Table of contents

This study investigates the influence of particle charge and electrorheological (ER) effects on microparticle dynamics and dust-acoustic wave propagation in low-pressure complex plasmas under microgravity conditions. Experiments were conducted using PK-4 during parabolic flights and onboard the International Space Station to analyze dust particle behavior in direct current (DC) and DC polarity switching discharge plasma. Key findings reveal that variations in particle charge potential and ER effects significantly affect particle dynamics, especially at different gas pressures. Specifically, we validated a dimensionless charge potential of $z = 0.34 \pm 0.17$ in a DC neon plasma discharge, noting a rapid increase in this potential at pressures below 15 Pa. Furthermore, we observed a reduction in charge of up to 50% due to quadrupole effects induced by polarity switching. These results provide critical insights into plasma behavior in microgravity and the role of external electric fields in particle interactions.

Most superconductors are thermal insulators. A disordered chiral p-wave superconductor, however, can make a transition to a thermal metal phase. Because heat is then transported by Majorana fermions, this phase is referred to as a Majorana metal. Here we present numerical evidence that the mechanism for the phase transition with increasing electrostatic disorder is the percolation of boundaries separating domains of different Chern number. We construct the network of domain walls using the spectral localizer as a 'topological landscape function', and obtain the thermal metal–insulator phase diagram from the percolation transition.

Laser spectroscopy of hot atomic vapours has been studied extensively. Theoretical models that predict the absolute value of the electric susceptibility are crucial for optimising the design of photonic devices that use hot vapours, and for extracting parameters, such as external fields, when these devices are used as sensors. To date, most of the models developed have been restricted to the weak-probe regime. However, fulfilling the weak-probe power constraint may not always be easy, desired or necessary. Here we present a model for simulating the spectra of alkali-metal vapours for a variety of experimental parameters, most distinctly at intensities beyond weak laser fields. The model incorporates optical pumping effects and transit-time broadening. We test the performance of the model by performing spectroscopy of ⁸⁷Rb in a magnetic field of 0.6 T, where isolated atomic resonances can be addressed. We find very good agreement between the model and data for three different beam diameters and a variation of intensity of over five orders of magnitude. The non-overlapping absorption lines allow us to differentiate the saturation behaviour of open and closed transitions. While our model was only experimentally verified for the D2 line of rubidium, the software is also capable of simulating spectra of rubidium, sodium, potassium and caesium over both D lines.

The decomposition of a square matrix into a sum of Pauli strings is a classical pre-processing step required to realize many quantum algorithms. Such a decomposition requires significant computational resources for large matrices. We present an exact and explicit formula for the Pauli string coefficients which inspires an efficient algorithm to compute them. More specifically, we show that up to a permutation of the matrix elements, the decomposition coefficients are related to the original matrix by a multiplication of a generalised Hadamard matrix. This allows one to use the Fast Walsh-Hadamard transform and calculate all Pauli decomposition coefficients in $\mathcal{O}(N^2\log N)$ time and using $\mathcal{O}(1)$ additional memory, for an N × N matrix. A numerical implementation of our equation outperforms currently available solutions.

High-precision displacement sensing serves as a cornerstone for measuring numerous physical quantities. Through plasmon-enhanced fluorescence, we propose a nitrogen-vacancy-based highly sensitive and microwave-free distance measurement scheme for metal tips with a sub-wavelength scale size. The best sensitivity is estimated to be $72\,\mathrm{fm/\sqrt{Hz}}$ with a high bandwidth of $21 \,\mathrm{GHz}$ through simulations and numerical analyses. The study reveals that the sensor performance remains insensitive to fluctuations in plasmon resonance wavelength, indicating the system's inherent tolerance to structural deviations, potentially stemming from manufacturing imperfections. Furthermore, a greater quantum radiation efficiency leads to an improved sensitivity and a wider working range. This low-noise, no-damage, and robust scheme with a high frequency bandwidth has potential applications in on-chip inertial devices and basic physical research.

