Relaxation dynamics of a quantum emitter resonantly coupled to a coherent state of a localized surface plasmon

Khachatur V Nerkararyan,Sergey I Bozhevolnyi

doi:10.1039/c4fd00165f

Khachatur V Nerkararyan, Sergey I Bozhevolnyi

Open Access

https://doi.org/10.1039/c4fd00165f

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Abstract

We investigate the relaxation dynamics of a quantum dipole emitter (QDE), e.g., a molecule or quantum dot, located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. A generic three-level QDE, which is pumped with an external laser pulse and thereby brought into an optically active excited state, is considered to be weakly coupled to the resonant LSP described by a coherent state. It is shown that, under the condition of the QDE-MNP characteristic relaxation time being much shorter than that of the QDE in free space but much longer than the LSP lifetime, the QDE relaxation dynamics can be described analytically and feature, in general, non-exponential decay with complicated transient behaviour. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. It is also shown that energy dissipation in the QDE-MNP system is relatively weak with the probability of the photon emission being ∼0.75, a number which, rather surprisingly, does not explicitly depend on the metal absorption characteristics. A large number of QDE-MNP system parameters in our analytical description open new possibilities for controlling quantum emitter dynamics.

Highlights

The interaction of quantum dipole emitters (QDEs), such as molecules or quantum dots, with metal nanoparticles (MNPs) at optical frequencies allows control over the ow of electromagnetic energy and lies at the core of an explosively growing eld of quantum plasmonics.[1]
For this con guration under pulsed excitation, we have found an intermediate regime of relaxation that occurs in a coherent fashion with a substantial delay of the emission followed by exponential relaxation dynamics akin to that of modi ed spontaneous emission in the weakcoupling regime.[3,4,7,8,9,14,15,16]
It is interesting that the effect is already pronounced at relatively large ($10 nm) distances between the QDEs and the MNP surface, which are in the range of distances explored in the recent experiments with 10 nm-size gold nanoparticles.[8]

Summary

Introduction

The interaction of quantum dipole emitters (QDEs), such as molecules or quantum dots, with metal nanoparticles (MNPs) at optical frequencies allows control over the ow of electromagnetic energy and lies at the core of an explosively growing eld of quantum plasmonics.[1]. Note that these expressions are consistent with those obtained previously by us using the quasi-classical approach, in which the QDE was represented by the coherent superposition of the excited and ground states obeying the time-dependent Schrodinger equation (for a two-level system), while the LSP eld was considered to be induced in the MNP by the classical electromagnetic eld created by the oscillating QDE dipole.[17] In this respect, the above derivation can be considered as a justi cation of the previously used approach.

Results

Conclusion