arXiv subjects

G. Torrioli

Publications and source records attributed to G. Torrioli.

At least 19 recordsLinked to original sources

arXiv2024

Thermalization of a SQUID chip at cryogenic temperature: Thermal conductance measurement for GE 7031 Varnish Glue, Apiezon N Grease and Rubber Cement between 20 and 200 mK

In the context of the ATHENA X-IFU Cryogenic AntiCoincidence Detector (CryoAC) development, we have studied the thermalization properties of a 2mm x 2mm SQUID chip. The chip is glued on a front-end PCB and operated on the cold stage of a dilution refrigerator (TBASE < 20 mK). We performed thermal conductance measurements by using different materials to glue the SQUID chip on the PCB. These have been repeated in subsequent cryostat runs, to highlight degradation effects due to thermal cycles. Here, we present the results obtained by glues and greases widely used in cryogenic environments, i.e. GE 7031 Varnish Glue, Apiezon N Grease and Rubber Cement.

astro-ph.IM↗

arXiv2024

The TES-based Cryogenic AntiCoincidence Detector (CryoAC) of ATHENA X-IFU: a large area silicon microcalorimeter for background particles detection

We are developing the Cryogenic AntiCoincidence detector (CryoAC) of the ATHENA X-IFU spectrometer. It is a TES-based particle detector aimed to reduce the background of the instrument. Here, we present the result obtained with the last CryoAC single-pixel prototype. It is based on a 1 cm2 silicon absorber sensed by a single 2mm x 1mm Ir/Au TES, featuring an on-chip heater for calibration and diagnostic purposes. We have illuminated the sample with 55Fe (6 keV line) and 241Am (60 keV line) radioactive sources, thus studying the detector response and the heater calibration accuracy at low energy. Furthermore, we have operated the sample in combination with a past-generation CryoAC prototype. Here, by analyzing the coincident detections between the two detectors, we have been able to characterize the background spectrum of the laboratory environment and disentangle the primary (i.e. cosmic muons) and secondaries (mostly secondary photons and electrons) signatures in the spectral shape.

astro-ph.IM↗

arXiv2023

Stepping closer to pulsed single microwave photon detectors for axions search

Axions detection requires the ultimate sensitivity down to the single photon limit. In the microwave region this corresponds to energies in the yJ range. This extreme sensitivity has to be combined with an extremely low dark count rate, since the probability of axions conversion into microwave photons is supposed to be very low. To face this complicated task, we followed two promising approaches that both rely on the use of superconducting devices based on the Josephson effect. The first one is to use a single Josephson junction (JJ) as a switching detector (i.e. exploiting the superconducting to normal state transition in presence of microwave photons). We designed a device composed of a coplanar waveguide terminated on a current biased Josephson junction. We tested its efficiency to pulsed (pulse duration 10 ns) microwave signals, since this configuration is closer to an actual axions search experiment. We show how our device is able to reach detection capability of the order of 10 photons with frequency 8 GHz. The second approach is based on an intrinsically quantum device formed by two resonators coupled only via a superconducting qubit network (SQN). This approach relies on quantum nondemolition measurements of the resonator photons. We show that injecting RF power into the resonator, the frequency position of the resonant drop in the transmission coefficient (S21) can be modulated up to 4 MHz. We anticipate that, once optimized, both the devices have the potential to reach single photon sensitivity.

quant-ph↗

arXiv2022

THz optical beat-note detection with a fast Hot Electron Bolometer operating up to 31 GHz

We study the performance of an hot-electron bolometer (HEB) operating at THz frequencies based on superconducting niobium nitride films. We report on the voltage response of the detector over a large optical bandwidth carried out with different THz sources. We show that the impulse response of the fully packaged HEB at 7.5 K has a 3 dB cut-off around 2 GHz. Remarkably, detection capability is still observed above 30 GHz in an heterodyne beating experiment using a THz quantum cascade laser frequency comb. Additionally, the HEB sensitivity has been evaluated and an optical noise equivalent power NEP of 0.8 pW/sqrt(Hz) has been measured at 1 MHz.

physics.optics↗

arXiv2022

ATHENA X-IFU Demonstration Model: First joint operation of the main TES Array and its Cryogenic AntiCoincidence Detector (CryoAC)

