Nonlinear response of biophoton emission to external perturbations

Qiao Gu

R. P. Bajpai, Santosh Kumar, V.A. Sivadasan

A. Kani, Harshawardhan Wanare

\n\nWeak coherent radiation interacting with multilevel atomic systems can excite a family of higher-order multiphoton transitions in contravention to conventional perturbative analysis. Monochromatic excitation leads to a strong anisotropic response arising from the interference of numerous underlying multiphoton pathways. The interference can be controlled through the polarization content of the input radiation. This anisotropic response is subnatural, quite unlike the anisotropy arising from spontaneous-emission–assisted optical pumping. Its sensitivity to external influences such as magnetic field suggests its utility in magnetometry. Specifically, we discover the presence of an elemental closed loop involving series of absorption and emission cycles that is central to the total response, and is universal to all atomic configurations. However, as not all atomic configurations support such anisotropy, we present a general classification of atomic transitions that exhibit anisotropic nonlinear response through quantum interference.\n

Shun Ogawa, Yoshiyuki Y. Yamaguchi

A nonlinear response theory is provided by use of the transient linearization method in the spatially one-dimensional Vlasov systems. The theory inclusively gives responses to external fields and to perturbations for initial stationary states, and is applicable even to the critical point of a second-order phase transition. We apply the theory to the Hamiltonian mean-field model, a toy model of a ferromagnetic body, and investigate the critical exponent associated with the response to the external field at the critical point in particular. The obtained critical exponent is the nonclassical value 3/2, while the classical value is 3. However, interestingly, one scaling relation holds with another nonclassical critical exponent of susceptibility in the isolated Vlasov systems. Validity of the theory is numerically confirmed by directly simulating temporal evolutions of the Vlasov equation.

Si Kun, CHUNLI LIU, HUN-YU JIA

Alexander Sazhin, V. N. Gladilin, Andris Erglis +5 more

The quantum regression theorem states that the correlations of a system at two different times are governed by the same equations of motion as the single-time averages. This provides a powerful framework for the investigation of the intrinsic microscopic behaviour of physical systems by studying their macroscopic response to a controlled external perturbation. Here we experimentally demonstrate that the two-time particle number correlations in a photon Bose-Einstein condensate inside a dye-filled microcavity exhibit the same dynamics as the response of the condensate to a sudden perturbation of the dye molecule bath. This confirms the regression theorem for a quantum gas, and, moreover, demonstrates it in an unconventional form where the perturbation acts on the bath and only the condensate response is monitored. For strong perturbations, we observe nonlinear relaxation dynamics which our microscopic theory relates to the equilibrium fluctuations, thereby extending the regression theorem beyond the regime of linear response.