Qubit arrays with access to high-fidelity single-and two-qubit gates are a key ingredient for building a quantum computer. As semiconductor-based devices with several qubits become available, issues like residual interqubit coupling and additional constraints from scalable control hardware need to be tackled to retain the high gate fidelities demonstrated in single-qubit devices. Focusing on two exchange-coupled singlet-triplet spin qubits, we address these issues by considering realistic control hardware as well as Coulomb and interqubit exchange coupling that cannot be fully turned off. We use measured noise spectra for charge and magnetic field noise to numerically optimize experimentally realistic pulse sequences and show that two-qubit (single-qubit) gate fidelities of 99.90% (≥ 99.69%) can be reached in GaAs, while 99.99% (≥ 99.95%) can be achieved with vanishing magnetic field noise as in Si.

While spin qubits based on gate-defined quantum dots have demonstrated very favorable properties for quantum computing, one remaining hurdle is the need to tune each of them into a good operating regime by adjusting the voltages applied to electrostatic gates. The automation of these tuning procedures is a necessary requirement for the operation of a quantum processor based on gate-defined quantum dots, which is yet to be fully addressed. We present an algorithm for the automated fine-tuning of quantum dots, and demonstrate its performance on a semiconductor singlet-triplet qubit in GaAs. The algorithm employs a Kalman filter based on Bayesian statistics to estimate the gradients of the target parameters as function of gate voltages, thus learning the system response. The algorithm's design is focused on the reduction of the number of required measurements. We experimentally demonstrate the ability to change the operation regime of the qubit within 3 to 5 iterations, corresponding to 10 to 15 minutes of lab-time.

The precise and automated calibration of quantum gates is a key requirement for building a reliable quantum computer. Unlike errors from decoherence, systematic errors can in principle be completely removed by tuning experimental parameters. Here, we present an iterative calibration routine which can remove systematic gate errors on several qubits. A central ingredient is the construction of pulse sequences that extract independent indicators for every linearly independent error generator. We show that decoherence errors only moderately degrade the achievable infidelity due to systematic errors. Furthermore, we investigate the convergence properties of our approach by performing simulations for a specific qubit encoded in a pair of spins. Our results indicate that a gate set with 230 gate parameters can be calibrated in about ten iterations, after which incoherent errors limit the gate fidelity.

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Zusammenfassung: Untersuchung an insgesamt 18 Desinfektionsmitteln zur Überprüfung der Frage, ob die in den offiziellen Desinfektionsmittellisten für die Wäschedesinfektion empfohlenen Konzentrationen und Anwendungszeiten auch für Strümpfe, Feingewebe und Leder, die mit Dermatophyten infiziert wurden, benutzt werden können. Diese Frage kann aufgrund der vorgelegten Ergebnisse bejaht werden. Allerdings lassen unterschiedliche Desinfektionsmittel unterschiedlich große Sicherheitszonen in den empfohlenen Konzentrationen und Anwendungszeiten erkennen. Summary: 18 disinfectants were tested against Trichophyton rubrum und other dermatophytes using a modified germ carrier method. Samples of different synthetic and mixed fabrics as well as leather samples were contaminated experimentally over a period of 2 to 3 weeks. The results showed that the recommended exposure times and concentrations as given in the official lists of chemical disinfectants for the disinfection of cotton cloth can also be used for disinfection of stocking fabrics or leather. There is, however, some variation between the different products with regard to margins of safety in the recommended exposure times or concentrations.

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