Research ArticlePHYSICS

Near-field strong coupling of single quantum dots

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Science Advances  02 Mar 2018:
Vol. 4, no. 3, eaar4906
DOI: 10.1126/sciadv.aar4906
  • Fig. 1 SC via precise nanopositioning of a resonator probe.

    (A) Illustration of the PNR probe interacting with QDs embedded in a polymer film. Left panel: The spectrum of a QD changes significantly when coupled to the slit-like PNR at the tip apex. Inset: SEM image of a nanoresonator at the apex of a probe tip. Scale bar, 100 nm. a.u., arbitrary unit. (B) Map of the electric field distribution of the resonator mode used in the experiment. The slightly different lengths of the two tines account for fabrication imperfections. The + and − signs indicate the instantaneous charge distribution highlighting the mode’s weakly radiative quadrupolar character. Scale bar, 50 nm.

  • Fig. 2 Separation-dependent coupling strength.

    (A) Second-order autocorrelation of the photons emitted by a single QD in the absence of the probe. (B) PL map of the QD scanned beneath a PNR. The white circles indicate the positions in which the spectra have been recorded. Scale bar, 100 nm. (C) Open yellow circles: Normalized line cut of the PL map in (B) (arrow). Full blue circles: Integrated spectral amplitude recorded at the positions indicated by white circles in (B). Red circles: Coupling strength (right axis) used to model the SC spectra in (D). (D) Gray lines: Normalized spectra recorded for different coupling strengths. Solid lines: Spectra obtained from the quantum optical model with contribution of neutral state (blue) and charged state (red).

  • Fig. 3 QD detuning at high excitation rates.

    (A) Fluorescence spectra of uncoupled QDs. With increasing excitation rate (bottom to top), the peak intensity indicates a blue shift. (B) Spectra for increasing pump rate (gray lines, bottom to top) overlaid with calculated spectra (solid lines) for different detunings. (C) Peak positions for a range of detunings induced by different excitation rates of three different QDs. The Rabi peak positions of the neutral (charged) QD state based on the quantum model are indicated by the solid black (gray) lines. The gray dashed (dotted) line indicates the QD (PNR) resonance.

  • Fig. 4 Enhanced coupling of QD and PNRs due to collective coupling of band-edge states and near-field proximity effect.

    (A) Diagram of energy levels of a CdSeTe/ZnS nanocrystal weakly coupled (top) and strongly coupled (bottom) to a resonator. Fine-structure splitting into bright (black lines) and dark states (gray lines). Incoherent excitation from the ground state G into a pump state P and subsequent relaxation to the band edge E. (B) Top: Sketch of the near-field distribution at the apex of the resonator (pure mode). Bottom: Strongly coupled mesoscopic emitter influences the pure mode field via near-field proximity interaction (influential and image charging).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaar4906/DC1

    Supplementary Text

    fig. S1. Scanning probe fabrication.

    fig. S2. SEM characterization.

    fig. S3. Schematic of the optical setup.

    fig. S4. Simulated mode profiles and far-field spectra of PNRs for different gap widths and slit lengths between 80 and 440 nm.

    fig. S5. Calculating the coupling strength.

    fig. S6. Near-field proximity coupling.

    fig. S7. Purcell factor of PNR.

    fig. S8. Emission and excitation near-field distribution.

    fig. S9. QD resonance shift for high excitation rates.

    fig. S10. Coupling of a QD to an unstructured gold tip.

    fig. S11. Weak coupling PNR scanning probe.

    fig. S12. Difference between excitation and emission enhancement.

    fig. S13. Calculated fluorescence peaks for different excitation rates for an emitter scanned through a Gaussian field profile with a Purcell factor reaching up to 1000.

    fig. S14. Cavity characterization.

    fig. S15. Five-level diagram of the QD.

    fig. S16. Decomposing the emission of a strongly coupled QD.

    fig. S17. Reversible blue shift for increased excitation rates during SC.

    fig. S18. Collection of spectra of five different QDs in SC with the PNR.

    fig. S19. Collective coupling of a multilevel emitter with a resonant cavity.

    fig. S20. Saturation of the strongly coupled system.

    References (4999)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Scanning probe fabrication.
    • fig. S2. SEM characterization.
    • fig. S3. Schematic of the optical setup.
    • fig. S4. Simulated mode profiles and far-field spectra of PNRs for different gap widths and slit lengths between 80 and 440 nm.
    • fig. S5. Calculating the coupling strength.
    • fig. S6. Near-field proximity coupling.
    • fig. S7. Purcell factor of PNR.
    • fig. S8. Emission and excitation near-field distribution.
    • fig. S9. QD resonance shift for high excitation rates.
    • fig. S10. Coupling of a QD to an unstructured gold tip.
    • fig. S11. Weak coupling PNR scanning probe.
    • fig. S12. Difference between excitation and emission enhancement.
    • fig. S13. Calculated fluorescence peaks for different excitation rates for an emitter scanned through a Gaussian field profile with a Purcell factor reaching up to 1000.
    • fig. S14. Cavity characterization.
    • fig. S15. Five-level diagram of the QD.
    • fig. S16. Decomposing the emission of a strongly coupled QD.
    • fig. S17. Reversible blue shift for increased excitation rates during SC.
    • fig. S18. Collection of spectra of five different QDs in SC with the PNR.
    • fig. S19. Collective coupling of a multilevel emitter with a resonant cavity.
    • fig. S20. Saturation of the strongly coupled system.
    • References (49–99)

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