Anna Levochkina

Three wave mixing vacuum squeezing generation in a SNAIL-based Traveling-Wave Parametric Amplifier with alternated flux polarity

  1. Isita Chatterjee,
  2. Pegah Darvehi,
  3. Antonio Orsi,
  4. Anna Levochkina,
  5. Pasquale Mastrovito,
  6. Gwenel Le Gal,
  7. Arpit Ranadive,
  8. Giulio Cappelli,
  9. Alberto Porzio,
  10. Francesco Tafuri,
  11. Davide Massarotti,
  12. and Martina Esposito
Recent demonstrations of squeezing generation using Traveling Wave Parametric Amplifiers (TWPAs) have opened the way for the application of broadband microwave squeezing in quantum
sensing, quantum-enhanced detection, and continuous-variable quantum information. Here we demonstrate vacuum squeezing generation via residual three-wave mixing (3WM) in a Josephson TWPA based on superconducting nonlinear asymmetric inductive elements (SNAILs) with alternated magnetic flux polarity. By investigating competition between four-wave mixing (4WM) and 3WM nonlinearities, we prove that vacuum squeezing generation via residual 3WM is possible when a careful choice of the operating flux point is adopted. Our study provides valuable insights on the impact of competing nonlinearities on TWPA squeezers, potentially extending the range of applications in the framework of microwave photonics.
arxiv pdf

Implementation and readout of maximally entangled two-qubit gates quantum circuits in a superconducting quantum processor

  1. Viviana Stasino,
  2. Pasquale Mastrovito,
  3. Carlo Cosenza,
  4. Anna Levochkina,
  5. Martina Esposito,
  6. Domenico Montemurro,
  7. Giovanni P. Pepe,
  8. Alessandro Bruno,
  9. Francesco Tafuri,
  10. Davide Massarotti,
  11. and Halima G. Ahmad
Besides noticeable challenges in implementing low-error single- and two-qubit quantum gates in superconducting quantum processors, the readout technique and analysis are a key factor
in determining the efficiency and performance of quantum processors. Being able to efficiently implement quantum algorithms involving entangling gates and asses their output is mandatory for quantum utility. In a transmon-based 5-qubit superconducting quantum processor, we compared the performance of quantum circuits involving an increasing level of complexity, from single-qubit circuits to maximally entangled Bell circuits. This comparison highlighted the importance of the readout analysis and helped us optimize the protocol for more advanced quantum algorithms. Here we report the results obtained from the analysis of the outputs of quantum circuits using two readout paradigms, referred to as „multiplied readout probabilities“ and „conditional readout probabilities“. The first method is suitable for single-qubit circuits, while the second is essential for accurately interpreting the outputs of circuits involving two-qubit gates.
arxiv pdf