Search

Radioactivity was recently discovered as a source of decoherence and correlated errors for the real-world implementation of superconducting quantum processors. In this work, we measure levels of radioactivity present in a typical laboratory environment (from muons, neutrons, and γ -rays emitted by naturally occurring radioactive isotopes) and in the most commonly used materials for the assembly and operation of state-of-the-art superconducting qubits. We present a GEANT-4 based simulation to predict the rate of impacts and the amount of energy released in a qubit chip from each of the mentioned sources. We finally propose mitigation strategies for the operation of next-generation qubits in a radio-pure environment. [ABSTRACT FROM AUTHOR]

The response of particle detectors to different types of radiation is not necessarily identical and, in some cases, neglecting this behavior can lead to a misinterpretation of the acquired data. While commercial radioactive sources are in general suitable to investigate the response to β 's and γ 's, in the case of α 's the need for custom-made sources arises from the intrinsic properties of α radiation, which imposes that the emitter directly faces the detector. In this work, we show how to flexibly produce α sources to be employed in multiple studies of detector characterization. These are obtained starting from a set of primary sources obtained from the collection of radioactive 228 Ra ions at the ISOLDE facility at CERN. We illustrate the potential of this technique with practical cases of application to scintillators and bolometric detectors and examples of the results obtained so far. [ABSTRACT FROM AUTHOR]

RES-NOVA is a newly proposed experiment for detecting neutrinos from astrophysical sources, mainly Supernovae, using an array of cryogenic detectors made of PbWO 4 crystals produced from archaeological Pb. This unconventional material, characterized by intrinsic high radiopurity, enables low-background levels in the region of interest for the neutrino detection via Coherent Elastic neutrino-Nucleus Scattering (CE ν NS). This signal lies at the detector energy threshold, O(1 keV), and it is expected to be hidden by naturally occurring radioactive contaminants of the crystal absorber. Here, we present the results of a radiopurity assay on a 0.84 kg PbWO 4 crystal produced from archaeological Pb operated as a cryogenic detector. The crystal internal radioactive contaminations are: 232 Th <40 μ Bq/kg, 238 U <30 μ Bq/kg, 226 Ra 1.3 mBq/kg and 210 Pb 22.5 mBq/kg. We also present a background projection for the final experiment and possible mitigation strategies for further background suppression. The achieved results demonstrate the feasibility of realizing this new class of detectors. [ABSTRACT FROM AUTHOR]

As quantum coherence times of superconducting circuits have increased from nanoseconds to hundreds of microseconds, they are currently one of the leading platforms for quantum information processing. However, coherence needs to further improve by orders of magnitude to reduce the prohibitive hardware overhead of current error correction schemes. Reaching this goal hinges on reducing the density of broken Cooper pairs, so-called quasiparticles. Here, we show that environmental radioactivity is a significant source of nonequilibrium quasiparticles. Moreover, ionizing radiation introduces time-correlated quasiparticle bursts in resonators on the same chip, further complicating quantum error correction. Operating in a deep-underground lead-shielded cryostat decreases the quasiparticle burst rate by a factor thirty and reduces dissipation up to a factor four, showcasing the importance of radiation abatement in future solid-state quantum hardware. Background radiation has been identified as a key factor limiting the coherence times of superconducting circuits. Here, the authors measure the impact of environmental and cosmic radiation on a superconducting resonator with varying degrees of shielding, including an underground facility. [ABSTRACT FROM AUTHOR]

Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators. We present a prototype scintillator fabricated by embedding MOF nanocrystals in a polymer. The MOF comprises zirconium oxo-hydroxy clusters, high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from 9,10-diphenylanthracene ligand emitters. Their incorporation in the framework enables fast sensitization of the ligand fluorescence, thus avoiding issues typically arising from the intimate mixing of complementary elements. This proof-of-concept prototype device shows an ultrafast scintillation rise time of ~50 ps, thus supporting the development of new scintillators based on engineered fluorescent MOF nanocrystals. Composites of fluorescent metal–organic framework nanocrystals in a polymer are exploited to create fast scintillators with a rise time of about 50 ps. [ABSTRACT FROM AUTHOR]

