Engineering the quantum states in solids using light

Date:
March 30, 2022
Source:
Pohang University of Science & Technology (POSTECH)
Summary:
A research team has developed a platform that can control the
properties of solid materials with light and measure them.



FULL STORY ==========================================================================
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.


========================================================================== Recognized for developing a platform to control and measure the properties
of materials in various ways with light, the findings from the study were published in the top international academic journal Nature on March 15,
2022 (GMT).

The electrical properties of a material are determined by the movement
of electrons in the material. For example, a material is defined as a
metal if electrons can move freely, otherwise it is an insulator. In
order to change the electrical properties of these solids, applying
heat or pressure or adding impurities have been generally used. This
is because the change in the position of the atoms in the solid changes
the movement of electrons accordingly.

In contrast, the Floquet state, in which the original quantum state is replicated when light is irradiated on matters, has been proposed. By
adopting such a concept, quantum states of the matters can be easily manipulated with light, which can be effectively used in quantum systems.

In previous experiments, the light intensity for realizing Floquet
state in solids was enormous due to the high frequency of light. Also,
Floquet states last only for a very short time of 250 femtoseconds (1 femtosecond is one trillionth of a second). Due to their transient nature,
more quantitative studies of their characteristics have been limited.

POSTECH research team succeeded in the experimental realization of
the steady Floquet state in a graphene Josephson junction (GJJ) and by irradiating continuous microwaves on it. The intensity of the light has
been decreased to one trillionth the value of previous experiments, significantly reducing the heat generation and enabling continuously long-lasting Floquet states.

The research team also developed a novel superconducting tunneling
spectroscopy to measure the Floquet states with high energy
resolution. This is necessary to quantitatively verify the characteristics
of the Floquet state that varies depending on the intensity, frequency
and polarization of light applied to the device.

"This study is significant in that we have created a platform that
can study the Floquet state in detail," explained professors Gil-Ho
Lee and Gil Young Cho who led the study. They added, "We plan to
further investigate the correlation between properties of light, such
as polarization, and the Floquet states." This study was conducted
with the support from the Samsung Science and Technology Foundation,
National Research Foundation of Korea, Institute for Basic Science, Air
Force Office of Scientific Research, and Elemental Strategy Initiative conducted by the MEXT.


========================================================================== Story Source: Materials provided by Pohang_University_of_Science_&_Technology_(POSTECH).

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sein Park, Wonjun Lee, Seong Jang, Yong-Bin Choi, Jinho Park,
Woochan
Jung, Kenji Watanabe, Takashi Taniguchi, Gil Young Cho, Gil-Ho Lee.

Steady Floquet-Andreev states in graphene Josephson
junctions. Nature, 2022; 603 (7901): 421 DOI:
10.1038/s41586-021-04364-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220330103106.htm

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