D. Zueco

Ultrastrong coupling in two-resonator circuit QED

  1. A. Baust,
  2. E. Hoffmann,
  3. M. Haeberlein,
  4. M. J. Schwarz,
  5. P. Eder,
  6. J. Goetz,
  7. F. Wulschner,
  8. E. Xie,
  9. L. Zhong,
  10. F. Quijandria,
  11. D. Zueco,
  12. J.J. García-Ripoll,
  13. L. Garcia-Alvarez,
  14. G. Romero,
  15. E. Solano,
  16. K. G. Fedorov,
  17. E. P. Menzel,
  18. F. Deppe,
  19. A. Marx,
  20. and R. Gross
We report on ultrastrong coupling between a superconducting flux qubit and a resonant mode of a system comprised of two superconducting coplanar stripline resonators coupled galvanically
to the qubit. With a coupling strength as high as 17% of the mode frequency, exceeding that of previous circuit quantum electrodynamics experiments, we observe a pronounced Bloch-Siegert shift. The spectroscopic response of our multimode system reveals a clear breakdown of the Jaynes-Cummings model. In contrast to earlier experiments, the high coupling strength is achieved without making use of an additional inductance provided by a Josephson junction.
arxiv pdf

Tunable and Switchable Coupling Between Two Superconducting Resonators

  1. A. Baust,
  2. E. Hoffmann,
  3. M. Haeberlein,
  4. M. J. Schwarz,
  5. P. Eder,
  6. E. P. Menzel,
  7. K. Fedorov,
  8. J. Goetz,
  9. F. Wulschner,
  10. E. Xie,
  11. L. Zhong,
  12. F. Quijandria,
  13. B. Peropadre,
  14. D. Zueco,
  15. J.J. García-Ripoll,
  16. E. Solano,
  17. F. Deppe,
  18. A. Marx,
  19. and R. Gross
We realize a device allowing for tunable and switchable coupling between two superconducting resonators mediated by an artificial atom. For the latter, we utilize a persistent current
flux qubit. We characterize the tunable and switchable coupling in frequency and time domain and find that the coupling between the relevant modes can be varied in a controlled way. Specifically, the coupling can be tuned by adjusting the flux through the qubit loop or by saturating the qubit. Our time domain measurements allow us to find parameter regimes for optimal switch performance with respect to qubit drive power and the dynamic range of the resonator input power
arxiv pdf

Nonequilibrium and nonperturbative dynamics of ultrastrong coupling in open lines

  1. B. Peropadre,
  2. D. Zueco,
  3. D. Porras,
  4. and J.J. García-Ripoll
We study the time and space resolved dynamics of a qubit with an Ohmic coupling to propagating 1D photons, from weak coupling to the ultrastrong coupling regime. A nonperturbative study
based on Matrix Product States (MPS) shows the following results: (i) The ground state of the combined systems contains excitations of both the qubit and the surrounding bosonic field. (ii) An initially excited qubit equilibrates through spontaneous emission to a state, which under certain conditions, is locally close to that ground state, both in the qubit and the field. (iii) The resonances of the combined qubit-photon system match those of the spontaneous emission process and also the predictions of the adiabatic renormalization [A. J. Leggett et al., Rev. Mod. Phys. 59, 1, (1987)]. Finally, a non-perturbative ab-initio calculations show that this physics can be studied using a flux qubit galvanically coupled to a superconducting transmission line.
arxiv pdf

From Josephson junction metamaterials to tunable pseudo-cavities

  1. D. Zueco,
  2. C. Fernández-Juez,
  3. J. Yago,
  4. U. Naether,
  5. B. Peropadre,
  6. J.J. Garcia-Ripoll,
  7. and J. J. Mazo
The scattering through a Josephson junction interrupting a superconducting line is revisited including power leakage. We discuss also how to make tunable and broadband resonant mirrors
by concatenating junctions. As an application, we show how to construct cavities using these mirrors, thus connecting two research fields: JJ quantum metamaterials and coupled cavity arrays. We finish by discussing the first non-linear corrections to the scattering and their measurable effects.
arxiv pdf

Fast microwave beam splitters from superconducting resonators

  1. M. Haeberlein,
  2. D. Zueco,
  3. P. Assum,
  4. T. Weißl,
  5. E. Hoffmann,
  6. B. Peropadre,
  7. J.J. Garcia-Ripoll,
  8. E. Solano,
  9. F. Deppe,
  10. A. Marx,
  11. and R. Gross
Coupled superconducting transmission line resonators have applications in quantum information processing and fundamental quantum mechanics. A particular example is the realization of
fast beam splitters, which however is hampered by two-mode squeezer terms. Here, we experimentally study superconducting microstrip resonators which are coupled over one third of their length. By varying the position of this coupling region we can tune the strength of the two-mode squeezer coupling from 2.4% to 12.9% of the resonance frequency of 5.44GHz. Nevertheless, the beam splitter coupling rate for maximally suppressed two-mode squeezing is 810MHz, enabling the construction of a fast and pure beam splitter.
arxiv pdf

Tunable coupling engineering between superconducting resonators: from sidebands to effective gauge fields

  1. B. Peropadre,
  2. D. Zueco,
  3. F. Wulschner,
  4. F. Deppe,
  5. A. Marx,
  6. R. Gross,
  7. and J.J. García-Ripoll
In this work we show that a tunable coupling between microwave resonators can be engineered by means of simple Josephson junctions circuits, such as dc- and rf-SQUIDs. We show that
by controlling the time dependence of the coupling it is possible to switch on and off and modulate the cross-talk, boost the interaction towards the ultrastrong regime, as well as to engineer red and blue sideband couplings, nonlinear photon hopping and classical gauge fields. We discuss how these dynamically tunable superconducting circuits enable key applications in the fields of all optical quantum computing, continuous variable quantum information and quantum simulation – all within the reach of state of the art in circuit-QED experiments.
arxiv pdf