One of the most important resources for quantum optical experiments and applications are on-demand highly entangled multiphoton quantum states. A promising way of generating them is heralding entanglement generation at a high rate from letting independent photons interfere. However, such schemes often work for a specific internal degree of freedom of the interfering photons only. Going to higher numbers of entangled photons, the success probabilities decrease while the number of necessary resources, e.g. auxiliary photons and optical elements, increases. To make probabilistic schemes feasible also for larger quantum states, it is therefore important to find resource-efficient generation schemes with high success probabilities. In this work, we introduce easily implementable schemes to herald qubit Greenberger–Horne–Zeilinger (GHZ) states, higher-dimensional Bell states and higher-dimensional three-party GHZ states. Our schemes solely rely on multiphoton interference, i.e. they can be adjusted to work for arbitrary degrees of freedom. Furthermore, they demonstrate high success probabilities and need comparably few auxiliary photons.

The coherence times of solid-state spin qubits are often limited by the presence of a spin bath. Characterizing the spectrum of the local magnetic field fluctuations of the bath is key to understanding spin qubit decoherence. Here we use pulsed electron paramagnetic resonance (pEPR) based noise spectroscopy to measure the magnetic noise power spectra for ensembles of substitutional nitrogen (P1) centers in diamond that typically form the bath for nitrogen-vacancy (NV) centers. The Carr–Purcell–Meiboom–Gill (CPMG) dynamical decoupling experiments on the P1 centers were performed on a low [N] chemical vapor deposition (CVD) sample and a high [N] high-temperature, high-pressure (HPHT) sample at 89 mT. We characterize the NV centers of the latter sample using the same 2.5 GHz pEPR spectrometer. All power spectra show two distinct features, a broad component that is observed to scale as approximately $1/\omega^{0.7-1.0}$, and a prominent peak at the ¹³C Larmor frequency. The behavior of the broad component is consistent with an inhomogeneous distribution of Lorentzian spectra due to clustering of P1 centers, which has recently been shown to be prevalent in HPHT diamond. We develop techniques utilizing harmonics of the CPMG filter function to improve characterization of high-frequency signals, which we demonstrate on the ¹³C nuclear Larmor frequency. At 190 mT this is 2.04 MHz, 5.7 times higher than the CPMG modulation frequency (${\lt}357$ kHz, hardware-limited). Understanding the properties of the bath allow us to either exploit it as a quantum resource or optimize decoupling performance, while also informing sample fabrication technologies. The techniques are applicable to ac magnetometry for nanoscale nuclear magnetic resonance and chemical sensing.

We analyze the effect of acoustic phonons on the photocurrent and the spectral characteristics of a simplified photovoltaic setup made of Mott insulating layers between two metallic leads with a bias voltage applied between them. We include acoustic phonons via the Migdal approximation and we use real-space Floquet dynamical mean-field theory to address the nonequilibrium Floquet steady-state. The so-called auxiliary master equation approach is employed as impurity solver. We find that impact ionization is only weakly affected by acoustic phonon dissipation at low bias voltages. For higher biases instead, the Hartree shift considerably alters the on-site energies of the Hubbard bands and suppresses the photocurrent for intermediate electron–phonon coupling strengths. Impact ionization processes play a fundamental role in enhancing the electrical output power, which decreases when electron–phonon interaction is considered.

We propose shortcut to adiabaticity protocols for Bose–Einstein condensates trapped in generalized anisotropic harmonic traps in three dimensions. These protocols enable high-fidelity tuning of trap geometries on time scales much faster than those required for adiabatic processes and are robust across a wide range of interaction strengths, from weakly interacting regimes to the Thomas-Fermi limit. Using the same approach, we also design STA paths to rapidly drive interaction strengths in both isotropic and anisotropic traps. Comparisons with standard linear ramps of system parameters demonstrate significant improvements in performance. Finally, we apply these STA techniques to a unitary engine cycle with a BEC as the working medium. The STA methods significantly enhance the engine's power output without reducing efficiency and remain highly effective even after multiple consecutive cycles.

q-Breathers (QBs) represent a quintessential phenomenon of energy localization, manifesting as stable periodic orbits exponentially localized in normal mode space. Their existence can hinder the thermalization process in nonlinear lattices. In this work, we employ the Newton's method to identify QB solutions in the diatomic Fermi–Pasta–Ulam–Tsingou chains and perform a comprehensive analysis of their linear stability. We derive an analytical expression for the instability thresholds of low-frequency QBs, which converges to the known results of monoatomic chains as the bandgap approaches zero. The expression reveals an inverse square relationship between instability thresholds and system size, as well as a quadratic dependence on the mass difference, both of which have been corroborated through extensive numerical simulations. Our results demonstrate that the presence of a bandgap can markedly enhance QB stability, providing a novel theoretical foundation and practical framework for controlling energy transport between modes in complex lattice systems. These results not only expand the applicability of QBs but also offer significant implications for understanding the thermalization dynamics in complex lattice structures, with wide potential applications in related low-dimensional materials.

