Anuradhi Rajapaksha, Sarath D. Gunapala, Malin Premaratne
The widespread success of electronic transistors is partly due to their ability to be modeled using equivalent circuits, which not only enables detailed analysis and efficient design but also provides greater insight for designers, facilitating the development of complex electronic systems. The Ebers–Moll model, for example, is a widely used large-signal equivalent circuit that replicates the operational characteristics of bipolar junction transistors. Similar to electronic transistors, research on quantum thermal transistors has gained considerable attention in recent years; however, minimal focus has been placed on developing equivalent circuit representations. Drawing inspiration from equivalent models of electronic transistors, our study proposes an equivalent model for a quantum thermal transistor built on a strongly coupled qubit–qutrit–qubit architecture. This configuration allows replication of its transistor behavior using a diode-based equivalent model, leveraging its property of splitting the qutrit into two individual qubits. The proposed quantum thermal diode-based equivalent model closely mirrors the diode-based representation of an electronic transistor. Using frameworks of open quantum systems and the quantum Markovian master equation, along with the Born approximation and rotating wave approximation, we conduct a comprehensive analysis and comparison of our quantum thermal diode-based equivalent model with an established quantum thermal transistor model. Furthermore, we discuss the intrinsic internal coupling between the two diodes and determine the optimum coupling strength necessary for efficient heat amplification. This equivalent model provides greater insight into the analysis of quantum thermal transistors and significantly contributes to the advancement of nanoscale thermal circuit designs.
Atomic physics. Constitution and properties of matter
Amanda A. Konieczna, David A. S. Kaib, Stephen M. Winter
et al.
Abstract Motivated by the on-going discussion on the nature of magnetism in the quantum Ising chain CoNb2O6, we present a first-principles-based analysis of its exchange interactions with additional modeling, addressing drawbacks of a purely density functional theory ansatz. This method allows us to extract and understand the origin of the magnetic couplings—including all symmetry-allowed terms - and resolve conflicting model descriptions in CoNb2O6. We find that the twisted Kitaev chain and transverse-field ferromagnetic Ising chain views are mutually compatible, although additional off-diagonal exchanges are required for a complete picture. We show that the dominant exchange interaction is a ligand-centered process—involving e g electrons -, rendered anisotropic by low-symmetry crystal fields in CoNb2O6, resulting in dominant Ising exchange. Smaller bond-dependent anisotropies are found to originate from d − d kinetic exchange processes involving t 2g electrons. We demonstrate the validity of our low-energy model by comparing its predictions to measured THz and INS spectra.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Varun Venkatesh, Niels de Graaf Sousa, Amin Doostmohammadi
Active matter has played a pivotal role in advancing our understanding of non-equilibrium systems, leading to a fundamental shift in the study of biophysical phenomena. The foundation of active matter research is built on assumptions regarding the symmetry of microscopic constituents. While these assumptions have been validated extensively, instances of mixed or joint symmetries are prevalent in biological systems. This review explores the coexistence of polar and nematic order in active matter, emphasizing the theoretical and experimental challenges associated with these systems. By integrating insights from recent studies, we highlight the importance of considering mixed symmetries to accurately describe biological processes. This exploration not only benefits the field of biology but could also open new horizons for non-equilibrium physics, offering a comprehensive framework for understanding complex behavior in active matter.
The London penetration depth, $\lambda(T)$ , was measured in various forms of niobium, including foils, thin films, single crystals, and samples from superconducting radio-frequency (SRF) cavities. We observed a significant difference in $\lambda(T)$ at low temperatures, $T \lt T_\mathrm{c}/3$ , due to low-energy quasiparticles. In particular, an unusual downturn of $\lambda(T)$ on cooling in the SRF cavity samples required to take into account deep in-gap bound states. Theoretical modeling using the generalized Dynes density of states shows that such in-gap states lead to a downturn or a peak in $\lambda(T)$ upon cooling. Combined, experimental and theoretical findings provide a method for detecting two-level systems or states related to magnetic impurities in the bulk of niobium. This result is particularly relevant for the quantum informatics sciences technologies used in qubits and circuit quantum electrodynamics architecture based on SRF cavities.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract This review aims to provide a comprehensive overview of the development and current understanding of GaAs and InAs heterostructures, with a special emphasis on achieving high material quality and high-mobility two-dimensional electron gases (2DEGs). The review discusses the evolution of structural designs that have significantly contributed to the enhancement of electron mobility, highlighting the critical considerations of scattering mechanisms of the 2DEGs. In addition, this review examines the substantial contributions of Molecular Beam Epitaxy (MBE) to these developments, particularly through advancements in vacuum technology, source material purification, and precision control of growth conditions. The intent of this review is to serve as a useful reference for researchers and practitioners in the field, offering insights into the historical progression and technical details of these semiconductor systems.
