Frontiers of Physics最新文献

Whether the complex game system composed of a large number of artificial intelligence (AI) agents empowered with reinforcement learning can produce extremely favorable collective behaviors just through the way of agent self-exploration is a matter of practical importance. In this paper, we address this question by combining the typical theoretical model of resource allocation system, the minority game model, with reinforcement learning. Each individual participating in the game is set to have a certain degree of intelligence based on reinforcement learning algorithm. In particular, we demonstrate that as AI agents gradually becomes familiar with the unknown environment and tries to provide optimal actions to maximize payoff, the whole system continues to approach the optimal state under certain parameter combinations, herding is effectively suppressed by an oscillating collective behavior which is a self-organizing pattern without any external interference. An interesting phenomenon is that a first-order phase transition is revealed based on some numerical results in our multi-agents system with reinforcement learning. In order to further understand the dynamic behavior of agent learning, we define and analyze the conversion path of belief mode, and find that the self-organizing condensation of belief modes appeared for the given trial and error rates in the AI system. Finally, we provide a detection method for period-two oscillation collective pattern emergence based on the Kullback–Leibler divergence and give the parameter position where the period-two appears.

We present a novel feedback control method for quantum systems. Feedback does not affect the controlled system itself. Instead, it controls the unravelling of the quantum channel of interaction between the system and its environment. This interaction can be represented as a history of events. If their informational content is changed, their back-action on the system is also modified. Feedback action is trigged by the events, thus granting the system the degree of control over its own state. The efficiency of the proposed scheme is demonstrated on the example of two-mode atomic Bose-Einstein condensate, with one of its modes subject to phase-contrast imaging in a Mach–Zehnder interferometer. The histories of photocounts in the output channels of the interferometer are used for feedback. Its capabilities of state engineering are studied for different settings of the feedback loop and different numbers of events in the recorded histories.

Nonmagnetic impurity scattering is known to shift up the Ginzburg–Landau parameter κ of a superconductor. In this case, when the system is initially in type I, it can change its magnetic response, crossing the intertype domain with κ ∼ 1 between the two standard superconductivity types and arriving at type II. In the present work we demonstrate that the impact of disorder can be much more profound in the presence of the multiband structure of the charge carrier states. In particular, when the band diffusivities differ from each other, the intertype domain tends to expand significantly, including points with κ ≫ 1 that belong to deep type-II in conventional single-band superconductors. Our finding sheds light on the nontrivial disorder effect and significantly complements earlier results on the enlargement of the intertype domain in clean multiband superconductors.

Periodic structures structured as photonic crystals and optical lattices are fascinating for nonlinear waves engineering in the optics and ultracold atoms communities. Moiré photonic and optical lattices — two-dimensional twisted patterns lie somewhere in between perfect periodic structures and aperiodic ones — are a new emerging investigative tool for studying nonlinear localized waves of diverse types. Herein, a theory of two-dimensional spatial localization in nonlinear periodic systems with fractional-order diffraction (linear nonlocality) and moiré optical lattices is investigated. Specifically, the flat-band feature is well preserved in shallow moiré optical lattices which, interact with the defocusing nonlinearity of the media, can support fundamental gap solitons, bound states composed of several fundamental solitons, and topological states (gap vortices) with vortex charge s = 1 and 2, all populated inside the finite gaps of the linear Bloch-wave spectrum. Employing the linear-stability analysis and direct perturbed simulations, the stability and instability properties of all the localized gap modes are surveyed, highlighting a wide stability region within the first gap and a limited one (to the central part) for the third gap. The findings enable insightful studies of highly localized gap modes in linear nonlocality (fractional) physical systems with shallow moiré patterns that exhibit extremely flat bands.

Currently, magnetic storage devices are encountering the problem of achieving lightweight and high integration in mobile computing devices during the information age. As a result, there is a growing urgency for two-dimensional half-metallic materials with a high Curie temperature (T_C). This study presents a theoretical investigation of the fundamental electromagnetic properties of the monolayer hexagonal lattice of Mn₂X₃ (X = S, Se, Te). Additionally, the potential application of Mn₂X₃ as magneto-resistive components is explored. All three of them fall into the category of ferromagnetic half-metals. In particular, the Monte Carlo simulations indicate that the T_C of Mn₂S₃ reachs 381 K, noticeably greater than room temperature. These findings present notable advantages for the application of Mn₂S₃ in spintronic devices. Hence, a prominent spin filtering effect is apparent when employing non-equilibrium Green’s function simulations to examine the transport parameters. The resulting current magnitude is approximately 2 × 10⁴ nA, while the peak gigantic magnetoresistance exhibits a substantial value of 8.36 × 10¹⁶ %. It is noteworthy that the device demonstrates a substantial spin Seebeck effect when the temperature differential between the electrodes is modified. In brief, Mn₂X₃ exhibits outstanding features as a high T_C half-metal, exhibiting exceptional capabilities in electrical and thermal drives spin transport. Therefore, it holds great potential for usage in spintronics applications.

