BUSCADOR RECOLECTA

Nuclear spins are candidates to encode qubits or qudits due to their isolation from magnetic noise and potentially long coherence times. However, their weak coupling to external stimuli makes them hard to integrate into circuit quantum electrodynamics architectures, the leading technology for solid-state quantum processors. Here, we study the coupling of 173Yb(III) nuclear spin states in an [Yb(trensal)] molecule to superconducting cavities. Experiments have been performed on magnetically dilute single crystals placed on the inductors of lumped-element LC superconducting resonators with characteristic frequencies spanning the range of nuclear and electronic spin transitions. We achieve a high cooperative coupling to all electronic and most nuclear [173Yb(trensal)] spin transitions, a necessary ingredient for the implementation of qudit protocols with molecular spins using a hybrid architecture., This work has been funded by the European Union Horizon 2020 research and innovation program through FET-OPEN grant FATMOLS-No 862893 and the QUANTERA project SUMO. It was also supported by the Spanish Ministry of Science and Innovation under grants RT2018-096075-B-C21, PCI2018-093116, PID2019-105552RB-C41 and C-44, PID2020- 115221GB-C41/AEI/10.13039/501100011033, and Grant SEV-2016-0686 (MCIU/AEI/FEDER, UE) and by Novo Nordisk Foundation grant NNF20OC0065610. The SUMO project was also co-funded by the Italian Ministry of University and Research. We also acknowledge financial support from the Gobierno de Aragón grant E09-17R-Q-MAD, from CSIC Research Platform PTI-001, and from ONR-Global through Grant DEFROST N62909-19-1-2053., Peer reviewed

We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented., SA and JM are supported by grants PID2019-108122GB-C32 and the Maria de Maeztu grant CEX-2019-000918-M of ICCUB. The work of UPCTand IFIC is supported by grant PID2019-108122GB-C33, funded by MCIN/AEI/10.13039/501100011033/ and by “ERDF A way of making Europe”. JMGB thanks the grant FPI BES-2017-079787, funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. The work of Universidad de Cantabria is supported by the Ministry of Science and Innovation under Grant PID2019-110610RB-C22. CAB and IMDEA-Nanoscience work is supported by grants PID2019-105552RB-C41 and PID2019-105552RB-C44 and by Comunidad de Madrid under Grant P2018/NMT-4291. IMDEA-Nanoscience acknowledges financial support from “Severo Ochoa” Programme for Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). D.G. and A.G also acknowledge Grant DEFROST N62909-19-1-2053 from ONR Global. RBB, FJC, BJK, EMG, JMS and PV thank the Spanish Agencia Estatal de Investigación (AEI, MICIU) for the support to the Unidad de Excelencia María de Maeztu Instituto de Física de Cantabria, ref. MDM-2017-0765. RBB, FJC, EMG and PV thank the Spanish Agencia Estatal de Investigación (AEI, MCI) for the funds received through the research project, ref. PID2019-110610RB-C21. RBB, FJC, BJK, EMG, JMS and PV also thank the ‘Dark Collaboration at IFCA’ working group for useful discussions. The work done by ANTERAL S.L. is supported by project QON-Space financed by the Navarra Government Project No. 0011-1365-2021-000220. UPNA acknowledges financial support from the Spanish State Research Agency, Project No. PID2019-109984RB-C43/AEI/10.13039/501100011033 and Project No. PID2020-112545RB-C53/MCIN/AEI/ 10.13039/501100011033., Peer reviewed

This article is an expanded version of the IEEE MTTS International Microwave Symposium (IMS 2023)., Lumped-element kinetic inductance detectors (LEKIDs) based on sawtooth inductors for W -band are presented in this article. A careful analysis is carried out for the cross-polarization in the inductor geometry, which brings out the absorption of the nondesired E -field component of an incident wave plane. The proposed inductor geometry with sawtooth sections demonstrates improved cross-polarization. The analytical results are verified by comparison with 3-D electromagnetic (EM) simulations. As the first proof of concept, W -band optical response is demonstrated through quasioptical characterization at room temperature of an aluminum LEKID array. Moreover, a LEKID array based on bilayer superconducting titanium/aluminum (Ti/Al) thin film is developed for evaluating the performance at millikelvin temperatures. Darkness characterization confirms the high-quality factor of the fabricated detectors and the low-frequency design reliability. In addition, cryogenic optical experiments are performed for spectroscopic and detector sensitivity characterization. The proposed geometry opens the possibility of developing large-format polarimetric cameras based on on-chip LEKID structures for future astronomical experiments., This work was supported in part by the Centro de Astrobiología and IMDEA-Nanociencia under Grant PID2019-105552RBC41 and Grant PID2019-105552RB-C44, in part by the Comunidad de Madrid under Grant P2018/NMT-4291 TEC2SPACE-CM, in part by the “Severo Ochoa” Programme for Centers of Excellence in Research and Development under Grant SEV-2016-0686, in part by the CSIC Research Platform under Grant PTI-001, and in part by the Comunidad de Madrid, the Recovery, Transformation and Resilience Plan from the Spanish State, and NextGenerationEU from the EU Recovery and Resilience Facility through the Project “Tecnologías avanzadas para la exploración del Universo y sus componentes” under Grant PR47/21 TAU-CM. The work of Universidad de Cantabria was supported by the Ministry of Science and Innovation under Grant PID2019 110610RB-C22. All groups were partially funded by the Research Network under Grant
RED2022-134839-T., Peer reviewed

