Distinctive characteristics of carrier-phonon interactions in optically driven semiconductor quantum dots

Abstract

We review distinct features arising from the unique nature of the carrier-phonon coupling in self-assembled semiconductor quantum dots. Because of the discrete electronic energy structure, the pure dephasing coupling usually dominates the phonon effects, of which two properties are of key importance: The resonant nature of the dot-phonon coupling, i.e. its nonmonotonic behavior as a function of energy, and the fact that it is of super-Ohmic type. Phonons do not only act destructively in quantum dots by introducing dephasing, they also offer new opportunities, e.g. in state preparation protocols. Apart from being an interesting model systems for studying fundamental physical aspects, quantum dot and quantum dot-microcavity systems are a hotspot for many innovative applications. We discuss recent developments related to the decisive impact of phonons on key figures of merit of photonic devices like single or entangled photon sources under aspects like indistinguishability, purity and brightness. All in all it follows that understanding and controlling the carrier-phonon interaction in semiconductor quantum dots is vital for their usage in quantum information technology.

Different Types of Photon Entanglement from a Constantly Driven Quantum Emitter Inside a Cavity

“…The generation procedure of entangled photons in a typical (nondriven) four-level system is as follows [see also Figure 1 (left)]: In a first step the uppermost state is prepared, for example, by using two-photon resonant or near-resonant excitation with short coherent pulses [16][17][18][19][20][21][22][23][24] or adiabatic rapid passage protocols. [25][26][27][28] The excited emitter then decays into a superposition of the two intermediate states which can be reached from the uppermost state by emission of either a horizontally or vertically polarized photon. In the subsequent decay to the ground state a second photon is emitted.…”

On-demand generation of higher-order Fock states in quantum-dot–cavity systems

“…The QDC is described by the Jaynes-Cummings model and the exciting and Stark laser pulses are represented by the function f X (t ), which is specified in Appendix A 1, in particular its two parts f pulses (t ) and f AC-Stark (t ). The cavity frequency is denoted by ω C and its coupling to the QD by g. We further account for the pure-dephasing type interaction with longitudinal acoustic (LA) phonons [29][30][31][32][33], the radiative decay of the QD excitons, and cavity losses. In this work, whenever we consider phononic effects, the phonons are assumed to be initially in thermal equilibrium at a temperature of T = 4 K. We solve the corresponding Liouville equation in a numerically complete manner by employing a path-integral formalism (for details see Refs.…”

“…Even though phonons always degrade the performance of the here proposed protocols, they suppress an unfavorable process when the sign of the binding energy is chosen accordingly. It is worthwhile to note that there are situations where phonons are even more beneficial [33]. Examples include phonon-assisted preparation schemes for excitons and biexcitons [59][60][61][62][63][64], the introduction of off-resonant QD-cavity couplings [65][66][67][68][69][70][71][72][73], the phonon-induced enhancement of photon purities [10] or the photon-pair entanglement [18] as well as enabling correlated emission from spatially remote QDs [64].…”

“…In contrast, a laser pulse can be shaped to vary the edge characteristics, which introduces additional dials for optimizing the protocol. The QD is coupled to LA phonons in a pure dephasing-type manner [29][30][31][32][33]:…”

“…In contrast to atoms, QDs are solid state systems and are therefore affected by the electron-phonon interaction. The pure-dephasing type coupling of the excitonic states to longitudinal acoustic phonons is known as the main source of decoherence in QDs even at cryogenic temperatures of a few Kelvin [29][30][31][32][33]. Accordingly, we study the influence of phonons as well as of cavity and radiative losses on the proposed protocols.…”