17 December 2012 Ultra-Gentle Measurement Using Quantum Entanglement

Schrödinger’s cat

Prof. Morgan Mitchell reports in Nature Photonics a new way to use quantum physics to observe delicate systems. The group led by ICREA Professor at ICFO Morgan Mitchell have introduced a new way to observe very delicate bodies based on quantum physics. They have shown that groups of photons organized in a certain quantum states can gently explore the properties of objects in a non-invasive way.

In the experiment, researchers prepared pairs of photons in a “Schrödinger cat” state, and then sent them through a cloud of atoms, measuring their polarization on the way out. In this way, they were able to deduce the number of atoms in the cloud and the magnetic field of their surroundings. At the same time, they were able to assess the damage, i.e. the number of photons absorbed by the cloud.

The results have shown that photons prepared in that quantum states can provide more information causing less damage. They overcome for the first time the so-called \"standard quantum limit\", and permit the observation of unknown properties of ultra-sensitive objects such as individual atoms or living cells.