Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J10: Focus Session: Optical Properties of Nanostructures II: Quantum-Dot-Coupled Systems |
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Sponsoring Units: DMP Chair: Feng Wang, University of California, Berkeley Room: 304 |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J10.00001: Optical Detection and Control of Single Magnetic Ions in Photonic Microcavities Invited Speaker: As the density of magnetic information storage scales upwards, the number of magnetic moments in each bit decreases. This pathway ends with the need to manipulate a single spin, a requirement that is also important for nascent information processing schemes including quantum computation. Current demonstrations of coherent single spin control include electron spins in semiconductor quantum dots and nitrogen-vacancy centers in diamond \footnote{R. Hanson and D. D. Awschalom, \textit{ Nature } \textbf{453}, 1043 (2008).} . Single magnetic ions in semiconductors have also emerged as an intriguing spin system due to their surprising ability to be manipulated in zero-field. Manganese (Mn) ions in gallium arsenide (GaAs) are strongly exchange coupled to the charge carriers and can be rapidly controlled either optically or electrically in bandgap- engineered heterostructures. Recently we demonstrated optical control and readout of a small ensemble of Mn ion spins in a GaAs quantum well without magnetic materials or applied magnetic fields\footnote{R. C. Myers, M. H. Mikkelsen, J.-M. Tang, A. C. Gossard, M. E. Flatt\'{e}, and D. D. Awschalom, \textit{ Nature Materials} \textbf{7}, 203 (2008).}. In the limit of low doping levels, their spin lifetimes increase with decreasing concentration as the ions become isolated. Here we describe the spatially-resolved observation and manipulation of isolated Mn spins integrated within photonic microcavities. A single magnetically-doped GaAs quantum well is fabricated within both microdisk and vertical Fabry-Perot cavities in which their respective cavity modes are coupled to the neutral Mn acceptor emission. Scanning micro-photoluminescence measurements reveal cavity-coupled emission and a dramatic increase in the measured signal to noise ratio, thereby allowing direct imaging of narrow linewidth luminescence from the Mn moments. These Mn ion spins are optically polarized at zero-field, exhibit long spin lifetimes, and may be manipulated through a variety of techniques. [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:03PM |
J10.00002: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 12:03PM - 12:15PM |
J10.00003: Silicon nanocrystal photoluminescence in cylindrical whispering gallery resonators P. Bianucci, J.R. Rodr\'Iguez, C.M. Clements, J.G.C. Veinot, A. Meldrum We present photoluminescence studies of Silicon-nanocrystal (Si-NC) coated cylindrycal microcavities. The coatings were prepared by dip-coating standard optical fibers with a solution-based precursor followed by a high-temperature annealing step. The photoluminescence spectra measured perpendicular to the fiber axis show high Q-factor ($\sim$2500) whispering gallery modes, and allows distinction between TE and TM modes. We also show a proof-of-principle implementation of a far-field refractometric sensor using a nanocrystal-coated fiber. [Preview Abstract] |
Tuesday, March 17, 2009 12:15PM - 12:27PM |
J10.00004: Optical Response of Strongly Coupled Quantum Dot-Metal Nanoparticle Systems: Double Peaked Fano Structure and Bistability Ryan Artuso, Garnett Bryant We study the optical response of a semiconductor quantum dot (SQD) coupled with a metal nanoparticle (MNP). In particular, we explore the relationship between the size of the constituents and the response of the system. We identify, three distinct regimes of behavior in the strong field limit that each exhibit novel properties. In the first regime, we find that the energy absorption spectrum displays an asymmetrical Fano shape (as previously predicted). It occurs when there is interference between the applied field and the induced field produced by the SQD at the MNP. When the coupling is increased by increasing the size of the SQD, we find a double peaked Fano structure in the response. This second peak occurs when the induced field becomes stronger than the external field. As the coupling is further increased by increasing the sizes of both the SQD and the MNP, we find a regime of bistability. This originates when the self-interaction of the SQD becomes significant. We explore these three regimes in detail and set bounds on each. [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 12:39PM |
J10.00005: Excitons and plasmons in coupled nanoparticles and nanowires Pedro L. Hernandez-Martinez, Alexander O. Govorov In this study, we develop theoretical models of coupled nanoparticles (NPs) and nanowires (NWs). In particular, we focus on exciton energy transfer between NPs and NWs and consider both metal and semiconductor nanocrystals. We obtain analytical equations for the long distance limit and a numerical solution for the general case. For long distances, the energy transfer rate is proportional to 1/d\^{}5, where $d$ is the distance between NP and NW [1]. In a coupled NP-NW structure, excitonic energy can be efficiently extracted and channeled to nanowires/nanotubes by utilizing the F\"{o}rster energy transfer mechanism [1,2]. The calculated energy transfer rates are in good agreement to the experimental values [2]. The NP-NW system has potential for applications in optoelectronic devices and sensors [3]. [1] P. Hernandez-Martinez, A. O. Govorov, Phys. Rev. B, B 78, 035314 (2008). [2] J. Lee, A. O. Govorov, and N. A. Kotov, Nano Letters 5, 2063-2069 (2005). [3] J. Lee, P. Hernandez, J. Lee, A. O. Govorov, and N. A. Kotov, Nature Materials, 6, 291 -- 295 (2007). [Preview Abstract] |
