The dual nature of light has long been a concern of scientists. It even led to the creation of the to the controversy between Albert Einstein and Niels Bohr on whether light can be observed simultaneously as a wave and as particles.
Recently, physicists from The Massachusetts Institute of Technology conducted a new experiment with slits through which light was transmitted with incredible atomic precision. The results of their experiment finally put an end to a long-standing dispute between Einstein and Bohr on the elusive nature of light.
«Physicists from the Massachusetts Institute of Technology confirm that, like Superman, light has two faces that cannot be seen simultaneously», — the researchers note in their experiment.
The two-slit experiment was first conducted by Thomas Jung in 1801. This experiment became is the cornerstone of quantum mechanics. This is a vivid example of light manifesting both wave and corpuscular nature. First, the experiment demonstrated that the interference pattern — bright and dark stripes that alternate and behave like waves.
However, when physicists tried to trace the slit through which the light was passing, the interference pattern disappeared and the light behaved like particles. This emphasizes the key principle of quantum mechanics — light exists in the form of waves and particles, but only one of its states can be observed at a time.
This led to a dispute between Einstein and Bohr in 1927. Einstein, in particular, was convinced, that he was able to develop an experiment that would allow simultaneous observation of the trajectory of light particles and the interference of light waves. Bohr, relying on the principle of uncertainty, argued that any attempt to measure the trajectory of a photon will inevitably disrupt it and destroy the interference pattern.
For decades after this controversy, numerous repetitions of the two-slit experiment confirmed Bohr’s point. But now physicists at the Massachusetts Institute of Technology, led by Professor Wolfgang Ketterle, have created the most idealized version to date, bringing it to a quantum basis.
Instead of physical slits, MIT physicists used individual ultracold atoms. They cooled more than 10 thousand atoms to almost absolute zero and used lasers to arrange them in a precise crystal-like lattice. Each atom actually represented an isolated analog of a slit.
Next, the physicists shone a very weak beam of light, ensuring that each atom scatter no more than one photon. Scientists have hypothesized that their setup, which uses individual, precisely structured atoms, is the best way to make a can be a miniature analog of the two-slit experiment. By directing a weak beam of light at atoms, physicists MIT could study how single atoms interact with two neighboring atoms, finding out whether light behaves like a wave or a particle.
«What we have done can be seen as a new variant of the two-slit experiment. These individual atoms are like the smallest slits that can be built», — explains the research leader, Professor Wolfgang Ketterle.
The scientists were able to fine-tune the «blurring» of these atomic slits by adjusting the laser beam that held them. The blurring of these atoms affected the amount of information about the photon’s trajectory. Their results were fully consistent with quantum theory and finally confirmed Bohr’s point of view.
The more accurately physicists determined the photon’s trajectory (confirming its corpuscular behavior), the more the wave-like interference pattern faded. The researchers observed that the wave interference pattern weakened each time the atom was exposed to a passing photon. This confirmed that obtaining information about the photon’s route automatically erased its wave properties.
The results of the study are published in the journal Physical Review Letters
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