The X-IFU is the cryogenic spectrometer onboard the future ATHENA X-ray observatory. It is based on a large array of TES microcalorimeters, which works in combination with a Cryogenic AntiCoincidence detector (CryoAC). This is necessary to reduce the particle background level thus enabling part of the mission science goals. Here we present the first joint test of X-IFU TES array and CryoAC Demonstration Models, performed in a FDM setup. We show that it is possible to operate properly both detectors, and we provide a preliminary demonstration of the anti-coincidence capability of the system achieved by the simultaneous detection of cosmic muons.

astro-ph.IM↗

arXiv2016

THz Discrimination of materials: demonstration of a bioinspired apparatus based on metasurfaces selective filters

We present an apparatus for terahertz fingerprint discrimination of materials designed to be fast, simple, compact and economical in order to be suitable for preliminary on-field analysis. The system working principles, bioinspired by the human vision of colors, are based on the use of microfabricated metamaterials selective filters and of a very compact optics based on metallic ellipsoidal mirrors in air. We experimentally demonstrate the operation of the apparatus in discriminating simple substances such as salt, staple foods and grease in an accurate and reproducible manner. We present the system and the obtained results and discuss issues and possible developments.

physics.ins-det↗

arXiv2014

Resonant effects in a SQUID qubit subjected to non adiabatic changes

By quickly modifying the shape of the effective potential of a double SQUID flux qubit from a single-well to a double-well condition, we experimentally observe an anomalous behavior, namely an alternance of resonance peaks, in the probability to find the qubit in a given flux state. The occurrence of Landau-Zener transitions as well as resonant tunneling between degenerate levels in the two wells may be invoked to partially justify the experimental results. A quantum simulation of the time evolution of the system indeed suggests that the observed anomalous behavior can be imputable to quantum coherence effects. The interplay among all these mechanisms has a practical implication for quantum computing purposes, giving a direct measurement of the limits on the sweeping rates possible for a correct manipulation of the qubit state by means of fast flux pulses, avoiding transitions to non-computational states.

cond-mat.supr-con↗

arXiv2013

Artificial Neural Network based on SQUIDs: demonstration of network training and operation

We propose a scheme for the realization of artificial neural networks based on Superconducting Quantum Interference Devices (SQUIDs). In order to demonstrate the operation of this scheme we designed and successfully tested a small network that implements a XOR gate and is trained by means of examples. The proposed scheme can be particularly convenient as support for superconducting applications such as detectors for astrophysics, high energy experiments, medicine imaging and so on.

cond-mat.supr-con↗

arXiv2013

Characterization of Anomalous Pair Currents in Josephson Junction Networks

Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependencies of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of a theoretical model which predicts, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network.

cond-mat.supr-con↗

arXiv2013

The Hot and Energetic Universe: The X-ray Integral Field Unit (X-IFU) for Athena+

The Athena+ mission concept is designed to implement the Hot and Energetic Universe science theme submitted to the European Space Agency in response to the call for White Papers for the definition of the L2 and L3 missions of its science program. The Athena+ science payload consists of a large aperture high angular resolution X-ray optics and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), offering 2.5 eV spectral resolution, with ~5" pixels, over a field of view of 5 arc minutes in diameter. In this paper, we briefly describe the Athena+ mission concept and the X-IFU performance requirements. We then present the X-IFU detector and readout electronics principles, the current design of the focal plane assembly, the cooling chain and review the global architecture design. Finally, we describe the current performance estimates, in terms of effective area, particle background rejection, count rate capability and velocity measurements. Finally, we emphasize on the latest technology developments concerning TES array fabrication, spectral resolution and readout performance achieved to show that significant progresses are being accomplished towards the demanding X-IFU requirements.

astro-ph.IM↗

arXiv2011

Superconducting qubit manipulated by fast pulses: experimental observation of distinct decoherence regimes

A particular superconducting quantum interference device (SQUID)qubit, indicated as double SQUID qubit, can be manipulated by rapidly modifying its potential with the application of fast flux pulses. In this system we observe coherent oscillations exhibiting non-exponential decay, indicating a non trivial decoherence mechanism. Moreover, by tuning the qubit in different conditions (different oscillation frequencies) by changing the pulse height, we observe a crossover between two distinct decoherence regimes and the existence of an "optimal" point where the qubit is only weakly sensitive to intrinsic noise. We find that this behaviour is in agreement with a model considering the decoherence caused essentially by low frequency noise contributions, and discuss the experimental results and possible issues.

