Coherent spectroscopy of single semiconductor quantum dots

C. Wolpert, L. Wang, P. Atkinson, A. Rastelli, O. Schmidt, M. Lippitz
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Abstract

Semiconductor quantum dots (QDs) are a promising candidate for the realization of qubits for quantum computation [1]. With coherence times of below 1 ns, writing, manipulation and read-out of a qubit requires ultrafast laser pulses interacting coherently with the system [2]. A key experiment in this context is the observation of Rabi oscillations, where the population of a two-level system can be driven coherently back and forth between the ground state and the excited state. The GaAs/AlGaAs material system is favourable for spectroscopy, because the emission energy of the exciton of around 1.7 eV falls into a region where Si-detectors have still a high quantum efficiency. As the GaAs substrate is absorbing at the exciton transition energy, we have to employ a shot-noise limited pump-probe technique operating in reflection geometry. We accomplished to observe Rabi oscillations in one of the fine-structure split ground state excitonic states of our GaAs QDs, monitoring its population by the bleaching it imposes on the second ground state exciton transition (see Fig.1 left). The first period of these population oscillations yields a dipole moment of about 15 D for the s-shell exciton. A second period is still visible, but stretched and shifted to higher pulse areas (see Fig.1). This behavior can be explained by a phenomenological model that takes into account the interaction with hot, delocalized carriers which are excited by the pump pulse in the GaAs substrate.
单半导体量子点的相干光谱学
半导体量子点(QDs)是实现量子计算量子比特的一个很有前途的候选者。在相干时间小于1ns的情况下,量子比特的写入、操作和读出需要超快激光脉冲与系统[2]相干地相互作用。在这种情况下,一个关键的实验是观察拉比振荡,其中两能级系统的人口可以在基态和激发态之间相干地来回驱动。GaAs/AlGaAs材料体系有利于光谱学,因为激子的发射能量约为1.7 eV,落在si探测器仍然具有高量子效率的区域。由于砷化镓衬底吸收激子跃迁能量,我们必须采用在反射几何中工作的限制短噪声的泵浦探测技术。我们完成了在我们的GaAs量子点的一个精细结构分裂基态激子态中观察Rabi振荡,通过它对第二个基态激子跃迁施加的漂白来监测其种群(见图1左)。这些居群振荡的第一个周期产生了s壳激子约15d的偶极矩。第二个周期仍然可见,但拉伸和移位到更高的脉冲区域(见图1)。这种行为可以用一种现象学模型来解释,该模型考虑了GaAs衬底中由泵浦脉冲激发的热的、离域的载流子的相互作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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