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image: Optical microcavity as a pulsating neuron (visualization: Mateusz Krol, source: Faculty of Physics, University of Warsaw)
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Credit: Mateusz Krol, source: Faculty of Physics, University of Warsaw)
Scientists from the Faculty of Physics of the University of Warsaw and the Polish Academy of Sciences have used photons to create a spiked neuron, that is, the building block of the future network processor of photonic neurons. So-called neuromorphic devices, i.e. systems that mimic the behavior of the biological brain, which researchers are working on, are the future of artificial intelligence, as they enable much faster information processing. and efficient. We can read the results of their work in the latest “Laser and Photonics Review”.
The mammalian brain is one of the most complex and efficient systems in the world. Already in the 1990s, neurobiological scientists showed that a single area of the macaque’s cortex was able to analyze and classify visual patterns in just 30 milliseconds, although each of the neurons involved in this process sends less than three messages in the form of electrical impulses. This is made possible by a large number of synapses – the connections between neurons – in the neural network of the macaque’s brain.
The human brain is part of an even more powerful machinery. It is made up of 100 billion neurons, each creating on average several thousand connections with other nerve cells. This creates a neural network of approx. 100 trillion connections, thanks to which our brain is able to recognize, reason and control movement at the same time – it performs trillions of operations per second, using only 20-25 watts of power. In comparison, conventional processors use ten times the power to recognize only a thousand different types of objects. This astonishing difference and the exceptional performance of the brain are due, among other things, to the biochemistry of neurons, the architecture of neuronal connections and the biophysics of neural computing algorithms.
Society’s appetite for information continues to grow, so we need to process that information faster and more comprehensively. Conventional computing systems may not meet the growing demand for more computing power while increasing energy efficiency. The solution to the problem may be so-called neuromorphic devices that mimic the actions of the biological brain. They are the future of artificial intelligence, as they enable much faster and more efficient processing of information in tasks such as image recognition.
Scientists from the Faculty of Physics of the University of Warsaw and the Polish Academy of Sciences, in an article published in “Laser and Photonics Review”, proposed the use of photons in a way that allows the creation of spiked neural networks. Krzysztof Tyszka of the Faculty of Physics at the University of Warsaw, who is the first author of the book, points out that photonic systems provide communication at the speed of light, low losses and low power consumption. The advantage of photons is that their propagation takes place practically without loss of energy. – Unfortunately, because they interact in a relatively weak way, it is difficult to use them to carry out computational operations in a way analogous to electronic systems – adds the scientist.
– In our research, we propose a solution in which photons interact strongly with particles of very low mass, called excitons – explains Barbara Pietka from the Polaritone Laboratory of the Faculty of Physics of the University of Warsaw. This strong interaction is possible when photons and excitons are trapped together in the so-called optical microcavities, which forces repetitive energy exchanges between them. This type of synergy generated in the microcavity between a photon and an exciton is so persistent that physicists call it a quasiparticle and call it excision-polariton (or polariton for short).
Polaritons have unique properties, especially under the right conditions they can show a phase transition in a Bose-Einstein condensate. In such a state, the previously independent multiple polaritons become indistinguishable. – Based on our latest experiment, we were the first to notice that when polaritons are excited by laser pulses, they emit light pulses in a way that mimics the spike of biological neurons – describes Magdalena Furman, Ph. D. student involved in research at the Polariton Laboratory of the Faculty of Physics of the University of Warsaw, This effect is directly related to the phenomenon of Bose-Einstein condensation, which inhibits or enhances the emission of pulses.
