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Solving complex tasks in a modern information-driven society requires novel materials and concepts for energy-efficient hardware. Antiferromagnets offer a promising platform for seeking such approaches due to their exceptional features: low power consumption and possible high integration density are desirable for information storage and processing or applications in unconventional computing. Among antiferromagnets, CuMnAs stands out for atomic-level scalable magnetic textures, analogue multilevel storage capability, and the magnetic state's control by a single electrical or femtosecond laser pulse. Using a pair of excitation laser pulses, this work examines synaptic and neuronal functionalities of CuMnAs for information processing, readily incorporating two principles of distinct characteristic timescales. Laser-induced transient heat dynamics at sub-nanosecond times represents the short-term memory and causes resistance switching due to quenching into a magnetically fragmented state. This quench switching, detectable electrically from ultrashort times to hours after writing, reminisces the long-term memory. The versatility of the principles' combination is demonstrated by operations commonly used in neural networks. Temporal latency coding, fundamental to spiking neural networks, is utilized to encode data from a grayscale image into sub-nanosecond pulse delays. Applying input laser pulses with distinct amplitudes then allows for pulse-pattern recognition. The results open pathways for designing novel computing architectures., Comment: 20 pages, 10 figures

We present a method for a precise determination of magnetic anisotropy and anisotropy of quadratic magneto-optical response of thin films of ferromagnetic and ferrimagnetic materials. The method is based on measurements of a magneto-optical response for light close to the normal incidence on the sample with a fixed position. The measurement is performed for a set of orientations of an external magnetic field and a series of incident light linear polarizations beyond the standard s and p orientations. Based on the symmetry of the signal, we are able to separate the part of magneto-optical response that is even with respect to magnetization and, in turn, to exclude all non-magnetic contributions which come from imperfections of the experimental setup or from the sample itself. It is, therefore, possible to study the sample placed inside a cryostat: the polarization changes due to cryostat windows and possible strain-induced optical anisotropy of the sample are removed by the applied data processing. Thanks to this, we can perform measurements on low or elevated temperatures (from 15 to 800 K in our case), making it possible to study the behavior of magnetic materials in different magnetic phases and/or close to phase transitions. The applicability of this experimental technique was tested by measuring the low-temperature response of two samples of ferromagnetic semiconductor (Ga,Mn)As with a different Mn content at several wavelengths, which enabled us to deduce the magnetic and quadratic magneto-optical anisotropies in this material. In particular, we observed that the anisotropy of quadratic magneto-optical coefficients in (Ga,Mn)As is much weaker than that reported previously for other magnetic material systems., Comment: 41 pages, 16 figures

Time-resolved terahertz spectroscopy is used to investigate formation and ultrafast long-distance propagation of electron-hole plasma in strongly photoexcited GaAs and InP. The observed phenomena involve fundamental interactions of electron-hole system with light, which manifest themselves in two different regimes: a coherent one with the plasma propagation speeds up to c/10 (in GaAs at 20 K) and an incoherent one reaching up to c/25 (in InP at 20 K), both over a macroscopic distance > 100 micrometers. We explore a broad range of experimental conditions by investigating the two materials, by tuning their band gap with temperature and by controlling the interaction strength with the optical pump fluence. Our interpretation suggests that the observed phenomena should occur in most direct band semiconductors upon strong photoexcitation with low excess energy.

Quantum synchronizable codes are quantum error correcting codes that can correct not only Pauli errors but also errors in block synchronization. The code can be constructed from two classical cyclic codes $\mathcal{C}$, $\mathcal{D}$ satisfying $\mathcal{C}^{\perp} \subset \mathcal{C} \subset \mathcal{D}$ through the Calderbank-Shor-Steane (CSS) code construction. In this work, we establish connections between quantum synchronizable codes, subsystem codes, and hybrid codes constructed from the same pair of classical cyclic codes. We also propose a method to construct a synchronizable hybrid subsystem code which can correct both Pauli and synchronization errors, is resilient to gauge errors by virtue of the subsystem structure, and can transmit both classical and quantum information, all at the same time. The trade-offs between the number of synchronization errors that the code can correct, the number of gauge qubits, and the number of logical classical bits of the code are also established. In addition, we propose general methods to construct hybrid and hybrid subsystem codes of CSS type from classical codes, which cover relevant codes from our main construction., Comment: 52 pages, 3 figures. V2: minor correction

This paper provides a semidefinite programming hierarchy based on state polynomial optimization to determine the existence of quantum codes with given parameters. The hierarchy is complete, in the sense that if a $(\!(n,K,\delta)\!)_2$ code does not exist then a level of the hierarchy is infeasible. It is not limited to stabilizer codes and thus applicable generally. While it is formally dimension-free, we restrict it to qubit codes through quasi-Clifford algebras. We derive the quantum analog of a range of classical results: first, from an intermediate level a Lov\'asz bound for self-dual quantum codes is recovered. Second, a symmetrization of a minor variation of this Lov\'asz bound recovers the quantum Delsarte bound. Third, a symmetry reduction using the Terwilliger algebra leads to semidefinite programming bounds of size $O(n^4)$. With this we give an alternative proof that there is no $(\!(7,1,4)\!)_2$ quantum code, and show that $(\!(8,9,3)\!)_2$ and $(\!(10,5,4)\!)_2$ codes do not exist., Comment: 51 pages

