The dispersion properties of photonic crystal fibers are calculated by expression of the modal field as a sum of localized orthogonal functions. Even simple designs of these fibers can yield zero dispersion at wavelengths shorter than 1.27 mum when the fibers are single mode, or a large normal dispersion that is suitable for dispersion compensation at 1.55 mum.

We report on an intrinsic relationship between the maximum-likelihood quantum-state estimation and the representation of the signal. A quantum analogy of the transfer function determines the space where the reconstruction should be done without the need for any ad hoc truncations of the Hilbert space. An illustration of this method is provided by a simple yet practically important tomography of an optical signal registered by realistic binary detectors. The development of effective and robust methods of quantum state reconstruction is a task of crucial importance for quantum optics and information. Such methods are needed for quantum diagnostics: for the verification of quantum state preparation, for the analysis of quantum dynamics and decoherence, and for information retrieval. Since the original proposal for quantum tomography and its experimental verification [1,2] this discipline has recorded significant progress and is considered as a routine experimental technique nowadays. Reconstruction has been successfully applied to probing the structure of entangled states of light and ions, operations (quantum gates) with entangled states of light and ions or internal angular momentum structure of correlated beams, just to mention a few examples [3].All these applications exhibit common features. Any successful quantum tomography scheme relies on three key ingredients: on the availability of a particular tomographically complete measurement, on a suitable representation of quantum states, and on an adequate mathematical algorithm for inverting the measured data. In addition, the entire reconstruction scheme must be robust with respect to noise. In real experiments the presence of noise is unavoidable due to losses and due to the fact that detectors are not ideal. The presence of losses poses a limit on the accuracy of a reconstruction. However, the very presence of losses can be turned into advantage and used for the reconstruction purposes. As has been predicted in Ref. [4], imperfect detectors, which are able to distinguish only between the presence and absence of signal (binary detectors) provide sufficient data for the reconstruction of the quantum state of a light mode provided their quantum efficiencies are less than 100%.

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We demonstrate that by an asymmetric coupling of two nonlinear waveguiding cores to the third strongly absorptive core, it is possible to realize single-photon generation on demand from an input coherent state. This three-core fiber setup can also be implemented for achieving strong photon-number squeezing even for large losses in side cores.

We build an operational scheme for the quantum state reconstruction based on the fitting of data patterns. Each data pattern corresponds to the response of the measurement setup to a predefined reference state. The set of data patterns can be measured experimentally in the calibration stage preceding to the reconstruction. The quorum of reference states plays the role of a positive operator valued measure in terms of which the reconstruction is done. As the main advantage, the procedure is free of notorious problems with projections into non-normalizable quadrature eigenstates, infinite dimensionality, ill-posed inversion, or imperfect detection. According to the pragmatic interpretation, the quantum theory is, first of all, the theory of measurement. All predictions must be phrased in terms of measurable quantities regardless of how abstract the structures used to describe the quantum features are. This is also the case for a quantum state reconstruction. Though its purpose is to identify the quantum state of the measured system, it may also be seen as the relationship between past and future observations of the same system. A quantum state is only an oxymoron for information about any possible future measurement encoded comprehensively into a convenient theoretical structure. Accepting this interpretation, any reconstruction procedure consists of classical data processing followed by quantum interpretation, which guarantees that any future prediction based on the original measurement must obey quantum rules, such as various uncertainty relations.In this Letter we will elaborate on this pragmatic interpretation exploring the common roots of quantum tomography and classical data processing. Quantum interpretation will be postponed up to the very last moment where one wants to apply the inferred information to future quantum predictions. In this way we shall guide ourselves by analogies with classical optics, for example, by the analysis of a blurred image registered by a CCD camera, provided the optical response function is known. This approach offers significant advantages for a practical implementation of the reconstruction procedure.

A photonic circuit is generally described as a structure in which light propagates by unitary exchange and transfers reversibly between channels. In contrast, the term ‘diffusive’ is more akin to a chaotic propagation in scattering media, where light is driven out of coherence towards a thermal mixture. Based on the dynamics of open quantum systems, the combination of these two opposites can result in novel techniques for coherent light control. The crucial feature of these photonic structures is dissipative coupling between modes, via an interaction with a common reservoir. Here, we demonstrate experimentally that such systems can perform optical equalisation to smooth multimode light, or act as a distributor, guiding it into selected channels. Quantum thermodynamically, these systems can act as catalytic coherent reservoirs by performing perfect non-Landauer erasure. For lattice structures, localised stationary states can be supported in the continuum, similar to compacton-like states in conventional flat-band lattices.

Light propagation through 1D disordered structures composed of alternating layers, with random thicknesses, of air and a dispersive metamaterial is theoretically investigated. Both normal and oblique incidences are considered. By means of numerical simulations and an analytical theory, we have established that Anderson localization of light may be suppressed: (i) in the long wavelength limit, for a finite angle of incidence which depends on the parameters of the dispersive metamaterial; (ii) for isolated frequencies and for specific angles of incidence, corresponding to Brewster anomalies in both positive-and negative-refraction regimes of the dispersive metamaterial. These results suggest that Anderson localization of light could be explored to control and tune light propagation in disordered metamaterials.

We propose a mechanism to explain the nature of the damping of Rabi oscillations with an increasing driving-pulse area in localized semiconductor systems and have suggested a general approach which describes a coherently driven two-level system interacting with a dephasing reservoir. Present calculations show that the non-Markovian character of the reservoir leads to the dependence of the dephasing rate on the driving-field intensity, as observed experimentally. Moreover, we have shown that the damping of Rabi oscillations might occur as a result of different dephasing mechanisms for both stationary and nonstationary effects due to coupling to the environment. Present calculated results are found in quite good agreement with available experimental measurements.