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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.

A first search for rare decays of gadolinium isotopes was performed with an ultra-low background high-purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 198 g$$\\hbox {Gd}_2$$Gd 2$$\\hbox {O}_3$$O 3 powder sample was measured for 63.8 d with a total Gd exposure of 12.6 kg$$\\times $$× d.$$^{152}$$152 Gd is the most promising isotope for resonant enhanced neutrinoless double electron capture which could significantly increase the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to$$>4.2\\times 10^{12}$$> 4.2 × 10 12  year (90% credibility). This limit is still orders of magnitude away from theoretical predictions but it is the first established limit on the transition paving the way for future experiments. In addition, other rare alpha and double beta decay modes were investigated in$$^{152}$$152 Gd,$$^{154}$$154 Gd, and$$^{160}$$160 Gd with half-life limits in the range of$$10^{17-20}$$10 17 - 20 year.

A first search for rare decays of gadolinium isotopes was performed with an ultra-low background high-purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 198 g Gd 2 O 3 powder sample was measured for 63.8 d with a total Gd exposure of 12.6 kg × d. 152 Gd is the most promising isotope for resonant enhanced neutrinoless double electron capture which could significantly increase the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to > 4.2 × 10 12  year (90% credibility). This limit is still orders of magnitude away from theoretical predictions but it is the first established limit on the transition paving the way for future experiments. In addition, other rare alpha and double beta decay modes were investigated in 152 Gd, 154 Gd, and 160 Gd with half-life limits in the range of 10 17 - 20 year.

We report on the development and construction of the high-purity germanium spectrometer setup GIOVE (Germanium Inner Outer VEto), recently built and now operated at the shallow underground laboratory of the Max-Planck-Institut für Kernphysik, Heidelberg. Particular attention was paid to the design of a novel passive and active shield, aiming at efficient rejection of environmental and muon induced radiation backgrounds. The achieved sensitivity level of ≤ 100 μ Bq kg - 1 for primordial radionuclides from U and Th in typical γ ray sample screening measurements is unique among instruments located at comparably shallow depths and can compete with instruments at far deeper underground sites.

A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra low-background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb2(C2O4)3 powder sample was measured for 11.3 days with a total Yb exposure of 1.25 kg×day. Half-life limits for α-decay modes of 168Yb, 170Yb, 171Yb, 172Yb, 173Yb, 174Yb and 176Yb into the first excited states have been obtained between 6×1014 years and 2×1016 years. These are the first experimental constraints of these decay modes. Double electron capture of 168Yb and double beta decay of 176Yb into the first excited 2+ and 0+ states could be excluded with limits between 1×1014 years to 8×1016 years. This improves the experimental information on some of the decay modes compared to previous constraints.

Gadolinium is widely used in multiple low-background experiments, making its isotopes accessible for rare decay searches both in-situ and through radiopurity screening data. This study presents an improved search for rare alpha and double-beta decay modes in 152 Gd , 154 Gd , and 160 Gd isotopes using ultra-low background HPGe detectors at the Boulby Underground Screening (BUGS) facility. A total exposure of 6.7  kg · years of natural gadolinium was achieved using gadolinium sulfate octahydrate ( Gd 2 ( SO 4 ) 3 · 8 H 2 O ) samples, originally screened for radiopurity prior to their deployment in the Super-Kamiokande neutrino experiment. Due to the detection methodology, only decays into excited states accompanied by gamma-ray emission were accessible. A Bayesian analysis incorporating prior experimental results was employed, leading to new lower half-life limits in the range of 10 19 - 10 21 years - an improvement of approximately two orders of magnitude over previous constraints. No statistically significant decay signals were observed. These results demonstrate the effectiveness of repurposing large-scale radiopurity screening campaigns for fundamental physics research.

A 510 day long-term measurement of a 45.3 g platinum foil acting as the sample and high voltage contact in an ultra-low-background high purity germanium detector was performed at Laboratori Nazionali del Gran Sasso (Italy). The data was used for a detailed study of double beta decay modes in natural platinum isotopes. Limits are set in the range O ( 10 14 - 10 19 )  years (90% C.L.) for several double beta decay transitions to excited states confirming, and partially extending existing limits. The highest sensitivity of the measurement, greater than 10 19  years, was achieved for the two neutrino and neutrinoless double beta decay modes of the isotope 198 Pt. Additionally, novel limits for inelastic dark matter scattering on 195 Pt are placed up to mass splittings of approximately 500 keV. We analyze several techniques to extend the sensitivity and propose a few approaches for future medium-scale experiments with platinum-group elements.

The Gerda collaboration is performing a sensitive search for neutrinoless double beta decay of 76Ge at the INFN Laboratori Nazionali del Gran Sasso, Italy. The upgrade of the Gerda experiment from Phase I to Phase II has been concluded in December 2015. The first Phase II data release shows that the goal to suppress the background by one order of magnitude compared to Phase I has been achieved. Gerda is thus the first experiment that will remain “background-free” up to its design exposure (100 kgyear). It will reach thereby a half-life sensitivity of more than 1026 year within 3 years of data collection. This paper describes in detail the modifications and improvements of the experimental setup for Phase II and discusses the performance of individual detector components.

[Formula omitted] is the longest-lived metastable state presently known. Its decay has not been observed yet. In this work, we report a new result on the decay of [Formula omitted] obtained with a 2015.12-g tantalum sample measured for 527.7 d with an ultra-low background HPGe detector in the STELLA laboratory of the Laboratori Nazionali del Gran Sasso (LNGS), in Italy. Before the measurement, the sample has been stored deep-underground for ten years, resulting in subdominant background contributions from cosmogenically activated [Formula omitted]. We observe no signal in the regions of interest and set half-life limits on the process for the two channels EC and [Formula omitted]: [Formula omitted] year and [Formula omitted] year (90% C. I.), respectively. We also set the limit on the [Formula omitted] de-excitation / IC channel: [Formula omitted] year (90% C. I.). These are, as of now, the most stringent bounds on the decay of [Formula omitted] worldwide. Finally, we test the hypothetical scenarios of de-excitation of [Formula omitted] by cosmological Dark Matter and constrain new parameter space for strongly-interacting dark-matter particle with mass up to [Formula omitted] GeV.

As one of the primordial radioactive isotopes, [Formula omitted] mainly undergoes [Formula omitted]-decay with a half-life of [Formula omitted] years. However, it is also one of 35 double beta decay candidates in which the single [Formula omitted]-decay is forbidden or strongly suppressed. 181 mg of thorium contained in a gas mantle were measured in a HPGe well-detector at the Gran Sasso Underground Laboratory with a total exposure of 3.25 g [Formula omitted]d.