Quantum mechanics introduces the possibility for particles to move in a direction opposite to their momentum—a counter-intuitive and classically impossible phenomenon known as quantum backflow. The magnitude of this effect is relatively small, making its experimental observation, which has yet to be achieved, particularly challenging. Here, we investigate the influence of quantum statistics on the maximal backflow attainable for two identical particles confined to a ring. Notably, we demonstrate that the fermionic statistics significantly impedes quantum backflow compared to the bosonic statistics. Our findings suggest that any future experimental realization of quantum backflow should prioritize systems involving bosons rather than fermions.

We report a detailed characterization of two inductively coupled superconducting fluxonium qubits for implementing high-fidelity cross-resonance gates. Our circuit stands out because it behaves very closely to the case of two transversely coupled spin-$1/2$ systems. In particular, the generally unwanted static ZZ-term due to the non-computational transitions is nearly absent despite a strong qubit–qubit hybridization. Spectroscopy of the non-computational transitions reveals a spurious LC-mode arising from the combination of the coupling inductance and the capacitive links between the terminals of the two-qubit circuit. Such a mode has a minor effect on the present device, but it must be carefully considered for optimizing future multi-qubit designs.

A Josephson diode is a superconducting circuit element that enables non-reciprocal transport, allowing a dissipationless supercurrent to preferentially flow in a single direction. Existing methods for achieving the required symmetry breaking mostly rely on specifically-designed materials or carefully-engineered circuits composed of multiple Josephson junctions. Here, we investigate the diode effect induced by applying a biharmonic drive to a conventional superconducting tunnel-junction. In the slow-driving regime, the effect is straightforward to understand in a simple adiabatic picture, providing insight in the tunability of the magnitude and directionality of the diode effect through the drive parameters. We then focus on the fast-driving regime, where we show how the more complex physics underlying the dynamics of the junction can be approximated as a cascaded two-tone mixing process. We derive analytic expressions for the diode efficiency as a function of drive parameters in the limit of small driving amplitudes.

Fourfold exchange anisotropy has recently been discovered in bilayers consisting of a ferromagnetic (FM) layer exchange-coupling with an epitaxial antiferromagnetic (AF) layer. The chemical ordering of the AF layer plays an important role in the interfacial exchange coupling of AF/FM bilayers. Herein, we studied the thickness dependence of the chemical ordering and fourfold exchange anisotropy of FeRh/CoFe bilayers before and after the AF–FM phase transition of FeRh. The chemical ordering parameter of FeRh obtained by x-ray diffraction increases with thickness due to the decrease in the proportion of low-order interfaces, which results in an increase in the magnetic phase transition temperature and a decrease in the phase transition width, residual magnetization in the AF state, and lattice constant. After the occurrence of the AF–FM phase transition, the fourfold exchange anisotropy observed in the CoFe layer by magneto-optical Kerr effect changes from the FeRh〈110〉 to 〈100〉 directions, indicating the orientation change in the cubic magnetocrystalline anisotropy of FeRh. The fourfold exchange anisotropy measured by ferromagnetic resonance continues to increase with the FeRh thickness, indicating an effective thickness by far larger than that of chemically disordered AF systems. The FeRh/FM exchange coupling is highly dependent on chemical ordering, not only on the low-order surface of a few nanometers but also on the high-order interior extending to a depth of tens of nanometers.

