We report an experimental and theoretical study of the dynamics of cold atoms subjected to pairs of closely spaced pulses in an optical lattice. For all previously studied delta-kicked systems, chaotic classical dynamics shows diffusion with short-time (2- or 3-kick) correlations; here, chaotic diffusion combines with new types of long-ranged global correlations, between all kick pairs, which control transport through trapping regions in phase space. Correlations are studied in the classical regime, but the diffusive behavior observed in experiment depends on the quantum dynamical localization.
We show that it is possible to obtain higher-order squeezing and entanglement between a pair of harmonic oscillators coupled to a single Δ-type artificial atom, which is realized because of the broken mirror symmetry of the effective potential in the superconducting circuits. Under the three-photon resonance and adiabatic conditions, the system can act as a coherence-controlled atomic reservoir, resulting in the generation of higher-order nonclassicality at steady state. The stable higher-order nonclassical correlations of the two harmonic oscillators in this solid-state device may find potential applications in quantum communications.
Abstract Quantum correlations in the polarization degree of freedom of the two-photon system have been extensively studied and form our current understanding of the quantum nature of our world. Most of the studies are concentrated on the low-energy (optical) photon pairs, for which efficient polarization measurement devices exist. However, for high-energetic (MeV) pairs of photons, e.g. produced in the decay of positronium atoms, no polarizers are available. Partial information about the polarization degree of freedom can be extracted by exploiting the measurements of photon pairs that undergo double Compton scattering. We present a Geant4-based Monte Carlo Vienna–Warsaw model capable of simulating any initial polarization state of bipartite photons. This puts us in a position to derive the behavior of the experimental observable, the angular difference
ΔΦ^ Δ Φ ^ formed by the two scattering planes. We validate our Vienna–Warsaw simulator with the high-statistics experimental sample – based on a total of
3×105 3 × 10 5 event candidates – of two-photon pairs measured with the J-PET Big Barrel detector. We deduce the value of the squared visibility (interference contrast) encoding the polarization in the angle difference of the two scattering planes,
ΔΦ^ Δ Φ ^ . The simulated spectra are in good agreement with the experimental correlation spectra and behave as predicted by theory.