Macroscopic Coherence and Remote Entanglement

On the tail of one recent experiment in quantum computing, we see two very interesting news about recent discoveries. The first one deals with superposition at the macroscopic level: "The researchers have successfully superposed light beams, which produces a state that appears to be both on and off at once.". Up to now experiments on superposition only dealt with particles, while in this case the superposition regards beams of light, so we are in a macroscopic scale. The paper infact claims to have proved the Schrodinger’s cat paradox "Previously, only smaller light particles had been superposed and the group has also proved a quantum physics theory known as Schrödinger’s cat. This theory, named after an Austrian physicist Erwin Schrödinger, proposed that a large object such as a cat could be simultaneously alive and dead".

A similar result anyway was already achieved last year in an experiment involving a small mirror, exhibiting quantum coherence at arbitrairly high temperatures. Also, we remember that Bose-Einstein condensates are other examples of large scale quantum coherence.

This said, we go to news number two, that instead deals with remote entangling of particles. "In this experiment, the researchers used two atoms to function as qubits, or quantum bits, storing a piece of information in their electron configuration. They then excited each atom, inducing electrons to fall into a lower energy state and emit one photon, or one particle of light, in the process." and then "By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fiber optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Monroe says the fiber optic thread was necessary to establish entanglement of the atoms, but then the fiber could be severed and the two atoms would remain entangled, even if one were (carefully) taken to Jupiter.". This means that entanglement is furtherly being proved to be extremely usable on long distances in several ways. Experiments on entanglment usually were performed on very small scale.

It took some time to experimentally observe that entanglment holds at long distances (read this and this old news regarding tests on long scale entanglement), but this case it is different. In the previous experiments entanglement was performend on two close particles, which were then physically separated at a macroscopic scale. In this case instead the particles are already separated, and the entanglement is performed "remotely" by driving their emitted photons to interact with each other.

Both news are taken from papers that are being published on the journal Nature (access to papers requires subscription).


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