The exploration of nonreciprocal dynamics carries substantial significance in both the field of quantum information processing and the domain of topological photonics. Here, we propose a quadruple-well system for generating nonreciprocity through the utilization of laser-assisted tunneling, wherein the generic principles governing the process can induce both purely real and complex asymmetric coupling mechanisms between adjacent wells. The complex asymmetric tunneling amplitudes induce an artificial gauge field that is equivalent to the Aharonov–Bohm phase experienced by charged particles in a magnetic field. The inclusion of purely real asymmetric tunneling amplitudes introduces pseudo-Hermiticity into the system. We explicitly delineate the conditions for the phase transitions of the system, transitioning from the parity–time ($\mathcal{PT}$)-symmetric phase to the spontaneously broken $\mathcal{PT}$-symmetric phase, along with the corresponding exceptional points (EPs). We then conduct a comprehensive investigation of the intriguing nonreciprocal dynamics both near and at the EPs, yielding notably distinct analytical results across all parametric regions. Furthermore, we demonstrate the tunability of nonreciprocal transport by manipulating the pseudo-Hermiticity and artificial gauge field, thereby enabling the reversal of the nonreciprocal directionality. Our study exhaustively elucidates the profound mechanisms underlying the interplay between pseudo-Hermiticity and artificial gauge fields on nonreciprocal dynamics, with potential implications for the design of innovative quantum nonreciprocal devices.

Providing accurate predictions from known information to future states of nonlinear dynamical systems is challenging, and data-driven techniques have emerged as powerful tools for addressing this problem. In this work, we proposed a data-driven and model-free framework delayed coordinate mapping-reservoir computing (DCM-RC) for long-term accurate prediction of nonlinear dynamical systems through the synergy between DCM and a novel RC method. For dynamic systems, DCM-RC constructs delayed attractors conjugated to the original attractor topology by converting the spatial information of the dynamic system into the temporal dynamics of the target variables through the delayed embedding theorem. The basic architecture of multistep prediction is constructed by finding DCM, and RC with fused polynomial libraries is applied to cross-predict all states of the dynamical system, thus obtaining information about the future of the dynamical system. The effectiveness and accuracy of DCM-RC are demonstrated on the Lorenz-63 system and the Rőssler system.

A single-layered diatomic metasurface (SDM) is proposed to manipulate multiple parameters of light field including the amplitude, phase and state of polarization and realize multiple channel holographic imaging. The diatom consists of two identical c-silicon nanopillars, complex amplitude holographic imaging, polarization multiplex imaging and structured light generation are realized by the rotated nanopillar array. Many applications are exemplified to verify the light manipulation abilities of the designed diatomic metasurfaces. The simple design, convenient operation and versatile functionalities of SDM will pave the road for the applications of metasurfaces in optical integration and optical multiplexing.

The interaction of a high-power laser with a solid target provides ways to produce beams of γ-photons. For normal incidence of the laser on the target the beams usually appear in a form of two lobes, which are symmetric with respect to the laser propagation axis. In this work we demonstrate via three-dimensional particle-in-cell simulations a regime where for oblique incidence the emission of a collimated γ-photon beam is in the direction parallel to the target surface. The process is ascribed to the interference pattern in the electromagnetic field formed by the incident and reflected laser pulse. The electromagnetic field accelerates electrons to the GeV energy level, while temporarily directing their momentum along the target surface. Consequently, they emit a collimated γ-photon beam in the same direction. The dependencies of γ-photon emission on the incident angle, laser pulse polarization, power and duration and target thickness and preplasma are also addressed in the paper. The beam directionality is important for designing future experiments. In addition, this setup causes the generation of high-order harmonics propagating along the target surface.

Diffraction gratings have simplified the optical implementation of magneto-optical traps (MOTs) to require only a single input beam, however reaching high atom number and fast loading has proven to be a challenge. We equipped an atom chip with a grating surface and paired it with a velocity-tunable 2D⁺-MOT as an atomic source to facilitate efficient loading together with magnetic trapping. Using uniform grating illumination, we magneto-optically trap ${1.0(1) \times 10^{9}}\,\mathrm{atoms}$ within one second, cool them to ${14.1(3)}\,\mu\textrm{K}$, and transfer a quarter of them into the magnetic chip trap. This is a key step towards simple portable quantum sensors employing (ultra-)cold atoms.