The results of a Fourier analysis of high-precision Kepler photometry of 75 double-mode RR~Lyrae (RRd) stars observed during NASA's K2 Mission (2014-18) are presented. Seventy-two of the stars are `classical' RRd (cRRd) stars lying along a well-defined curve in the Petersen diagram and showing no evidence of Blazhko modulations. The remaining three stars are `anomalous' RRd (aRRd) stars that lie well below the cRRd curve in the Petersen diagram. These stars have larger fundamental-mode amplitudes than first-overtone amplitudes and exhibit Blazhko variations. Period-amplitude relations for the individual pulsation components of the cRRd stars are examined, as well as correlations involving Fourier phase-difference and amplitude-ratio parameters that characterize the light curves for the two radial modes. A simple statistical model relating the fundamental (P0) and first-overtone (P1) periods to [Fe/H] provides insight into the functional form of the Petersen diagram. A calibration equation for estimating [Fe/H]phot abundances of `classical' RRd stars is derived by inverting the model and using 211 field and 57 globular cluster cRRd stars with spectroscopic metallicities to estimate the model coefficients. The equation is used to obtain [Fe/H]phot for the full sample of 72 K2 cRRd stars and for 2130 cRRd stars observed by the ESA Gaia Mission. Of the 49 K2 cRRd stars that are in the Gaia DR3 catalogue only five were found to be correctly classified, the remainder having been misclassified `RRc' or `RRab'., Comment: 23 pages, 12 figures, 10 tables plus Supplementary Information (two Appendices, two tables, 1 animated gif); accepted for publication in MNRAS

Single-molecule magnets (SMMs) with chemically tailorable properties are potential building blocks for quantum computing, high-density magnetic memory, and spintronics.1 2 3,4 These applications require isolated or few molecules on substrates, but studies of SMMs have mainly focused on bulk crystals. Moreover, fabrication of SMM-based devices and electrical detection of the SMM magnetic state are still coveted milestones that have so far been achieved mainly for double-decker rare-earth phthalocyanines at temperatures below 1 K.5-8 Here we demonstrate electrical detection of magnetization switching for a modification of the archetypal SMM Mn12, up to 70 K, based on the supramolecular spin valve effect5 with graphene quantum dots9. Notably, the exchange interaction between the molecules and the graphene, as well as the dot-mediated intermolecular interaction, can be directly extracted from the electrical response, opening the way to an effective characterization of the quantum properties of different types of SMMs in a wide temperature range.

Optical pump-terahertz probe spectroscopy has been used to investigate ultrafast photo-induced charge carrier transport in 3.4 $\mu$m wide graphene ribbons upon scaling the optical pump intensity. For low pump fluences, the deposited pump energy is rapidly redistributed through carrier-carrier scattering, producing secondary hot carriers: the picosecond THz photoconductivity then acquires a negative sign and scales linearly with an increasing pump fluence. At higher fluences, there are not enough equilibrium carriers able to accept the deposited energy, directly generated (excess) carriers start to contribute significantly to the photoconductivity with a positive sign leading to its saturation behavior. This leads to a non-monotonic variation of the carrier mobility and plasmonic resonance frequency as a function of the pump fluence and, at high fluences, to a balance between a decreasing carrier scattering time and an increasing Drude weight. In addition, a weak carrier localization observed for the polarization parallel to the ribbons at low pump fluences is progressively lifted upon increasing the pump fluence as a result of the rise of initial carrier temperature.

Dynamics of plasmons in nanoribbons of (hydrogen intercalated) quasi-free-standing single layer graphene is studied by terahertz spectroscopy both in the steady state and upon photoexcitation by an ultrashort near infrared laser pulse. The use of two-dimensional frequency domain analysis of the optical pump - THz probe signals allows us to determine the evolution of carrier temperature and plasmon characteristics with ~100 fs time resolution. Namely, we find that the carrier temperature decreases from more than 5000 K to the lattice temperature within about 7 ps and that during this evolution the carrier mobility remains practically constant. The time-resolved THz conductivity spectra suggest that graphene nanoribbons contain defects which act as low potential barriers causing a weak localization of charges; the potential barriers are overcome upon photoexcitation. Furthermore, the edges of graphene nanoribbons are found to slightly enhance the scattering of carriers. The results are supported by complementary measurements using THz scanning near-field microscopy which confirm a high uniformity of the THz conductivity across the sample and demonstrate high enough sensitivity to resolve even the impact of nanometric terrace steps on SiC substrate under the graphene monolayer.

