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We employed the contact forces induced by a near-field tip to tune and probe the optical resonances of a mechanically compliant photonic crystal molecule. Here, the pressure induced by the near-field tip is exploited to control the spectral proprieties of the coupled cavities in an ultrawide spectral range, demonstrating a reversible mode shift of $37.5\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. Besides, by monitoring the coupling strength variation due to the vertical nanodeformation of the dielectric structure, distinct tip-sample interaction regimes have been unambiguously reconstructed with a nano-Newton sensitivity. These results demonstrate an optical method for mapping mechanical forces at the nanoscale with a lateral spatial resolution below 100 nm.

We theoretically investigate the multipolar effects on the dipole-forbidden transitions of a semiconductor quantum dot. An approximated expression for the decay rate of these transitions is derived. Unlike the general theory of the spontaneous emission beyond the dipole approximation, the distinct roles of the emitter and the vacuum electric field in the transition rate are here clearly recognizable and can be separately optimized. We illustrate the potential of this formalism by calculating the spontaneous emission decay rate of an InAs/GaAs quantum dot embedded into two realistic nanostructures---an L3 photonic crystal cavity and a plasmonic dimer antenna. The obtained results show that, although the two structures provide an enhancement of the same order of magnitude, the plasmonic antenna constitutes a more promising candidate for the experimental observation of the dipole-forbidden transitions of a quantum dot.

We report a study of single quantum dots inside photonic crystal cavities with a low-temperature scanning near-field optical microscope. The spatial maps of single excitonic lines from the quantum dot show the clear signature of coupling to the cavity modes for small detunings. We also show that the near-field tip can be used to control the exciton-photon coupling at the nanoscale. A general framework for the interpretation of near-field maps of single emitters in cavities is proposed.

The authors develop a theory within the effective-mass approxn. of the 2nd-order susceptibility of a quantum well subject to an applied elec. field. Close to the midgap of the structure it is possible within that approxn. to reduce the normally derived triple sums over subbands to a simple sum over all the optically allowed transitions. In realistic structures, higher-energy transitions play a strong role for quant. results. This strong influence of the higher-energy transitions on the 2nd-order susceptibility has the consequence that it is not generally possible to define a quantum-well susceptibility independent of the structure in which the well is inserted. Numerical results indicate that the quantum wells should not lead to spectacular enhancements of the 2nd-harmonic-generation susceptibility. [on SciFinder (R)]

We theoretically investigate the dynamic interaction of a quantum dot in a nanocavity with time-symmetric single-photon pulses. The simulations, based on a wave-function approach, reveal that almost perfect single-photon absorption occurs for quantum-dot--cavity systems operating on the edge between strong- and weak-coupling regimes. The computed maximum absorption probability is close to unity for pulses with a typical length comparable to half of the Rabi period. Furthermore, the dynamic control of the quantum-dot energy via electric fields allows the freezing of the light-matter interaction, leaving the quantum dot in its excited state. Shaping of single-photon wave packets by the electric field control is limited by the occurrence of chirping of the single-photon pulse. This understanding of the interaction of single-photon pulses with the quantum-dot--cavity system provides the basis for the development of advanced protocols for quantum-information processing in the solid state.

A revisited realization of the Young’s double slit experiment is introduced to directly probe the photonic mode symmetry by photoluminescence experiments. We experimentally measure the far field angular emission pattern of quantum dots embedded in photonic molecules. The experimental data well agree with predictions from Young’s interference and numerical simulations. Moreover, the vectorial nature of photonic eigenmodes results in a rather complicated parity property for different polarizations, a feature which has no counterpart in quantum mechanics.