Generation of compressed light (“squeezing”)
The compressed states of light are those in which an observable ≤ ℏ2/4 (here p is the conjugate magnitude of x, for example the magnetic field in suitable units).
The compressed states of light are non-classical states, this means that they are not generated naturally by means of thermal sources or by means of classical electric currents (antennas or similar). The non-classical character of compressed states makes them a valuable resource for the study of purely quantum effects such as entanglement, non-locality, etc. and for quantum information processing.
Possibly one of the simplest methods of generating compressed light is by passing a linearly polarized laser light beam (classical state) through a cell of an atomic vapor that has transitions between levels for frequencies close to that of the incident light. At the exit of the cell it is observed that the radiation component, with polarization perpendicular to the incident one, is in a compressed (non-classical) state. This phenomenon was originally designated as polarization self-rotation squeezing.
The main contribution of our laboratory to this topic consisted of re-interpreting the phenomenon as polarization squeezing. From this point of view, the observables whose fluctuations are modified are the so-called Stokes parameters that describe the polarization state of any light field. This conceptual innovation has important experimental consequences that led to a considerable simplification of the assembly, reducing it to a one-dimensional geometry without moving parts. Thanks to these advances, the highest level of compression so far achieved with this technique was achieved [Bar11] and the complete characterization of the state of light was facilitated [Val14].
[Bar11] “Polarization squeezing of light by single passage through an atomic vapor“, S. Barreiro, P. Valente, H. Failache, A. Lezama, Phys. Rev. A 84, 33851 (2011).
[Val14] “Experimental characterization of the Gaussian state of squeezed light obtained via single-passage through an atomic vapor“, P. Valente, A. Auyuanet, Barreiro, H. Failache, A. Lezama. Phys. Rev. A, 91, 053848 (2015).