Self-seeding free-electron laser (FEL) enables the generation of a quasi-fully coherent hard x-ray pulse, and yet the stability of the pulse energy remains to be enhanced. Combining self-seeding with the superradiance, we propose a scheme for generating hard x-ray pulses characterized by stable intensity and narrow bandwidth. In this scheme, a large energy chirp is induced at the bunch head using a few-cycle laser. Powerful FEL radiation is generated in the linear chirp region and further evolves into an intensity-stable, single-spike spectral structure in the nonlinear chirp region. This evolution is driven by the superradiant effect, which utilizes the interaction between a nonlinear undulator taper and the nonlinear chirp of the bunch head. A diamond monochromator filters a narrow-bandwidth spectrum from the stable pulse, which is subsequently amplified to FEL saturation through interaction with the flat–top of the bunch tail. Numerical simulations and statistical analysis indicate that the stability of the hard x-ray FEL pulse is improved to 1.5%, providing a feasible pathway to generate stable and coherent hard x-ray pulses, enhancing the application potential of hard x-ray FEL facilities.

Topological insulators (TIs) are materials with unique surface conductive properties that distinguish them from normal insulators and have attracted significant interest due to their potential applications in electronics and spintronics. However, their weak magnetic field response in traditional setups has limited their practical applications. Here, we show that integrating TIs with active metamaterial substrates can significantly enhance the induced magnetic field by more than 10⁴ times. Our results demonstrate that selecting specific permittivity and permeability values for the active metamaterial substrate optimizes the magnetic field at the interface between the TI layer and the metamaterial, extending it into free space. This represents a substantial improvement over previous methods, where the magnetic field decayed rapidly. The findings reveal that the TI-metamaterial approach enhances the magnetic field response, unveiling new aspects of TI electromagnetic behavior and suggesting novel pathways for developing materials with tailored electromagnetic properties. The integration of metamaterials with TIs offers promising opportunities for advancements in materials science and various technological applications. Overall, our study provides a practical and effective approach to exploring the unique magnetic field responses of TIs, potentially benefiting other complex material systems.

Recent emerge of dielectric nanoparticle chains featuring subwavelength topological states has opened unprecedented avenues for light. Here, we demonstrate a mechanical analogy of zigzag nanoparticle chain that supports vibrational and rotational localizations in the form of subwavelength topological edge states at extremely low frequency (near zero). We elaborate analytical methodology to thoroughly analyze the wave dynamics in the near zero-frequency (NZF) regime. Due to weak rotational couplings, we find that motion can be efficiently confined on the boundaries of the chains. Interestingly, the vibration-rotation coupled property enables the granular chain for exotic NZF waves with spreading rotation inside the chain but localized vibration on the boundaries. We characterize the propagation properties of elastic waves in the chain, and exhibit the fingerprints of topological edge states on the boundaries. Our study provides the possibilities for vibration control techniques using granular media at extremely low frequency.

Biological molecules interact with their active and living surroundings, playing a crucial role in a variety of biofunctional processes. However, experimental studies on the morphological changes and diffusion behavior of real bio-macromolecules under active forces remain challenging. Here, suspensions of swimming bacteria at varying number densities are employed as an active bath, with fluorescently dyed DNA chains serving as model biopolymers. Our results show that DNA chains in bacterial baths undergo significant stretching and exhibit repetitive stretching and coiling dynamics, distinctly different from their behavior in thermal baths. The extent of elongation increases linearly with the bacteria density and the correlation length of the flow disturbed by motile bacteria. Furthermore, DNA chains exhibit short-time super-diffusion and long-time normal diffusion, with an effective diffusion coefficient surpassing that of rigid particles with hydrodynamic radii comparable to DNA macromolecules. The stretching deformation also induces anisotropic diffusion in the DNA body frame, characterized by faster transport along the elongated direction attributed to the chain's incapability to resist bending forces. These findings provide valuable insights into the behavior of chain-like biopolymers in active environments and enhance our understanding of the coupling between the deformation and diffusion of polymers in active systems.

