reading out the power from the hybrid system collected by an antenna coupled to the cavity. A particular attention is given to the measurement of the noise temperature of the amplifier. As it measures variation in the magnetization of the sample, the ferromagnetic haloscope is configured as a spin-magnetometer. Three different prototypes of increasing sensitivity make up the part of the thesis dedicated to physics results, namely limits on the axionic Dark Matter field. For every prototype it is verified that larger sample dimensions do not compromise the signal transduction or increase the noise. The working temperature of the haloscope ranges from the 300 K of the first device, to 90 mK of the last one. In every step the noise temperature is also decreased. The final prototype reached the sensitivity limit imposed by quantum mechanics, the Standard Quantum Limit, and can be improved only by quantum technologies like single photon counters. The haloscope embodies a large quantity of magnetic material, i. e. ten 2 mm YIG spheres, and is designed to be further up-scaled. The quantum-limited ultra cryogenic prototype meets the expectations, and, to present knowledge, is the most sensitive rf spin-magnetometer existing. The minimum detectable field results in 5.5 × 10−19 T for 8 h integration, and corresponds to a limit on the axion-electron coupling constant gaee ≤ 1.7 × 10−11. This result is the best limit on the DM-axions coupling to electron spins in a frequency span of about 150 MHz, corresponding to an axion mass range from 42.4 µeV to 43.1 µeV. The efforts to enhance the haloscope sensitivity include improvements in both the hybrid system and the detector. The deposited axion power can be increased by means of a larger material volume, possibly with a narrower linewidth. To overcome the standard quantum limit of linear amplifiers one must rely on quantum counters. Novel studies on microwave photon counters, together with some preliminary results, are reported. Other possible usages of the spin-magnetometer are eventually discussed

Towards the development of the ferromagnetic axion haloscope

The axion is an hypothetical beyond the Standard Model particle, first introduced in the seventies as a consequence of the strong CP problem of QCD. Axions can be the main constituents of the galactic Dark Matter halos. Their experimental search can be carried out with Earth-based instruments immersed in the Milky Way’s halo, which are therefore called “haloscopes”. Nowadays haloscopes rely on the inverse Primakoff effect to detect axioninduced excesses of photons in a microwave cavity under a static magnetic field. This thesis describes the process leading to the successful peration of a ferromagnetic axion haloscope, which does not exploit the axion-to-photon conversion but its interaction with the electron spin. The study of the axionspin interaction and of the Dark Matter halo properties yields the features of the axionic signal, and is fundamental to devise a proper detector. A scheme of a realistic ferromagnetic haloscope is drawn to realize the challenges of its development. It emerges that there are a number of requirements for a this setup to get to the sensitivity needed for a QCD-axion search. These are kept in mind when designing the prototypes, to overcome the problems without compromising other requirements. A state-of-the-art sensitivity to rf signals allows for the detection of extremely weak signals as the axionic one. The number of monitored spins is necessarily large to increase the exposure of the setup, thus its scalability is a key part of the design process. A ferromagnetic haloscope consists in a transducer of the axionic signal, which is then measured by a suitable detector. The transducer is a hybrid system formed by a magnetic material coupled to a microwave cavity through a static magnetic field. Its two parts are separately studied to find the materials which match the detection conditions imposed by the axionsignal. The detector is an amplifier, an HEMT or a JPA, reading out the power from the hybrid system collected by an antenna coupled to the cavity. A particular attention is given to the measurement of the noise temperature of the amplifier. As it measures variation in the magnetization of the sample, the ferromagnetic haloscope is configured as a spin-magnetometer. Three different prototypes of increasing sensitivity make up the part of the thesis dedicated to physics results, namely limits on the axionic Dark Matter field. For every prototype it is verified that larger sample dimensions do not compromise the signal transduction or increase the noise. The working temperature of the haloscope ranges from the 300 K of the first device, to 90 mK of the last one. In every step the noise temperature is also decreased. The final prototype reached the sensitivity limit imposed by quantum mechanics, the Standard Quantum Limit, and can be improved only by quantum technologies like single photon counters. The haloscope embodies a large quantity of magnetic material, i. e. ten 2 mm YIG spheres, and is designed to be further up-scaled. The quantum-limited ultra cryogenic prototype meets the expectations, and, to present knowledge, is the most sensitive rf spin-magnetometer existing. The minimum detectable field results in 5.5 × 10−19 T for 8 h integration, and corresponds to a limit on the axion-electron coupling constant gaee ≤ 1.7 × 10−11. This result is the best limit on the DM-axions coupling to electron spins in a frequency span of about 150 MHz, corresponding to an axion mass range from 42.4 µeV to 43.1 µeV. The efforts to enhance the haloscope sensitivity include improvements in both the hybrid system and the detector. The deposited axion power can be increased by means of a larger material volume, possibly with a narrower linewidth. To overcome the standard quantum limit of linear amplifiers one must rely on quantum counters. Novel studies on microwave photon counters, together with some preliminary results, are reported. Other possible usages of the spin-magnetometer are eventually discussed

Building instructions for a ferromagnetic axion haloscope

International audienceA ferromagnetic haloscope is a rf spin magnetometer used for searching dark matter in the form of axions. A magnetic material is monitored searching for anomalous magnetization oscillations which can be induced by dark matter axions. To properly devise such instrument, one first needs to understand the features of the searched-for signal, namely the effective rf field of dark matter axions $B_\mathrm{{a}}$ acting on electronic spins. Once the properties of $B_\mathrm{{a}}$ are defined, the design and test of the apparatus may start. The optimal sample is a narrow linewidth and high spin-density material such as yttrium-iron garnet, coupled to a microwave cavity with almost matched linewidth to collect the signal. The power in the resonator is collected with an antenna and amplified with a Josephson parametric amplifier, a quantum-limited device which, however, adds most of the setup noise. The signal is further amplified with low-noise HEMT and down-converted for storage with an heterodyne receiver. This work describes how to build such apparatus, with all the experimental details, the main issues one might face, and some solutions

Evidence of dual Shapiro steps in a Josephson junctions array

The modern primary voltage standard is based on the AC Josephson effect and the ensuing Shapiro steps, where a microwave tone applied to a Josephson junction yields a constant voltage $hf/2e$ ($h$ is Planck's constant and $e$ the electron charge) determined by only the microwave frequency $f$ and fundamental constants. Duality arguments for current and voltage have long suggested the possibility of dual Shapiro steps -- that a Josephson junction device could produce current steps with heights determined only on the applied frequency. In this report, we embed an ultrasmall Josephson junction in a high impedance array of larger junctions to reveal dual Shapiro steps. For multiple frequencies, we detect that the AC response of the circuit is synchronised with the microwave tone at frequency $f$, and the corresponding emergence of flat steps in the DC response with current $2ef$, equal to the tunnelling of a Cooper pair per tone period. This work sheds new light on phase-charge duality, omnipresent in condensed matter physics, and extends it to Josephson circuits. Looking forward, it opens a broad range of possibilities for new experiments in the field of circuit quantum electrodynamics and is an important step towards the long-sought closure of the quantum metrology electrical triangle

An Haloscope Amplification Chain based on a Travelling Wave Parametric Amplifier

International audienceIn this paper we will describe the characterisation of a rf detection chain based on a travelling wave parametric amplifier (TWPA). The detection chain is meant to be used for dark matter axion searches and thus it is mounted coupled to a high Q microwave resonant cavity. A system noise temperature $T_{\rm sys} = (3.3 \pm 0.1$) K has been measured at a frequency of 10.77 GHz, using a novel scheme allowing measurement of $T_{\rm sys}$ exactly at the cavity output port