Nuclear spins are candidates to encode qubits or qudits due to their isolation from magnetic noise and potentially long coherence times. However, their weak coupling to external stimuli makes them hard to integrate into circuit quantum electrodynamics architectures, the leading technology for solid-state quantum processors. Here, we study the coupling of 173Yb(III) nuclear spin states in an [Yb(trensal)] molecule to superconducting cavities. Experiments have been performed on magnetically dilute single crystals placed on the inductors of lumped-element LC superconducting resonators with characteristic frequencies spanning the range of nuclear and electronic spin transitions. We achieve a high cooperative coupling to all electronic and most nuclear [173Yb(trensal)] spin transitions, a necessary ingredient for the implementation of qudit protocols with molecular spins using a hybrid architecture.

A central goal in quantum technologies is to maximize GT<sub>2, where G stands for the coupling of a qubit to control and readout signals and T<sub>2 is the qubit’s coherence time. This is challenging, as increasing G (e.g., by coupling the qubit more strongly to external stimuli) often leads to deleterious effects on T<sub>2. Here, we study the coupling of pure and magnetically diluted crystals of Ho W<sub>10 magnetic clusters to microwave superconducting coplanar waveguides. Absorption lines give a broadband picture of the magnetic energy level scheme and, in particular, confirm the existence of level anticrossings at equidistant magnetic fields determined by the combination of crystal field and hyperfine interactions. Such “spin clock transitions” are known to shield the electronic spins against magnetic field fluctuations. The analysis of the microwave transmission shows that the spin-photon coupling also becomes maximum at these transitions. The results show that engineering spin-clock states of molecular systems offers a promising strategy to combine sizable spin-photon interactions with a sufficient isolation from unwanted magnetic noise sources.

Lumped-element kinetic inductance detectors (LEKIDs) based on sawtooth inductors for W -band are presented in this article. A careful analysis is carried out for the cross-polarization in the inductor geometry, which brings out the absorption of the nondesired E -field component of an incident wave plane. The proposed inductor geometry with sawtooth sections demonstrates improved cross-polarization. The analytical results are verified by comparison with 3-D electromagnetic (EM) simulations. As the first proof of concept, W -band optical response is demonstrated through quasioptical characterization at room temperature of an aluminum LEKID array. Moreover, a LEKID array based on bilayer superconducting titanium/aluminum (Ti/Al) thin film is developed for evaluating the performance at millikelvin temperatures. Darkness characterization confirms the high-quality factor of the fabricated detectors and the low-frequency design reliability. In addition, cryogenic optical experiments are performed for spectroscopic and detector sensitivity characterization. The proposed geometry opens the possibility of developing large-format polarimetric cameras based on on-chip LEKID structures for future astronomical experiments.

We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented., SA and JM are supported by
grants PID2019-108122GB-C32 and the Maria de Maeztu grant CEX-2019-000918-M of
ICCUB. The work of UPCT and IFIC is supported by grant PID2019-108122GB-C33, funded
by MCIN/AEI/10.13039/501100011033/ and by “ERDF A way of making Europe”. JMGB
thanks the grant FPI BES-2017-079787, funded by MCIN/AEI/10.13039/501100011033
and by “ESF Investing in your future”. The work of Universidad de Cantabria is supported by the Ministry of Science and Innovation under Grant PID2019-110610RB-C22.
CAB and IMDEA-Nanoscience work is supported by grants PID2019-105552RB-C41 and
PID2019-105552RB-C44 and by Comunidad de Madrid under Grant P2018/NMT-4291.
IMDEA-Nanoscience acknowledges financial support from “Severo Ochoa” Programme for
Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). D.G. and A.G also
acknowledge Grant DEFROST N62909-19-1-2053 from ONR Global. RBB, FJC, BJK,
EMG, JMS and PV thank the Spanish Agencia Estatal de Investigación (AEI, MICIU)
for the support to the Unidad de Excelencia María de Maeztu Instituto de Física de
Cantabria, ref. MDM-2017-0765. RBB, FJC, EMG and PV thank the Spanish Agencia
Estatal de Investigación (AEI, MCI) for the funds received through the research project,
ref. PID2019-110610RB-C21. RBB, FJC, BJK, EMG, JMS and PV also thank the ‘Dark
Collaboration at IFCA’ working group for useful discussions. The work done by ANTERAL
S.L. is supported by project QON-Space financed by the Navarra Government Project No.
0011-1365-2021-000220. UPNA acknowledges financial support from the Spanish State
Research Agency, Project No. PID2019-109984RB-C43/AEI/10.13039/501100011033 and
Project No. PID2020-112545RB-C53/MCIN/AEI/ 10.13039/501100011033.