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  • Weak unitary symmetries of open quantum dynamics: beyond quantum master equations
    We consider Markovian open quantum dynamics with weak unitary symmetries. Starting from the quantum master equation (QME) for the system alone, it is known that the joint dynamics of the system and its environment can be obtained by dilation, leading to a closed dynamics for a continuous matrix product state. Performing counting measurements on the environment gives rise to stochastic dynamics of quantum trajectories for the system, which when averaged yield back the QME. In this work, we identify necessary and sufficient conditions under which the dynamics of these different descriptions retain the weak symmetry of the QME and we characterise the resulting symmetries of the different descriptions in terms of their generators. We find that the joint dynamics always features a separable symmetry directly related to that of the QME, but for quantum trajectories the corresponding symmetry is present only if the counting measurement satisfies certain conditions.

  • Wide-mass-scanning-range setup and phase-resolved protocol for axion dark matter detection
    We propose a paradigm for quantum enhanced axion dark matter search, which does not rely on power measurements. We propose to measure directly the axion amplitude and phase in an interferometric protocol at the quantum limit, using a non-linear cavity. In addition, we introduce gyromagnetic modes as wide mass range transducers for axion signals compatible with standard haloscope designs. We expect this scheme to offer an improvement of at least 4 orders of magnitude in figure of merit and at least 2 orders of magnitude in mass window with respect to standard haloscopes. Owing to its generality, our proposed protocol has the potential to speed up axion search but also the search for dark photons or other cosmological objects, such as galactic masers.

  • An efficient deep reinforcement method for smart particle navigation in complex flows
    As a quintessential example of soft matter, smart microswimmers bridge the gap between soft matter physics and functional robotics. The development of autonomous navigation of smart microswimmers in complex fluid environments is thus vital, addressing core challenges in the development of robotics in targeted drug delivery and precision surgery. Reinforcement learning is rapidly emerging as an effective solution for such challenges. Traditional deep Q-network (DQN) method often exhibits the limitations of insufficient exploration and low learning and sampling efficiency in complex fluid environments. To address these limitations, we present an efficient deep Q-learning-based approach, which incorporates a novel exploration strategy and an experience sampling strategy into the classic DQN method. The proposed approach enhances exploration through a learned network that generates state-dependent weights and improves sampling efficiency through the use of state-experience clustering in experience replay. We apply the proposed method to three particle navigation tasks in complex fluid environments and show that the proposed method outperforms many existing DQN-variants. The proposed approach enables the efficient calculation of optimal strategies, serving as an effective solver for intelligent navigation challenges across various physics and engineering scenarios.

  • Ponderomotive electron–light interactions in multi-electron pulses
    We investigate the impact of space-charge effects on the ponderomotive interaction between electron pulses and laser fields in the context of ponderomotive lenses. We present a numerical framework that self-consistently models both the ponderomotive electron–light interaction and the electron–electron Coulomb repulsion within multi-electron, ultrashort pulses. By comparing these simulations with a single-electron, wave-based description, we demonstrate that space-charge effects significantly degrade the performance of ponderomotive lenses for electron beam shaping and focusing. Our results show that this deterioration appears already at very low bunch charges, setting clear limits for the manipulation of dense electron pulses with ponderomotive optics.

  • Unveiling novel resonant interband contribution to polarizability in three-dimensional systems
    Polarizability plays an essential role in characterizing key phenomena, such as the screening effects, collective excitations, and dielectric functions present in the system. In three-dimensional (3D) materials, it typically comprises an intraband contribution, dependent on the chemical potential, and an interband contribution, largely independent of it. In this study, within the random phase approximation framework, we uncover a novel interband contribution that, unlike the conventional case, exhibits an explicit dependence on the chemical potential, which has no counterpart in two dimensions. In the long-wavelength limit, this term introduces a resonance feature with cubic wave-vector dependence when the chemical potential approaches the band edge, in contrast to the quadratic behavior characteristic of standard intraband and interband processes. Focusing on 3D Dirac nodal line semimetals, we show that the polarizability is intraband-dominated at low frequencies, while interband processes prevail at intermediate and high frequencies, with the overall response being tunable via the chemical potential. Material-specific estimates for Ca3P2 and ZrSiS reveal a strong tunability of both contributions. These findings open new directions for probing frequency-dependent dielectric properties and hold promise for applications in tunable plasmonic and optoelectronic devices.