Strong radiation-matter interaction in a driven superconducting quantum system

Juan José García‐Ripoll

Ivan Gonoskov, Christian Hünecke, Stefanie Gräfe

We present an analytical framework for the emergence of nonclassical radiation in strongly laser-driven quantum systems, with a focus on high-order harmonic generation (HHG). Starting from a Pauli-Fierz description, we employ a parametric factorization of the coupled light-matter wavefunction that reduces the dynamics to coupled equations for a field-driven electronic state and a quantized light mode. Within this framework, we identify a simple and predictive mechanism for nonclassicality: it originates from the nonlinear dependence of the electronic dipole response on the light-mode coordinate. An approximately constant dipole yields coherent radiation, a linear dependence produces squeezing, and higher-order nonlinearities give rise to Wigner-function negativity. We illustrate this mechanism for atomic and molecular model systems and analyze its scaling in multi-emitter configurations, indicating routes toward high-photon-number nonclassical radiation in HHG. Our results provide a transparent connection between strong-field dynamics and quantum-optical properties of emitted light, offering a basis for engineering nonclassical states in intense laser-matter interactions.

P. Forn-Díaz, Jean-Luc Orgiazzi, Martin R. Otto +5 more

Luca Magazzù, P. Forn-Díaz, Ron Belyansky +6 more

Quantum two-level systems interacting with the surroundings are ubiquitous in nature. The interaction suppresses quantum coherence and forces the system towards a steady state. Such dissipative processes are captured by the paradigmatic spin-boson model, describing a two-state particle, the "spin", interacting with an environment formed by harmonic oscillators. A fundamental question to date is to what extent intense coherent driving impacts a strongly dissipative system. Here we investigate experimentally and theoretically a superconducting qubit strongly coupled to an electromagnetic environment and subjected to a coherent drive. This setup realizes the driven Ohmic spin-boson model. We show that the drive reinforces environmental suppression of quantum coherence, and that a coherent-to-incoherent transition can be achieved by tuning the drive amplitude. An out-of-equilibrium detailed balance relation is demonstrated. These results advance fundamental understanding of open quantum systems and bear potential for the design of entangled light-matter states.

A. H. Dayem, Rudolph Martin

Alessandro Zenesini, Hans Lignier, D. Ciampini +2 more

The tunneling properties of a quantum system of matter waves inside a periodic potential can be dramatically changed if the potential is driven back and forth. Similarly to an atom in a strong radiation field, the matter waves inside the strongly driven potential are "dressed" and acquire new properties. In this paper, the authors have demonstrated that such dressed matter waves can be coherently and adiabatically loaded and controlled in one, two and three dimensional strongly driven optical lattices. In the driven lattices the tunneling probability and the tunneling phase between adjacent lattice sites become a function of the driving parameters. The regimes in which the driving parameters can be changed without exciting the system have been identified, thus allowing coherent and adiabatic following. This coherent control is then used in order to reversibly induce the superfluid-Mott insulator phase transition by changing the the driving strength.