Andrzej Opala of the Institute of Physics of the Polish Academy of Sciences, who together with Michal Matuszewski developed the theoretical foundations combining polariton research with the LIF model of a neuron (Leaky Integrate-and-Fire model), that now the group is working on solving the problem of scalability, ie connecting many neurons in a network. – We propose to use a new computing paradigm based on the coding of information with pulses that trigger a signal only when it successively arrives at the neuron, at the right time – explains the researcher. Currently, neural networks use layers of interconnected neurons that fire pulses based on the importance assigned to each connection (in the mathematical description we speak of “weight”). Unlike this type of solution, in the optical neural network developed by Polish researchers, described in the journal “Laser and Photonics Review”, neurons fire (i.e. activate) in response to a pulse train, which can have different intensities and different time intervals. As for biological neurons which are excited by electrical impulses, there is a certain threshold above which this train of impulses reaching the neuron triggers a signal which will be transmitted. Polaritons make it possible to imitate a biological system, since only stimulation with the appropriate number of photons, beyond a certain threshold, leads to the formation of a Bose-Einstein condensate, then to the emission of a flash runs on the picosecond scale which is a signal for the next neuron.
Importantly, the sample, which was used by scientists to trap photons and observe the condensate of exciton polaritons, was synthesized on-site at the Faculty of Physics, University of Warsaw, in Wojciech’s group Pacuski. Scientists arranged the atoms of different types of semiconductor crystals layer by layer through molecular beam epitaxy to create a prototype photonic neuron. A temperature of 4K (liquid helium) was needed to reach the Bose-Einstein condensate state. – Our additional goal is to transfer the experiment from cryogenic conditions to room temperature – says Jacek Szczytko from the Faculty of Physics of the University of Warsaw. – Research is needed on new materials which will make it possible to obtain Bose-Einstein condensates also at high temperatures. For photonic neurons to network, they must be able to transmit signals to each other. Ideally, the direction of transmission, i.e. the wiring diagram, could be easily changed as needed.
– Scientists are always facing new challenges in their research on neuromorphic systems. Our new idea of recreating the peak of biological neurons in the optical domain can be used to create a network and then a neuromorphic system in which information is sent orders of magnitude faster and more energy-efficiently compared to solutions existing – concludes Krzysztof Tyszka.
An international team of scientists conducted research supported by, among others, the National Science Center (grants 2020/37B/ST3/01657, 2020/04/X/ST7 01379, 2020/36/T/ST3/00417), Center for Atomic Molecular and Optical Physics, and the European Union FET-Open Horizon 2020 program, “TopoLight” grant (964770).
Physics and Astronomy at the University of Warsaw appeared in 1816 as part of the then Faculty of Philosophy. In 1825, the Astronomical Observatory was established. Currently, the Faculty of Physics at the University of Warsaw includes the following institutes: Experimental Physics, Theoretical Physics, Geophysics, the Department of Mathematical Methods in Physics and the Astronomical Observatory. Research covers almost all areas of modern physics, at scales ranging from quantum to cosmological. The Faculty’s research and teaching staff numbers more than 200 university professors, including 81 professors. About 1,000 students and more than 170 doctoral students study at the Faculty of Physics of the University of Warsaw.
SCIENTIFIC PUBLICATION :
K. Tyszka, M. Furman, R. Mirek, M. Krol, A. Opala, B. Seredynski, J. Suffczynski, W. Pacuski, M. Matuszewski, J. Szczytko, B. Pietka Leaky integration and firing mechanism in exciton-polariton condensates for the photon-spiked neuron
Laser and Photonics Opinion 2022, 2100660
https://doi.org/10.1002/lpor.202100660
CONTACT:
Krzysztof Tyszka
Faculty of Physics, University of Warsaw
Email: [email protected]
phone: +48 22 55 32 749
RELATED WEBSITES:
http://polariton.fuw.edu.pl/
Polariton Group website
https://www.fuw.edu.pl/faculty-of-physics-home.html
Website of the Faculty of Physics, University of Warsaw
https://www.fuw.edu.pl/press-releases.html
Press service of the Faculty of Physics of the University of Warsaw
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Optical microcavity as a pulsating neuron (visualization: Mateusz Krol, source: Faculty of Physics, University of Warsaw)
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Laser and Photonics Review
The title of the article
Leaky integration and firing mechanism in exciton-polariton condensates for the photon-spiked neuron
Publication date of articles
30-Sep-2022
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