Unveiling Hidden Dynamics: Speed Measurements of Tunneling Particles

For nearly a century, quantum tunneling has been a subject of sustained scientific interest. In a prior investigation [1], we introduced an unconventional method to explore evanescent phenomena at step potentials by examining particle motion within a system of coupled waveguides. In this system, the transfer of particles between waveguides serves as a clock, facilitating the determination of particle speeds even in classically forbidden regions. We implement this idea for photons in optical microcavity, which has full experimental access to the wave function. Using a novel nanostructuring method [2], we can guide photons in diverse potential landscapes, specifically within a coupled waveguiding structure. We measure particle speeds both in classically allowed and forbidden regions. Our measurements show that classically forbidden regions speed up the motion of photons. Moreover, our findings emphasize the significance of density gradients in wave functions for the motion of particles. We hope, these outcomes will provide valuable insights into the intricate dynamics of quantum tunneling phenomena, in particular make useful contribution to the tunneling time debate. [1] Klaers, J., Sharoglazova, V., & Toebes, C. (2023). Physical Review A, 107(5), 052201.[2] Vretenar, M., Puplauskis, M., Klaers, J.. Adv. Optical Mater. 2023, 2202820

Inverse problems for microcavity tilt readout

Inverse problems in physics involve deducing system causes from observed effects, presenting challenges due to potential ill-posedness. Regularization techniques, addressing errors and instability, are vital in solving these problems, often combining analytical and numerical methods.In this work we want to inversely solve a Schrödinger equation to deduce the potential inside an optical microcavity. We apply this method to read out and stabilize the angular orientation of the two mirrors comprising an optical microcavity.To do so we observe mode patterns inside the microcavity and utilize key properties of the Schrödinger equation. We introducing and compare different regularization methods for efficacy assessment.</div

Photon motion in classically forbidden regions

Quantum mechanics suggests a variety of velocity definitions, and some of them are not fully consistent with each other. For instance, in the issue of including density gradients of the wave function. Here we intend to reveal the significance of density gradients in determining photon velocity. We consider photon motion in a system of waveguide potentials described in our recent theoretical proposal [1]. In such a system, density transfer between two coupled waveguides acts as a clock and allows photon velocities to be determined. We implement a system of waveguides, confining 2D gas of massive photons, on one of the microcavity mirrors using a novel direct laser writing technique for mirror nanostructuring [2]. Such a microcavity platform has full experimental access to the wave function, and allows us to measure the period of density transfer, which is related to photon in-plane velocity. Application of this scheme to tunneling phenomena at a reflective step potential also makes it possible to measure the velocity in the classically forbidden regime and reveals the existence of a classically forbidden long-range photon transport as predicted

Phase Randomness in a Semiconductor Laser: the Issue of Quantum Random Number Generation

Gain-switched lasers are in demand in numerous quantum applications, particularly, in systems of quantum key distribution and in various optical quantum random number generators. The reason for this popularity is natural phase randomization between gain-switched laser pulses. The idea of such randomization has become so familiar that most authors use it without regard to the features of the laser operation mode they use. However, at high repetition rates of laser pulses or when pulses are generated at a bias current close to the threshold, the phase randomization condition may be violated. This paper describes theoretical and experimental methods for estimating the degree of phase randomization in a gain-switched laser. We consider in detail different situations of laser pulse interference and show that the interference signal remains quantum in nature even in the presence of classical phase drift in the interferometer provided that the phase diffusion in a laser is efficient enough. Moreover, we formulate the relationship between the previously introduced quantum reduction factor and the leftover hash lemma. Using this relationship, we develop a method to estimate the quantum noise contribution to the interference signal in the presence of phase correlations. Finally, we introduce a simple experimental method based on the analysis of statistical interference fringes, providing more detailed information about the probabilistic properties of laser pulse interference