Resolving Fock states near the Kerr-free point of a superconducting resonator

  1. Yong Lu,
  2. Marina Kudra,
  3. Timo Hillmann,
  4. Jiaying Yang,
  5. Hangxi Li,
  6. Fernando Quijandría,
  7. and Per Delsing
We have designed a tunable nonlinear resonator terminated by a SNAIL (Superconducting Nonlinear Asymmetric Inductive eLement). Such a device possesses a sweet spot in which the external
magnetic flux allows to suppress the Kerr interaction. We have excited photons near this Kerr-free point and characterized the device using a transmon qubit. The excitation spectrum of the qubit allows to observe photon-number-dependent frequency shifts about nine times larger than the qubit linewidth. Our study demonstrates a compact integrated platform for continuous-variable quantum processing that combines large couplings, considerable relaxation times and excellent control over the photon mode structure in the microwave domain.

Universal Gate Set for Continuous-Variable Quantum Computation with Microwave Circuits

  1. Timo Hillmann,
  2. Fernando Quijandría,
  3. Göran Johansson,
  4. Alessandro Ferraro,
  5. Simone Gasparinetti,
  6. and Giulia Ferrini
We provide an explicit construction of a universal gate set for continuous-variable quantum computation with microwave circuits. Such a universal set has been first proposed in quantum-optical
setups, but its experimental implementation has remained elusive in that domain due to the difficulties in engineering strong nonlinearities. Here, we show that a realistic microwave architecture allows to overcome this difficulty. As an application, we show that this architecture allows to generate a cubic phase state with an experimentally feasible procedure. This work highlights a practical advantage of microwave circuits with respect to optical systems for the purpose of engineering non-Gaussian states, and opens the quest for continuous-variable algorithms based on a few repetitions of elementary gates from the continuous-variable universal set.