In the Floquet state, the original quantum state is replicated when light is irradiated on matters. It is generated by time-periodically driving the Bloch wavefunctions in crystals. By adopting such a concept, quantum states of matters can be easily manipulated with light, effectively used in quantum systems.
A POSTECH research team led by Professor Gil-Ho Lee and Gil Young Cho (Department of Physics) has developed a platform that can control the properties of solid materials with light and measure them.
Previous attempts to realize such states in condensed-matter systems have been limited by the transient nature of the Floquet states produced by optical pulses. Also, Floquet states last only for a short time of 250 femtoseconds.
In this new study, scientists reported on the generation of steady Floquet–Andreev states in a graphene Josephson junction (GJJ) by irradiating continuous microwaves. The intensity of the light has been decreased to one-trillionth the value of previous experiments. This mainly reduces the heat generation and enables continuously long-lasting Floquet states.
By developing novel superconducting tunneling spectroscopy, scientists could measure the Floquet states with high energy resolution. It was essential to demonstrate the Floquet state’s characteristics that vary depending on the intensity, frequency, and polarization of light applied to the device.
Professors Gil-Ho Lee and Gil Young Cho, who led the study, said, “This study is significant in that we have created a platform that can study the Floquet state in detail. We plan to investigate further the correlation between properties of light, such as polarization, and the Floquet states.”
- Park, S., Lee, W., Jang, S. et al. Steady Floquet–Andreev states in graphene Josephson junctions. Nature 603, 421–426 (2022). DOI: 10.1038/s41586-021-04364-8