Resonant and Anti-resonant Exciton-Phonon Coupling in Quantum Dot Molecules

TL;DR

This paper investigates phonon-mediated relaxation in quantum dot molecules, revealing resonant and anti-resonant behaviors that influence quantum state coherence, with implications for quantum information applications.

Contribution

It provides the first direct spectral measurement of phonon relaxation in QDMs and benchmarks it against microscopic theory, highlighting voltage-dependent coupling effects.

Findings

Phonon relaxation rates show pronounced resonances and anti-resonances.

Anti-resonances can extend charge state lifetimes for quantum information.

Spectral function measurements agree with microscopic kp theory.

Abstract

Optically active quantum dot molecules (QDMs) can host multi-spin quantum states with the potential for the deterministic generation of photonic graph states with tailored entanglement structures. Their usefulness for the generation of such non-classical states of light is determined by orbital and spin decoherence mechanisms, particularly phonon-mediated processes dominant at energy scales up to a few millielectronvolts. Here, we directly measure the spectral function of orbital phonon relaxation in a QDM and benchmark our findings against microscopic kp theory. Our results reveal phonon-mediated relaxation rates exhibiting pronounced resonances and anti-resonances, with rates ranging from several ten ns$^{-1}$ to tens of $\mu$s$^{-1}$. Comparison with a kinetic model reveals the voltage (energy) dependent phonon coupling strength and fully explains the interplay between phonon-assisted relaxation and radiative recombination. These anti-resonances can be leveraged to increase the lifetime of energetically unfavorable charge configurations needed for realizing efficient spin-photon interfaces and multi-dimensional cluster states.