1. 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

2. 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

3. 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 :

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

5. 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

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

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

8. ~ 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)

9. 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

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

11. 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

12. 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.