Frederic S. F. Brossard

Strongly coupled single quantum dot in a photonic crystal waveguide cavity

Cavities embedded in photonic crystal waveguides offer a promising route toward large scale integration of coupled resonators for quantum electrodynamics applications. In this letter, we demonstrate a strongly coupled system formed by a single quantum dot and such a photonic crystal cavity. The resonance originating from the cavity is clearly identified from the photoluminescence mapping of the out-of-plane scattered signal along the photonic crystal waveguide. The quantum dot exciton is tuned toward the cavity mode by temperature control. A vacuum Rabi splitting of ∼140 μeV is observed at resonance.

Registration of single quantum dots using cryogenic laser photolithography

We have registered the position of single InGaAs quantum dots using a cryogenic laser photolithography technique. This is an important advance towards the reproducible fabrication of solid-state cavity quantum electrodynamic devices, a key requirement for commercial exploitation of quantum information processing. The quantum dot positions were registered with an estimated accuracy of 50 nm by fabricating metal alignment markers around them. Photoluminescence spectra from quantum dots before and after marker fabrication were identical except for a small redshift (~1 nm), probably introduced during the reactive ion etching.

Plug and play single photons at 1.3 μm approaching gigahertz operation

We report a “plug and play” single photon source, fully integrated with an optical fiber, emitting at 1.3μm. Micropillars were patterned on a single layer InAs quantum dot wafer to guarantee a single pillar per fiber core. The single exciton peak filtered with a tunable optical filter was fed to a Hanbury Brown and Twiss interferometer, and the second order correlation function at zero delay was less than 0.5, indicating single photon emission. The measured decay dynamics under double-pulse excitation show that the single photon device can be operated at speeds greater than 0.5GHz.

Mapping cavity modes of ZnO nanobelts

ZnO nanostructures attract current interest because they have the potential to implement cavity quantum electrodynamics at room temperature. We report a photoluminescence mapping of ZnO nanobelts both at room temperature and 4.2 K. The multicavity modes were observed all over the belt surface, which were induced by Fabry–Perot interference. The emission from the belt surface is enhanced at both the ends and the sides of the belt, and is highly linearly polarized in the direction perpendicular to the long axis of the belt. The results are explained using finite-difference time-domain simulations.

Defect-Free Self-Catalyzed GaAs/GaAsP Nanowire Quantum Dots Grown on Silicon Substrate.

The III-V nanowire quantum dots (NWQDs) monolithically grown on silicon substrates, combining the advantages of both one- and zero-dimensional materials, represent one of the most promising technologies for integrating advanced III-V photonic technologies on a silicon microelectronics platform. However, there are great challenges in the fabrication of high-quality III-V NWQDs by a bottom-up approach, that is, growth by the vapor-liquid-solid method, because of the potential contamination caused by external metal catalysts and the various types of interfacial defects introduced by self-catalyzed growth. Here, we report the defect-free self-catalyzed III-V NWQDs, GaAs quantum dots in GaAsP nanowires, on a silicon substrate with pure zinc blende structure for the first time. Well-resolved excitonic emission is observed with a narrow line width. These results pave the way toward on-chip III-V quantum information and photonic devices on silicon platform.

Confocal microphotoluminescence mapping of coupled and detuned states in photonic molecules

We study the coupling of cavities defined by the local modulation of the waveguide width using confocal photoluminescence microscopy. We are able to spatially map the profile of the antisymmetric (antibonding) and symmetric (bonding) modes of a pair of strongly coupled cavities (photonic molecule) and follow the coupled cavity system from the strong coupling to the weak coupling regime in the presence of structural disorder. The effect of disorder on this photonic molecule is also investigated numerically with a finite-difference time-domain method and a semi-analytical approach, which enables us to quantify the light localization observed in either cavity as a function of detuning.

Cryogenic two-photon laser photolithography with SU-8

We have shown that photolithography can be used to create alignment markers on a semiconductor substrate at cryogenic temperatures. The epoxy resist SU-8 can be exposed effectively by two-photon absorption at a temperature of 4K. By this means a spectroscopy apparatus can be used to find the positions of randomly distributed structures at low temperatures, such as InGaAs∕GaAs quantum dots, and mark their positions. We present a systematic study of the optical exposure parameters for cryogenic two-photon laser photolithography with SU-8.

Cavity modes of tapered ZnO nanowires

We report on a cavity mode mapping of ZnO tapered nanowires using micro-photoluminescence spectroscopy at room temperature. Both the Fabry–Perot (FP) and the whispering gallery (WG) modes are identified in a single wire. The emission spectra from single nanowires comprise regular Lorentzian peaks, which arise from the FP interference between the ends of the nanowire. The overall intensity along the tapered wire varies periodically. This variation is ascribed to WG mode resonances across the nanowire. The results agree well with the theoretical calculations using the finite-difference time-domain method.

Optical fabrication and characterisation of SU-8 disk photonic waveguide heterostructure cavities

In order to demonstrate cavity quantum electrodynamics using photonic crystal (PhC) cavities fabricated around self-assembled quantum dots (QDs), reliable spectral and spatial overlap between the cavity mode and the quantum dot is required. We present a method for using photoresist to optically fabricate heterostructure cavities in a PhC waveguide with a combined photolithography and micro-photoluminescence spectroscopy system. The system can identify single QDs with a spatial precision of ±25 nm, and we confirm the creation of high quality factor cavity modes deterministically placed with the same spatial precision. This method offers a promising route towards bright, on-chip single photon sources for quantum information applications.

Inkjet-Printed Nanocavities on a Photonic Crystal Template

The possibility to create high Q cavities by the deposition of a thin film of a low refractive index material on the surface of a photonic crystal (PhC) template [1] has been rarely explored. The few experimental demonstrations to date have involved material-specific e-beam or UV exposure techniques. In this work we use a commercially available inkjet printer with fL droplet delivery to create nanocavities on-demand with structurally tunable resonance on the surface of a PhC template. We show that this fabrication method is particularly suited to the creation of 1 μm-wide strips with sub-100 nm film thicknesses on the PhC surface, resulting in high Q cavity modes with mode volume approaching a cubic wavelength. A new paradigm for a direct-written nanophotonics is thus established, allowing the efficient coupling of any solution-processable material [2] to optical modes by a simple, non-contaminating and local deposition method.