Hole Quantum Research Articles

High-quality Ge/SiGe heterostructure with atomically sharp interface grown by molecular beam epitaxy

Germanium is a versatile material for realization of spin and topological quantum computing. Here, we report on the epitaxial growth of an undoped Ge/SiGe heterostructure in which a hole quantum well is formed in the sandwiched Ge layer. The heterostructure is grown on Si (001) via molecular beam epitaxy (MBE). Atomic force microscopy characterizations display a flat surface with a root mean square roughness of 0.956 nm, and spherical aberration corrected transmission electron microscopy data show a sharp interface with a characteristic length of 0.49 nm. A mobility of up to 1.2 × 105 cm2 V−1 s−1 was achieved in the SiGe/Ge/SiGe two-dimensional hole gas (2DHG). The low percolation density of 3.70 × 1010 cm−2, light effective mass of 0.079 m0 (where m0 is the free electron mass), and large effective g-factor of 9.5 were obtained. These results show the potential of MBE-grown Ge 2DHG for semiconductor quantum computing.

Classification of large black holes

The black-hole--qubit correspondence has been proven to be ``useful for obtaining additional insight into one of the string black hole theory and quantum information theory by exploiting approaches of the other"[Phys. Rev. D 82, 026003 (2010)]. Though different classes of stringy black holes can be related to the well-known stochastic local operations and classical communication (SLOCC) entanglement classes of pure states, the string theory requires a more detailed classification than the SLOCC classification of three qubits. In this paper, we derive the entanglement family of three qubits under local unitary operations (LU), and use the black-hole--qubit correspondence to classify \textquotedblleft large\textquotedblright\ black holes into seven inequivalent families. In particular, we show that two black holes with 4 non-vanishing charges ($q_{0}$, $p^{1}$, $p^{2}$, and $p^{3}$) are LU equivalent if their difference is only in the signs of charges. Thus, the classification of black holes is independent of the signs of charges and is only related to the ratio of the absolute values of charges. This observation simplifies the classification task, as one would only need to consider either the classification of non-BPS black holes or the classification of BPS black holes, but not both. Moreover, through the LU classification, the physical basis for this black-hole--qubit correspondence can be observed, and a relation between the black-hole entropy and the von Neumann entanglement entropy is revealed. Therefore, the LU classification offers a more straightforward physical connection than the SLOCC classification. Based on the LU classification, we further study the properties of von Neumann entanglement entropy for each of the seven families, and find the black holes with the maximal von Neumann entanglement entropy.

Black hole quantum pressure

This article is a brief review of the work on black hole quantum pressure published in 2021 in Physical Review D with Folkert Kuipers. We highlight how to define the volume of a black hole making the link to previous works where such a definition had appeared in the context of black holes with a cosmological constant.

Signatures of the black hole quantum atmosphere in nonlocal correlations

Recently, it was suggested that the Hawking radiation may originate not at the event horizon but in the quantum region outside of it, known as the quantum atmosphere. The present study attempts to explore this argument further by assessing its role in shaping quantum correlations in a bipartite system near a black hole. Herein, these correlations are conveniently captured within the geometric measure of nonlocality, termed as the measurement-induced nonlocality, and found to exhibit signatures of the atmosphere. In particular, a notable loss of the correlations is observed well outside the event horizon, coinciding with the peak of particles radiation in the atmosphere region. Still, the correlations are shown to be always finite therein and to continuously scale with not only the radiation temperature but also with the horizon size. Hence, some characteristics of the atmosphere appears to be detectable at the quantum correlations level, providing novel insight and means to help verify the concept of interest.

Modification Study on Quantum Tunneling Radiation of Kinnersley Black Hole

In the spacetime of a linearly accelerating Kinnersley black hole, the Lorentz-breaking theory is used to modify the dynamical equations of Dirac particles by selecting gamma matrices and aether-like field vectors in the curved spacetime of this black hole. Using the WKB approximation and black hole quantum tunneling radiation theory, we investigate the characteristics of quantum tunneling radiation in this black hole.By solving the modified spinor field equations, we obtain expressions for the corrected quantum tunneling rate, Hawking temperature, and surface gravitation of the black hole. By studying the particle radial component of the general momentum in this curved spacetime, a new expression for the modified distribution of positive and negative energy levels of Dirac particles, as well as their maximum value of crossing energy level, is obtained. In order to further elucidate the physical significance of the research methodology employed in the article and a series of conclusions obtained, a detailed discussion of the corresponding results is provided in the later sections of this paper.

