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

Candice Thomas, Pablo Renaud, Meriem Guergour et al.

For cryogenic systems, the development of superconducting interconnects is nowadays essential to reach large-scale integration schemes while addressing the associated challenges of signal dispersion and cross talk as well as thermal management. To achieve interconnects with micrometer and potentially sub-micrometer pitches, we investigate wafer-to-wafer direct bonding of Nb pads, using 200 mm processes developed for Cu/SiO _2 hybrid bonding and for Nb routing levels. Contrarily to standard hybrid bonding, the Nb pads of these interconnects are surrounded by air instead of dielectric to reduce signal and thermal losses in between the wafers. We report on the fabrication and characterization of this technology using 20–7 μ m-pitch direct bonded Nb pads. Transmission electron microscopy of the bonded interface and wafer-level parametric tests at 300 K of various daisy chains assess the bonding quality with a yield exceeding 90%. Low temperature electrical measurements in a cryostat demonstrate the promise of these interconnects with a critical temperature of 4.6 K, a critical magnetic field of 3.2 T and a critical current density of 1.25 kA/cm ^2 at 2 K and 0 T for 10 µ m × 10 μ m bonded Nb pads.

Hiroomi Chono, Hayato Goto

Kerr parametric oscillators (KPOs), two-photon driven Kerr-nonlinear resonators, can stably hold coherent states with opposite-sign amplitudes and are promising devices for quantum computing. Recently, we have theoretically proposed a two-qubit gate Rzz for highly detuned KPOs and called it a conditional-driving gate [Chono et al., Phys. Rev. Res. 4, 043054 (2022)]. In this study, analyzing its superconducting-circuit model and deriving a corresponding static model, we find that an AC-Zeeman shift due to the flux pulse for the gate operation largely affects the gate performance. This effect becomes a more aggravating factor with shorter gate times, leading to an increase in the error rate. We thus propose a method to cancel this undesirable effect. Furthermore, through the use of shortcuts to adiabaticity and the optimization of flux pulses, we numerically demonstrate a conditional-driving gate with average fidelity exceeding 99.9% twice faster than that without the proposed cancellation method and the shortcuts to adiabaticity.

Sabrina J. Li, Guru Khalsa, Jeffrey Z. Kaaret et al.

Abstract Experiments involving resonant optical excitation of infrared-active phonons in crystals have emerged as a powerful new way to tune materials properties. A puzzling and so far unexplained aspect of some so-called nonlinear phononics experiments is that the observed lifetimes of the optically created metastable phases are sometimes orders of magnitude longer than expected based on the nonlinear phononics mechanism assumed in most works. We use a combination of phenomenological theory and first-principles calculations to demonstrate that strong coupling between different lattice degrees of freedom (strains and Raman-active phonons) can give rise to a long-lived metastable phase recently observed in experiments on perovskite LaAlO3 [Hortensius et al. npj Quantum Mater.5 95 (2020)]. We show that the long-timescale oscillatory response in the experimental optical reflectivity data is not due solely to shear strains, as originally suggested, but arises from a “hybrid” mode involving displacements of Raman-active phonons of the same symmetry. Our work suggests that strong coupling between different order parameters can provide a mechanism for long-lived optically created metastable phases and points towards strategies, such as strain engineering, for modifying or increasing the lifetime of light-induced phases in ultrafast optical experiments.

Manh Hong Nguyen, Giung Park, Je-Geun Park et al.

Abstract Interlayer interactions in few-layer NiPS3 were investigated by analyzing low-frequency interlayer vibration modes and Davydov splitting of an intralayer, A1g vibration mode at ~255 cm–1 by Raman spectroscopy as a function of temperature. The interlayer force constants were estimated from the low-frequency Raman spectra by using the linear chain model. The out-of-plane direction interlayer force constant could also be estimated separately from the Davydov splitting, which agrees well with the linear chain model analysis. The dependence of the low-frequency shear and breathing modes and the Davydov splitting on the number of layers provide a unique, reliable tool for determining the number of layers.

Guangpeng Xu, Jeffrey Carvalho, Chiran Wijesundara et al.

The classification of higher-order photon emission becomes important with more methods being developed for deterministic multiphoton generation. The widely used second-order correlation g(2) is not sufficient to determine the quantum purity of higher photon Fock states. Traditional characterization methods require a large amount of photon detection events, which leads to increased measurement and computation time. Here, we demonstrate a machine learning model based on a 2D Convolutional Neural Network (CNN) for rapid classification of multiphoton Fock states up to |3⟩ with an overall accuracy of 94%. By fitting the g(3) correlation with simulated photon detection events, the model exhibits an efficient performance particularly with sparse correlation data, with 800 co-detection events to achieve an accuracy of 90%. Using the proposed experimental setup, this CNN classifier opens up the possibility for quasi-real-time classification of higher photon states, which holds broad applications in quantum technologies.

Shanshan Liu, Enze Zhang, Zihan Li et al.

