A. N. Vamivakas

Subnatural linewidth single photons from a quantum dot.

The observation of quantum-dot resonance fluorescence enabled a new solid-state approach to generating single photons with a bandwidth approaching the natural linewidth of a quantum-dot transition. Here, we operate in the small Rabi frequency limit of resonance fluorescence--the Heitler regime--to generate subnatural linewidth and high-coherence quantum light from a single quantum dot. The measured single-photon coherence is 30 times longer than the lifetime of the quantum-dot transition, and the single photons exhibit a linewidth which is inherited from the excitation laser. In contrast, intensity-correlation measurements reveal that this photon source maintains a high degree of antibunching behavior on the order of the transition lifetime with vanishing two-photon scattering probability. Generating decoherence-free phase-locked single photons from multiple quantum systems will be feasible with our approach.

Strong extinction of a far-field laser beam by a single quantum dot.

Through the utilization of index-matched GaAs immersion lens techniques, we demonstrate a record extinction (12%) of a far-field focused laser beam by a single InAs/GaAs quantum dot. This contrast level enables us to report for the first time resonant laser transmission spectroscopy on a single InAs/GaAs quantum dot without the need for phase-sensitive lock-in detection.

Optical determination of electron-phonon coupling in carbon nanotubes

We report on an optical method to directly measure electron-phonon coupling in carbon nanotubes by correlating the first and second harmonic of the resonant Raman excitation profile. The method is applicable to 1D and 0D systems and is not limited to materials that exhibit photoluminescence. Experimental results for electron-phonon coupling with the radial breathing mode in 5 different nanotubes show coupling strengths from 3-11 meV. The results are in good agreement with the chirality and diameter dependence of the e-ph coupling calculated by Goupalov et al.

Widefield subsurface microscopy of integrated circuits

We apply the numerical aperture increasing lens technique to widefield subsurface imaging of silicon integrated circuits. We demonstrate lateral and longitudinal resolutions well beyond the limits of conventional backside imaging. With a simple infrared widefield microscope (lambda(0) = 1.2 microm), we demonstrate a lateral spatial resolution of 0.26 microm (0.22 lambda(0)) and a longitudinal resolution of 1.24 microm (1.03 lambda(0)) for backside imaging through the silicon substrate of an integrated circuit. We present a spatial resolution comparison between widefield and confocal microscopy, which are essential in integrated circuit analysis for emission and excitation microscopy, respectively.

Wide-range electrical tunability of single-photon emission from chromium-based colour centres in diamond

We demonstrate electrical control of the single-photon emission spectrum from chromium-based colour centres implanted in monolithic diamond. Under an external electric field, the tunability range is typically three orders of magnitude larger than the radiative linewidth and at least one order of magnitude larger than the observed linewidth. The electric and magnetic field dependence of luminescence gives indications of the inherent symmetry, and we propose Cr-X or X-Cr-Y-type non-centrosymmetric atomic configurations as the most probable candidates for these centres.

High Resolution, High Collection Efficiency in Numerical Aperture Increasing Lens Microscopy of Individual Quantum Dots

We demonstrate the application of a subsurface solid immersion technique to the photoluminescence spectroscopy of individual quantum dots. Contrasted with the conventional solid immersion microscopy, we used a numerical aperture increasing lens and moved the interface between the sample and the solid immersion lens away from the focal plane, thus diminished the influence of interface artifacts on the images obtained in a two-dimensional scan. Meanwhile, our technique has achieved a high spatial resolution of λ∕3 that is capable of resolving the spectroscopic features of single QDs. We also demonstrate that the collection efficiency of our system is six times better than that of a conventional confocal microscope with a high NA objective.

Single-dot optical emission from ultralow density well-isolated InP quantum dots

We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/μm2 is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

Direct measurement of spin dynamics in InAs/GaAs quantum dots using time-resolved resonance fluorescence

We temporally resolve the resonance fluorescence from an electron spin confined to a single self-assembled quantum dot to measure directly the spins optical initialization and natural relaxation timescales. Our measurements demonstrate that spin initialization occurs on the order of microseconds in the Faraday configuration when a laser resonantly drives the quantum dot transition. We show that the mechanism mediating the optically induced spin-flip changes from electron-nuclei interaction to hole-mixing interaction at 0.6 Tesla external magnetic field. Spin relaxation measurements result in times on the order of milliseconds and suggest that a

Nanoscale optical electrometer.

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Exciton-mediated one-phonon resonant Raman scattering from one-dimensional systems

magnetic field dependence, due to spin-orbit coupling, is sustained all the way down to 2.2 Tesla.