A group of researchers from the Faculty of Physics at the University of Warsaw has shed new light on the famous paradox of Einstein, Podolsky and Rosen after 80 years. They created a multidimensional entangled state of a single photon and a trillion hot rubidium atoms, and stored this hybrid entanglement in the laboratory for several microseconds. The research has been published in Optica.
In their famous Physical Review article, published in 1935, Einstein, Podolsky and Rosen considered the decay of a particle into two products. In their thought experiment, two products of decay were projected in exactly opposite directions—or more scientifically speaking, their momenta were anti-correlated. Though not be a mystery within the framework of classical physics, when applying the rules of quantum theory, the three researchers arrived at a paradox. The Heisenberg uncertainty principle, dictating that position and momentum of a particle cannot be measured at the same time, lies at the center of this paradox. In Einstein’s thought experiment, it is possible to measure the momentum of one particle and immediately know the momentum of the other without measurement, as it is exactly opposite. Then, by measuring the position of the second particle, the Heisenberg uncertainty principle is seemingly violated, an apparent paradox that seriously baffled the three physicists.
We now know that this experiment is not, in fact, a paradox. The mistake of Einstein and co-workers was applying one-particle uncertainty to a system of two particles. If we treat these two particles as described by a single quantum state, we learn that the original uncertainty principle ceases to apply, especially if these particles are entangled.
The experiment is unique in one other way, as well. The quantum memory storing the entangled state allows for storage of up to 12 photons at once. This enhanced capacity is promising in terms of applications in quantum information processing. “The multidimensional entanglement is stored in our device for several microseconds, which is roughly a thousand times longer than in any previous experiments, and at the same time, long enough to perform subtle quantum operations on the atomic state during storage,” explains Dr. Wojciech Wasilewski, group leader of the Quantum Memories Laboratory team. More.
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