When simulating the response of a particle detector to an energy deposition, the pulse shape and the electronic noise are important features to be taken into account. In this work, we present a method to simulate a continuous stream of detector-like data, produced to mock the salient characteristics of the chosen setup. This technique allows the full reproduction of an experimental measurement, as well as providing a predictive tool to validate or train new analysis procedures. We present the algorithm used to produce these data, and we test its capabilities by reproducing the data output of an high-purity germanium detector. [ABSTRACT FROM AUTHOR]

Non-equilibrium quasiparticles can deteriorate the performance of superconducting qubits by reducing their coherence. We are investigating a source of quasiparticles that has been too long neglected, namely radioactivity: cosmic rays, environmental radioactivity and contaminants in the materials can all generate phonons of energy sufficient to break Cooper pairs and thus increase the number of quasiparticles. In this contribution, we describe the status of the project and its perspectives. [ABSTRACT FROM AUTHOR]

The Cryogenic Observatory for SIgnals seen in Next-generation Underground Searches (COSINUS) project aims to provide a model-independent cross-check of the long-standing DAMA/LIBRA claim on the observation of dark matter by using the same target material, but in a different experimental approach. Operating sodium iodide (NaI) scintillating crystals as low-temperature scintillating calorimeters has the distinct advantage of providing a lower energy threshold for nuclear recoil events as expected from dark matter particle interactions combined with particle discrimination. The dual readout of phonon and light allows us to provide background rejection on an event-by-event basis, a unique feature in comparison with other NaI-based dark matter searches. The manuscript discusses in detail the COSINUS detector concept and presents the results and performance parameters from our second prototype detector. [ABSTRACT FROM AUTHOR]

In the view of exploring the inverted hierarchy region future experiments investigating the neutrinoless double beta decay have to demand for detectors with excellent energy resolution and zero background in the energy region of interest. Cryogenic scintillating bolometers are very suitable detectors for this task since they provide particle discrimination: the simultaneous detection of the phonon and light signal allows us to identify the interacting type of particle and thus guarantees a suppression of $$\alpha $$ -induced backgrounds, the key-issue for next-generation tonne-scale bolometric experiments. The LUCIFER project aims at running the first array of enriched scintillating Zn $$^{\text {82}}$$ Se bolometers (total mass of about 8kg of $$^{\text {82}}$$ Se) with a background level as low as 10 $$^{\text {--3}}$$ counts/(keV kg y) in the energy region of interest. The main effort is currently focused on the finalization of the crystal growth procedure in order to achieve high quality Zn $$^{\text {82}}$$ Se crystals both in terms of radiopurity and bolometric properties. We present results from tests of such crystals operated at mK temperatures which demonstrate the excellent background rejection capabilities of this detection approach towards a background-free demonstrator experiment. Besides, the high purity of the enriched $$^{\text {82}}$$ Se material allows us to establish the most stringent limits on the half-life of the double beta decay of $$^{\text {82}}$$ Se on excited levels. [ABSTRACT FROM AUTHOR]

We present the performances of a 330 g zinc molybdate (ZnMoO) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of Mo. The energy resolution, evaluated at the 2615 keV γ-line of Tl, is 6.3 keV FWHM. The internal radioactive contaminations of the ZnMoO were evaluated as <6 μBq/kg (Th) and 27±6 μBq/kg (Ra). We also present the results of the α vs β/ γ discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. [ABSTRACT FROM AUTHOR]

Bolometers are suitable detectors for fundamental physics experiments, like neutrinoless Double Beta Decay, because of their very good intrinsic characteristics (high detection efficiency, excellent energy resolution, ...). The bolometric technique has already obtained excellent results on the neutrino mass study with Cuoricino, the ancestor of CUORE, an array of 19 towers with 52 crystals each, which will achieve a sensitivity below 100meV. Cuoricino has also shown that the surface contaminations of materials facing the detectors would be the limiting factor for the sensitivity of next-generation experiments with bolometers. Mainly for this reason scintillating bolometers have been developed allowing a very efficient discrimination of alpha particles thanks to their double readout. Excellent results were obtained with different compounds such as CdWO , ZnSe and ZnMoO. Tests performed on these crystals showed the possibility to discriminate the interacting particles through a pulse shape analysis. This feature is very interesting because it allows to obtain the same (or even better) discrimination power achieved with the double readout but with a much easier and cheaper assembly. Finally, the sensitivity that could be achieved with a large mass array of scintillating bolometers is analyzed on the basis of the results obtained on background and energy resolution. [ABSTRACT FROM AUTHOR]

