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.

Robust preparation of Wigner-negative states with optimized SNAP-displacement sequences

  1. Marina Kudra,
  2. Mikael Kervinen,
  3. Ingrid Strandberg,
  4. Shahnawaz Ahmed,
  5. Marco Scigliuzzo,
  6. Amr Osman,
  7. Daniel Pérez Lozano,
  8. Giulia Ferrini,
  9. Jonas Bylander,
  10. Anton Frisk Kockum,
  11. Fernando Quijandría,
  12. Per Delsing,
  13. and Simone Gasparinetti
Hosting non-classical states of light in three-dimensional microwave cavities has emerged as a promising paradigm for continuous-variable quantum information processing. Here we experimentally
demonstrate high-fidelity generation of a range of Wigner-negative states useful for quantum computation, such as Schrödinger-cat states, binomial states, Gottesman-Kitaev-Preskill (GKP) states, as well as cubic phase states. The latter states have been long sought after in quantum optics and were never achieved experimentally before. To do so, we use a sequence of interleaved selective number-dependent arbitrary phase (SNAP) gates and displacements. We optimize the state preparation in two steps. First we use a gradient-descent algorithm to optimize the parameters of the SNAP and displacement gates. Then we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly non-classical states in a harmonic oscillator is robust to fluctuations of the system parameters such as the qubit frequency and the dispersive shift.