A maximum force perspective on black hole thermodynamics, quantum pressure, and near-extremality

I re-examined the notion of the thermodynamic force constructed from the first law of black hole thermodynamics. In general relativity, the value of the charge (or angular momentum) at which the thermodynamic force equals the conjectured maximum force F=1/4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F=1/4$$\\end{document} is found to correspond to Q2/M2=8/9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q^2/M^2=8/9$$\\end{document} (respectively, a2/M2=8/9\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a^2/M^2=8/9$$\\end{document}), which is known in the literature to exhibit some special properties. This provides a possible characterization of near-extremality. In addition, taking the maximum force conjecture seriously amounts to introducing a pressure term in the first law of black hole thermodynamics. This resolves the factor of two problem between the proposed maximum value F=1/4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F=1/4$$\\end{document} and the thermodynamic force of Schwarzschild spacetime F=1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F=1/2$$\\end{document}. Surprisingly it also provides another indication for the instability of the inner horizon. For a Schwarzschild black hole, under some reasonable assumptions, this pressure can be interpreted as being induced by the quantum fluctuation of the horizon position, effectively giving rise to a diffused “shell” of characteristic width M\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{M}$$\\end{document}. The maximum force can therefore, in some contexts, be associated with inherently quantum phenomena, despite the fact that it is free of ħ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbar $$\\end{document}. Some implications are discussed as more questions are raised.

The chaotic behavior of black holes: Investigating a topological retraction in anti-de Sitter spaces

In some topological universe models, a special type of curved space called the anti-de Sitter (AdS) of black hole space appears. Due to general relativity, this space has negative curvature. Here we present a novel variant of AdS space, known as chaotic AdS black hole space. We investigate the correlation between the folding of chaotic AdS black hole space and its chaotic deformation retract. In order to better understand how objects move in space, we can also use Lagrangian equations to determine the geodesics of the chaotic AdS space, and explore the properties and behavior of this new type of space. This would enable us to focus our attention and efforts better on black hole thermodynamics and quantum gravity. Finally, various types of chaotic quantum retractions in this space are identified, as well as the final limits on chaotic AdS spaces and their extensions to astrophysics. Exploring these ideas has consequently increased our understanding of the complex dynamics of the universe and the potential for developing a theory of quantum gravity that combines the principles of general relativity and quantum mechanics.

A nonperturbative approach to Hawking radiation and black hole quantum hair

We present a nonperturbative derivation of the subleading order in Hawking radiation based on diffeomorphism symmetry breaking during black hole evaporation. The diffeomorphism group of horizon admits a nontrivial phase factor which encodes information about infalling matter during formation. This nonintegrable phase represents the black hole quantum hair as it arises from the diffeomorphisms that change the physical state of the black hole. During evaporation, the decrease in total area breaks the diffeomorphism symmetry and leads to a dynamical shift in that phase factor. This shift affects the usual Hawking spectrum via dispersion relation and results in the subleading term in Hawking radiation. The higher order terms are locally insensitive to the Unruh radiation due to the lack of diffeomorphism groups on the local Rindler horizon at the low energy scale. This explains the generic difference between Hawking radiation and Unruh radiation. In addition, this phase shift indicates the decrease of the total number of degrees of freedom in horizon phase space during evaporation as past Page time. This enables us to escape from the firewall paradox and provide an account for the resolution to the information paradox.

Fermions dynamic equation with Lorentz invariance violation and the corrected Hawking temperature in arbitrarily accelerating black hole* *Supported by the National Natural Science Foundation of China under Grant No. U2031121.

Containing Lorentz invariance violation (LIV), a new form of the fermions dynamic equation under the background of the curved space-time of the arbitrarily accelerating black hole, is studied. Firstly, we consider the new form of the fermions dynamic equation with arbitrary spin containing LIV in curved space-time, and research the fermions dynamic equation with spin containing LIV. On this basis, according to the semi-classical theory and black hole quantum tunneling radiation theory, the quantum tunneling radiation of the arbitrarily accelerating Kinnersly black hole is modified correctly, and the corrected physical quantities such as black hole temperature and quantum tunneling rate are deeply discussed. The fermions dynamic equation with arbitrary spin in the arbitrarily accelerating black hole space-time and its solution are explained in detail. In order to further obtain the correction effect of the Planck scale, this article considers beyond the semi-classical theory and further obtains new expressions of the black hole temperature and tunneling radiation rate.

Superconformal quantum mechanics and growth of sheaf cohomology

We give a geometric interpretation for superconformal quantum mechanics defined on a hyper-Kähler cone which has an equivariant symplectic resolution. BPS states are identified with certain twisted Dolbeault cohomology classes on the resolved space and their index degeneracies can also be related to the Euler characteristic computed in equivariant sheaf cohomology. In the special case of the Hilbert scheme of K points on ℂ2, we obtain a rigorous estimate for the exponential growth of the index degeneracies of BPS states as K → ∞. This growth serves as a toy model for our recently proposed duality between a seven dimensional black hole and superconformal quantum mechanics.

