Quantum Mechanics: Bohr's Idea Wins Again

A recent experiment in China has shown that Niels Bohr was right in his debate with Albert Einstein about quantum mechanics. The experiment was based on a thought experiment proposed by Einstein almost a century ago. Bohr argued that certain properties of particles cannot be measured at the same time. The new experiment supports Bohr's idea and could help answer other questions in quantum mechanics. Einstein and Bohr often debated quantum mechanics at physics conferences. Einstein was skeptical of the standard picture of quantum mechanics and claimed to find holes in Bohr's interpretation. Bohr was always ready to defend his ideas. At the 1927 Solvay conference in Brussels, Einstein famously said, "God does not play dice with the universe. " He proposed an experiment to show that Bohr's principle of complementarity was flawed. This principle states that pairs of properties of particles, such as position and momentum, cannot be measured at the same time.Einstein's thought experiment involved two narrow slits. Particles aimed at the slits would display interference fringes on a screen behind the slits, showing their wave-like nature. Einstein proposed that the particles first pass through a single slit held by momentum-sensitive springs. Particles headed for the upper slit would impact a downward momentum on the single slit, showing their particle nature. However, after the double slits, the interference pattern would reveal their wave-like nature. Einstein claimed this would contradict the complementarity principle. Bohr disagreed. The experiment was performed by Jian-Wei Pan and colleagues at the University of Science and Technology of China. They used a photon as the particle and a single rubidium atom as the single slit. The atom was cooled and trapped by an optical tweezer. The experiment showed that precisely measuring the particle's momentum left a large uncertainty in its position, resulting in a blurring of the interference fringes. This supports Bohr's argument. The team also investigated the difference between the quantum limit and the classical heating of the atom's motional states. This allows observation of the quantum-to-classical transitions. The experiment shows that the complementarity principle of quantum mechanics is still valid. The team plans to use quantum state tomography to determine the quantum state of the quantum slit and probe the interplay between decoherence and entanglement.