Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots

TL;DR

This paper demonstrates that applying a transverse magnetic field to negatively charged InGaAs quantum dots significantly extends the coherent optical response time, from sub-nanoseconds to several nanoseconds, by leveraging spin dynamics.

Contribution

The study reveals how a moderate transverse magnetic field enhances the coherence time in quantum dot ensembles by exploiting spin-dependent photon echoes, introducing a new method to prolong optical coherence.

Findings

Photon echo decay time extended to ~4 ns with magnetic field

Without magnetic field, decay time is 0.45 ns, limited by radiative lifetime

Heavy hole g-factor influences photon echo evolution and magnetic dependence

Abstract

The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study 3-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with $T_ 2$ = 0.45 ns which is determined by the radiative lifetime of trions $T_1$ = 0.27 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons $T_{2,e}$ ~ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.