J. C. Rivera Hernández

Continuous-variable two-dimensional cluster states in the microwave domain

  1. Fabio Lingua,
  2. Michele Cortinovis,
  3. J. C. Rivera Hernández,
  4. and David B. Haviland
We demonstrate the experimental realization of two-dimensional, continuous variable (CV) cluster states between 191 microwave frequency modes. This result is obtained by exposing vacuum
fluctuations to the input of a Josephson Parametric Amplifier, parametrically pumped by a sum of coherent tones around twice its resonant frequency. By carefully tuning pump frequencies, amplitudes, and phases we engineer the interference between mixing products and realize honeycomb and square lattice CV cluster states with three and four pump tones respectively. We prove the presence of the cluster states with a suitable nullifier test, reaching up to −1.2 dB of squeezing of the cluster state’s nullifiers. We study hidden entanglement (HE) and show no hidden entanglement up to ∼−1 dB of squeezing and negligible HE at optimal squeezing.
arxiv pdf

Intermodulation spectroscopy and the nonlinear response of two-level systems in superconducting coplanar waveguide resonators

  1. Janka Biznárová,
  2. J. C. Rivera Hernández,
  3. Daniel Forchheimer,
  4. Jonas Bylander,
  5. David B. Haviland,
  6. and Gustav Andersson
Two-level system (TLS) loss is typically limiting the coherence of superconducting quantum circuits. The loss induced by TLS defects is nonlinear, resulting in quality factors with
a strong dependence on the circulating microwave power. We observe frequency mixing due to this nonlinearity by applying a two-tone drive to a coplanar waveguide resonator and measuring the intermodulation products using a multifrequency lock-in technique. This intermodulation spectroscopy method provides an efficient approach to characterizing TLS loss in superconducting circuits. Using harmonic balance reconstruction, we recover the nonlinear parameters of the device-TLS interaction, which are in good agreement with the standard tunnelling model for TLSs.
arxiv pdf

Multipartite entanglement in a microwave frequency comb

  1. Shan W. Jolin,
  2. Gustav Andersson,
  3. J. C. Rivera Hernández,
  4. Ingrid Strandberg,
  5. Fernando Quijandría,
  6. Joe Aumentado,
  7. Riccardo Borgani,
  8. Mats O. Tholén,
  9. and David B. Haviland
Significant progress has been made with multipartite entanglement of discrete qubits, but continuous variable systems may provide a more scalable path toward entanglement of large ensembles.
We demonstrate multipartite entanglement in a microwave frequency comb generated by a Josephson parametric amplifier subject to a bichromatic pump. We find 64 correlated modes in the transmission line using a multifrequency digital signal processing platform. Full inseparability is verified in a subset of seven modes. Our method can be expanded to generate even more entangled modes in the near future.
arxiv pdf