Spontaneous collapse models predict that a weak force noise acts on any mechanical system, as a consequence of the collapse of the wave function. Significant upper limits on the collapse rate have ...been recently inferred from precision mechanical experiments, such as ultracold cantilevers and the space mission LISA Pathfinder. Here, we report new results from an experiment based on a high-Q cantilever cooled to millikelvin temperatures, which is potentially able to improve the current bounds on the continuous spontaneous localization (CSL) model by 1 order of magnitude. High accuracy measurements of the cantilever thermal fluctuations reveal a nonthermal force noise of unknown origin. This excess noise is compatible with the CSL heating predicted by Adler. Several physical mechanisms able to explain the observed noise have been ruled out.
We present a single-quadrature feedback scheme able to overcome the conventional 3 dB limit on parametric squeezing. The method is experimentally demonstrated in a micromechanical system based on a ...cantilever with a magnetic tip. The cantilever is detected at low temperature by a SQUID susceptometer, while parametric pumping is obtained by modulating the magnetic field gradient at twice the cantilever frequency. A maximum squeezing of 11.5 dB and 11.3 dB is observed, respectively, in the response to a sinusoidal test signal and in the thermomechanical noise. So far, the maximum squeezing factor is limited only by the maximum achievable parametric modulation. The proposed technique might be used to squeeze one quadrature of a mechanical resonator below the quantum noise level, even without the need for a quantum limited detector.
Despite the unquestionable empirical success of quantum theory, witnessed by the recent uprising of quantum technologies, the debate on how to reconcile the theory with the macroscopic classical ...world is still open. Spontaneous collapse models are one of the few testable solutions so far proposed. In particular, the continuous spontaneous localization (CSL) model has become subject of intense experimental research. Experiments looking for the universal force noise predicted by CSL in ultrasensitive mechanical resonators have recently set the strongest unambiguous bounds on CSL. Further improving these experiments by direct reduction of mechanical noise is technically challenging. Here, we implement a recently proposed alternative strategy that aims at enhancing the CSL noise by exploiting a multilayer test mass attached on a high quality factor microcantilever. The test mass is specifically designed to enhance the effect of CSL noise at the characteristic length rc=10−7 m. The measurements are in good agreement with pure thermal motion for temperatures down to 100 mK. From the absence of excess noise, we infer a new bound on the collapse rate at the characteristic length rc=10−7 m, which improves over previous mechanical experiments by more than 1 order of magnitude. Our results explicitly challenge a well-motivated region of the CSL parameter space proposed by Adler.
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. The hybrid system consists of ten 2.1 mm diameter yttrium iron garnet spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin magnetometer ever realized. The minimum detectable field is 5.5×10^{-19} T with 9 h integration time, corresponding to a limit on the axion-electron coupling constant g_{aee}≤1.7×10^{-11} at 95% C.L. The scientific run of our haloscope resulted in the best limit on dark matter axions to electron coupling constant in a frequency span of about 120 MHz, corresponding to the axion-mass range 42.4-43.1 μeV. This is also the first apparatus to perform a wide axion-mass scanning by only changing the static magnetic field.
A haloscope of the QUAX– a γ experiment composed of an oxygen-free high thermal conductivity-Cu cavity inside an 8.1 T magnet and cooled to ∼ 200 mK is put in operation for the search of galactic ...axion with mass ma ≃ 43 μ eV . The power emitted by the resonant cavity is amplified with a Josephson parametric amplifier whose noise fluctuations are at the standard quantum limit. With the data collected in about 1 h at the cavity frequency νc = 10.40176 GHz , the experiment reaches the sensitivity necessary for the detection of galactic QCD-axion, setting the 90% confidence level limit to the axion-photon coupling gaγγ < 0.766 × 10−13 GeV−1.