Atomic physics. Constitution and properties of matter
Quantum state tomography (QST) aims at reconstructing the state of a quantum system. However, in conventional QST, the number of measurements scales exponentially with the number of qubits. Here, we propose a QST protocol, in which the introduction of a threshold allows one to drastically reduce the number of measurements required for the reconstruction of the state density matrix without compromising the result accuracy. In addition, one can also use the same approach to reconstruct an approximated density matrix tailoring the number of measurements on the available resources. We experimentally demonstrate this protocol by performing the tomography of states up to 7 qubits. We show that our approach can lead to results in agreement with those obtained by QST even when the number of measurements is reduced by more than two orders of magnitude.
Atomic physics. Constitution and properties of matter
The quest to understand the nature of dark matter and dark energy motivates a deep exploration into axion physics, particularly within the framework of string theory. Axions, originally proposed to solve the strong CP problem, emerge as compelling candidates for both dark matter and dark energy components of the universe. String theory, offering a unified perspective on fundamental forces, predicts a rich spectrum of axion-like particles (ALPs) arising from its compactification schemes. This paper provides a comprehensive review of axion physics within string theory, detailing their theoretical foundations, emergence from compactification processes, and roles in cosmological models. Key aspects covered include the Peccei-Quinn mechanism, the structure of ALPs, their moduli stabilization, and implications for observational signatures in dark matter, dark energy, and cosmological inflation scenarios. Insights from ongoing experimental efforts and future directions in axion cosmology are also discussed
Prabhakar Palni, Amal Sarkar, Santosh K. Das
et al.
The second Hot QCD Matter 2024 conference at IIT Mandi focused on various ongoing topics in high-energy heavy-ion collisions, encompassing theoretical and experimental perspectives. This proceedings volume includes 19 contributions that collectively explore diverse aspects of the bulk properties of hot QCD matter. The topics encompass the dynamics of electromagnetic fields, transport properties, hadronic matter, spin hydrodynamics, and the role of conserved charges in high-energy environments. These studies significantly enhance our understanding of the complex dynamics of hot QCD matter, the quark-gluon plasma (QGP) formed in high-energy nuclear collisions. Advances in theoretical frameworks, including hydrodynamics, spin dynamics, and fluctuation studies, aim to improve theoretical calculations and refine our knowledge of the thermodynamic properties of strongly interacting matter. Experimental efforts, such as those conducted by the ALICE and STAR collaborations, play a vital role in validating these theoretical predictions and deepening our insight into the QCD phase diagram, collectivity in small systems, and the early-stage behavior of strongly interacting matter. Combining theoretical models with experimental observations offers a comprehensive understanding of the extreme conditions encountered in relativistic heavy-ion and proton-proton collisions.
The performance and scalability of silicon spin qubits depend directly on the value of the conduction band valley splitting (VS). In this work, we investigate the influence of electromagnetic fields and the interface width on the VS of a quantum dot in a Si/SiGe heterostructure. We propose a new three-dimensional theoretical model within the effective mass theory for the calculation of the VS in such heterostructures that takes into account the concentration fluctuation at the interfaces and the lateral confinement. With this model, we predict that the electric field is an important parameter for VS engineering, since it can shift the probability distribution away from small VSs for some interface widths. We also obtain a critical softness of the interfaces in the heterostructure, above which the best option for spin qubits is to consider an interface as wide as possible.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract Finding materials exhibiting superconductivity at room temperature has long been one of the ultimate goals in physics and material science. Recently, room-temperature superconducting properties have been claimed in a copper substituted lead phosphate apatite (Pb10-xCux(PO4)6O, or called LK-99) (Lee et al. in J. Korean Cryst. Growth Cryst. Technol. 33:61, 2023; Lee et al. in The first room-temperature ambient-pressure superconductor, 2023; Lee et al. in Superconductor Pb10-xCux(PO4)6O showing levitation at room temperature and atmospheric pressure and mechanism, 2023). Using a similar approach, we have prepared LK-99 like samples and confirmed the half-levitation behaviors in some small specimens under the influence of a magnet at room temperature. To examine the magnetic properties of our samples, we have performed systematic magnetization measurements on the as-grown LK-99 like samples, including the half-levitated and non-levitated samples. The magnetization measurements show the coexistence of soft-ferromagnetic and diamagnetic signals in both half-levitated and non-levitated samples. The electrical transport measurements on the as-grown LK-99 like samples including both half-levitated and non-levitated samples show an insulating behavior characterized by the increasing resistivity with the decreasing temperature.
Atomic physics. Constitution and properties of matter
Daniele Filippetto, Pietro Musumeci, Renkai Li
et al.