Vortex wave and plane wave, as two most fundamental forms of wave propagation, are widely applied in various research fields. However, there is currently a lack of basic mechanism to enable arbitrary conversion between them. In this paper, we propose a new paradigm of extremely anisotropic acoustic metasurface (AM) to achieve the efficient conversion from 2D vortex waves with arbitrary orbital angular momentum (OAM) to plane waves. The underlying physics of this conversion process is ensured by the symmetry shift of AM medium parameters and the directional compensation of phase. Moreover, this novel phenomenon is further verified by analytical calculations, numerical demonstrations, and acoustic experiments, and the deflection angle and direction of the converted plane waves are qualitatively and quantitatively confirmed by a simple formula. Our work provides new possibilities for arbitrary manipulation of acoustic vortex, and holds potential applications in acoustic communication and OAM-based devices.

Two-dimensional (2D) ferroelectric materials, which possess electrically switchable spontaneous polarization and can be easily integrated with semiconductor technologies, is of utmost importance in the advancement of high-integration low-power nanoelectronics. Despite the experimental discovery of certain 2D ferroelectric materials such as CuInP₂S₆ and In₂Se₃, achieving stable ferroelectricity at room temperature in these materials continues to present a significant challenge. Herein, stable ferroelectric order at room temperature in the 2D limit is demonstrated in van der Waals SnP₂S₆ atom layers, which can be fabricated via mechanical exfoliation of bulk SnP₂S₆ crystals. Switchable polarization is observed in thin SnP₂S₆ of ∼7 nm. Importantly, a van der Waals ferroelectric field-effect transistor (Fe-FET) with ferroelectric SnP₂S₆ as top-gate insulator and p-type WTe_0.6Se_1.4 as the channel was designed and fabricated successfully, which exhibits a clear clockwise hysteresis loop in transfer characteristics, demonstrating ferroelectric properties of SnP₂S₆ atomic layers. In addition, a multilayer graphene/SnP₂S₆/multilayer graphene van der Waals vertical heterostructure phototransistor was also fabricated successfully, exhibiting improved optoelectronic performances with a responsivity (R) of 2.9 A/W and a detectivity (D) of 1.4 × 10¹² Jones. Our results show that SnP₂S₆ is a promising 2D ferroelectric material for ferroelectric-integrated low-power 2D devices.

Vortex beam with fractional orbital angular momentum (FOAM) is the excellent candidate for improving the capacity of free-space optical (FSO) communication system due to its infinite modes. Therefore, the recognition of FOAM modes with higher resolution is always of great concern. In this work, through an improved EfficientNetV2 based convolutional neural network (CNN), we experimentally achieve the implementation of the recognition of FOAM modes with a resolution as high as 0.001. To the best of our knowledge, it is the first time this high resolution has been achieved. Under the strong atmospheric turbulence (AT) ((C_n^2 = {10^{ - 15}},{{rm{m}}^{ - 2/3}})), the recognition accuracy of FOAM modes at 0.1 and 0.01 resolution with our model is up to 99.12% and 92.24% for a long transmission distance of 2000 m. Even for the resolution at 0.001, the recognition accuracy can still remain at 78.77%. This work provides an effective method for the recognition of FOAM modes, which may largely improve the channel capacity of the free-space optical communication.

Atom interferometer has been proven to be a powerful tool for precision metrology. Here we propose a cavity-aided nonlinear atom interferometer, based on the quasi-periodic spin mixing dynamics of an atomic spin-1 Bose–Einstein condensate trapped in an optical cavity. We unravel that the phase sensitivity can be greatly enhanced with the cavity-mediated nonlinear interaction. The influence of encoding phase, splitting time and recombining time on phase sensitivity are carefully studied. In addition, we demonstrate a dynamical phase transition in the system. Around the criticality, a small cavity light field variation can arouse a strong response of the atomic condensate, which can serve as a new resource for enhanced sensing. This work provides a robust protocol for cavity-enhanced metrology.

The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resistance. This problem becomes the major barrier for this field. From plume dynamics perspective, we found the synthesis of superconducting nickelates is a complex process and the challenge is twofold, i.e., how to stabilize an ideal infinite-layer structure Nd_0.8Sr_0.2NiO₂, and then how to make Nd_0.8Sr_0.2NiO₂ superconducting? The competition between perovskite Nd_0.8Sr_0.2NiO₃ and Ruddlesden–Popper defect phase is crucial for obtaining infinite-layer structure. Due to inequivalent angular distributions of condensate during laser ablation, the laser energy density is critical to obtain phase-pure Nd_0.8Sr_0.2NiO₃. However, for obtaining superconductivity, both laser energy density and substrate temperature are very important. We also demonstrate the superconducting Nd_0.8Sr_0.2NiO₂ epitaxial film is very stable in ambient conditions up to 512 days. Our results provide important insights for fabrication of superconducting infinite-layer nickelates towards future device applications.