Collini Elisabetta, Gattuso Hugo, Levine R D, Remacle F
Department of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova, Italy.
Theoretical Physical Chemistry, RU MOLSYS, University of Liège, Allée du 6 Août 11, B4000 Liège, Belgium.
J Chem Phys. 2021 Jan 7;154(1):014301. doi: 10.1063/5.0031420.
We show in a joint experimental and theoretical study that ultrafast femto-second (fs) electronic coherences can be characterized in semi-conducting colloidal quantum dot (QD) assemblies at room temperature. The dynamics of the electronic response of ensembles of CdSe QDs in the solution and of QD dimers in the solid state is probed by a sequence of 3 fs laser pulses as in two-dimensional (2D) electronic spectroscopy. The quantum dynamics is computed using an excitonic model Hamiltonian based on the effective mass approximation. The Hamiltonian includes the Coulomb, spin-orbit, and crystal field interactions that give rise to the fine structure splittings. In the dimers studied, the interdot distance is sufficiently small to allow for an efficient interdot coupling and delocalization of the excitons over the two QDs of the dimer. To account for the inherent few percent size dispersion of colloidal QDs, the optical response is modeled by averaging over an ensemble of 2000 dimers. The size dispersion is responsible for an inhomogeneous broadening that limits the lifetimes of the excitonic coherences that can be probed to about 150 fs-200 fs. Simulations and experimental measurements in the solid state and in the solution demonstrate that during that time scale, a very rich electronic coherent dynamics takes place that involves several types of intradot and interdot (in the case of dimers) coherences. These electronic coherences exhibit a wide range of beating periods and provide a versatile basis for a quantum information processing device on a fs time scale at room temperature.
我们在一项联合实验与理论研究中表明，在室温下的半导体胶体量子点（QD）组件中，可以对超快飞秒（fs）电子相干性进行表征。如在二维（2D）电子光谱中那样，通过一系列3 fs激光脉冲探测溶液中CdSe量子点集合体以及固态量子点二聚体的电子响应动力学。使用基于有效质量近似的激子模型哈密顿量来计算量子动力学。该哈密顿量包括导致精细结构分裂的库仑、自旋轨道和晶体场相互作用。在所研究的二聚体中，点间距离足够小，以允许有效的点间耦合以及激子在二聚体的两个量子点上离域。为了考虑胶体量子点固有的百分之几的尺寸分散性，通过对2000个二聚体的集合进行平均来模拟光学响应。尺寸分散导致非均匀展宽，这将可探测的激子相干寿命限制在约150 fs - 200 fs。固态和溶液中的模拟与实验测量表明，在该时间尺度内，会发生非常丰富的电子相干动力学，涉及几种类型的点内和点间（在二聚体情况下）相干性。这些电子相干性展现出广泛的拍频周期，并为室温下飞秒时间尺度的量子信息处理设备提供了一个通用基础。