Abstract Transition-metal doped topological insulators have been widely explored since the observation of quantum anomalous Hall effect (QAHE). Subsequently, the magnetic (Pb,Sn)(Te,Se) was predicted to possibly possess a high-temperature QAHE state. However, the fundamental understanding of Cr-doping-induced ferromagnetism in this system remains unclear. Here, we report the stable ferromagnetism in the high-crystalline Cr-doped SnTe films. Upon Cr doping, the magnetoconductance unveils a crossover from weak antilocalization to weak localization. Further increasing the Cr concentration to Cr0.17Sn0.83Te introduces a strong ferromagnetism with a Curie temperature of ~140 K. We detected a sizable spin moment m s = 2.28 ± 0.23 μ B/Cr and a suppressed orbital moment m l = 0.02 μ B/Cr. Cr dopants prefer to substitute the Sn sites and behave as divalent cations, as indicated by the experimental results and density function theory calculations. The controllable growth of magnetic SnTe thin films provides enlightenment towards the high-temperature QAHE in magnetic TCIs for the desired dissipationless transport in electronics.

Valentin Zimmermann, Arvind Kumar Yogi, Deniz Wong et al.

Abstract Collective excitations such as plasmons and paramagnons are fingerprints of atomic-scale Coulomb and exchange interactions between conduction electrons in metals. The strength and range of these interactions, which are encoded in the excitations’ dispersion relations, are of primary interest in research on the origin of collective instabilities such as superconductivity and magnetism in quantum materials. Here we report resonant inelastic x-ray scattering experiments on the correlated 4d-electron metal Sr2RhO4, which reveal a spin-orbit entangled collective excitation. The dispersion relation of this mode is opposite to those of antiferromagnetic insulators such as Sr2IrO4, where the spin-orbit excitons are dressed by magnons. The presence of propagating spin-orbit excitons implies that the spin-orbit coupling in Sr2RhO4 is unquenched, and that collective instabilities in 4d-electron metals and superconductors must be described in terms of spin-orbit entangled electronic states.

Rui-Chun Xiao, Ding-Fu Shao, Wei Gan et al.

Abstract The relationship between magnetic order and the second harmonic generation (SHG) effect is a fundamental area of study in condensed matter physics with significant practical implications. In order to gain a clearer understanding of this intricate relation, this study presents a comprehensive classification scheme for the SHG effect in magnetically ordered materials. This framework offers a straightforward approach to connecting magnetic order and the SHG effect. The characteristics of the SHG tensors in all magnetic point groups are studied using the isomorphic group method, followed by a comprehensive SHG effect classification scheme that includes seven types based on the symmetries of the magnetic phases and their corresponding parent phases. In addition, a tensor dictionary containing the SHG and linear magneto-optic (LMO) effect is established. Furthermore, an extensive SHG database of magnetically ordered materials is also built up. This classification strategy exposes an anomalous SHG effect with even characteristics (i.e., invariant) under time-reversal symmetry, which is solely contributed by magnetic structure. Moreover, the proposed classification scheme facilitates the determination of magnetic structures through the SHG effect.

Kai Yang, Xianxiang Zeng, Li Hu et al.

This research was aimed to investigate the magnetic resonance imaging (MRI) features of brain structure and neuroendocrine levels in patients with first-episode schizophrenia. 25 hospitalized patients with first-episode schizophrenia were selected as the observation group, while 25 healthy people were selected as the control group. All the objects underwent MRI examination, and the images as well as gray matter density of the original image data were analyzed under voxel-based morphometry (VBM). The cortisol and prolactin in the observation group were detected, and the levels were compared. The Pearson correlation analysis was adopted to analyze the correlation between cortisol and prolactin levels and the total score of the Positive and Negative Syndrome Scale (PANSS). The results showed that the gray matter volume of the precentral gyrus, superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, postcentral gyrus, inferior parietal lobule, superior parietal lobule, and anterior cingulate cortex of the observation group decreased, while the volume of cerebellar gray matter increased. The levels of cortisol and prolactin in the observation group (387.54 ± 117.69 μg/L and 804.16 ± 267.13 μIU/mL, respectively) were significantly higher than those in the control group (138.46 ± 62.47 μg/L and 397.54 ± 203.82 μIU/mL, respectively), and the differences were statistically significant (P<0.05). The results of the Pearson correlation test showed that the higher the cortisol level, the more severe the schizophrenia (r = 0.421 and P=0.013), while the prolactin level was not directly related to the severity of schizophrenia (r = 0.019 and P=0.568). In conclusion, the MRI features based on the VBM technology can accurately assess the changes of gray matter; the levels of cortisol and prolactin in patients with first-episode schizophrenia were significantly higher than those in healthy people; and the higher the cortisol level, the more severe the schizophrenia symptoms. This study provided a certain research basis for MRI features of brain structure and neuroendocrine changes in patients with first-episode schizophrenia.

Thomas G. Mertens, Gustavo J. Turiaci

Abstract We review recent developments in Jackiw–Teitelboim gravity. This is a simple solvable model of quantum gravity in two dimensions (that arises e.g. from the s-wave sector of higher dimensional gravity systems with spherical symmetry). Due to its solvability, it has proven to be a fruitful toy model to analyze important questions such as the relation between black holes and chaos, the role of wormholes in black hole physics and holography, and the way in which information that falls into a black hole can be recovered.

