Hasil untuk "Atomic physics. Constitution and properties of matter"

Carlos Sagaseta, M J Calderón, José C Abadillo-Uriel

Spin qubits in semiconductor quantum dots offer a gate-tunable platform for quantum information processing. While two-qubit interactions are typically realized through exchange coupling between neighboring spins, coupling spin qubits to photons via hybrid spin-circuit QED (cQED) devices enables long-range interactions and integration with other cQED platforms. Here, we investigate hole spin–photon coupling in compact single quantum dot setups. By incorporating ubiquitous strain inhomogeneities to our theory, we identify three main spin–photon coupling channels: a vector-potential-spin–orbit geometric mechanism–dominant for vertical magnetic fields–, an inhomogeneous Rashba term generalizing previous spin–orbit field models, and strain-induced g -tensor terms–most relevant for in-plane fields. Comparing Si, unstrained (relaxed) Ge, and biaxially strained Ge wells, we find that Si and unstrained Ge provide optimal coupling strengths (tens of MHz) thanks to their reduced heavy-hole, light-hole splitting. We demonstrate efficient switching of the spin–photon coupling while preserving sweet spot conditions by operating with an in-plane magnetic field. Finally, we evaluate quantum state transfer and two-qubit gate protocols, achieving $\gtrsim 99\%$ fidelity for state transfer and ${\gt} 90\%$ for two-qubit gates with realistic coherence times, establishing single-dot hole spins as a viable platform for compact spin-cQED architectures and highlighting unstrained Ge as a promising candidate for spin–photon interactions.

Sascha Heußen

Magic state distillation (MSD) is a quantum algorithm that enables performing logical non-Clifford gates with, in principle, arbitrarily low noise levels. It is typically assumed herein that logical Clifford gates can be executed without noise. Therefore, MSD is a standard subroutine used to obtain a fault-tolerant universal set of quantum gate operations on error-corrected logical qubits. Well-known schemes conventionally rely on performing operator measurements and post-selection based on the measurement result, which makes distillation protocols non-deterministic in the presence of noise. In this work, we adapt the 15-to-1 MSD protocol such that it deterministically suppresses noise by using a coherent feedback network on the output states without the need to perform individual-qubit measurements. These advantages over textbook MSD come at the price of reducing the noise suppression per round from O(p3) to O(p2). Our technique can be applied to any MSD protocol with an acceptance rate of 1 in the absence of noise. It may be desirable to use our scheme if the coherent feedback network can be executed faster and more reliably than the measurements, and/or if logical clock cycles in the quantum processor should be kept synchronous at all times. Our result broadens the path of potential experimental realizations of MSD in near-term devices and advances the development of fault-tolerant quantum computers with practical use.

Yu Zhang, Hengdi Zhao, Tristan R. Cao et al.

Abstract The 4d-electron trimer lattice Ba₄Nb₁₋ₓRu₃₊ₓO₁₂ exhibits either a quantum spin liquid (QSL) or a heavy-fermion strange metal (HFSM) phase, depending on Nb content. In the QSL state, itinerant spinons act as effective heat carriers, enhancing thermal conductivity. Strikingly, applying a magnetic field up to 14 T causes an abrupt, up-to-5000% increase in heat capacity below 150 mK, disrupting the linear temperature dependence typical of both phases. Meanwhile, AC susceptibility and electrical resistivity remain nearly unchanged, while thermal conductivity drops by up to 40% below 4 K. These results suggest spinons, despite being charge-neutral, are highly sensitive to magnetic fields at low temperatures. We propose that the magnetic field could induce Anderson localization of spinons, creating emergent non-magnetic two-level systems responsible for the Schottky-like anomaly in heat capacity. These findings point to a previously unexplored regime of spinon dynamics, potentially governed by field-induced localization and distinct from conventional magnetic or transport signatures.