Tuesday, March 17, 2009 12:39PM - 12:51PM |
J10.00006: High-transmission ridge nanoapertures for quantum dot devices Akihiro Kirihara, Junichi Fujikata, Toshihiro Nakaoka, Naoto Kumagai, Katsuyuki Watanabe, Masayuki Shirane, Shunsuke Ohkouchi, Shinichi Yorozu, Yasuhiko Arakawa We report on double-ridge apertures to enhance the coupling between a single quantum dot (QD) and optical field. The double-ridge aperture has two metallic tips protruding inward and facing each other, which work as an effective antenna for a QD just below the tips. We performed FDTD simulation to optimize the apertures, and fabricated them on InAs/GaAs QDs emitting at 960nm. By single-dot PL spectroscopy through the double-ridge aperture, we demonstrated 5-6 times enhancement in PL extraction efficiency, compared to that through a conventional circular aperture. Because our double-ridge aperture works not only as an optical antenna but also as an electrode for a QD, it will be applicable to electrically-driven photon generators or photon detectors. [Preview Abstract] |
Tuesday, March 17, 2009 12:51PM - 1:03PM |
J10.00007: Polarization and Angle Dependent Spontaneous Emission Rates in Hybrid Metal-Semiconductor Nanostructures Yikuan Wang, Tianyu Yang, Mark Tuominen, Marc Achermann Recently, the coupling of a dipole emitter to surface plasmons (SPs) of metal nanostructures has attracted much attention for its potential applications in light emitting devices. Our time-resolved photoluminescence (PL) study on the emission of CdSe/ZnS core/shell nanocrystals (NCs) deposited on a two-dimensional array of gold nanodiscs demonstrates that the spontaneous emission of dipole emitters is strongly dependent on the detection angles and polarizations. The in-plane, s-polarized PL measurements are independent on detection angles, and can be described by the PL decay dynamics of two NC subsets: the emission from NCs on the dielectric substrate and from NCs on the gold nanodiscs that experience non-radiative quenching by the metal structures. The out-of-plane, p-polarized PL measurements show an additional decay caused by SP-induced enhancement of the spontaneous emission rate. This angular-dependent enhancement is explained by interactions between NC dipole moments and the out-of-plane SP resonance of the gold nanodiscs. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:15PM |
J10.00008: Decay-rate distribution of single quantum dots in nanometer-scale proximity to a metal film Matthew Pelton, Xiaohua Wu Recently, the interaction between fluoresecent colloidal semiconductor quantum dots and plasmonic metal nanostructures has attracted great interest, both for the development of a basic understanding of nanoscale photophysics and for potential applications in improved light-emitting devices and integrated plasmonic circuits. Time-resolved measurements on single dots are required in order to overcome the obscuring effects of ensemble averaging and of time averaging, and thus reveal the physical mechanisms of dot-metal interaction. In this work, we present measurements of photoluminescence decay dynamics from single colloidal CdSe/ZnS core-shell quantum dots in nanometer-scale proximity to a smooth gold film. We extract the decay rate, $k_m$, for each dot when it is in its maximum-intensity state, thereby removing the effects of nonradiative decay-rate fluctuations. We find that, as the separation between the dot and the metal decreases, the $k_m$ distribution becomes broader and its maximum increases. The increase in maximum decay rate is caused by stronger energy tranfer from the quantum dot to the metal film, as expected. The broader distribution of decay rate, on the other hand, reflects inherent variations in the interactions between individual dots and the metal film. [Preview Abstract] |
Tuesday, March 17, 2009 1:15PM - 1:27PM |
J10.00009: Demonstration of Optical Resonances in a Cylinder-Shell Lattice of Quantum Dots Jared Maxson, Slava Rotkin We present a model for the calculation of the optical response of a cylinder-shell of quantum dots or metallic nanoparticles. We model such a shell cluster as a lattice of non-permanent point dipoles with a known polarizability and a single transition frequency. We then utilize the second quantization formalism to compute the cluster response. The eigenmodes and quantum mechanical response function of the lattice interacting with an external field, polarized respective to the cylinder axis, are calculated numerically. The cylinder radius is treated as a parameter to identify resonator effects due to the cylindrical geometry. Varying the frequency of the external field, regions of response maxima are determined. In these regions resonant interaction between the coupled dipoles results in transferring significant oscillator strength into a few eigenmodes of the cluster, having high spatial and temporal coherence with the external field. Further analysis of the spatial distribution of dipoles in each region of response maxima reveals significant contributions from groups of modes with equal angular momenta, permitting rigorous excitation classification. [Preview Abstract] |
Tuesday, March 17, 2009 1:27PM - 1:39PM |
