Scientists enable quantum imaging of synapses of artificial neurons

Professor Sun Fangwen’s research group of Academician Guo Guangcan’s team of University of Science and Technology of China and the research group of Zou Chongwen, researcher of the National Synchrotron Radiation Laboratory/School of Nuclear Science and Technology, prepared brain-like neuronal devices based on vanadium dioxide phase change films, and used the nitrogen-vacancy (NV) color center in diamond as a solid-state spin quantum sensor to detect the dynamic connection of neuronal synapses under external stimulation, demonstrating the multi-channel signal transmission and processing process in the brain-like nervous system. The results of this research were recently published in Science Advances.

Schematic diagram of the dynamic network structure of brain-like neurons Courtesy of University of Science and Technology of China

Brain-like neuronal devices, commonly known as brain-like chips, refer to the use of neuromorphic devices to simulate basic functions such as neurons and synapses in the human brain, and then further connect these neuromorphic devices to artificial neural networks to simulate complex functions such as information processing and storage of the “brain”. As a typical oxide quantum material, vanadium dioxide has a reversible insulating-metal phase transition near room temperature, which is an ideal material for the preparation of high switching ratio synaptic devices.

In this study, based on the research basis of vanadium dioxide in the past ten years, the researchers in the research group overcame the bottleneck of the preparation of single-crystal vanadium dioxide films with high-purity phase structure by using oxide molecular beam epitaxy equipment, grew high-quality vanadium dioxide epitaxial films, and prepared biological neurons and synaptic arrays through micro-nano processing, so as to realize the selective circuit conduction of multi-channel vanadium dioxide biterminal devices under electric field modulation and laser induction, thereby directly simulating the synaptic dynamic connection process between neurons. This connection between synapses is reflected in the formation of vanadium dioxide conductive wires and selectivity in spatial location, and is directly modulated by the applied electric field and the laser signal as an applied stimulus.

In addition, for the dynamic connection process between neuronal synaptic units, the experimenters innovatively used diamond NV color center as a solid-state spin quantum sensor to detect the formation of conductive filaments and real-time imaging. Due to the photothermal sensitivity of vanadium dioxide phase change system, compared with traditional microscopic imaging techniques, such as polarization infrared, Raman or near-field optics, the quantum sensing method based on diamond NV color center avoids the interference of the laser signal of the measurement system during the imaging process, thus showing unique advantages in the dynamic connection of synaptic units and real-time imaging research under the modulation of external stimulation laser signals.

According to the researchers, this quantum sensing imaging technology clearly reveals the association between multi-channel signal processing and conduction pathways and external stimuli in the vanadium dioxide brain nervous system, and provides a direct experimental basis for the construction of large-scale artificial synaptic stratification tissues and neuromorphological structures. (Source: Wang Min, China Science News)

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