Energy dynamics, information and heat flow in quenched cooling and the crossover from quantum to classical thermodynamics

The dynamics when a hot many-body quantum system is brought into instantaneous contact with a cold many-body quantum system can be understood as a combination of early time quantum correlation (von Neumann entropy) gain and late time energy relaxation. We show that at the shortest timescales there is an energy increase in each system linked to the entropy gain, even though equilibrium thermodynamics does not apply. This energy increase is of quantum origin and results from the collective binding energy between the two systems. Counter-intuitively, this implies that also the hotter of the two systems generically experiences an initial energy increase when brought into contact with the other colder system. In the limit where the energy relaxation overwhelms the (quantum) correlation build-up, classical energy dynamics emerges where the energy in the hot system decreases immediately upon contact with a cooler system. We use both strongly correlated SYK systems and weakly correlated mixed field Ising chains to exhibit these characteristics, and comment on its implications for both black hole evaporation and quantum thermodynamics.

Polarization-independent high contrast grating 1300 nm dot-in-a-well InAs quantum-dot VCSEL

High contrast grating (HCG) 1300 nm InAs/GaAs quantum dot (QD) vertical-cavity surface-emitting laser (VCSEL) has been introduced in this manuscript and the impact of device structure on the self-heating effect and device temperature has been investigated. A self-consistent model that couples the opto-electro-thermal model of the device to the optical gain model is used to calculate optical gain. Simulated results indicate that the proposed structure significantly lowers the hole-burning effect due to a decrease in temperature. So, in contrast to the conventional QD-VCSELs, the HCG QD-VCSEL exhibits better carrier confinement due to hole quantum efficiency of 54% as opposed to 45% for the conventional QD-VCSELs at their rollover current density. Also, results show an improvement of 66% in the maximum output power from the HCG QD-VCSEL compared to a conventional QD-VCSEL structure. In addition, the 3-dB modulation bandwidth has been boosted compared to conventional QD-VCSELs.

Emergence and Relaxation of an e–h Quantum Liquid Phase in Photoexcited MoS2 Nanoparticles at Room Temperature

AbstractLow‐dimensional transition metal dichalcogenide (TMDC) materials are heralding a new era in optoelectronics and valleytronics owing to their unique properties. Photo‐induced dynamics in these systems is mostly studied from the perspective of individual quasi‐particles—excitons, bi‐excitons, or, even, trions—their formation, evolution, and decay. The role of multi‐body and exciton dynamics, the associated collective behavior, condensation, and inter‐excitonic interactions remain intriguing and seek attention, especially in room‐temperature scenarios that are relevant for device applications. In this work, the formation and decay of an unexpected electron–hole quantum liquid phase at room‐temperature on ultrafast timescales in multi‐layer MoS2 nanoparticles is evidenced through femtosecond broadband transient absorption spectroscopy. The studies presented here reveal the complete dynamical picture: the initial electron–hole plasma (EHP) condenses into a quantum electron–hole liquid (EHL) phase that typically lasts as long as 10 ps, revealing its robustness, whereafter the system decays through phonons. The authors employ a successful physical model using a set of coupled nonlinear rate equations governing the individual populations of these constituent phases to extract their contributions to bandgap renormalization (BGR). Beyond the observation of the electron–hole liquid‐like state at room temperature, this work reveals the ultrafast dynamics of photo‐excited low‐dimensional systems arising out of collective many‐particle behavior and correlations.

Impact of Local Composition on the Emission Spectra of InGaN Quantum-Dot LEDs.

A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) exploits InGaN-quantum-dot-based active regions. However, the role of local composition fluctuations inside the quantum dots and their effect of the device characteristics have not yet been examined in sufficient detail. Here, we present numerical simulations of a quantum-dot structure restored from an experimental high-resolution transmission electron microscopy image. A single InGaN island with the size of ten nanometers and nonuniform indium content distribution is analyzed. A number of two- and three-dimensional models of the quantum dot are derived from the experimental image by a special numerical algorithm, which enables electromechanical, continuum k→·p→, and empirical tight-binding calculations, including emission spectra prediction. Effectiveness of continuous and atomistic approaches are compared, and the impact of InGaN composition fluctuations on the ground-state electron and hole wave functions and quantum dot emission spectrum is analyzed in detail. Finally, comparison of the predicted spectrum with the experimental one is performed to assess the applicability of various simulation approaches.

Легкие и тяжелые экситоны в напряженных квантовых ямах CdTe/CdZnTe

The spectra of photoluminescence and polarized reflection under normal and oblique incidence of light from structures with quantum wells with symmetric Cd0.9Zn0.1Te/CdTe/Cd0.9Zn0.1Te and asymmetric Cd0.9Zn0.1Te/CdTe/Cd0.4Mg0.6Te barriers have been studied. Due to the mechanical stresses caused by the mismatch of the crystal lattices of the wells and barriers, the energy of light holes in quantum wells was higher than in barriers, i. e., the zone structure for them was of type II. However, in the reflection spectra, the lines of heavy and light excitons had comparable intensities. In structures with symmetric barriers, exciton resonances, which do not appear in the photoluminescence spectra, were found in the reflection spectra. A detailed calculation of the energy levels and reflection spectra has been carried out.

