Dawn of a new era: A new type of quantum bit achieved in semiconductor nanostructures

Scientists have created quantum superposition states in semiconductor nanostructures, a significant advance for quantum computing. Using two carefully calibrated optical laser pulses, they facilitated a unique energy conversion process, forming quantum bits within a semiconductor nanostructure. (Artist’s concept.)

A German-Chinese research team has successfully created a quantum superposition state in semiconductor nanostructures, marking a significant breakthrough for Quantum computing. Achieving this using two specially calibrated short-wavelength optical laser pulses, the team was able to create quantum bits, or qubits, in semiconductor nanostructures.

A German-Chinese research team has successfully created quantum bits in semiconductor nanostructures. Using a special energy conversion process, the researchers created a superposition state in a quantum dot – an extremely small region of a semiconductor – in which an electron hole simultaneously possesses two levels. different energy. Such superpositions are fundamental to quantum computing.

Previously, creating such a state required a large-scale free-electron laser capable of emitting light in the terahertz range. Unfortunately, this wavelength is too long to precisely focus the beam on the quantum dot. However, this team achieved excitation with two carefully calibrated short-wavelength optical laser pulses.

The team led by Feng Liu from Zhejiang University in Hangzhou, along with a team led by Dr. Arne Ludwig from Ruhr University Bochum and other researchers from China and the UK, report their findings in the journal will Natural nanotechnologypublished online July 24, 2023.

Researchers have successfully created quantum superposition states in semiconductor nanostructures that can serve as a basis for quantum computing. The secret: two optical laser pulses act like one terahertz laser pulse. (Bochum research team: Hans-Georg Babin (left) and Arne Ludwig.) Image credit: RUB, Marquard

Exploitation of radiation enhancement processes

To achieve this superposition, the researchers used a radiative Auger transition. During this process, an electron recombines with a hole, releasing some of its energy in the form of photon and transfers part of it to another electron. The same process can be witnessed with electron holes – or in other words, electron shortages. In 2021, a team of researchers succeeded for the first time in specifically stimulating the radiative Auger transition in semiconductors.

In the current project, the researchers have shown that the Auger radiation process can be coherently controlled: they used two different laser beams whose intensities are in a specific ratio to each other. With the first laser, they excited an electron-hole pair in a quantum dot to create a quasiparticle consisting of two holes and one electron. With the second laser, they triggered the Auger radiation process to elevate a hole to a series of higher energy states.

Creating quantum superposition

The researchers used finely tuned laser pulses to create a superposition between the hole state and the higher energy state. Therefore, the hole exists in both states simultaneously. Such a superposition is the basis for quantum bits, which, unlike regular bits, exist not only in a “0” and a “1” state, but also in a superposition of both.

Hans-Georg Babin produced high-purity semiconductor samples for the experiment at Ruhr University Bochum under the supervision of Dr. Arne Ludwig at the Chair of Applied Solid State Physics headed by Professor Andreas Wieck. In the process, the researchers increased the overall uniformity of the quantum dots and ensured high purity of the structures created. These measures created favorable conditions for the Chinese partners working with Jun-Yong Yan and Feng Liu to carry out the experiments.

Reference: “Coherent control of high orbital holes in semiconductor quantum dots” by Jun-Yong Yan, Chen Chen, Xiao-Dong Zhang, Yu-Tong Wang, Hans-Georg Babin, Andreas D. Wieck, Arne Ludwig , Yun Meng, Xiaolong Hu, Huali Duan, Wenchao Chen, Wei Fang, Moritz Cygorek, Xing Lin, Da-Wei Wang, Chao-Yuan Jin and Feng Liu, July 24, 2023, Natural nanotechnology.
DOI: 10.1038/s41565-023-01442-y

The research was funded by the National Natural Science Foundation of China (grant codes 62075194, 61975177, U21A6006, U20A20164, 62122067), the Fundamental Research Funds for the Central Universities (2021QNA5006), the Ministry of Education and Federal Research (16KISQ009) and the German Research Foundation (DFH/UFA CDFA-05-06).