cond-mat.supr-con↗

arXiv2009

Catastrophe observation in a Josephson junction system

We report on a direct quantitative comparison between Thom's general catastrophe theory for systems presenting discontinuous behavior and experimental reality. It is demonstrated that the model provides a striking quantitative description of the measured experimental features of the complex nonlinear system generating the most appealing class of sensors and devices nowadays used in experiments, namely the Superconducting Quantum Interference Devices (SQUIDs). The parameter space of the SQUID system that we investigate displays all the features associated with a butterfly catastrophe, namely a catastrophe expected for a system having four control parameters and one state variable.

cond-mat.supr-con↗

arXiv2008

Coherent Activation of Zero-Field Fiske Modes in Arrays of Josephson Junctions

Series arrays of Josephson junctions show evidence of a mode in which all the junctions oscillate in synchronism on voltage resonances appearing, in zero external magnetic field, at multiples of the fundamental Fiske step spacing. The measurements show that the current amplitude of the resonances increases linearly as their voltages are summed. Investigation of the nature of the coherent mode by magnetic field responses of arrays and isolated juctions reveals that the oscillations take place in a parameter plane region where dc magnetic fields only activate boundary current and flux-quanta dynamics can take place.

cond-mat.supr-con↗

arXiv2008

Coherent oscillations in a superconducting tunable flux qubit manipulated without microwaves

We experimentally demonstrate the coherent oscillations of a tunable superconducting flux qubit by manipulating its energy potential with a nanosecond-long pulse of magnetic flux. The occupation probabilities of two persistent current states oscillate at a frequency ranging from 6 GHz to 21 GHz, tunable via the amplitude of the flux pulse. The demonstrated operation mode allows to realize quantum gates which take less than 100 ps time and are thus much faster compared to other superconducting qubits. An other advantage of this type of qubit is its insensitivity to both thermal and magnetic field fluctuations.

cond-mat.supr-con↗

arXiv2008

An Optimal Tunable Josephson Element for Quantum Computing

We introduce a three-junction SQUID that can be effectively used as an optimal tunable element in Josephson quantum computing applications. This device can replace the simple dc SQUID generally used as tunable element in this kind of applications, with a series of advantages for the coherence time and for the tolerance to small errors. We study the device both theoretically and experimentally at 4.2 K, obtaining a good agreement between the results.

quant-ph↗

arXiv2007

All-sky incoherent search for periodic signals with Explorer 2005 data

The data collected during 2005 by the resonant bar Explorer are divided into segments and incoherently summed in order to perform an all-sky search for periodic gravitational wave signals. The parameter space of the search spanned about 40 Hz in frequency, over 23927 positions in the sky. Neither source orbital corrections nor spindown parameters have been included, with the result that the search was sensible to isolated neutron stars with a frequency drift less than 6 X 10^{-11} Hz/s. No gravitational wave candidates have been found by means of the present analysis, which led to a best upper limit of 3.1 X 10^{-23} for the dimensionless strain amplitude.

gr-qc↗

arXiv2005

Cumulative analysis of the association between the gravitational wave detectors NAUTILUS and EXPLORER and the gamma-ray bursts detected by BATSE and BeppoSAX

The statistical association between the output of the Gravitational Wave (GW) detectors EXPLORER and NAUTILUS and a list of Gamma Ray Bursts (GRBs) detected by the satellite experiments BATSE and BeppoSAX has been analyzed using cumulative algorithms. GW detector data collected between 1991 and 1999 have been correlated to the GRB flux peak times. The cumulative analysis of a large number of GRBs (387) allows to push the upper bound for the corresponding GW burst amplitude down to $h = 2.5\cdot10^{-19}$.

astro-ph↗

arXiv2004

Anomalous thermal escape in Josephson systems perturbed by microwaves

We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multi-valued temperature ranges both below and above the the classical to quantum crossover temperature. Switching current distributions are obtained both experimentally and numerically at temperatures both near and far above the quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with a simple anharmonic theory for Josephson resonance frequency as a function of bias current. Throughout, experimental results and direct numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement.

cond-mat.stat-mech↗