Artificial intelligence (AI), although not able to currently capture the many complexities of humans, are slowly adapting to have certain capabilities of humans, many of which can revolutionize our world. AI systems, such as ChatGPT and others utilized within various industries for specific processes, have been transforming rapidly. However, this transformation can occur in an extremely concerning way if certain measures are not taken. This article touches on some of the current issues within the artificial intelligence ethical crisis, such as the concerns of discrimination within AI and false information that is becoming readily available with AI. Within this article, plausible solutions involving regulation are discussed and how they would mitigate ethical concerns. These include the self-regulation of businesses along with government regulation, and the effects these possible solutions can both have on current AI concerns.

Previous experiments in compensated magnets have demonstrated a potential for approaching the limit of fastest and least-dissipative operation of digital memory bits. However, the analog route has been virtually unexplored at (sub)ps time scales. In this paper, we report on experimental separation of heat-related and quench-switching-related resistance signal dynamics induced at room temperature by a single femtosecond-laser-pulse in memory devices from metallic antiferromagnetic CuMnAs. We show that the heat-related dynamics, on picosecond to hundreds of nanoseconds time scales, can be used as a short-term memory where information about input stimuli, represented by laser-pulses, is stored temporarily. When the quench-switching threshold is reached, information is transferred to the device variable resistance, serving as a long-term memory, with time components of 10 ms and 10 s. We also deduced 10 ps time scale as an upper estimate for a conversion of the short-lived transient temperature increase to the quench-switched metastable states., Comment: 19 pages, 4 figures

Angle-twisting engineering has emerged as a powerful tool for modulating electronic properties in van der Waals heterostructures. Recent theoretical works have predicted the modulation of spin texture in graphene-based heterostructures by twist angle, although an experimental verification is missing. Here, we demonstrate the tunability of the spin texture and associated spin-charge interconversion with twist angle in WSe$_2$/graphene heterostructures by using spin precession experiments. For specific twist angles, we experimentally detect a spin component radial with the electron's momentum, in addition to the standard orthogonal component. Our results show that the helicity of the spin texture can be reversed by angle twisting, highlighting its critical role on the spin-orbit properties of WSe$_2$/graphene heterostructures and paving the way for the development of novel spin-twistronic devices., Comment: 14 pages, 5 figures and Supplementary Information

We present a family of quantum stabilizer codes using the structure of duadic constacyclic codes over $\mathbb{F}_4$. Within this family, quantum codes can possess varying dimensions, and their minimum distances are lower bounded by a square root bound. For each fixed dimension, this allows us to construct an infinite sequence of binary quantum codes with a growing minimum distance. Additionally, we prove that this family of quantum codes includes an infinite subclass of degenerate codes. We also introduce a technique for extending splittings of duadic constacyclic codes, providing new insights into the minimum distance and minimum odd-like weight of specific duadic constacyclic codes. Finally, we provide numerical examples of some quantum codes with short lengths within this family., Comment: 31 pages, 2 tables

The donor-acceptor interaction of a charge-coupled heterostructure encompassing a metal and an amorphous semiconductor subjected to a laser field has many potential applications in the realm of nonlinear optics. In this work, we fabricate an electron donor gold nanoparticle (AuNP) and acceptor amorphous Ge24Se76 heterostructure on a quartz substrate using a sequential thermal evaporation technique. In this charge-coupled heterostructure, we demonstrate the ultrafast third-order nonlinear absorptive and refractive response and their sign reversal compared to pristine Ge24Se76. Enhanced optical nonlinearity in these heterostructures of varying plasmonic wavelengths is due to charge transfer, verified by the Raman spectroscopy. Further, the ultrafast transient absorption measurements support the thesis of charge transfer in the AuNP/Ge24Se76 heterostructure. These findings open up exciting opportunities for developing novel device technologies with far-reaching applications in nonlinear optics.

The quantum Hamming bound was originally put forward as an upper bound on the parameters of nondegenerate quantum codes, but over the past few decades much work has been done to show that many degenerate quantum codes must also obey this bound. In this paper, we show that there is a Hamming-like bound stricter than the quantum Hamming bound that applies to degenerate $t$-error-correcting stabilizer codes of length greater than some positive integer $N(t)$. We show that this bound holds for all single-error-correcting degenerate stabilizer codes, forcing all but a handful of optimal distance-3 stabilizer codes to be nondegenerate., Comment: 11 pages, 3 figures

This paper introduces a wall construction planner for Unmanned Aerial Vehicles (UAVs), which uses a Greedy Randomized Adaptive Search Procedure (GRASP) metaheuristic to generate near-time-optimal building plans for even large walls within seconds. This approach addresses one of the most time-consuming and labor-intensive tasks, while also minimizing workers' safety risks. To achieve this, the wall-building problem is modeled as a variant of the Team Orienteering Problem and is formulated as Mixed-Integer Linear Programming (MILP), with added precedence and concurrence constraints that ensure bricks are built in the correct order and without collision between cooperating agents. The GRASP planner is validated in a realistic simulation and demonstrated to find solutions with similar quality as the optimal MILP, but much faster. Moreover, it outperforms all other state-of-the-art planning approaches in the majority of test cases. This paper presents a significant advancement in the field of automated wall construction, demonstrating the potential of UAVs and optimization algorithms in improving the efficiency and safety of construction projects.