Laser manipulation at a quantum scale

“Valleytronics”, an emerging alternative to standard electronics, has just received a boost. An international team of physicists has developed a new technique for manipulating information encoded in electrons, using ultra-fast lasers — as reported in Science¹ .

In conventional electronics, information is stored in binary digits as a series of 0s and 1s. But quantum theory allows information to be encoded in certain properties of electrons as “superpositions” of both 0 and 1 at the same time. This could potentially allow for faster, more efficient data processing.

Examples of such quantum properties are the so-called “valleys” found in single-layer samples of specific transition metals dichalcogenides. A valley is a state in which electrons have certain values of momentum, at which point they become particularly responsive to manipulation with polarized light. To be of practical use, researchers need to precisely control these valley states, allowing information to be encoded in them. 

It was thought that to achieve this level of manipulation you would need to control the valleys using a magnetic field that was so strong, it could only be generated by expensive magnets that are not easily available. But the team of physicists — including Lain-Jong Li and Ming-Hui Chiu at the King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia — has created this level of control without any magnets, using lasers instead. They used a series of ultra-fast laser pulses to manipulate two valleys in a single-layer sample of tungsten diselenide, by shifting their valley states energies. 

“We have shown the capability to manipulate the quantum states. If you give us a 0, we can manipulate it to become a 1, or even a superposition of 0 and 1.” says team member Xiaoping Hong at the University of California, Berkeley. “And you can do this within one picosecond.”

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