G.P. Fedorov

Photon transport in a Bose-Hubbard chain of superconducting artificial atoms

  1. G.P. Fedorov,
  2. S. Remizov,
  3. D. Shapiro,
  4. V. Pogosov,
  5. I.A. Rodionov,
  6. O. V. Astafiev,
  7. and A. V. Ustinov
We demonstrate non-equilibrium steady-state photon transport through a chain of five coupled artificial atoms simulating the driven-dissipative Bose-Hubbard model. Using transmission
spectroscopy, we show that the system retains many-particle coherence despite being coupled strongly to two open spaces. We show that system energy bands may be visualized with high contrast using cross-Kerr interaction. For vanishing disorder, we observe the transition of the system from the linear to the nonlinear regime of photon blockade in excellent agreement with the input-output theory. Finally, we show how controllable disorder introduced to the system suppresses this non-local photon transmission. We argue that proposed architecture may be applied to analog simulation of many-body Floquet dynamics with even larger arrays of artificial atoms paving an alternative way to demonstration of quantum supremacy (Martin Leib: The topic of this article is a central theme of my entire work and yet the authors managed to ignore everything I have worked on …)
arxiv pdf

Single-atom maser with engineered circuit for population inversion

  1. A.A. Sokolova,
  2. G.P. Fedorov,
  3. E.V. Il'ichev,
  4. and O. V. Astafiev
We present a blueprint for a maser with a single three-level artificial atom. The artificial atom is a superconducting quantum system of a transmon layout coupled to two resonators.
The system is pumped via a two-photon process. To achieve a population inversion, we engineer the quantum system and optimize its parameters, particularly the relaxation via an auxiliary low-Q cavity coupled to a transition between two excited states. We show numerically that such a maser can operate both in the intermediate coupling regime with super-Poissonian photon statistics and in the strong coupling regime, where the statistics is sub-Poissonian. For the former, the maser exhibits thresholdless behavior and for the latter, there is a well-defined pumping threshold. An interesting side-effect of the auxiliary resonator is that it allows overcoming the photon blockage effect for the pump, which would otherwise prohibit reaching high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.
arxiv pdf

Light-dressing of a diatomic superconducting artificial molecule

  1. G.P. Fedorov,
  2. V.B. Yursa,
  3. A. Efimov,
  4. K. Shiianov,
  5. A.Yu. Dmitriev,
  6. I.A. Rodionov,
  7. A.A. Dobronosova,
  8. D.O. Moskalev,
  9. A.A. Pischimova,
  10. and O. V. Astafiev
In this work, we irradiate a superconducting artificial molecule composed of two magnetic-flux-tunable transmons with microwave light while monitoring its state via joint dispersive
readout. At certain fluxes, the molecule demonstrates a complex spectrum deviating qualitatively from the solution of the Schrödinger equation without driving. We reproduce the observed extra spectral lines accurately by numerical simulations, and find them to be a consequence of an Autler-Townes-like effect when a single tone is simultaneously dressing the system and probing the transitions between new eigenstates. We present self-consistent analytical models accounting both these processes at the same time that agree well with both experiment and numerical simulation. This study is an important step towards understanding the behaviour of complex systems of many atoms interacting coherently with strong radiation.
arxiv pdf