Detection of quantum-vacuum field correlations outside the light cone

There is interest in measuring the vacuum fluctuations of electromagnetic radiation. Here the authors demonstrate quantum-vacuum electric field correlations between two regions which are outside the light-cone. According to quantum field theory, empty space-the ground state with all real excitations removed-is not empty, but filled with quantum-vacuum fluctuations. Their presence can manifest itself through phenomena such as the Casimir force, spontaneous emission, or dispersion forces. These fluctuating fields possess correlations between space-time points outside the light cone, i.e. points causally disconnected according to special relativity. As a consequence, two initially uncorrelated quantum objects in empty space which are located in causally disconnected space-time regions, and therefore unable to exchange information, can become correlated. Here, we have experimentally demonstrated the existence of correlations of the vacuum fields for non-causally connected space-time points by using electro-optic sampling. This result is obtained by detecting vacuum-induced correlations between two 195 fs laser pulses separated by a time of flight of 470 fs. This work marks a first step in analyzing the space-time structure of vacuum correlations in quantum field theory.

Automated summary

This research demonstrates the correlation between quantum vacuum electric fields in regions outside the light-cone. According to quantum field theory, empty space is not truly empty, but filled with fluctuations known as quantum-vacuum fluctuations. These fluctuations can be observed through various phenomena. The experimental results show the existence of vacuum field correlations between non-causally connected space-time points.