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Photon correlations probe spectral diffusion

Semiconductor quantum dots have potential applications, in particular in the field of quantum cryptography. The precise determination of the emission properties of these emitters is thus an important stake. The NPSC team has developed a new experimental technique that can be used to measure a fundamental property of these emitters based on the correlation of photons stemming from the same transition.

Published on 4 March 2011

A single quantum dot can be considered to be an artificial atom that emits photons at a well defined wavelength upon the radiative relaxation of an excited electron. This nanometer-scale box is not isolated but is embedded in a matrix in which other charges fluctuate, for instance by trapping/detrapping on crystal defects. This fluctuating environment leads to fast random spectral jumps (called spectral diffusion) of the narrow emission line and results in an apparent broadening of the transition.

We present a new experimental method for measuring the characteristic times of spectral diffusion of the photoluminescence based on the correlation of photons emitted by the same quantum dot transition. We performed both autocorrelation measurements on half of the emission peak and cross-correlation measurements between the high energy and low energy halves of the emission peak. This allowed us to measure its characteristic times τD and τCX. This measurement is done with a time resolution of 90 ps, four orders of magnitude better than previously reported results.

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