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The cross-integration of spin-wave and superconducting technologies is a promising method for creating novel hybrid devices for future information processing technologies to store, manipulate, or convert data in both classical and quantum regimes. Hybrid magnon–polariton systems have been widely studied using bulk Yttrium Iron Garnet (Y3Fe5O12, YIG) and three-dimensional microwave photon cavities. However, limitations in YIG growth have, thus far, prevented its incorporation into CMOS compatible technologies, such as high-quality factor superconducting quantum technology. To overcome this impediment, we have used Plasma Focused Ion Beam (PFIB) technology—taking advantage of precision placement down to the micrometer scale—to integrate YIG with superconducting microwave devices. Ferromagnetic resonance has been measured at milliKelvin temperatures on PFIB-processed YIG samples using planar microwave circuits. Furthermore, we demonstrate strong coupling between superconducting resonators and YIG ferromagnetic resonance modes by maintaining reasonably low loss while reducing the system down to the micrometer scale. This achievement of strong coupling on-chip is a crucial step toward fabrication of functional hybrid quantum devices from spin-wave and superconducting components.

The phenomenon of dark counts in nanostripes of different superconductor systems such as high-temperature superconducting YBa 2 Cu 3 O 7-x and superconductor/ferromagnet hybrids consisting of either NbN/NiCu or YBa 2 Cu 3 O 7x /L 0.7 Sr 0.3 MnO 3 bilayers have been investigated. For NbN/NiCu the rate of dark-count transients have been reduced with respect to pure NbN nanostripes and the events were dominated by a single vortex entry from the edge of the stripe. In the case of nanostripes based on YBa 2 Cu 3 O 7-x , we have found that thermal activation of vortices was also, apparently, responsible for triggering dark-count signals.

One of the major challenges in the deployment of quantum communications (QC) over solid-core silica optical fiber is the performance degradation due to the optical noise generated with co-propagating classical optical signals. To reduce the impact of the optical noise, research teams are turning to new and novel architectures of solid-core and hollow-core optical fiber. We studied the impact when co-propagating a single-photon level (850 nm) and two classical optical signals (940 nm and 1550 nm) while utilizing a nested antiresonant nodeless fiber (NANF) with two low-loss windows. The 940 nm signal was shown to impact the single-photon measurement due to the silicon detector technology implemented; however, multiplexing techniques and filtering could reduce the impact. The 1550 nm signal was shown to have no detrimental impact. The results highlight that both high bandwidth optical traffic at 1550 nm and a QC channel at 850 nm could co-propagate without degradation to the QC channel.

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Nanostripes of hybrid superconductor/ferromagnetic (S/F) NbN/NiCu bilayers and pure superconducting NbN nanostripes have been investigated in dark count experiments. Presence of a ferromagnetic layer influences the superconducting properties of the S/F bilayer, such as the critical current density and the transient photoresponse. The observed significant decrease of the dark-count rate is discussed in terms of vortex-related fluctuation models to shed more light in the intriguing question of the basic mechanism responsible for dark counts in superconducting nanostripe single photon detectors

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