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01/09/2014 www.neel.cnrs.fr 1 Subnanosecond spectral diffusion of a single quantum dot in a nanowire G. Sallen, A. Tribu, T. Aichele*, R. André, L. Besombes, C. Bougerol, M. Richard, S. Tatarenko, K. Kheng, and J.-Ph. Poizat CEA/CNRS/UJF joint team "Nanophysics and semi-conductors" Institut Néel and INAC, Grenoble, France * Present address :Physics Institute, Humboldt University, Berlin, Germany

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01/09/2014 www.neel.cnrs.fr 2 Spectral diffusion Random spectral jumps of a narrow line as a result of fluctuating environment Described by two parameters : diffusion amplitude d : diffusion time d < : motional narrowing (dephasing) Lorentzian lineshape A. Berthelot et al, Nat Phys (2006) d > : wandering line : Gaussian lineshape

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Besombes et al, PRB (2002) Spectral diffusion of a single emitter Standard method : Record spectra time serie Time resolution > 1 ms * Resonant excitation of a fluctuating line, photon correlation on the luminescence. Time resolution > 1µs Zambusch et al, PRL (1993) * Photon-correlation Fourier spectroscopy. Time resolution > 20 µs Coolen et al, PRL (2008) Alternative methods :

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Our method Photon correlations on parts of the line : Best time resolution : 90 ps L sideH side t t t

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Whole line auto- correlation L side Auto- correlation L- H cross- correlation Results L sideH side a) b) t t t Slow detectors : time resolution = 800ps

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Robustness with respect to energy slot size Cross-correlation The cross-correlation does not depend on the size of the energy slots

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Robustness with respect to energy separation The probability of a spectral jump does not depend on its amplitude Cross-correlation

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~ 400 nm ~ 10 nm Our sample Single CdSe quantum dot inserted in a ZnSe nanowire XX CX X Lifetimes : X = 500 ps CX = 650 ps CX = 450 ps Antibunching @ T=220K : Tribu et al, NanoLett (2008) Photon correlation spectroscopy : Sallen et al, PRB (2009)

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Diffusion rate vs excitation power T=4K T=10K CX to X diffusion rate Spectral diffusion of the CX line (T=4K, T=10K) 10K / 4K => E trap = 1.1 meV Linewidth = cste => Single charge exploring the traps P CX sat

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Spectral diffusion possible scenario Conduction band QD 1.1 meV ZnSeCdSeZnSe 10 nm ~3 nm

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XX CX X The sign of the energy shift induced by the fluctuating environment is the same on X and XX. Correlated spectral diffusion XX X Fast detectors : time resolution= 90ps

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Conclusions * Simple and robust method to measure spectral diffusion with 90 ps resolution (4 orders of magnitude improvement compared to best existing resolution). * Spectral duration time gives the under which there is no spectral diffusion. * Opens new possibilities for the investigation of the very local environnement of single emitters.

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