Stefano Bosco

Non-reciprocal devices are key components in both classical and quantum electronics. One approach to realizing passive non-reciprocal microwave devices is through capacitive coupling between external electrodes and materials exhibiting non-reciprocal conductance. In this work, we develop an analytic framework that captures the response of such devices in the presence of dissipation while accounting for the full AC dynamics of the material. Our results yield an effective circuit model that accurately describes the device response in experimentally relevant regimes even at small dissipation levels. Furthermore, our analysis reveals counterpropagating features arising from the intrinsic AC response of the material that could be exploited to dynamically switch the non-reciprocity of the device, opening pathways for tunable non-reciprocal microwave technologies.

K. Haydukivska

The influence of monomer-monomer interactions on the scaling exponents and shape characteristics of a single polymer chain in a selective solvent is investigated using Langevin dynamics simulations. By systematically increasing the temperature of the solution, the effects of interactions between blocks on the conformational properties of the chain are explored. The results demonstrate that longer-range interactions cause a transition of a polymer similar to the transition for homopolymers; short-range repulsive interactions between different blocks have a negligible impact on the effective scaling exponents: they are the same regardless of the blocks being globule and coil or ideal and swollen coils.

D. Maurin, L. Audouin, E. Berti et al.

Cosmic-ray physics in the GeV-to-TeV energy range has entered a precision era thanks to recent data from space-based experiments. However, the poor knowledge of nuclear reactions, in particular for the production of antimatter and secondary nuclei, limits the information that can be extracted from these data, such as source properties, transport in the Galaxy and indirect searches for particle dark matter. The Cross-Section for Cosmic Rays at CERN workshop series has addressed the challenges encountered in the interpretation of high-precision cosmic-ray data, with the goal of strengthening emergent synergies and taking advantage of the complementarity and know-how in different communities, from theoretical and experimental astroparticle physics to high-energy and nuclear physics. In this paper, we present the outcomes of the third edition of the workshop that took place in 2024. We present the current state of cosmic-ray experiments and their perspectives, and provide a detailed road map to close the most urgent gaps in cross-section data, in order to efficiently progress on many open physics cases, which are motivated in the paper. Finally, with the aim of being as exhaustive as possible, this report touches several other fields -- such as cosmogenic studies, space radiation protection and hadrontherapy -- where overlapping and specific new cross-section measurements, as well as nuclear code improvement and benchmarking efforts, are also needed. We also briefly highlight further synergies between astroparticle and high-energy physics on the question of cross-sections.

Antun Balaz, Diego Blas, Oliver Buchmueller et al.

Long-baseline atom interferometry is a promising technique for probing various aspects of fundamental physics, astrophysics and cosmology, including searches for ultralight dark matter (ULDM) and for gravitational waves (GWs) in the frequency range around 1~Hz that is not covered by present and planned detectors using laser interferometry. The MAGIS detector is under construction at Fermilab, as is the MIGA detector in France. The PX46 access shaft to the LHC has been identified as a very suitable site for an atom interferometer of height $\sim 100$m, sites at the Boulby mine in the UK and the Canfranc Laboratory are also under investigation, and possible sites for km-class detectors have been suggested. The Terrestrial Very-Long-Baseline Atom Interferometry (TVLBAI) Proto-Collaboration proposes a coordinated programme of interferometers of increasing baselines.

Francisco S. N. Lobo, Tiberiu Harko

Recent studies suggest that dark matter could take the form of a Bose-Einstein condensate (BEC), a possibility motivated by anomalies in galactic rotation curves and the missing mass problem in galaxy clusters. We investigate the astrophysical properties of BEC dark matter halos and their potential observational signatures distinguishing them from alternative models. In this framework, dark matter behaves as a self-gravitating Newtonian fluid with a polytropic equation of state of index $n=1$. We derive analytic expressions for the mass distribution, gravitational potential, and dynamical profiles such as the density slope and tangential velocity. The lensing behavior of BEC halos is analyzed, yielding a general series representation of the projected surface density that enables precise predictions for deflection angles, lensing potentials, and magnifications. Finally, halo equilibrium and stability are examined via the scalar and tensor virial theorems, leading to perturbation equations that describe their response to small disturbances. Together, these results provide a unified framework linking the microscopic physics of condensate dark matter to macroscopic halo observables.

