Measurement of the time coherence of the single photons emitted by CdSe nanocrystals using photon correlation Fourier spectroscopy (PCFS)

摘要

CdSe nanocrystals are nanoobjects with remarkable fluorescence properties. At these scales (a few nm), quantum confinement creates discrete energy levels, depending on the nanocrystal size. The emission wavelength can be tuned from 450 to 600 nm by adjusting the nanocrystals diameter during their synthesis reaction. These emitters have many interesting optical properties, such as a broad absorption spectrum and a sharp emission line. They can be easily handled, and attached to molecules of biological interest (using the nanocrystals as fluorescent probes for instance). When deposited as a close-packed layer, they can be used in optoelectronics for the realization of solar cells, electroluminescent diodes or lasers. Finally, in the context of quantum optics, single photon emission can be obtained from an individual nanocrystal, even at room temperature. Such single photons can be used as bits in quantum cryptography. Interferences between single photons could also be used in quantum computing in order to realize logic gates, but for such experiments it is crucial to have coherent single photons. For an individual emitter to be used as a source of coherent photons, its emission spectrum must not be broadened by any dephasing mechanism. This property has been demonstrated by interferometric measurements for self-assembled InAs quantum dots in micropillars, showing coherence times as long as 650 ps, and two-photon interferences have been observed.