Nov 7 2019
Scientists at KAIST have reported that they have detected a picosecond electron motion in a silicon transistor. The research has produced a new protocol for evaluating ultrafast electronic dynamics in an effective time-resolved mode of picosecond resolution.
Professor Heung-Sun Sim (left) and Co-author Dr Sungguen Ryu (right). Image credit: Korea Advanced Institute of Science and Technology
The electron motion was detected jointly with Nippon Telegraph and Telephone Corp. (NTT) in Japan and National Physical Laboratory (NPL) in the United Kingdom. This is the first-ever detection of such an effect.
Upon capturing an electron in a nanoscale trap in solids, its quantum mechanical wave function can present spatial oscillation at sub-terahertz frequencies. It is crucial to perform time-resolved detection of such picosecond dynamics of quantum waves because the detection offers a means to understand the quantum behavior of electrons in nano-electronics.
It is also applicable to quantum information technologies like the ultrafast quantum-bit processing of quantum computing and electromagnetic-field sensing with high sensitivity. However, it has been difficult to detect picosecond dynamics as the sub-terahertz scale is far more than the most advanced bandwidth measurement tools.
A research team from KAIST headed by Professor Heung-Sun Sim proposed a theory of ultrafast electron dynamics in a nanoscale trap, and put forward a scheme for the detection of the dynamics, which involves using a quantum-mechanical resonant state that forms next to the trap.
The coupling between the resonant state and the electron dynamics is turned on and off at a picosecond such that information related to the dynamics can be read out on the electric current that is produced when the coupling is turned on.
In collaboration with NPL, NTT achieved the detection scheme and used it on electron motions in a nanoscale trap developed in a silicon transistor. Through the control of electrostatic gates, a single electron was captured in the trap, and a resonant state developed in the potential barrier of the trap.
The turning on and off of the coupling between the resonant state and the electron was realized by aligning the resonance energy with the electron’s energy within a picosecond. The electric current that flows from the trap to an electrode through the resonant state was evaluated at just a few Kelvin degrees, unraveling the spatial quantum-coherent oscillation of the electron with a frequency of 250 GHz within the trap.
This work suggests a scheme of detecting picosecond electron motions in submicron scales by utilizing quantum resonance. It will be useful in dynamical control of quantum mechanical electron waves for various purposes in nano-electronics, quantum sensing, and quantum information.
Heung-Sun Sim, Professor, Korea Advanced Institute of Science and Technology
This study was published online in Nature Nanotechnology on November 4th, 2019. It was partially funded by the Korea National Research Foundation through the SRC Center for Quantum Coherence in Condensed Matter.