C. F. A. Baynham, R. Hobson, O. Buchmueller et al.

The AION project has built a tabletop prototype of a single-photon long-baseline atom interferometer using the 87Sr clock transition - a type of quantum sensor designed to search for dark matter and gravitational waves. Our prototype detector operates at the Standard Quantum Limit (SQL), producing a signal with no unexpected noise beyond atom shot noise. Importantly, the detector remains at the SQL even when additional laser phase noise is introduced, emulating conditions in a long-baseline detector such as AION or AEDGE where significant laser phase deviations will accumulate during long atom interrogation times. Our results mark a key milestone in extending atom interferometers to long baselines. Such interferometers can complement laser-interferometer gravitational wave detectors by accessing the mid-frequency gravitational wave band around 1 Hz, and can search for physics beyond the Standard Model.

M. Cruz-Méndez, H. Cruz

In this study, we present a one-dimensional tight-binding model designed to explore the impact of electric fields on an incommensurate quantum system. We specifically focus on the Aubry–André–Harper model, a quasiperiodic model known to exhibit a metal–insulator transition at a critical potential value of λc = 2. This model combines Anderson and Aubry–André–Harper localization phenomena in a quantum system, leading to intriguing effects on the lattice band structure upon the application of an electric field F to the Aubry–André–Harper potential. Our investigation reveals that by choosing a specific value for the applied electric field, it becomes feasible to generate effective massless Dirac fermions within our Aubry–André–Harper system. Furthermore, we note that the extension or localization of the massless particle wave function is contingent upon the potential strength value λ within our incommensurate model. Importantly, our findings highlight the potential for detecting this intriguing phenomenon through experimental means.

Jorge M. Ramirez, Elaine Wong, Caio Alves et al.

This study investigates the frame potential and expressiveness of commutative quantum circuits. Based on the Fourier series representation of these circuits, we express quantum expectation and pairwise fidelity as characteristic functions of random variables, and we characterize expressiveness as the recurrence probability of a random walk on a lattice. A central outcome of our work includes formulas to approximate the frame potential and expressiveness for any commutative quantum circuit, underpinned by convergence theorems in the probability theory. We identify the lattice volume of the random walk as means to approximate expressiveness based on circuit architecture. In the specific case of commutative circuits involving Pauli-<inline-formula><tex-math notation="LaTeX">$Z$</tex-math></inline-formula> rotations, we provide theoretical results relating expressiveness and circuit structure. Our probabilistic representation also provides means for bounding and approximately calculating the frame potential of a circuit through sampling methods.

C. Santamarina Ríos, P. Rodríguez Cacheda, J. J. Saborido Silva

The hydrogen atom perturbed by a constant 1-dimensional weak quadratic potential $λz^2$ is solved at first-order perturbation theory using the eigenstates of the total angular momentum operator - the coupled basis. Physical applications of this result could be found, for example, in the study of a quadratic Zeeman effect weaker than fine-structure effects, or in a perturbation caused by instantaneous generalised van der Waals interactions.

H. Ye. Polozhii, A. G. Ponomarev, S. V. Kolinko et al.

Proton beam writing is a promising lithography method that is being developed in many countries. This method has significant advantages over other lithography methods, amongst all, there is the absence of the need for prefabricated pattern masks and a high aspect ratio of fabricated structures. Numerous publications demonstrate prospective applications of proton beam writing in different fields related to micro- and nanostructures fabrication. Proton beam writing may be used both for nanoelectronics and three-dimensional microstructures with a high aspect ratio. Work on proton beam writing technology is being conducted at the Institute of Applied Physics of the National Academy of Sciences of Ukraine. Last years there were introduced vector proton beam writing method, an electrostatic blanker system for proton beam distortion, and experiments on proton beam writing on chitosan films were conducted, including the films covered with thin films of metals and metal compounds.

Chung-Hsien Wang, Nai-Yu Tsai, Yi-Cheng Wang et al.