Go Kato, Mikio Fujiwara, Toyohiro Tsurumaru

The key relay protocol (KRP) plays an important role in improving the performance and the security of quantum key distribution networks. On the other hand, there is also an existing research field called secure network coding (SNC), which has similar goal and structure. In this article, we analyze differences and similarities between KRPs in general and key relay using SNC schemes (KRPs-by-SNC) rigorously. We found, rather surprisingly, that there is a definite gap in security between KRPs in general and KRPs-by-SNC; that is, certain KRPs achieve better security than any SNC schemes on the same graph. We also found that this gap can be closed if we generalize the notion of SNC by adding authenticated public channels; that is, KRPs are equivalent to KRPs-by-SNC schemes augmented with authenticated public channels.

Andreu Blasco Coll, Javier R. Fonollosa

In this article, we explore perfect and quasi-perfect codes for the Bosonic channel, where information is generated by a laser and conveyed in the form of coherent states. In particular, we consider the phase-modulation codebook for coherent states in a Bosonic channel. We show that these phase-modulation codes are quasi-perfect as long as the cardinality of the code is the same as the dimension of the coherent states. These codes feature the smallest error probability among all codes of the same cardinality and the same dimension of the channel Hilbert space. We study the performance of these codes in terms of error probability, incorporating the degradation caused by a depolarizing or an erasure quantum channel.

Lucas A. Pressley, Dave Edey, Romy Hanna et al.

Abstract The presence of inclusions, twinning, and low-angle grain boundaries, demanded to exist by the third law of thermodynamics, drive the behavior of quantum materials. Identification and quantification of these structural complexities often requires destructive techniques. X-ray micro-computed tomography (µCT) uses high-energy X-rays to non-destructively generate 3D representations of a material with micron/nanometer precision, taking advantage of various contrast mechanisms to enable the quantification of the types and number of inhomogeneities. We present case studies of µCT informing materials design of electronic and quantum materials, and the benefits to characterizing inclusions, twinning, and low-angle grain boundaries as well as optimizing crystal growth processes. We discuss recent improvements in µCT instrumentation that enable elemental analysis and orientation to be obtained on crystalline samples. The benefits of µCT as a non-destructive tool to analyze bulk samples should encourage the community to adapt this technology into everyday use for quantum materials discovery.

Tony Wu, Tzu-Chien Hsueh

An almost all-digital time-to-digital converter (TDC) possessing subpicosecond resolutions, scalable dynamic ranges, high linearity, high noise immunity, and moderate conversion rates can be achieved by a random sampling-and-averaging (RSA) approach with the self-antithetic variance reduction (SAVR) technique for time-correlated single-photon counting (TCSPC) quantum measurements. This article presents detailed theoretical analysis and behavior-model verifications of the SAVR technique to effectively enhance the conversion rate of an asynchronous RSA-based TDC by more than 62 times with 7&#x0025; power overhead. In addition, the proposed performance estimation methodology for SAVR can greatly improve the computation efficiency during the system-level design and reduce the read-out circuit complexity in the silicon-photonics RSA-based TCSPC realization.

S. Shlomo

Hao-Hua Sun, Jin-Feng Jia

Abstract Majorana zero modes, which behave like Majorana fermions, are quasiparticle excitations in condensed matter systems. They obey non-Abelian statistics, and have been proposed as building blocks of topological quantum computers. They are predicted to exist in the vortex of topological superconductors. In 2012, such a topological superconductor was engineered by depositing topological insulator thin films on top of an s-wave superconductor. Thereafter, several evidences have been reported to prove the Majorana zero modes’ existence in the vortex. In this review, by putting all experimental and theoretical results together, we show that these experimental evidences are consistent and they are also strongly supported by the theories, so the existence of Majorana zero mode is firmly established. Moreover, the adjacent Majorana zero modes annihilate when two vortices are close enough, which demonstrate that they have the nature of Majorana fermions. Finally, their potential application in topological quantum computing is discussed.

V. M. Shestopalov, A. J. Moiseev, N. K. Rodionova et al.

Effectiveness of radiomodifying action of natural mineral water (MW) of Berezovsky deposit in comparison with MW “Naftusya” was studied. It is shown that MW Berezovsky deposits are characterized by mild radioprotective properties. With prolonged use, MW deregulates prooxidant-antioxidant ratio and inhibits the oxidative metabolism in the peripheral blood of the animals.

I. O. Korzh, A. D. Foursat

Based on the generalized nuclear model, energy spectra of the odd nuclei of such elements as 25Mg, 41K, and 65Cu are determined, and the structure of wave functions of these nuclei in the excited and normal states is studied. High quality in determining the energy spectra is possible due to the accurate calculations of all elements of the energy matrix. It is demonstrated that the structure of the wave functions so determined provides the possibility to more accurately select the nuclear model and the method for calculating the nucleon cross-sections of the inelastic scattering of nucleons by odd nuclei.

J.T. Mendonça, Hugo Terças

J Kioseoglou, E Kalesaki, L Lymperakis et al.