We present a more stringent upper limit on long-range axion-mediated forces obtained by the QUAX-gpgs experiment, located at the INFN – Laboratori Nazionali di Legnaro. By measuring variations of a ...paramagnetic GSO crystal magnetization with a dc-SQUID magnetometer we investigate the possible coupling between electron spins and unpolarized nucleons in lead disks. The induced magnetization can be interpreted as the effect of a long-range spin dependent interaction mediated by axions or Axion Like Particles (ALPs). The corresponding coupling strength is proportional to the CP violating term gpegsN, i.e. the product of the pseudoscalar and scalar coupling constants of electron and nucleon, respectively. Our upper limit is more constraining than previous ones in the interaction range 0.01 m<λa<0.2 m, with a best result on gpegsN/(ħc) of 4.3×10−30 at 95% confidence level in the interval 0.1 m<λa<0.2 m. We eventually discuss our plans to improve the QUAX-gpgs sensitivity by a few orders of magnitude, which will allow us to investigate the ϑ≃10−10 range of CP-violating parameter and test some QCD axion models.
To account for the dark-matter content in our Universe, postinflationary scenarios predict for the QCD axion a mass in the range (10–103) μeV. Searches with haloscope experiments in this mass range ...require the monitoring of resonant cavity modes with frequency above 5 GHz, where several experimental limitations occur due to linear amplifiers, small volumes, and low quality factors of copper resonant cavities. In this paper, we deal with the last issue, presenting the result of a search for galactic axions using a haloscope based on a 36 cm3 NbTi superconducting cavity. The cavity worked at T=4 K in a 2 T magnetic field and exhibited a quality factor Q0=4.5×105 for the TM010 mode at 9 GHz. With such values of Q, the axion signal is significantly increased with respect to copper cavity haloscopes. Operating this setup, we set the limit gaγγ<1.03×10−12 GeV−1 on the axion photon coupling for a mass of about 37 μeV. A comprehensive study of the NbTi cavity at different magnetic fields, temperatures, and frequencies is also presented.
Abstract A wide-bandwidth and low-noise amplification chain in the microwave regime is crucial for the efficient read-out of quantum systems based on superconducting detectors, such as Microwave ...Kinetic Inductance Detectors (MKIDs), Transition Edge Sensors (TESs), Magnetic Microcalorimeters (MMCs), and RF cavities, as well as qubits. Kinetic Inductance Travelling Wave Parametric Amplifiers (KI-TWPAs) operated in a three-wave mixing fashion have demonstrated exceptional dynamic range and low-noise performance, approaching the quantum limit. These amplifiers can be fabricated using a single layer of a high kinetic inductance film as weakly dispersive artificial transmission lines, with the ability to control the phase-matched bandwidth through dispersion engineering. In this study, we present the optimisation of the rf sputter-deposition process of NbTiN films using a Nb 80% Ti 20% target, with the goal of achieving precise control over film characteristics, resulting in high kinetic inductance while maintaining a high transition temperature. The parameter landscape related to the different sputtering conditions, such as pressure, power, and nitrogen flow, has been explored and the film thickness has been used as a fine-tuning parameter to adjust the properties of the final NbTiN films used for the fabrication of KI-TWPAs. As a final result, we have obtained a NbTiN film with a kinetic inductance of 8.5 pH/sq which we have exploited to fabricate KI-TWPA prototype devices, showing promising amplification performance.
The Italian institute for nuclear physics (INFN) has financed the SIMP project (2019–2021) in order to strengthen its skills and technologies in the field of meV detectors with the ultimate aim of ...developing a single microwave photon detector. This goal will be pursued by improving the sensitivity and the dark-count rate of two types of photodetectors: current-biased Josephson junction (CBJJ) for the frequency range 10–50 GHz and transition-edge sensor (TES) for the frequency range 30–100 GHz. Preliminary results on materials and devices characterization are presented.
Reducing noise to the quantum limit over a large bandwidth is a fundamental requirement for future applications operating at millikelvin temperatures, such as the neutrino mass measurement, the ...next-generation X-ray observatory, the CMB measurement, the dark matter and axion detection, and the rapid high-fidelity readout of superconducting qubits. The read out sensitivity of arrays of microcalorimeter detectors, resonant axion-detectors, and qubits, is currently limited by the noise temperature and bandwidth of the cryogenic amplifiers. The Detector Array Readout with Traveling Wave Amplifiers project has the goal of developing high-performing innovative traveling wave parametric amplifiers with a high gain, a high saturation power, and a quantum-limited or nearly quantum-limited noise. The practical development follows two different promising approaches, one based on the Josephson junctions and the other one based on the kinetic inductance of a high-resistivity superconductor. In this contribution, we present the aims of the project, the adopted design solutions and preliminary results from simulations and measurements.
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