Spin in the famous double-slit experiment questions Einstein’s quantum doubt
It is known that Albert Einstein did not like the assertion of quantum theory that physical objects, including light, exist both as particles and as waves, and that this duality cannot be observed simultaneously. However, a new and simple iteration of a fundamental quantum experiment provides the most conclusive direct evidence that perhaps Einstein was wrong.
In a recent work for , scientists from MIT managed to replicate the double-slit experiment on an atomic scale, resulting in an unprecedented level of empirical precision. Using supercooled atoms as “slits” for light to pass through, the team confirmed that the wave-particle duality of light – with all its paradoxical properties – holds even at the most fundamental quantum scales.
The discussion
Niels Bohr, Einstein’s main opponent in this debate, referred to this result as , the idea that it is impossible to simultaneously measure the complementary properties of a quantum system. Einstein, on the other hand, argued that if a thin slit like a paper held by a spring was illuminated, the individual photons would cause the spring to vibrate like particles. Thus, we could observe the duality of light in action.
To test this hypothesis, the MIT team cleared the experiment to the scale of individual atoms that they cooled to microkelvin temperatures (for context, one kelvin equals -272 °C). They used lasers to arrange more than 10,000 atoms in a very neat configuration. This highly controlled environment allowed the researchers to adjust the blurring of each atom, or the certainty of its location. A blurred atom increases the probability that the passing photon will exhibit particle behavior.
“These atoms are like the smallest possible slits you could form,” explained Wolfgang Ketterle, the lead author of the study. By bombarding the atomic “slits” repeatedly with photons, Ketterle, who won the Nobel Prize in 2001, and his team were able to record the diffraction pattern of the photons that dispersed as they passed through the atomic slits.
They found what was expected: Bohr was right. The more they focused on the path of each photon, the smaller the diffraction pattern became, confirming that we cannot see light as both a wave and a particle simultaneously. They also tried to close the lasers by holding the atoms in place – which would be “the spring” of their experiment. Even so, it was impossible to track the path of the photon without causing disruption to the wave-like interference pattern.
Sometimes Einstein is accused of hating quantum physics. This is not necessarily true. Einstein believed that more work was needed on quantum theory, especially in terms of its increased reliance on randomness, but he never completely rejected its validity. In a letter to physicist Max Bohr, he said that quantum mechanics is “certainly imposing,” but his instinct is that “it is not yet real… [God] does not play dice.”
Einstein had many questions about quantum mechanics, and many remain unanswered. As in the debate between Einstein and Bohr, and in MIT’s new finding, his rigorous and provocative challenges to what physicists take for granted continue to improve our understanding of the strange and paradoxical world of quantum mechanics.
This article has been translated from Gizmodo US by Lucas Handley. you can find the original version.
