Quantum Dot Photon Research Articles

Spontaneous emission spectra and quantum light-matter interactions from a strongly coupled quantum dot metal-nanoparticle system

We investigate the quantum optical properties of a single photon emitter coupled to a finite-size metal nanoparticle using a photon Green function technique that rigorously quantizes the electromagnetic fields. We first obtain pronounced Purcell factors and photonic Lamb shifts for both a 7-nm and 20-nm radius metal nanoparticle, without adopting a dipole approximation. We then consider a quantum-dot photon emitter positioned sufficiently near to the metal nanoparticle so that the strong coupling regime is possible. Accounting for non-dipole interactions, quenching, and photon transport from the dot to the detector, we demonstrate that the strong coupling regime should be observable in the far-field spontaneous emission spectrum, even at room temperature. The emission spectra show that the usual vacuum Rabi doublet becomes a rich spectral triplet or quartet with two of the four peaks anticrossing, which survives in spite of significant non-radiative decays. We discuss the emitted light spectrum and the effects of quenching for two different dipole polarizations.

Controlled cavity-assisted generation of single and entangled photons in semiconductor quantum dots

We propose a scheme, based on a single semiconductor quantum dot inside a microcavity, for the creation of single and entangled photons with controllable waveform. A lateral electric field allows to charge the quantum dot with a single electron, and breaks the usual optical selection rules. Our scheme utilizes cavity-assisted stimulated Raman adiabatic passage (STIRAP) in order to promote the surplus electron from the ground to the excited state, via excitation of a pump pulse and optical coupling to the charged exciton. This transfer is accompanied by a synchronized emission of a single-photon wavepacket, whose waveform can be controlled by the pump pulse. We investigate the influence of phonon scatterings, and show that they allow to reset the single-photon source. Finally, we propose a slight variant of our scheme which would allow for the creation of entangled multi-photon states. All our simulations are performed with realistic quantum dot and cavity parameters, which allows us to argue that our scheme can be implemented with state-of-the-art quantum dots and microcavities.

Entanglement transfer from electrons to photons in quantum dots: an open quantumsystem approach

We investigate entanglement transfer from a system of two spin-entangled electron–holepairs, each placed in a separate single mode cavity, to the photons emitted due to cavityleakage. Dipole selection rules and a splitting between the light hole and the heavy holesubbands are the crucial ingredients establishing a one-to-one correspondence betweenelectron spins and circular photon polarizations. To account for the measurement of thephotons as well as dephasing effects, we choose a stochastic Schrödinger equation and aconditional master equation approach, respectively. The influence of interactions with theenvironment as well as asymmetries in the coherent couplings on the photon entanglementis analysed for two concrete measurement schemes. The first one is designed to violate theClauser–Horne–Shimony–Holt (CHSH) inequality, while the second one employs thevisibility of interference fringes to prove the entanglement of the photons. Because of thespatial separation of the entangled electronic system over two quantum dots, asuccessful verification of entangled photons emitted by this system would imply thedetection of nonlocal spin entanglement of massive particles in a solid state structure.

Quasimode-projection approach to quantum-dot–photon interactions in photonic-crystal-slab coupled-cavity systems

We treat multiple-quantum-dot-multiple-photon dynamics in coupled-cavity photonic crystal slab systems by projecting the Hamiltonian onto a discrete basis of quasimodes. We apply this approach to spontaneous emission into two coupled cavities.

Photoionization cross section and intersublevel transitions in a one- and two-electron spherical quantum dot with a hydrogenic impurity

A detailed investigation of the optical properties of a spherical quantum dot (QD) containing one and two electrons has been performed for cases with and without a hydrogenic impurity. First, the photoionization cross section of both ${D}^{0}$ and ${D}^{\ensuremath{-}}$ impurities in the QD has been calculated for an on-center impurity. Second, the intersublevel optical absorption and oscillator strength between the ground and excited states have been examined based on the computed energies and wave functions. The full numeric matrix diagonalization technique has been employed in determining sublevel energy eigenvalues and their wave functions. The Poisson-Schr\odinger equations have been solved self-consistently in the Hartree approximation. In addition, quantum-mechanical many-body effects have been investigated in the local density approximation. The results are presented as a function of quantum dot radii and photon energies.

Quantum Dot Photon Statistics Measured by Three-Dimensional Particle Tracking

We present an instrument for performing correlation spectroscopy on single fluorescent particles while tracking their Brownian motion in three dimensions using real-time feedback. By tracking CdSe/ZnS quantum dots in water (diffusion coefficient approximately 20 microm2/s), we make the first measurements of photon antibunching (at approximately 10 ns) on single fluorophores free in solution and find fluorescence lifetime heterogeneity within a quantum dot sample. In addition, we show that 2-mercaptoethanol suppresses short time-scale intermittency (1 ms to 1 s) in quantum dot fluorescence by reducing time spent in the off-state.

Radiative emission dynamics of quantum dots in a single cavity micropillar

The light emission of self-assembled (In,Ga)As/GaAs quantum dots embedded in single GaAs-based micropillars has been studied by time-resolved photoluminescence spectroscopy. The altered spontaneous emission is found to be accompanied by a non-exponential decay of the photoluminescence where the decay rate strongly depends on the excitation intensity. A microscopic theory of the quantum dot photon emission is used to explain both, the non-exponential decay and its intensity dependence. Also the transition from spontaneous to stimulated emission is studied.