The demonstration of degeneracy of the exciton spin states is an important step towards the production of entangled photons pairs from the biexciton cascade. We measure the fine structure of exciton and biexciton states for a large number of single InAs quantum dots in a GaAs matrix; the energetic splitting of the horizontally and vertically polarised components of the exciton doublet is shown to decrease as the exciton confinement decreases, crucially passing through zero and changing sign. Thermal annealing is shown to reduce the exciton confinement, thereby increasing the number of dots with splitting close to zero.
The spin structure and spin dynamics of excitons in an ensemble of (In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both direct and indirect band gap dots, are studied. Time-resolved and spectral selective techniques are used to distinguish between the direct and indirect QDs. The exciton fine structure is studied by means of optical alignment and optical orientation techniques in magnetic fields applied in the Faraday or Voigt geometries. A drastic difference in emission polarization is found for the excitons in the direct QDs involving a $Γ$-valley electron and the ex…
Suppression of exciton dephasing in quantum dots through ultrafast multipulse control
我们研究了Viola和Lloyd [Phys. Rev. A 58，2733（1998）]开发的方案在基于激子的自组装量子点量子计算中控制退相的有用性和可行性。我们证明了通过施加一个简单的周期性控制脉冲序列，可以显著增强受声子诱导的退相作用的受限激子量子比特的光学相干性。量子点的形状对退相特性有显著影响。值得注意的是，我们发现，具有为实现量子计算而优化的参数的量子点是最容易受到失相影响的，然而周期性去耦对于这种类型的量子点是最有效的。我们还表明，电场的存在下，这是一个必要的成分，许多激子为基础的量子计算计划，可以进一步提高控制效率。我们的研究结果表明，动态解耦可能是一种方法的选择，在量子算法的空闲阶段的激子量子比特的鲁棒存储。
he properties of excitons formed in spherical quantum dots are studied using the $\mathbf{k}\cdot\mathbf{p}$ method within the Hartree approximation. The spherical quantum dots considered have a central core and several concentric layers of different semiconductor materials that are modeled as a succession of potential wells and barriers. The $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian and the Coulomb equations for the electron-hole pair are solved using a self-consistent iterative method. The calculation of the spectrum of the empty quantum dot and the electron-hole pair is performed by means of …
Multiply-excited states in semiconductor quantum dots feature intriguing physics and play a crucial role in nanocrystal-based technologies. While photoluminescence provides a natural probe to investigate these states, room temperature single-particle spectroscopy of their emission has so far proved elusive due to the temporal and spectral overlap with emission from the singly-excited and charged states. Here we introduce biexciton heralded spectroscopy, enabled by a single-photon avalanche diode array based spectrometer. This allows us to directly observe biexciton-exciton emission cascades an…
