AAPPS Bulletin最新文献

In this short review article, we aim to provide physicists not working within the quantum computing community a hopefully easy-to-read introduction to the state of the art in the field, with minimal mathematics involved. In particular, we focus on what is termed the Noisy Intermediate Scale Quantum era of quantum computing. We describe how this is increasingly seen to be a distinct phase in the development of quantum computers, heralding an era where we have quantum computers that are capable of doing certain quantum computations in a limited fashion, and subject to certain constraints and noise. We further discuss the prominent algorithms that are believed to hold the most potential for this era, and also describe the competing physical platforms on which to build a quantum computer that have seen the most success so far. We then talk about the applications that are most feasible in the near-term, and finish off with a short discussion on the state of the field. We hope that as non-experts read this article, it will give context to the recent developments in quantum computers that have garnered much popular press, and help the community understand how to place such developments in the timeline of quantum computing.

We review a recent progress of a superconductivity and a charge Kondo effect mediated by valence skippers which are elements skipping the valence state. To understand the valence skipping phenomenon, we introduce a negative-U effect phenomenologically, and we show an origin of the negative-U effect, a superconductivity and charge Kondo effect based on the negative-U effect. We also show a new mechanism in which the valence skipping phenomenon and charge Kondo effect are understood unifiedly by the pair hopping interaction. As an experimental progress, we review a charge Kondo effect and a superconductivity discovered in Tl-doped PbTe. Especially, we focus on a drastic increase of the inverse of the relaxation time (1/T₁) observed around the Kondo temperature by the nuclear magnetic resonance experiment, and we suggest a possible theoretical scenario on the basis of the effective model with the pair hopping interaction. Finally, we discuss the related materials, and describe the perspective of valence skipping phenomenon.

Random matrix products arise in many science and engineering problems. An efficient evaluation of its growth rate is of great interest to researchers in diverse fields. In the current paper, we reformulate this problem with a generating function approach, based on which two analytic methods are proposed to compute the growth rate. The new formalism is demonstrated in a series of examples including an Ising model subject to on-site random magnetic fields, which seems very efficient and easy to implement. Through an extensive comparison with numerical computation, we see that the analytic results are valid in a region of considerable size.The formulation could be conveniently applied to stochastic processes with more complex structures.

We report on a monolayer (ML) MoS₂ belt-like single crystal directly fabricated on the Rutile-TiO₂(001) surface via chemical vapor deposition (CVD). We find that the photoluminescence (PL) behaviors in the ML MoS₂ single crystal strongly depend on their shapes and the interface of MoS₂/TiO₂. Compared with the as-grown triangular ML MoS₂, the PL peak position is in a blue shift and the PL intensity is increased for the as-grown ML MoS₂ belt. Moreover, the PL peak position is in the blue shift by about 38 meV and the intensity is enhanced by nearly 15 times for the as-grown ML MoS₂ belt crystal on TiO₂ than those samples transferred onto SiO₂/Si substrate. This special PL behavior can be attributed to the in-plane compressive strain that is introduced during the CVD growth of ML MoS₂ belts confined by the substrate. The energy band of the strained ML MoS₂ belt is changed with an up-shift in the conduction band minimum (VBM) and a down-shift in the valence band maximum (CBM), and the band gap is thus enlarged. This results in the energy band structural realignment in the interface of MoS₂/TiO₂, thereby weakening the charge transferring from the TiO₂ substrate to MoS₂ and suppressing the concentration of charged excitons to finally enhance the PL intensity of the ML MoS₂ belt. The substrate-confined ML MoS₂ belts provide a new route for tailoring light-matter interactions to upgrade their weak quantum yields and low light absorption, which can be utilized in optoelectronic and nanophotonic devices.

We briefly review the research on second sound in ultracold atomic physics, with emphasis on strongly interacting unitary Fermi gases with infinitely large s-wave scattering length. Second sound is a smoking-gun feature of superfluidity in any quantum superfluids. The observation and characterization of second sound in ultracold quantum gases have been a long-standing challenge, and in recent years, there are rapid developments due to the experimental realization of a uniform box-trap potential. The purpose of this review is to present a brief historical account of the key research activities on second sound over the past two decades. We summarize the initial theoretical works that reveal the characteristics of second sound in a unitary Fermi gas, and introduce its first observation in a highly elongated harmonic trap. We then discuss the most recent measurement on second sound attenuation in a uniform setup, which may open a new era to understand quantum transport near quantum criticality in the strongly interacting regime. The observation of second sound in homogeneous weakly interacting Bose condensates in both two and three dimensions are also briefly introduced.

The performance limitations of conventional electronic materials pose a major problem in the era of digital transformation (DX). Consequently, extensive research is being conducted on the development of quantum materials that may overcome such limitations, by utilizing quantum effects to achieve remarkable performances. In particular, considerable progress has been made on the fundamental theories of topological magnets and has had a widespread impact on related fields of applied research. An important advance in the field of quantum manipulation is the development of the technology to control the quantum phase of conduction electron wavefunctions through the spin structure. This new technology has led to the realization of phenomena that had been considered infeasible for more than a century, such as the anomalous Hall effect in antiferromagnets and the giant magneto-thermoelectric effect in ferromagnets. This review article presents the remarkable properties of Weyl antiferromagnets and topological ferromagnets, which have been discovered recently. Additionally, this paper examines the current status of how advances in the basic principles of topological magnetism are facilitating the development of next-generation technologies that support the DX era, such as energy harvesting, heat flow sensors, and ultrafast nonvolatile memory.

The uncertainty relation is regarded as a remarkable feature of quantum mechanics differing from the classical counterpart, and it plays a backbone role in the region of quantum information theory. In principle, the uncertainty relation offers a nontrivial limit to predict the outcome of arbitrarily incompatible observed variables. Therefore, to pursue a more general uncertainty relations ought to be considerably important for obtaining accurate predictions of multi-observable measurement results in genuine multipartite systems. In this article, we derive a generalized entropic uncertainty relation (EUR) for multi-measurement in a multipartite framework. It is proved that the bound we proposed is stronger than the one derived from Renes et al. in [Phys. Rev. Lett. 103,020402(2009) ] for the arbitrary multipartite case. As an illustration, we take several typical scenarios that confirm that our proposed bound outperforms that presented by Renes et al. Hence, we believe our findings provide generalized uncertainty relations with regard to multi-measurement setting, and facilitate the EUR’s applications on quantum precision measurement regarding genuine multipartite systems.

In this paper, we review and discuss the main properties of the time-reversal operator T and its action in classical electromagnetism and in quantum mechanics. In particular, we discuss the relation (and differences) between time-reversal invariance and reciprocity.