The experiments, conducted independently by teams at the Massachusetts Institute of Technology (MIT) and the University of Science and Technology of China (USTC), used different setups to test whether the wave and particle natures of photons can be measured simultaneously. In both cases, researchers found that acquiring information about a photon’s path, the particle aspect, caused the interference pattern, linked to its wave nature, to vanish.
The disagreement between Einstein and Bohr centered on the nature of quantum reality. In the late 1920s, Bohr proposed that a quantum particle like a photon cannot display both wave-like and particle-like behaviors at the same time. Einstein disagreed, suggesting that a carefully designed double-slit experiment could detect both aspects. Bohr responded that the uncertainty principle would prevent such measurements from occurring simultaneously. For nearly a century, this argument remained unresolved in practical terms, until the publication of these two new studies.
MIT Team Develops Idealized Double-slit Setup
At MIT, Wolfgang Ketterle and his colleagues built what the authors described as an “idealized version of the double slit experiment.” The experiment used individual atoms as slits and weak light beams designed to ensure that each atom scattered only one photon. This design allowed the researchers to observe the interaction between the photon’s particle path and wave behavior with high precision.
According to Popular Mechanics, Ketterle’s team observed an inverse relationship between the amount of information obtained about the photon’s path and the visibility of the interference pattern. As more information about the particle nature was gathered, the wave-like interference diminished. These findings support Bohr’s argument that both properties cannot be measured simultaneously.
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USTC Team Traps Single Atom With Optical Tweezers
In China, a separate group at the University of Science and Technology of China explored the same question using a different method. The researchers trapped a rubidium atom using optical tweezers and manipulated its quantum properties using lasers and electromagnetic forces. The team then scattered photons in two directions to observe their behavior.
As with the MIT experiment, the USTC team found that attempting to detect the photon’s path resulted in the disappearance of the interference pattern. Chao-Yang Lu, a member of the research team, described the outcome to New Scientist as a confirmation of Bohr’s prediction. “Bohr’s counterargument was brilliant,” he said. “But the thought experiment remained theoretical for almost a century.”
Both experiments were published in the journal Physical Review Letters. According to the same source, Lu’s team aims to use their setup to further investigate areas of quantum mechanics such as decoherence and entanglement. The results from both studies show that Bohr’s interpretation of complementarity holds under experimental conditions, and that the attempt to measure one aspect of a photon inevitably erases the other.