Jiří Svozilík

Revealing Hidden Coherence in Partially Coherent Light

Coherence and correlations represent two related properties of a compound system. The system can be, for instance, the polarization of a photon, which forms part of a polarization-entangled two-photon state, or the spatial shape of a coherent beam, where each spatial mode bears different polarizations. Whereas a local unitary transformation of the system does not affect its coherence, global unitary transformations modifying both the system and its surroundings can enhance its coherence, transforming mutual correlations into coherence. The question naturally arises of what is the best measure that quantifies the correlations that can be turned into coherence, and how much coherence can be extracted. We answer both questions, and illustrate its application for some typical simple systems, with the aim at illuminating the general concept of enhancing coherence by modifying correlations.

Nonclassicality Invariant of General Two-Mode Gaussian States.

We introduce a new quantity for describing nonclassicality of an arbitrary optical two-mode Gaussian state which remains invariant under any global photon-number preserving unitary transformation of the covariance matrix of the state. The invariant naturally splits into an entanglement monotone and local-nonclassicality quantifiers applied to the reduced states. This shows how entanglement can be converted into local squeezing and vice versa. Twin beams and their transformations at a beam splitter are analyzed as an example providing squeezed light. An extension of this approach to pure three-mode Gaussian states is given.

One-state vector formalism for the evolution of a quantum state through nested Mach-Zehnder interferometers

Karol Bartkiewicz, 2, ∗ Antońın Černoch, † Dalibor Jav̊urek, Karel Lemr, ‡ Jan Soubusta, and Jǐŕı Svoziĺık Faculty of Physics, Adam Mickiewicz University, PL-61-614 Poznań, Poland RCPTM, Joint Laboratory of Optics of Palacký University and Institute of Physics of Academy of Sciences of the Czech Republic, 17. listopadu 12, 771 46 Olomouc, Czech Republic Institute of Physics of Academy of Sciences of the Czech Republic, Joint Laboratory of Optics of PU and IP AS CR, 17. listopadu 50A, 772 07 Olomouc, Czech Republic (Dated: November 19, 2014)

Spatial and spectral properties of fields generated by pulsed second-harmonic generation in a periodically poled potassium-titanyl-phosphate waveguide

Spatial and spectral properties of the pulsed second harmon ic generation in a periodically-poled KTP waveguide exploiti ng simultaneously the first, second, and third harmonics of periodic nonl i ear modulation are analyzed. Experimental results are interpreted using a model based on finite elements method. Correlations between spatial and sp ectral properties of the fundamental and second-harmonic fields are revealed. Individual nonlinear processes can be exploited combining spatial and spectral filtering. Also the influence of waveguide parameters to the second -harmonic spectra is addressed.

Proposal for the generation of photon pairs with nonzero orbital angular momentum in a ring fiber

We present a method for the generation of correlated photon pairs in desired orbital-angular-momentum states using a non-linear silica ring fiber and spontaneous parametric down-conversion. Photon-pair emission under quasi-phase-matching conditions with quantum conversion efficiency 6 × 10(-11) is found in a 1-m long fiber with a thermally induced χ(2) nonlinearity in a ring-shaped core.

Localizable entanglement as a necessary resource of controlled quantum teleportation

We analyze the controlled teleportation protocol through three-qubit mixed states. In particular, we investigate the relation between the faithfulness of the controlled teleportation scheme and entanglement. While our knowledge concerning controlled teleportation and entanglement in pure states is well established, for mixed states it is considerably much harder task and very little has been done in this field. Here, we present counterintuitive results that provide a new light on controlled teleportation protocol. It is shown that even mixed biseparable states are useful for this protocol along with genuine entangled three-qubit states.