Seminarium Optyczne

"A quantum particle prepared as a superposition of positive momentum states can have a negative probability current during local instances of time [1]. The phenomenon of probability flow in the ‘wrong’ direction is referred to as ‘backflow’ and is a manifestation of wave interference. Superoscillations refer to situations where the local oscillation of a superposition is faster than its fastest Fourier component [2]. M.V. Berry’s work [3] highlighted the correspondence between backflow in quantum mechanics and superoscillations in waves. This correspondence has been used to demonstrate backflow in transverse linear momentum for optical waves [4,5]. Following this, we examine the interference of classical light carrying only negative orbital angular momentum (OAM) and observe in the dark fringes of such an interference pattern, positive local OAM [6]. We refer to this as azimuthal backflow. The associated strong phase gradients within the dark fringes have implications for the studies of light-matter interaction.[1] A. J. Bracken and G. F. Melloy, “Probability backflow and a new dimensionless quantum number” J. Phys. A: Math. Gen. 27, 2197 (1994).[2] M. V. Berry and S. Popescu, “Evolution of quantum superoscillations and optical superresolution without evanescent waves” J. Phys. A: Math. Gen. 39, 6965(2006). [3] M. V. Berry, “Quantum backflow, negative kinetic energy and optical retro-propagation” J. Phys. A: Math. Theor. 43, 415302 (2010). [4] Y. Eliezer, T. Zacharias, and A. Bahabad, “Observation of optical backflow” Optica 7, 72 (2020). [5] A. Daniel, B. Ghosh, B. Gorzkowski, and R. Lapkiewicz, “Demonstrating backflow in classical two beams’ interference” New. J. Phys. 24, 123011(2022). [6] B. Ghosh, A. Daniel, B. Gorzkowski, and R. Lapkiewicz, “Azimuthal backflow in light carrying orbital angular momentum” Optica 10 (9), 2334-2536 (2023)."