Subtracting photons from photon pairs leads to increase of their nonclassicality

The group of quantum and nonlinear optics at the Joint Laboratory of Optics deals long-term with twin beams that became an important tool for quantum optics as they exhibit quantum correlations and entanglement. A. Aspect, J. Clauser, and A. Zeilinger were awarded 2022 Nobel prize for physics for experiments with entangled photons. Quantum correlations cause that the results of measurements of properties of paired photons are not independent but bound together at a distance with invisible ties unparalleled in classical physics. This is why we call the paired photons nonclassical light.

The amount of this nonclassicality is in fact directly related to the applicability of paired photons for modern quantum technologies. Significant attention is therefore dedicated to the possibilities of quantification and control of the nonclassicality of quantum states. The team at the Joint Laboratory of Optics focuses on quantum correlations in numbers of photons in paired beams and a variety of instruments have been developed to discover and quantify nonclassical properties in beams containing units or tens of photon pairs.

In a recent experiment, the JLO team has shown that subtracting a few photons from one or both beams has significant impact on their nonclassicality. Even though this intervention decreases the entanglement between the beams (but it still remains nonclassical), the noise in each of the beams get significantly lowered to the extent that both beams become nonclassical (their noise will be below classical limit). Photon beams with entirely new type of nonclassical behavior is thus created.

The research has been performed through joint efforts of scientists from Palacký University and Institute of Physics AS CR and results have been published in Physical Review Research [Thapliyal2024].

[Thapliyal2024] Kishore Thapliyal, Jan Peřina, Jr., Ondřej Haderka, Václav Michálek, and Radek Machulka: Experimental characterization of multimode photon-subtracted twin beams, Phys. Rev. Research (2024) 6, 013065.