Quantum light from a carbon nanotube

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  • 13 July 2007
Abstract
Carbon nanotubes provide a unique paradigm for mesoscopic physics: while strong one-dimensional (1D) confinement enhanced Coulomb interactions lead to striking new phenomena such as spin-charge separation, absence of spin-orbit and hyperfine interactions promise ultra-long electron spin coherence for applications in quantum information processing. Since the first observation of photoluminescence (PL) from semiconducting single-walled carbon nanotubes (CNTs), a basic understanding of their linear optical properties such as the role of strong exciton binding and chirality dictated optical excitations of CNTs has emerged. However, all optical experiments on CNTs to date can be explained using classical Maxwell's equations. Here, we report the first observation of quantum correlations in PL from a single CNT. Remarkably, the degree of antibunching that we obtain in photon correlation measurements indicates that a nanotube emits photons predominantly one-by-one, with a probability of two-photon emission that can be less than 5%. Unintentional carrier localization in random quantum dots (QDs) appears to be important in the CNTs that we studied: however, antibunching in photon cross-correlation measurements on nanotubes that exhibits two distinct PL lines, most likely originating from two different QDs within the same CNT, strongly suggest that inhibition of two-exciton generation by Auger processes is playing a dominant role in ensuring that photons are generated one at a time. In this sense, CNTs differ from atoms or molecules since they exhibit an optical anharmonicity primarily induced by interactions rather than phase-space filling. Ultra-low multi-photon emission probability suggests that carbon nanotubes could be used as a source of single photons for applications in quantum cryptography.

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