Performance of high impedance resonators in dirty dielectric environments

High-impedance resonators are a promising contender for realizing long-distance entangling gates between spin qubits. Often, the fabrication of spin qubits relies on the use of gate dielectrics which are detrimental to the quality of the resonator. Here, we investigate loss mechanisms of high-impedance NbTiN resonators in the vicinity of thermally grown SiO2 and Al2O3 fabricated by atomic layer deposition. We benchmark the resonator performance in elevated magnetic fields and at elevated temperatures and find that the internal quality factors are limited by the coupling between the resonator and two-level systems of the employed oxides. Nonetheless, the internal quality factors of high-impedance resonators exceed 103 in all investigated oxide configurations which implies that the dielectric configuration would not limit the performance of resonators integrated in a spin-qubit device. Because these oxides are commonly used for spin qubit device fabrication, our results allow for straightforward integration of high-impedance resonators into spin-based quantum processors. Hence, these experiments pave the way for large-scale, spin-based quantum computers

Phase-dependent microwave response of a graphene Josephson junction

Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing a radio frequency SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss, and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we estimate lifetimes on the order of ∼10 ps for nonequilibrium populations

Phase-dependent microwave response of a graphene Josephson junction

Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in-situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing an rf SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we deduce a lifetime of ~17 ps for non-equilibrium populations

Bescherming gegeven? Evaluatie UAVG, meldplicht datalekken en de boetebe- voegdheid

De overkoepelende vraag die in het onderzoek centraal staat luidt als volgt: Hoe werden in de periode 2018 - 2020 de normen van de Uitvoeringswet Algemene Verordening Gegevensbescherming (UAVG) nageleefd en in hoeverre heeft de UAVG bijgedragen aan een doelmatige en doeltreffende uitvoering en handhaving van de Algemene Verordening Gegevensbescherming (AVG)? Het onderzoek is uitgevoerd langs de lijnen van de volgende zestiental onderzoeksvragen: Hoe beoordelen juristen, de Autoriteit Persoonsgegevens (AP) en verwerkers van persoonsgegevens de duidelijkheid en toegankelijkheid van de UAVG? In hoeverre worden de normen van de UAVG verduidelijkt door de AP en de jurisprudentie? Welke informatie wordt op welk moment aan de verschillende doelgroepen gegeven en op welke manier? Wat is de rol van de AP hierbij? Hoe beoordelen juristen, de AP en verwerkers van persoonsgegevens de uitvoerbaarheid van de UAVG? Hoe beoordelen juristen, de AP en verwerkers van persoonsgegevens de handhaafbaarheid van de UAVG? Hoe leven verwerkers van persoonsgegevens de bepalingen van de UAVG na? In welke mate wordt de meldplicht datalekken nageleefd door verwerkers van persoonsgegevens? Wat is de rol van de Functionaris voor Gegevensbescherming binnen organisaties, onder meer bij de naleving van de meldplicht? In hoeverre heeft de jurisprudentie preventieve werking voor de naleving van de bepalingen van de UAVG en de meldplicht datalekken en hoe zou deze kunnen worden vergroot? Hoe ziet de toezichtstrategie van de AP er uit? Hoe luidt het handhavingsbeleid van de AP? Op welke wijze vinden toezicht en handhaving door de AP in de praktijk plaats? Hoe worden bij het uitoefenen van de boetebevoegdheid door de AP de ernst van de normschending, de mate van verwijtbaarheid en een passende wijze van optreden bepaald? In hoeverre draagt de boetebevoegdheid en het toepassen daarvan door de AP bij aan een doelmatige en doeltreffende uitvoering en handhaving van de AVG? Is er aanleiding tot een wijziging van de toepassing van de bevoegdheden door de AP en zo ja, in welk opzicht? Hoe beoordelen juristen, de AP en verwerkers van persoonsgegevens de mate waarin de UAVG de ruimte heeft benut die de AVG laat voor nationale keuzes bij de uitvoering van de AVG? INHOUD: 1. Inleiding, 2. Juridisch kader, 3. Jurisprudentieonderzoek, 4. Vragenlijstonderzoek en interviews: FG’s aan het woord, 5. De meldplicht datalekken en de bestuurlijke boete in de praktijk, 6. Het functioneren van de UAVG, 7. Conclusies en aanbevelingen

Trajectories for the Wave Function of the Universe from a Simple Detector Model

Inspired by Mott's (1929) analysis of particle tracks in a cloud chamber, we consider a simple model for quantum cosmology which includes, in the total Hamiltonian, model detectors registering whether or not the system, at any stage in its entire history, passes through a series of regions in configuration space. We thus derive a variety of well-defined formulas for the probabilities for trajectories associated with the solutions to the Wheeler-DeWitt equation. The probability distribution is peaked about classical trajectories in configuration space. The ``measured'' wave functions still satisfy the Wheeler-DeWitt equation, except for small corrections due to the disturbance of the measuring device. With modified boundary conditions, the measurement amplitudes essentially agree with an earlier result of Hartle derived on rather different grounds. In the special case where the system is a collection of harmonic oscillators, the interpretation of the results is aided by the introduction of ``timeless'' coherent states -- eigenstates of the Hamiltonian which are concentrated about entire classical trajectories.Comment: 37 pages, plain Tex. Second draft. Substantial revision