arXiv subjects

Kevin Hennessy

Publications and source records attributed to Kevin Hennessy.

6 recordsLinked to original sources

arXiv2009

Resolution of the mystery of counter-intuitive photon correlations in far off-resonance emission from a quantum dot-cavity system

Cavity quantum-electrodynamics experiments using an atom coupled to a single radiation-field mode have played a central role in testing foundations of quantum mechanics, thus motivating solid-state implementations using single quantum dots coupled to monolithic nano-cavities. In stark contrast to their atom based counterparts, the latter experiments revealed strong cavity emission, even when the quantum dot is far off resonance. Here we present experimental and theoretical results demonstrating that this effect arises from the mesoscopic nature of quantum dot confinement, ensuring the presence of a quasi-continuum of transitions between excited quantum dot states that are enhanced by the cavity mode. Our model fully explains photon correlation measurements demonstrating that photons emitted at the cavity frequency are essentially uncorrelated with each other even though they are generated by a single quantum dot.

cond-mat.mes-hall↗

arXiv2008

Quantum dot spectroscopy using cavity QED

Cavity quantum electrodynamics has attracted substantial interest, both due to its potential role in the field of quantum information processing and as a testbed for basic experiments in quantum mechanics. Here, we show how cavity quantum electrodynamics using a tunable photonic crystal nanocavity in the strong coupling regime can be used for single quantum dot spectroscopy. From the distinctive avoided crossings observed in the strongly coupled system we can identify the neutral and single positively charged exciton as well as the biexciton transitions. Moreover we are able to investigate the fine structure of those transitions and to identify a novel cavity mediated mixing of bright and dark exciton states, where the hyperfine interactions with lattice nuclei presumably play a key role. These results are enabled by a deterministic coupling scheme which allowed us to achieve unprecedented coupling strengths in excess of 0.15 meV.

cond-mat.mes-hall↗

arXiv2006

Strong coupling between single photons in semiconductor microcavities

We discuss the observability of strong coupling between single photons in semiconductor microcavities coupled by a chi(2) nonlinearity. We present two schemes and analyze the feasibility of their practical implementation in three systems: photonic crystal defects, micropillars and microdisks, fabricated out of GaAs. We show that if a weak coherent state is used to enhance the chi(2) interaction, the strong coupling regime between two modes at different frequencies occupied by a single photon is within reach of current technology. The unstimulated strong coupling of a single photon and a photon pair is very challenging and will require an improvement in mirocavity quality factors of 2-4 orders of magnitude to be observable.

quant-ph↗

arXiv2006

Validation of Lasing in Active Nanocavities

An unambiguous proof of lasing in an active nanocavity with ultrahigh spontaneous emission coupling factor (beta = 0.65) is presented. To distinguish the subtle lasing threshold features from possible material-related phenomena, such as saturable absorption in the gain medium, a series of active nanocavities with different values of beta have been designed to systematically approach the high-beta device. The demonstration of the lasing threshold is obtained through the observation of the transition from thermal to coherent light photon statistics that is well understood and identified in the beta << 1 lasing regime. The systematic investigation allows a more definitive validation of the onset of lasing in these active nanocavities.

physics.optics↗

arXiv2005

Frequency control of photonic crystal membrane resonators by mono-layer deposition

We study the response of GaAs photonic crystal membrane resonators to thin film deposition. Slow spectral shifts of the cavity mode of several nanometers are observed at low temperatures, caused by cryo-gettering of background molecules. Heating the membrane resets the drift and shielding will prevent drift altogether. In order to explore the drift as a tool to detect surface layers, or to intentionally shift the cavity resonance frequency, we studied the effect of self-assembled monolayers of polypeptide molecules attached to the membranes. The 2 nm thick monolayers lead to a discrete step in the resonance frequency and partially passivate the surface.

cond-mat.mtrl-sci↗

arXiv2005

Photon statistics from coupled quantum dots

We present an optical study of closely-spaced self-assembled InAs/GaAs quantum dots. The energy spectrum and correlations between photons subsequently emitted from a single pair provide not only clear evidence of coupling between the quantum dots but also insight into the coupling mechanism. Our results are in agreement with recent theories predicting that tunneling is largely suppressed between nonidentical quantum dots and that the interaction is instead dominated by dipole-dipole coupling and phonon-assisted energy transfer processes.

cond-mat.other↗