We analyze the effect of circuit parameter variation on the performance of Josephson traveling-wave parametric amplifiers (JTWPAs). Specifically, the JTWPA concept we investigate is using flux-biased ...nonhysteretic rf-SQUIDs in a transmission line configuration, which harnesses the three-wave mixing (3WM) regime. Dispersion engineering enables phase-matching to achieve power gain of <inline-formula><tex-math notation="LaTeX">\sim</tex-math></inline-formula>20 dB, while suppressing the generation of unwanted mixing processes. Two dispersion engineering concepts using a 3WM-JTWPA circuit model, i.e., resonant phase-matching (RPM) and periodic capacitance modulation (PCM), are discussed, with results potentially also applicable to four-wave-mixing (4WM) JTWPAs. We propose suitable circuit parameter sets and evaluate amplifier performance with and without circuit parameter variance using transient circuit simulations. This approach inherently takes into account microwave reflections, unwanted mixing products, imperfect phase-matching, pump depletion, etc. In the case of RPM the resonance frequency spread is critical, while PCM is much less sensitive to parameter spread. We discuss degrees of freedom to make the JTWPA circuits more tolerant to parameter spread. Finally, our analysis shows that the flux-bias point where rf-SQUIDs exhibit Kerr-free nonlinearity is close to the sweet spot regarding critical current spread.
High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metal-oxide-semiconductor logic. The ...remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to hold a magnetic flux quantum Φ0. Inserting a π-type Josephson junction in the cell is equivalent to applying flux Φ0/2 and thus makes it possible to solve this problem. Moreover, using π-junctions in superconducting qubits may help to protect them from noise. Here we demonstrate the operation of three superconducting circuits-two of them are classical and one quantum-that all utilize such π-phase shifters realized using superconductor/ferromagnet/superconductor sandwich technology. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a π-biased phase qubit, for which we observe coherent Rabi oscillations. We find no degradation of the measured coherence time compared to that of a reference qubit without a π-junction.
Motivated by the realization of bifurcation regimes of operation, we report on experiments with superconducting microwave resonators comprising short serial arrays of Nb/AlOx/Nb SIS Josephson ...junctions and low-inductance SQUIDs. These elements provide sufficiently large Josephson inductance LJ ∝ N (N is the number of elements in the chain) enabling nonlinear dynamics of the circuits and detection of low power signals.
The roadmap gives an overview on status and future developments in Superconducting Digital Electronics (SDE). Key areas in SDE under focus are applications, circuit simulation and design, circuit ...fabrication, interfacing and testing, cooling and system aspects, and new devices and materials. Care was taken to establish the vital link between research and development on the one hand and the industrial view on the other hand. The present roadmap is based on extensive input from the roadmap working group on SDE established by
SCENET – the European Network for Superconductivity, intensified by the activities of the
FLUXONICS Network – the European Foundry for Superconducting Electronics. It is the result of many years of discussion in the group and of consultations with experts in the field, on the way to bring together industrial expectations and visionary extrapolation and current status of technology.
We investigate the current–voltage characteristics of high-transparency superconductor–insulator–normal metal (SIN) junctions with the specific tunnel resistance ρ≲30Ωμm2. The junctions were ...fabricated from different superconducting and normal conducting materials, including Nb, Al, AuPd and Cu. The subgap leakage currents were found to be appreciably larger than those given by the standard tunnelling model. We explain our results using the model of two-electron tunnelling in the coherent diffusive transport regime. We demonstrate that even in the high-transparency SIN-junctions, a noticeable reduction of the subgap current can be achieved by splitting a junction into several submicron sub-junctions. These structures can be used as nonlinear low-noise shunts in rapid-single-flux-quantum (RSFQ) circuitry for controlling Josephson qubits.
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