Compared to classical light sources, quantum sources based on N00N states consisting of <i>N</i> photons achieve an <i>N</i>-times higher phase sensitivity, giving rise to super-resolution.<sup>1, 2, 3</sup> N00N-state creation schemes based on linear optics and projective measurements only have a success probability <i>p</i> that decreases exponentially with N,<i>4, 5, 6</i> e.g. p = 4.4x10<sup>-14 </sup>for <i>N</i> = 20.<sup>7</sup> Feed-forward improves the scaling but<i> N </i>fluctuates nondeterministically in each attempt.<sup>8, 9</sup> Schemes based on parametric down-conversion suffer from low production efficiency and low fidelity.<sup>9</sup> A recent scheme based on atoms in a cavity combines deterministic time evolution, local unitary operations, and projective measurements.<sup>10</sup> Here we propose a novel scheme based on the off-resonant interaction of <i>N</i> photons with four semiconductor quantum dots (QDs) in a cavity to create GHZ states, also called polarization N00N states, deterministically with<i> p</i> = 1 and fidelity above 90% for N≤ 60, without the need of any projective
measurement or local unitary operation. Using our measure we obtain maximum N-photon entanglement E<sub>N</sub> = 1 for arbitrary <i>N</i>. Our method paves the way to the miniaturization of N00N and GHZ-state sources to the nanoscale regime, with the possibility to integrate them on a computer chip based on semiconductor materials.
The interplay between disorder and Coulomb interactions ubiquitously affects the properties of condensed matter
systems. We examine its role in the nonlinear optical response of semiconductor quantum wells. In particular, we
investigate the coherent coupling strength between exciton resonances that are spectrally split by interface fluctuations.
Previous studies yielded conflicting results. In light of rising interest in semiconductor devices that rely on spatial and/or
temporal coherence, we revisit this problem by applying a newly developed spectroscopy method: electronic two-dimensional
Fourier transform spectroscopy (2DFTS). 2DFTS is a powerful technique for revealing the presence of
coupling and for distinguishing the (coherent or incoherent) nature of such coupling, especially in complex systems with
several spectrally overlapping resonances. Even the most basic information about such complex systems, including the
homogeneous and inhomogeneous linewidths of various resonances, cannot be extracted reliably using conventional
spectroscopic tools. In these new 2DFTS measurements, we did not observe any clear cross peaks corresponding to
coherent couplings between either heavy-hole or light-hole excitons. These measurements allow us to place a
quantitative upper bound on the possible coupling strength in this prototypical system. A modified mean-field theory
reveals a simple yet important relation that determines how the coherent coupling strength depends on the disorder
correlation length and Coulomb interaction length.
Light emitted within a photonic crystal structure can be used to probe both the photonic density of states and the
anisotropic propagation of light through the structure. Here we present results of angle- and polarization-resolved
measurements of photoluminescence from three-dimensional ZnO photonic crystals. The ZnO inverse opals were
fabricated by infiltration of polystyrene synthetic opal templates using atomic layer deposition. The resulting
nanocrystalline ZnO structures exhibit strong UV emission as well as a broad defect emission peak, allowing us to
observe the dispersion of the primary as well as higher-order PBGs over the entire visible spectrum. The spontaneous
emission spectrum is strongly modified and anisotropic due to the effect of the photonic band structure. The observed
features are correlated to transmission and reflection measurements as well as calculated (reduced) band structures in the Γ-L-K plane of the fcc Brillouin zone. Apart from the suppression and redistribution of light near the primary and higher band gaps, we observe a strong enhancement in the PL peaks due to light propagation in higher (e.g. 5th and 6th)photonic bands at frequencies and angles where no PBG exists.
The exciton polaritons dispersion law is analyzed in a one-dimensional multiple-quantum-well based photonic crystal. An effective approach allowing to consider structures with an arbitrary periodic spatial modulation of the dielectric function and the multilevel structure of the exciton spectrum is developed. It is shown that the condition of the Bragg resonance has to be modified to take into account the symmetry of the exciton states and the non-trivial dispersion law of the electromagnetic waves in photonic crystals. For a particular case of a one-level excitonic susceptibility it is shown that the Bragg resonance occurs when the exciton frequency falls to the high-frequency boundary of the photonic band-gap. The polariton's dispersion law is considered. The
angular dependence of the spectrum is analyzed. The effect of multiple exciton levels on the polariton spectrum is discussed.