The paper published in Physica Scripta (endorsed by the Royal Swedish Academy of Sciences and published by IOP Publishing), volume 96 (2021), p. 125101 on August 12, 2021, is a very noteworthy piece of scientific research. It was written by Dr. Vo Van Thuan, who is a scientist at the DTU Institute of Theoretical & Applied Research (ITAR), and entitled: “A possible solution to the which-way problem by way of an asymmetric double slit experiment with mono-chromatical photons.”
From the moment of publication, his paper attracted the attention of many scientists around the world, because research on this topic has a direct relation to the famous unresolved debates between the scientists Albert Einstein and Niels Bohr, representing two completely contradictory viewpoints on physical reality in quantum mechanics, which have discussed over the past ninety years.
In 1801, the scientist Thomas Young performed an optic (using photon bundles) interference experiment for the first time, using two symmetric slits. Later experiments were conducted to understand the wave-particle duality of quantum theory. When both slits are open, the interference pattern that arises confirms a wave pattern, but the actual particle nature of the quantum is still unknown, because it cannot be determined which slit the wave went through before interference. In 2019, a new symmetric double-slit interference experiment was repeated with electron bundles, still without any way of determining which slit the electron went through without interaction. In 2018, researchers in Japan performed the experiment with an electron bundle and an asymmetric double slit (one slit wider than the other). When doing near-field observations, interference fringes of differing lengths were distinguished, corresponding to electrons going through one of the two slits. The result, however, is only qualitative, as it is not possible to determine through which of the two slits each electron went.
Dr. Vo Van Thuan at the International Atomic Energy Agency (IAEA) headquarters
The difference, and a key factor determining the success of Dr. Thuan’s work is that he chose to use an asymmetric double slit and observed the interference pattern from further away. He was able to observe two superimposed interference patterns of different lengths in the center, with coincident fringes. At two special minima of the narrow fringes (corresponding to the wide slit), where the amplitude should have been canceled, there appeared to be another fringe which could only have been caused by a wide fringe (coming from the narrow slit). This allowed him to verify with certainty that this special fringe is from photons that went through the narrow slit, thus solving the which-way problem.
This result is completely consistent with Einstein’s point of view that electrons (like photons) exist as particles before being detected, moving freely through spacetime without interacting with the measurer. This theory is incompatible with Bohr’s, that electrons can only be determined to be particles with specific characteristics after measuring their probability waves. Before measuring, nobody can know an electron’s nature, particle or wave. Stated differently, Bohr said that, in the microscopic world, there is no independent or objective physical reality. We can only speak of physical reality after it has been observed and interacted with. Einstein and Bohr had already debated the wave-particle duality in quantum mechanics at the 5th Solvay Conference in 1927 on the subject of Electrons and Photons, after the two microscopic entities clearly showed its quantum nature.
“Forty years ago, in a philosophy course on the nature of quantum probability, before I defended my PhD thesis at the Joint Institute for Nuclear Research in Moscow, I started thinking about physical reality in quantum mechanics,” explained Dr. Thuan. “In 2015, I decided to start in-depth research on the topic. Over the past five years, I have published one paper in an ISI-indexed journal and four papers in national journals and given five talks at international conferences and workshops. That, however, was all theoretical. My paper ‘A possible solution to the which-way problem by an asymmetric double slit experiment with mono-chromatical photons’ is the first experimental research.”
“However clear it may be, a new experimental result must still be picked apart by the scientific community before it can be accepted as a unique interpretation. Strict and cautious checking and cross-checking will ensure the veracity of the research. Then it must be considered that this issue is part of a huge debate between two scientific schools with incompatible views. For now, I will continue collaborating with my colleagues at the Vietnam Atomic Energy Institute to use the standard software the IAEA has provided to transform 2D planar spectral images into laser-strength spectral distributions. This will allow us to complete the next step in our research and obtain better results to evaluate and confirm the experimental results in the published paper. Or future research will also be submitted to an international journal.”
Answering the question of physical reality in quantum mechanics – whether electrons and photons exist of their own as particles in space or whether they only possess characteristics after their probability waves have been measured, is very important. It is the key to open a door that has been tightly shut for over ninety years and behind which there will be a path towards a more complete quantum theory that can explain objective physical reality in the microscopic world in agreement with experimental observations. The paper that was recently published is the first discovery of the experimental phenomenon of distinguishing photons based on their paths, giving direct proof of a solution to the classical which-way problem, which has been vexing scientists around the world.
Dr. Thuan studied Experimental Nuclear Physics and Cosmic Rays in the Soviet Union, served as consultant to the State Steering Committee of the Ninh Thuan Nuclear Power Plant and chaired the Institute for Nuclear Sciences & Technology (INST-VINATOM, Hanoi). His current research focuses on fundamental science:
- The fundamental issues in quantum mechanics and general relativity
- Experiments in fundamental-particle physics
Having authored and co-authored over eighty science & technology papers in domestic and international journals, including 25 in ISI-indexed international journals and 20 in the proceedings of prestigious international conferences, he has several preprints on specialized international open websites awaiting submission to journals.
“On my return to the university, I now benefit from a better environment to focus on fundamental science research,” said Dr Thuan. “In Vietnam, several specialized and technological subfields of physics are currently given investment precedence, attracting young, energetic and aspiring researchers to Materials Science, IT and Automation, who have the potential of making significant contributions with outstanding research. Compared with the rest of the world however, the quality of our research and equipment in Vietnam is still inferior. In my own area, we are still lacking specialized facilities and skilled workers. The microscopic world demands diverse and abstract reasoning skills and the knowledge and experience that can only be acquired at the most advanced international scientific institutions. At DTU’s ITAR however, the scale is still small but our research team is strong and staffed by dedicated young scientists with the creativity for us to progress even further, according to the university’s strategy for the overall development and upgrading of research to international standards.”
(Media Center)