Since the discovery of electron-wave duality, electron scattering instrumentation has developed into a powerful array of techniques for revealing the atomic structure of matter. Beyond detecting local lattice variations in equilibrium structures, recent research efforts have been directed towards the long sought-after dream of visualizing the dynamic evolution of matter in real-time. The atomic behavior at ultrafast timescales carries critical information on phase transition and chemical reaction dynamics, the coupling of electronic and nuclear degrees of freedom in materials and molecules, the correlation between structure, function and previously hidden metastable or nonequilibrium states of matter. Ultrafast electron pulses play an essential role in this scientific endeavor, and their generation has been facilitated by rapid technical advances in both ultrafast laser and particle accelerator technologies. This review presents a summary of the remarkable developments in this field over the last few decades. The physics and technology of ultrafast electron beams is presented with an emphasis on the figures of merit most relevant for ultrafast electron diffraction (UED) experiments. We discuss recent developments in the generation, manipulation and characterization of ultrashort electron beams aimed at improving the combined spatio-temporal resolution of these measurements. The fundamentals of electron scattering from atomic matter and the theoretical frameworks for retrieving dynamic structural information from solid-state and gas-phase samples are described, together with essential experimental techniques and several landmark works. Ultrafast electron probes with ever improving capabilities, combined with other complementary photon-based or spectroscopic approaches, hold tremendous potential for revolutionizing our ability to observe and understand energy and matter at atomic scales.
Vladimir Schkolnik, Dmitry Budker, Oliver Fartmann
et al.
We present a concept for a high-precision optical atomic clock (OAC) operating on an Earth-orbiting space station. This pathfinder science mission will compare the space-based OAC with one or more ultra-stable terrestrial OACs to search for space-time-dependent signatures of dark scalar fields that manifest as anomalies in the relative frequencies of station-based and ground-based clocks. This opens the possibility of probing models of new physics that are inaccessible to purely ground-based OAC experiments where a dark scalar field may potentially be strongly screened near Earth's surface. This unique enhancement of sensitivity to potential dark matter candidates harnesses the potential of space-based OACs.
Abstract We describe the creation and characterisation of a velocity tunable, spin-polarized beam of slow metastable argon atoms. We show that the beam velocity can be determined with a precision below 1% using matter-wave interferometry. The profile of the interference pattern was also used to determine the velocity spread of the beam, as well as the Van der Waals (VdW) co-efficient for the interaction between the metastable atoms and the multi-slit silicon nitride grating. The VdW co-efficient was determined to be C 3 = 1.84 ± 0.17 a.u., in good agreement with values derived from spectroscopic data. Finally, the spin polarization of the beam produced during acceleration of the beam was also measured, demonstrating a spatially uniform spin polarization of 96% in the m = +2 state.
Abstract Coulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T = 0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing both physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε 1 when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Most atomic physics experiments are controlled by a digital pattern generator used to synchronize all equipment by providing triggers and clocks. Recently, the availability of well-documented open-source development tools has lifted the barriers to using programmable systems on chip (PSoC), making them a convenient and versatile tool for synthesizing digital patterns. Here, we take advantage of these advancements in the design of a versatile clock and pattern generator using a PSoC. We present our design with the intent of highlighting the new possibilities that PSoCs have to offer in terms of flexibility. We provide a robust hardware carrier and basic firmware implementation that can be expanded and modified for other uses.
We propose a complete, quantitative quantum computing system that satisfies the five DiVincenzo criteria. The model is based on magnetic clusters with uniaxial anisotropy, where two-state qubits are formed utilizing the two lowest lying states of an anisotropic potential energy. We outline the quantum dynamics required by quantum computing for single-qubit structures, and then define a measurement scheme in which qubit states can be measured by sharp changes in current as voltage across the cluster is varied. We then extend the single-qubit description to multiple qubit interactions, facilitated specifically by an entanglement method that propagates the controlled-not quantum gate.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
We present tabulated data for the nuclear magnetic shielding constants ($σ$) of the Dirac one-electron atoms with a pointlike, motionless and spinless nucleus of charge $Ze$. Utilizing the exact general analytical formula for $σ$ derived by us \mbox{[P. Stefa{ń}ska, Phys. Rev. A. 94 (2016) 012508/1-15],} valid for an arbitrary discrete energy eigenstate, we have computed the numerical values of the magnetic shielding factors for the ground state and for the first and the second set of excited states, i.e.: 2s$_{1/2}$, 2p$_{1/2}$, 2p$_{3/2}$, 3s$_{1/2}$, 3p$_{1/2}$, 3p$_{3/2}$, 3d$_{3/2}$, and 3d$_{5/2}$, of the relativistic hydrogenic ions with the nuclear charge numbers from the range $1 \leqslant Z \leqslant 137$. The comparisons of our results with the numerical values reported by other authors for some atomic states are also presented.