Multi-wave coherent control of a solid-state single emitter

The authors acknowledge support by the European Research Council Starting Grant 'PICSEN' contract no. 306387.Coherent control of individual two-level systems (TLSs) is at the basis of any implementation of quantum information. An impressive level of control is now achieved using nuclear, vacancies and charge spins. Manipulation of bright exciton transitions in semiconductor quantum dots (QDs) is less advanced, principally due to the sub-nanosecond dephasing. Conversely, owing to their robust coupling to light, one can apply tools of nonlinear spectroscopy to achieve all-optical command. Here, we report on the coherent manipulation of an exciton via multi-wave mixing. Specifically, we employ three resonant pulses driving a single InAs QD. The first two induce a four-wave mixing (FWM) transient, which is projected onto a six-wave mixing (SWM) depending on the delay and area of the third pulse, in agreement with analytical predictions. Such a switch enables to demonstrate the generation of SWM on a single emitter and to engineer the spectro-temporal shape of the coherent response originating from a TLS. These results pave the way toward multi-pulse manipulations of solid state qubits via implementing the NMR-like control schemes in the optical domain.PostprintPeer reviewe

Ultrafast carrier and phonon dynamics in GaAs and GaN quantum dots

We analyse the electronic and phononic dynamics in GaAs and GaN quantum dot structures due to their interaction with acoustic phonons. We compare results for two specific quantum dot heterostructures which have been proposed as hardware building blocks for a quantum computer in recent quantum computation/information schemes. In particular, we are interested in the loss of coherence after excitation with an ultrashort laser pulse and in the dynamics of phonons which are created as a consequence of the optical excitation process. Our results are non-perturbative with respect to both carrier-phonon and carrier-light interaction and therefore include multi-phonon processes of arbitrary order. We find that, due to different quantum dot sizes, involved electric fields and material parameters, the decoherence is stronger in the GaN dots. The interplay of these effects also strongly determines the details of the created phonon occupation, which splits into two parts: one remains in the vicinity of the dot and forms a stable polaron and another leaves the dot as a phononic wave packet travelling with the velocity of sound. Due to the dot geometry and the carrier-phonon coupling matrix elements this phonon emission is strongly anisotropic

Ultrafast carrier and phonon dynamics in GaAs and GaN quantum dots

We analyse the electronic and phononic dynamics in GaAs and GaN quantum dot structures due to their interaction with acoustic phonons. We compare results for two specific quantum dot heterostructures which have been proposed as hardware building blocks for a quantum computer in recent quantum computation/information schemes. In particular, we are interested in the loss of coherence after excitation with an ultrashort laser pulse and in the dynamics of phonons which are created as a consequence of the optical excitation process. Our results are non-perturbative with respect to both carrier–phonon and carrier–light interaction and therefore include multi-phonon processes of arbitrary order. We find that, due to different quantum dot sizes, involved electric fields and material parameters, the decoherence is stronger in the GaN dots. The interplay of these effects also strongly determines the details of the created phonon occupation, which splits into two parts: one remains in the vicinity of the dot and forms a stable polaron and another leaves the dot as a phononic wave packet travelling with the velocity of sound. Due to the dot geometry and the carrier–phonon coupling matrix elements this phonon emission is strongly anisotropic