In the study of optical properties of large atomic system, a weak laser driving is often assumed to simplify the system dynamics by linearly coupled equations. Here, we investigate the light scattering properties of atomic ensembles beyond weak-field excitation through the cumulant expansion method. By progressively incorporating higher-order correlations into the steady-state equations, an enhanced accuracy can be achieved in comparison to the exact solutions from solving a full density matrix. Our analysis reveals that, in the regime of weak dipole-dipole interaction (DDI), the first-order expansion yields satisfactory predictions for optical depth, while denser atomic configurations necessitate consideration of higher-order correlations. As the intensity of incident light increases, atom saturation effects become noticeable, giving rise to significant changes in light transparency, energy shift, and decay rate. This saturation phenomenon extends to subradiant atom arrays even under weak driving conditions, leading to substantial deviations from the linear model. Our findings demonstrate the mean-field models as good extensions to linear models as it balances both accuracy and computational complexity. However, the crucial role of higher-order cumulants in large and dense atom systems remains unclear, since it is challenging theoretically owing to the exponentially increasing Hilbert space in such light-matter interacting systems.

Shuting Peng, Christopher Lane, Yong Hu et al.

Abstract In high-temperature (T c) cuprate superconductors, many exotic phenomena are rooted in the enigmatic pseudogap state, which has been interpreted as consisting of preformed Cooper pairs or competing orders or a combination thereof. Observation of pseudogap phenomenologically in electron-doped Sr2IrO4—the 5d electron counterpart of the cuprates, has spurred intense interest in the strontium iridates as a testbed for exploring the exotic physics of the cuprates. Here, we examine the pseudogap state of electron-doped Sr2IrO4 by angle-resolved photoemission spectroscopy (ARPES) and parallel theoretical modeling. Our analysis demonstrates that the pseudogap state of Sr2IrO4 appears without breaking the particle–hole symmetry or inducing spectral broadening which are telltale signatures of competing orders in the cuprates. We find quasiparticle dispersion and its temperature dependence in the pseudogap state of Sr2IrO4 to point to an electronic order with a zero scattering wave vector and limited correlation length. Particle–hole symmetric preformed Cooper pairs are discussed as a viable mechanism for such an electronic order. The potential roles of incommensurate density waves are also discussed.

Rinku Sharma, Sunny Aggarwal

S. Chibani, D. Farina, P. Massat et al.

Abstract We report the evolution of nematic fluctuations in FeSe1−x S x single crystals as a function of Sulfur content x across the nematic quantum critical point (QCP) x c  ~ 0.17 via Raman scattering. The Raman spectra in the B 1g nematic channel consist of two components, but only the low energy one displays clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie–Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling, which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund’s metals, with both itinerant carriers and local moments contributing to the nematic susceptibility.

F. Espinoza, Department of Physics, Astronomy et al.

The current public sense of anxiety in dealing with disinformation as manifested by so-called fake news is acutely displayed by the reaction to recent events prompted by a belief in conspiracies among certain groups. A model to deal with disinformation is proposed; it is based on a demonstration of the analogous behavior of disinformation to that of wave phenomena. Two criteria form the basis to combat the deleterious effects of disinformation: the use of a refractive medium based on skepticism as the default mode, and polarization as a filter mechanism to analyze its merits based on evidence. Critical thinking is enhanced since the first one tackles the pernicious effect of the confirmation bias, and the second the tendency towards attribution, both of which undermine our efforts to think and act rationally. The benefits of such a strategy include an epistemic reformulation of disinformation as an independently existing phenomenon, that removes its negative connotations when perceived as being possessed by groups or individuals.

Ahmed G. Mostafa, Sayed A. Makhlouf, Elham El-Hakim et al.

In this paper, the physical inventory taking of nuclear materials (NM) (under safeguards application) at the nuclear fuel research laboratory at Inshas, Egypt has been considered. NM with different forms and sizes were verified. The verification method based on non-destructive measurements of gamma radiation emitted from NM was tested. Monte Carlo method (MCNP5) and Multi-Group Analysis software (MGAU Genie 2000, version 3.2) were used to estimate 235U mass content in the studied forms. Some of the parameters which affect NM mass estimation were also investigated. The proposed procedure covers different forms found at the nuclear fuel research laboratory such as pellets, sludge, and rods. The average accuracies for the estimated 235U masses ranged between -0.351 and -1.005 %, while the precision was about 2.065 and 7.45 % for MCNP5 and MGAU respectively. These results are found to be acceptable within the limits of the International Target Values.

Luca Salasnich