Non-projective measurements play a crucial role in various information-processing protocols. In this work, we propose an operational task to identify measurements that are neither projective nor classical post-processing of data obtained from projective measurements. Our setup involves space-like separated parties with access to a shared state with bounded local dimensions. Specifically, in the case of qubits, we focus on a bipartite scenario with different sets of target correlations. While some of these correlations can be obtained through non-projective measurements on a shared two-qubit state, it is impossible to generate these correlations using projective simulable measurements on bipartite qubit states, or equivalently, by using one bit of shared randomness and local post-processing. For certain target correlations, we show that detecting qubit non-projective measurements is robust under arbitrary depolarizing noise, except in the limiting case. We extend this task for qutrits and demonstrate that some correlations achievable via local non-projective measurements cannot be reproduced by both parties performing the same qutrit projective simulable measurements on their pre-shared state. We provide numerical evidence for the robustness of this scheme under arbitrary depolarizing noise. For a more generic consideration (bipartite and tripartite scenario), we provide numerical evidence for a projective-simulable bound on the reward function for our task. We also show a violation of this bound by using qutrit positive operator valued measures. From a foundational perspective, we extend the notion of non-projective measurements to general probabilistic theories (GPTs) and use a randomness-free test to demonstrate that a class of GPTs, called square-bits or box-world are unphysical.

Odd-diffusive systems, characterised by broken time-reversal and/or parity, have recently been shown to display counterintuitive features such as interaction-enhanced dynamics in the dilute limit. Here we extend the investigation to the high-density limit of an odd tracer embedded in a soft medium described by the Gaussian core model (GCM) using a field-theoretic approach based on the Dean–Kawasaki equation. Our analysis reveals that interactions can enhance the dynamics of an odd tracer even in dense systems. We demonstrate that oddness results in a complete reversal of the well-known self-diffusion ($D_\mathrm{s}$) anomaly of the GCM. Ordinarily, $D_\mathrm{s}$ exhibits a non-monotonic trend with increasing density, approaching but remaining below the interaction-free diffusion, D₀, ($D_\mathrm{s} \lt D_0$) so that $D_\mathrm{s} \uparrow D_0$ at high densities. In contrast, for an odd tracer, self-diffusion is enhanced ($D_\mathrm{s} \gt D_0$) and the GCM anomaly is inverted, displaying $D_\mathrm{s} \downarrow D_0$ at high densities. The transition between the standard and reversed GCM anomaly is governed by the tracer's oddness, with a critical oddness value at which the tracer diffuses as a free particle ($D_\mathrm{s} \approx D_0$) across all densities. We validate our theoretical predictions with Brownian dynamics simulations, finding strong agreement between the them.

The tetragonal heavy fermion compound CeRh₂As₂ exhibits unconventional superconductivity accompanied by other broken symmetry phases that have been identified as presumably small moment intrinsic antiferromagnetism at low magnetic fields and induced quadrupolar order at higher in-plane fields. The latter may extend to very large pulsed-field range. The phase boundaries can be investigated by following thermodynamic anomalies like specific heat, magnetocaloric coefficient, thermal expansion and magnetostriction. We calculate their discontinuities and identify the influence of the field induced quadrupole on them. Furthermore we investigate the elastic constant anomalies which are determined by the static homogeneous quadrupolar RPA response functions. We present a calculation of these anomalies for the appropriate symmetry mode both in the disordered and ordered regime and investigate their change with applied field. In addition we consider the dynamical momentum dependent magnetic susceptibility and the associated dispersion of low energy magnetic modes and how their characteristics change across the phase boundary.

Typically practical realizations of discrete-variable quantum key distribution (QKD) protocols, based on exchanging single-photon signals between the trusted parties, can provide its users with only very low key generation rates. One of the potential solutions for this problem, that can be adapted for the case of entanglement-based QKD schemes using broadband photon-pair sources, is to utilize wavelength-division-multiplexing (WDM) modules in order to split the photons with different wavelengths to separate detection channels and generate multiple keys in parallel. Here, we theoretically investigate this idea in the case of pulsed laser used to pump spontaneous parametric down-conversion source. We optimize the effective phase-matching function width of the nonlinear crystal, and the intensity and duration of the pump laser pulses in order to maximize the advantage of the overall key generation rate provided by the WDM-based QKD scheme over the traditional no-WDM scenario. The results of our analysis show that the considered method can significantly accelerate the production of cryptographic keys, but proper optimization of the photon-pair source is needed to exploit its full potential.