J.J. García-Ripoll

Bose-Hubbard models with photon pairing in circuit-QED

  1. Benjamin Villalonga Correa,
  2. Andreas Kurcz,
  3. and J.J. Garcia-Ripoll
In this work we study a family of bosonic lattice models that combine an on-site repulsion term with a nearest-neighbor pairing term, $sum_{< i,j>} a^dagger_i a^dagger_j + mathrm{H.c.}$
Like the original Bose-Hubbard model, the nearest-neighbor term is responsible for the mobility of bosons and it competes with the local interaction, inducing two-mode squeezing. However, unlike a trivial hopping, the counter-rotating terms form pairing cannot be studied with a simple mean-field theory and does not present a quantum phase transition in phase space. Instead, we show that there is a cross-over from a pure insulator to long-range correlations that start up as soon as the two-mode squeezing is switched on. We also show how this model can be naturally implemented using coupled microwave resonators and superconducting qubits.
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

Circuit QED bright source for chiral entangled light based on dissipation

  1. Fernando Quijandría,
  2. Diego Porras,
  3. Juan José García-Ripoll,
  4. and David Zueco
Based on a circuit QED qubit-cavity array a source of two-mode entangled microwave radiation is designed. Our scheme is rooted in the combination of external driving, collective phenomena
and dissipation. On top of that the reflexion symmetry is broken via external driving permitting the appearance of chiral emission. Our findings go beyond the applications and are relevant for fundamental physics, since we show how to implement quantum lattice models exhibiting criticality driven by dissipation.
arxiv pdf

Scattering of coherent states on a single artificial atom

  1. B. Peropadre,
  2. J. Lindkvist,
  3. I.-C. Hoi,
  4. C.M. Wilson,
  5. J.J. Garcia-Ripoll,
  6. P. Delsing,
  7. and G. Johansson
In this work we theoretically analyze a circuit QED design where propagating quantum microwaves interact with a single artificial atom, a single Cooper pair box. In particular, we derive
a master equation in the so-called transmon regime, including coherent drives. Inspired by recent experiments, we then apply the master equation to describe the dynamics in both a two-level and a three-level approximation of the atom. In the two-level case, we also discuss how to measure photon antibunching in the reflected field and how it is affected by finite temperature and finite detection bandwidth.
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