We report the first experimental demonstration of the interference-induced spectral line elimination predicted by Zhu and Scully [Phys. Rev. Lett. 76, 388 (1996)] and Ficek and Rudolph [Phys. Rev. A 60, R4245 (1999)]. We drive an exciton transition of a self-assembled quantum dot in order to realize a twolevel system exposed to a bichromatic laser field and observe the nearly complete elimination of the resonance fluorescence spectral line at the driving laser frequency. This is caused by quantum interference between coupled transitions among the doubly dressed excitonic states, without population trapping. We also demonstrate a multiphoton ac Stark effect with shifted subharmonic resonances and dynamical modifications of resonance fluorescence spectra by using double dressing. New physics beyond the Mollow fluorescence triplet arises when a two-level system is exposed to strong bichromatic driving fields, exhibiting a range of nonlinear and multiphoton dynamics of light-matter interaction [22,23]. In particular, it has been pointed out that a dynamical cancellation of the spontaneous emission spectral line, initially predicted for a three-level system [24,25], may be possible in a two-level atom [26,27], which is not due to population trapping, but induced by quantum interferences between different transition channels in a doubly dressed atom. This occurs when a two-level atom is driven by a strong resonant laser with a Rabi frequency 2Ω [28], and a second, weaker laser is detuned by 2Ω from the strong field. The suppression of spontaneous emission spectral lines also appears when the second laser is coupled to the shifted subharmonics of 2Ω, which can be attributed to the multiphoton ac Stark effect [22]. Despite the extensive efforts undertaken to observe this phenomenon [29][30][31][32][33][34], the experimental demonstration of a complete cancellation of spontaneous emission lines has been claimed once in a V-type level atom [29], where there was also an alternative interpretation based on population trapping possible [32]. Here, we use a single QD, doubly dressed by bichromatic fields, to demonstrate unequivocally the complete cancellation of spontaneous emission spectral lines and other features arising from this phenomenon including shifted subharmonic resonances and modifications of sideband spectra.Our experiments are carried out on self-assembled InGaAs QDs embeded in a low-Q planar microcavity (Q ≈ 200) and housed in a cryogen-free bath cryostat operating at 4.2 K, as shown in Fig. 1(a). The measurements are performed on the neutral exciton transition of a single QD with a confocal microscope allowing bichromatic excitations of the QD from the side arm and collection of PRL 114, 097402 (2015) P H Y S I C A L

A theoretical model for the electron-hole exchange interaction in three-dimensionally ͑3D͒ confining semiconductor nanostructures is presented to explain the observed decreasing tendency of the fine-structure splittings ͑FSSs͒ of small InGaAs/GaAs self-assembled quantum dots ͑QDs͒ with increasing the emission energies. The experimentally revealed FSS reduction is shown to be highly associated with the significant 3D spreading of electronic orbitals and reduced overlap of electron and hole wave functions in small and/or Ga-diffused QDs. The combination of quantum size and Ga-diffusion effects substantially reduces the averaged e-h exchange interaction and leads to the reduced FSSs in the regime of high emission energy.

We theoretically study the effects of bias-controlled interdot tunneling in vertically coupled quantum dots on the emission properties of spin excitons in various bias-controlled tunneling regimes. As a main result, we predict substantial reduction of optical fine-structure splitting without any drop in the optical oscillator strength for the coupled dots with high tunneling rates. This special reduction diminishes the distinguishability of polarized decay paths in cascade emission processes suggesting the use of stacked quantum-dot molecules as entangled photon-pair sources.

The temporal evolution of an electron in a double rectangular quantum dot in the presence of an electric field pulse is explored in this work. In the framework of the effective mass approximation, first-order scattering rates for electron–electron and electron–longitudinal acoustic phonon interaction at room temperature are calculated in the high tunnelling regime, and used to evaluate the dynamics of the population and coherence of the first three confined levels under an electric field pulse. Small values of these rates dependent upon the coupling barrier make feasible the emission of coherent radiation near 0.1 THz.