J10.00010: Two-Photon Transitions in Molecular Quantum Dot System Michael Scheibner, Ilya Ponomarev, Danny Kim, Allan Bracker, Daniel Gammon Two-photon excitations are at the heart of important nonlinear optical processes and provide a key to the rich physics and fresh opportunities of designer quantum materials. In this study we consider double dot quantum dot molecules (QDMs) that were designed by molecular beam epitaxial growth to exhibit either electron or hole tunnel coupling of the two dots. The electron or hole levels of the two dots can be tuned into resonance with an applied electric field which is created by a Schottky diode structure surrounding the QDMs. Highly sensitive photoluminescence excitation spectroscopy is used to study sequential and simultaneous two-photon transitions in the absorption spectrum of the molecular biexciton in such a QDM. We identify a new two-photon transition which is the first example of a simultaneous, coherent optical excitation of a pair of QDs in a weakly tunnel coupled regime. We further show that a photoluminescence excitation measurement with stereo-chromatic detection can be used to gain access to the spin physics in this regime. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 1:51PM |
J10.00011: Qubit extraction and manipulation in optically-driven self-assembled quantum dot molecules. J.E. Rolon, S.E. Ulloa Semiconductor quantum dot molecules (QDMs) allow studies of different mechanisms of coherent optoelectronic control of excitonic states in the pursuit of stable and well characterized qubits. In this work, we develop a realistic calculation of the dressed spectrum and exciton dynamics of InAs/GaAs QDMs. The dressed spectrum contains electron and hole tunneling as well as exciton F\"{o}rster resonant energy transfer (FRET) level anticrossing signatures, from which we derive an effective Hamiltonian using a projection operator formalism. The state dynamics is analyzed using a multilevel Lindblad master equation, in which the projected density matrix is obtained by partial tracing of the irrelevant exciton degrees of freedom. We find that the interplay of FRET and carrier tunneling can produce a charge qubit subspace whose indirect exciton character makes it resilient to lifetime limited decoherence. Furthermore, it is shown that a set of universal quantum gates can be constructed and its unitarity assured by the application of an external electric field that prevents the mixture of qubit subspace dynamics with other excitonic degrees of freedom, present upon optical excitation. [Preview Abstract] |
Tuesday, March 17, 2009 1:51PM - 2:03PM |
J10.00012: Electric field induced manipulation of static and dynamic optical properties of coupled quantum dots Y.K. Verma, S.N. Ghosh, C.G.L Ferri, M. Gallardo, D. Kelley, S. Ghosh A system of coupled quantum dots (QDs) provides pathways for efficient and controlled energy transfer. In such a system, electronic excitations get delocalized over the several QDs and lead to the creation of macroscopic electronic states. We present a novel way to induce structural order in chemically synthesized GaSe QDs by embedding them in a matrix of nematic liquid-crystal (NLC) molecules. Photoluminescence (PL) from the QD-NLC mixture exhibits large red-shift in the emission spectrum ($\sim $200 meV) which implies the formation of strongly coupled QD aggregates. Dynamic Light Scattering measurements on isolated and QD-NLC matrix reveal the aggregates to be composed of several tens of QDs, while PL measurements show that their emission is highly anisotropic, being strongly polarized along the axis of aggregation. These structures can further be spatially re-aligned in situ without destroying the inter-dot coupling by the application of an in-plane electric field. Time-resolved measurements reveal a faster excitonic recombination in the QD-NLC matrix in comparison to that in isolated QDs which is attributed to facile energy transfer processes. [Preview Abstract] |
Tuesday, March 17, 2009 2:03PM - 2:15PM |
J10.00013: Electronic and optical properties of laterally coupled InGaAs quantum dots Jie Peng, Gabriel Bester We calculate the electronic and optical properties of laterally coupled InGaAs/GaAs quantum dot molecules under lateral electric field using empirical pseudopotentials and configuration interaction. Our model structure is directly taken from recent experiments where an In-poor basin develops below the dots. The coupling of the electron states is significantly enhanced by the presence of the basin, while the holes remain mainly uncoupled. At the proper electric field ---between 0 V/cm and 200 V/cm, depending on the dot molecule--- the electron states can be tuned to be evenly distributed between both dots, forming bonding and antibonding states. The optical absorption is shown to exhibit two bright transitions, mostly independent of the applied field. In emission, we argue that a fast electron-dynamics must be introduced, since the electrons are not subject to a true potential barrier between the dots and consequently only the lowest of the electron states is occupied. Following this approach, we obtain only one bright peak at high electric fields and two peaks (at higher temperature, four peaks) at the tuning point of the electron states. The results are shown to compare very well with recent experiments. A simple 4x4 Hamiltonian is derived to explain the results in the intuitive dot-localized basis. [Preview Abstract] |
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