F. Tafuri

Modeling flux tunability in Josephson Traveling Wave Parametric Amplifiers with an open-source frequency-domain simulator

  1. A. Levochkina,
  2. I. Chatterjee,
  3. P. Darvehi,
  4. H. G. Ahmad,
  5. P. Mastrovito,
  6. D. Massarotti,
  7. D. Montemurro,
  8. F. Tafuri,
  9. G.P. Pepe,
  10. Kevin P. O'Brien,
  11. and M. Esposito
Josephson Traveling Wave Parametric Amplifiers (JTWPAs) are integral parts of many experiments carried out in quantum technologies. Being composed of hundreds of Josephson junction-based
unit cells, such devices exhibit complex nonlinear behavior that typically cannot be fully explained with simple analytical models, thus necessitating the use of numerical simulators. A very useful characteristic of JTWPAs is the possibility of being biased by an external magnetic flux, allowing insitu control of the nonlinearity. It is therefore very desirable for numerical simulators to support this feature. Open-source numerical tools that allow to model JTWPA flux biasing, such as WRSPICE or PSCAN2, are based on time-domain approaches,which typically require long simulation times to get accurate results. In this work, we model the gain performance in a prototypical flux-tunable JTWPA by using JosephsonCircuits.jl,a recently developed frequency-domain open-source numerical simulator, which has the benefit of simulation times about 10,000 faster than time-domain methods. By comparing the numerical and experimental results, we validate this approach for modeling the flux dependent behavior of JTWPAs.
arxiv pdf

Investigating pump harmonics generation in a SNAIL-based Traveling Wave Parametric Amplifier

  1. A. Yu. Levochkina,
  2. H. G. Ahmad,
  3. P. Mastrovito,
  4. I. Chantarjee,
  5. G.Serpico,
  6. L. Di Palma,
  7. R. Ferroiuolo,
  8. R. Satariano,
  9. P. Darvehi,
  10. A. Ranadive,
  11. G. Cappelli,
  12. G. Le Gal,
  13. L. Planat,
  14. D. Montemurro,
  15. D. Massarotti,
  16. F. Tafuri,
  17. N. Roch,
  18. G.P. Pepe,
  19. and M. Esposito
Traveling Wave Parametric Amplifiers (TWPAs) are extensively employed in experiments involving weak microwave signals for their highly desirable quantum-limited and broadband characteristics.
However, TWPAs‘ broadband nature comes with the disadvantage of admitting the activation of spurious nonlinear processes, such as harmonics generation, that can potentially degrade amplification performance. Here we experimentally investigate a Josephson TWPA device with SNAIL (Superconducting Nonlinear Asymmetric Inductive Element)-based unit cells focusing on the amplification behaviour along with the generation of second and third harmonics of the pump. By comparing experimental results with transient numerical simulations, we demonstrate the influence of Josephson junctions‘ fabrication imperfections on the occurrence of harmonics and on the gain behaviour.
arxiv pdf

Numerical simulations of Josephson Traveling Wave Parametric Amplifiers (JTWPAs): comparative study of open-source tools

  1. A. Yu. Levochkina,
  2. H. G. Ahmad,
  3. P. Mastrovito,
  4. I. Chatterjee,
  5. D. Massarotti,
  6. D. Montemurro,
  7. F. Tafuri,
  8. G.P. Pepe,
  9. and M. Esposito
Josephson Traveling Wave Parametric Amplifiers (JTWPAs) are largely exploited in quantum technologies for their broadband and low noise performance in the microwave regime. When one
or more microwave tones are applied at the input, such devices show a complex wave-mixing response due to their intrinsic nonlinear nature. Numerical simulations of the JTWPAs nonlinear behaviour provide useful insights not only for the design of such devices, but also for the interpretation and validation of the experimental results. Here we present and discuss a comparative analysis of different open-source tools which can be used for JTWPAs numerical simulations. We focus on two tools for transient simulations, WRSPICE and PSCAN2, and on one tool for direct simulation of the frequency domain behaviour, JosephsonCircuit.jl. We describe the working principle of these three tools and test them considering as a benchmark a JTWPA based on SNAILs (Superconducting Nonlinear Asymmetric Inductive eLement) with realistic experimental parameters. Our results can serve as a guide for numerical simulations of JTWPAs with open-source tools, highlighting advantages and disadvantages depending on the simulation tasks.
arxiv pdf