Energy is information. Lengthening the time during which a system is capable of retaining energy before losing it to the local environment is a key goal for the development of quantum information. This interval is called the “coherence time”. Several studies have been performed with the aim of retarding decoherence.
A study conducted by researchers at the University of Campinas’s Gleb Wataghin Institute of Physics (IFGW-UNICAMP) in São Paulo State, Brazil, in partnership with colleagues at the University of Michigan’s Physics Department in Ann Arbor, USA, and Sungkyunkwan University’s Advanced Institute of Nanotechnology (SAINT SKKU) in Seoul, South Korea, set out to understand the decoherence process on the femtosecond (10-15s) timescale.
An article describing the results was published inPhysical Review Letters(“Non-Markovian Exciton-Phonon Interactions in Core-Shell Colloidal Quantum Dots at Femtosecond Timescales”).
In the study, interactions between excitons (excited electrons) and phonons (quantum units of vibrational energy in a crystal lattice) were observed on the femtosecond timescale. A femtosecond is one quadrillionth of a second.
The use of a revolutionary ultrafast spectroscopy technique with high temporal and spectral resolution was fundamental to the success of the study, which was supported by FAPESP via a Young Investigator Grant awarded to Lázaro Aurélio Padilha Junior and a project conducted in partnership with the University of Michigan under the aegis of the São Paulo Research Foundation – FAPESP program São Paulo Researchers in International Collaboration (SPRINT).
Padilha was one of the principal investigators for the project, and Diogo Burigo Almeida, then a postdoctoral fellow at Michigan, was one of the main authors. The experiment was performed with semiconducting nanocrystals dispersed in a colloidal solution at cryogenic temperatures.
“We found that when the material is excited [by light], the light it emits changes color in under 200 femtoseconds. This is due to interaction between excitons and phonons. The excitons transfer part of the energy they receive to the crystal lattice. This causes a change of frequency and hence a change of emission color,” Padilha told.