The design of CUORE (an array of 988 TeO bolometers working at ∼10 mK) was based on the information acquired with a 40.7 kg prototype, named Cuoricino, that allowed to obtain the present best limit on the half-life of 0 νDBD of Te. In addition to providing important information on the different sources of spurious counts that limit the sensitivity for rare event experiments, Cuoricino allowed to study in detail the underground operation of a large array of bolometers (detector stability, noise sources and their reduction, off-line amplitude correction, ...). Moreover, additional CUORE R&D tests, carried out after Cuoricino, have already brought considerable improvements on the detector such as a lower acquisition threshold, with the consequent possibility to study additional physics such as Dark Matter, a standardization of the assembly and a special wiring to reduce the microphonic noise. The results thus obtained allow to assert that CUORE will be the largest mass cryogenic experiment put into operation, with an excellent sensitivity for the study of rare events thanks to an expected extremely low radioactive background level of 0.01 counts/keV/kg/yr in the 0 νDBD region. [ABSTRACT FROM AUTHOR]

Among the detectors used for rare event searches, such as neutrinoless Double Beta Decay (0 νDBD) and Dark Matter experiments, bolometers are very promising because of their favorable properties (excellent energy resolution, high detector efficiency, a wide choice of different materials used as absorber, ...). However, up to now, the actual interesting possibility to identify the interacting particle, and thus to greatly reduce the background, can be fulfilled only with a double read-out (i.e. the simultaneous and independent read out of heat and scintillation light or heat and ionization). This double read-out could greatly complicate the assembly of a huge, multi-detector array, such as CUORE and EURECA. The possibility to recognize the interacting particle through the shape of the thermal pulse is then clearly a very interesting opportunity. While detailed analyses of the signal time development in purely thermal detectors have not produced so far interesting results, similar analyses on macro-bolometers (∼10-500 g) built with scintillating crystals showed that it is possible to distinguish between an electron or γ-ray and an α particle interaction (i.e. the main source of background for 0 νDBD experiments based on the bolometric technique). Results on pulse shape analysis of a CaMoO crystal operated as bolometer are reported as an example. An explanation of this behavior, based on the energy partition in the heat and scintillation channels, is also presented. [ABSTRACT FROM AUTHOR]

Large-mass bolometers are today extensively used for dark matter and double beta decay searches, in both cases the ultimate experimental sensitivity is defined by the background level reached in such devices. The most common background sources and the techniques used for their identification and reduction are here reviewed, with a particular focus on double beta decay searches. The relevant role played by Monte Carlo simulations in this field is discussed. As a real case, the background optimization in the MiDBD experiment is described. [ABSTRACT FROM AUTHOR]

The problem of background reduction in bolometers used to search for ββ(0ν) is reviewed with particular emphasis on bulk and surface radioactive contamination of the detectors. [ABSTRACT FROM AUTHOR]

CUPID-0 is the first large mass array of enriched Zn 82 Se scintillating low temperature calorimeters, operated at LNGS since 2017. During its first scientific runs, CUPID-0 collected an exposure of 9.95 kg year. Thanks to the excellent rejection of α particles, we attained the lowest background ever measured with thermal detectors in the energy region where we search for the signature of 82 Se neutrinoless double beta decay. In this work we develop a model to reconstruct the CUPID-0 background over the whole energy range of experimental data. We identify the background sources exploiting their distinctive signatures and we assess their extremely low contribution [down to ∼ 10 - 4 counts/(keV kg year)] in the region of interest for 82 Se neutrinoless double beta decay search. This result represents a crucial step towards the comprehension of the background in experiments based on scintillating calorimeters and in next generation projects such as CUPID. [ABSTRACT FROM AUTHOR]