A Multiscale Simulation Approach for Germanium-Hole-Based Quantum Processor

A multiscale simulation method is developed to model a quantum dot (QD) array of germanium (Ge) holes for quantum computing. Guided by three-dimensional numerical quantum device simulations of QD structures, an analytical model of the tunnel coupling between the neighboring hole QDs is obtained. Two-qubit entangling quantum gate operations and quantum circuit characteristics of the QD array processor are then modeled. Device analysis of two-qubit Ge hole quantum gates demonstrates faster gate speed, smaller process variability, and less stringent requirement of feature size, compared to its silicon counterpart. The multiscale simulation method allows assessment of the quantum processor circuit performance from a bottom-up, physics-informed perspective. Application of the simulation method to the Ge QD array processor indicates its promising potential for preparing high-fidelity ansatz states in quantum chemistry simulations.

Coulomb drag effect in coupled quantum wire systems: Finite-[formula omitted] and exchange–correlation effects

In this paper, we study the Coulomb drag in GaAs-based coupled electron–electron (e–e) and electron–hole (e–h) quantum wire systems by calculating the drag rate over a wide range of temperature T, particle (electron/hole) number density, and some selected values of inter-wire separation. The exchange–correlations among particles are treated within the self-consistent mean-field approximation of Singwi et al. (the STLS theory) and the inter-wire interaction potential is assumed to be statically screened. We find that the drag rate increases with decrease in particle number density and/or inter-wire separation due to the increased intra- and inter-wire coupling among particles. Further, the drag rate is found to be more for coupled e–h than the e–e quantum wire system due to the stronger e–h correlations on behalf of hole’s larger effective mass. As an important finding, we assert that the drag rate abruptly enhances at the critical system parameters for which the charge-density-wave (CDW) instability has been recently reported to occur in the e–h system. On the other side, the random-phase approximation (RPA) underestimates the drag rate in comparison to the STLS theory and the difference is seen to be more in the particle’s strong coupling domain i.e. at low inter-wire spacing and/or particle number density. In addition, we report for the first time the plasmon dispersion of both the coupled e–h and e–e systems at non-zero T and find that the plasma modes get dispersed into four branches among which two are recognized as optic (in-phase) and remaining two as the acoustic (out-of-phase) plasma modes. All the four plasma energy modes show a consistent blue shift with rise in T, however, the uppermost branches of the optical and acoustic plasma modes seem to repel each other as inter-wire spacing and/or particle number density is lowered. Interestingly, the inclusion of exchange–correlations in the RPA causes a red (blue)-shift in the upper (lower) branch of both the optic and acoustic plasma modes for each of the system leading to an overall enhancement in the Coulomb drag rate.

Zoo of silicon-based quantum bits

Zoo of silicon-based quantum bits

Modification method of NUT-Kerr-Newman-de Sitter black hole entropy by Lorentz symmetry breaking and beyond the semi-classical approximation

According to Lorentz symmetry breaking and black hole quantum tunneling radiation theory, aether-like field is correctly introduced into the general stationary black hole space-time, and the modified boson dynamic equation is obtained. On this basis, the Hawking temperature and black hole entropy of NUT-Kerr-Newman-de Sitter black hole with general stationary characteristics are modified, and the method used in this paper and the significance of the conclusions are deeply discussed.

Particle–hole asymmetry and quantum confinement effects on the magneto-optical response of topological insulator thin-films

Intrinsically broken symmetries in the bulk of topological insulators (TIs) are manifested in their surface states. Despite particle–hole asymmetry in TIs, it has often been assumed that their surface states are characterized by a particle–hole symmetric Dirac energy dispersion. In this work, we demonstrate that the effect of particle–hole asymmetry is essential to correctly describe the energy spectrum and the magneto-optical response in TIs thin-films. In thin-films of TIs with a substantial degree of particle–hole symmetry breaking, such as Sb2Te3, the longitudinal optical conductivity displays absorption peaks arising from optical transitions between bulk and surface Landau levels for low photon energies. The transition energies between the bulk and surface Landau levels exhibit clearly discernable signatures from those between surface Landau levels due to their distinct magnetic field dependence. Bulk contributions to the magneto-optical conductivity in a TI thin-film are enhanced via one type of doping while being suppressed by the other. This asymmetric dependence on the type of doping aids in revealing the particle–hole asymmetry in TI thin-films.