Particle Tunneling Research Articles

Quantum-Gravity Stochastic Effects on the de Sitter Event Horizon.

The stochastic character of the cosmological constant arising from the non-linear quantum-vacuum Bohm interaction in the framework of the manifestly-covariant theory of quantum gravity (CQG theory) is pointed out. This feature is shown to be consistent with the axiomatic formulation of quantum gravity based on the hydrodynamic representation of the same CQG theory developed recently. The conclusion follows by investigating the indeterminacy properties of the probability density function and its representation associated with the quantum gravity state, which corresponds to a hydrodynamic continuity equation that satisfies the unitarity principle. As a result, the corresponding form of stochastic quantum-modified Einstein field equations is obtained and shown to admit a stochastic cosmological de Sitter solution for the space-time metric tensor. The analytical calculation of the stochastic averages of relevant physical observables is obtained. These include in particular the radius of the de Sitter sphere fixing the location of the event horizon and the expression of the Hawking temperature associated with the related particle tunneling effect. Theoretical implications for cosmology and field theories are pointed out.

Electronic and Cooper pair tunneling signatures in the electronic spectra of superconductors coupled to quantum dot nano-junction

We present here calculations on electronic spectra of a system consisting of a quantum dot connected to superconducting leads on its either side. In these calculations the generated spectra has contributions from both, the single particle tunneling, and from the tunneling Cooper pair of electrons. In this, the Anderson model is used for the theoretical construct, and hence, the single particle tunneling, the Josephson tunneling, the energy states of the quantum dot and the super conducting order parameter for BCS superconductors are principally considered. The Green's function equation of motion technique is used to obtain the single particle spectral function. Our results from the numerical computations in the present work indicate, under certain conditions, the occurrence of breaking of Cooper pairs at the junctions between the superconducting leads and the quantum dot. These are seen to be, understandably, depending on the interaction terms included in our model. Our present work suggests a way to understand the interplay of single particle and the ‘Cooper pairs tunneling’ in the resultant electronic spectra in the light of extended Anderson model applicable to the system. It thus presents a theoretical understanding on the transmission of supercurrents through nanoscopic junctions, such as that considered here.

Fermion tunneling, instability, and first law of Rindler modified Schwarzschild black hole as a thermodynamic system

This study investigated quantum tunneling of spin-half particles through the event horizon of a Rindler modified Schwarzschild black hole (RMSBH) in the presence of quintessence matter. We analyzed the thermodynamics of RMSBH in Kiselev coordinates. In particular, we explore the RMSBH’s entropy and thermal stability. We showed that RMSBH serves as an unstable system, causing fluctuations. The integral formulation of the first law of RMSBH in the absence of a cosmological constant was also represented. By using the first law, we have studied the Ruppeiner geometry for Rindler acceleration and pressure with fixed ensembles.

Detection of Terahertz, Mid- and Near Infrared Radiation by a Multilayer Metal—Insulator Heterostructure

An analogy between the tunneling of quantum particles through a chain of barriers and the propagation of electromagnetic waves through a metamedium has allowed new methods for the fabrication of selective detectors of terahertz, mid-infrared, and near infrared radiation. The calculations have shown that a resonance metal-insulator heterostructure with one and two metal layers allows achieving nearly 100% absorption of radiation in a narrow frequency range. The use of a large number of metal layers makes it possible to detect ultrashort (including picosecond) field pulses with a broad spectrum.

Magnetic field enhanced single particle tunneling in MoS2–superconductor vertical Josephson junction**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0703703 and 2016YFA0300802) and the National Natural Science Foundation of China (Grant Nos. 91964201, 61825401, and 11774004).

As a prototypical transition-metal dichalcogenide semiconductor, MoS2 possesses strong spin–orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN–MoS2–NbN sandwich junctions at low temperatures. Above the critical temperature around ∼11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ∼11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS2 layer induced by the superconducting proximity effect. When a perpendicular magnetic field ∼1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS2 can further lead to the enhancement of the junction conductance.

Tunnelling of charged particles from black holes

We state and explain the total rate at which a charged non-rotating black hole emits charged particles, taking into account both Hawking radiation and Schwinger pair production simultaneously. We give concrete formulae for this emission rate in certain limits, with the greatest simplification occurring when the black hole is much larger than the particle’s Compton wavelength. We provide an interpretation of the result in terms of a tunnelling process, both through the black hole horizon and the surrounding electric field, and comment on how suppression due to tunnelling modifies the emission spectrum.

Tuning Plasmonic Coupling from Capacitive to Conductive Regimes via Atomic Control of Dielectric Spacing

The gap length between plasmonic nanoparticles determines the strength of the optical coupling that results in electromagnetic field enhancement for spectroscopic and other applications. Although gap plasmon resonances have been the focus of increasing research interest, experimental observations have primarily been limited to the coupling of spherical nanoparticles that may not provide clear spectral contrast of the optical response as the interaction evolves from capacitive to charge transfer with the gap size decreasing to sub-nanometer. Here, by taking advantage of the sharp plasmon resonances of colloidal gold nanorods coupled to gold film, we present the spectral evolution of gap plasmon resonance as the particle–film spacing varies from over 30 nm to the touching limit. We find that the capacitive gap plasmon resonance of the coupled system red-shifts and narrows continuously until it vanishes at the quantum tunneling limit, in contrast to the nonlocal and Landau damping effects that are expected to result in relative blue-shifting and spectral broadening. When the spacer thickness is further decreased, high order cavity modes appear, and eventually single peak broad resonances that are characteristic of tunneling and direct contact particle–film interaction emerge. The experimental observations show that nanorods are better suited for creating cavity plasmon resonances with high quality factor, and the spectral contrast at the transition provides clarity to develop improved theoretical modeling of optical coupling at sub-nanometer gap lengths.

Emergent Optoelectronic Properties of Mixed-Dimensional Heterojunctions.

ConspectusThe electronic dimensionality of a material is defined by the number of spatial degrees of confinement of its electronic wave function. Low-dimensional semiconductor nanomaterials with at least one degree of spatial confinement have optoelectronic properties that are tunable with size and environment (dielectric and chemical) and are of particular interest for optoelectronic applications such as light detection, light harvesting, and photocatalysis. By combining nanomaterials of differing dimensionalities, mixed-dimensional heterojunctions (MDHJs) exploit the desirable characteristics of their components. For example, the strong optical absorption of zero-dimensional (0D) materials combined with the high charge carrier mobilities of two-dimensional (2D) materials widens the spectral response and enhances the responsivity of mixed-dimensional photodetectors, which has implications for ultrathin, flexible optoelectronic devices. MDHJs are highly sensitive to (i) interfacial chemistry because of large surface area-to-volume ratios and (ii) electric fields, which are incompletely screened because of the ultrathin nature of MDHJs. This sensitivity presents opportunities for control of physical phenomena in MDHJs through chemical modification, optical excitation, externally applied electric fields, and other environmental parameters. Since this fast-moving research area is beginning to pose and answer fundamental questions that underlie the fundamental optoelectronic behavior of MDHJs, it is an opportune time to assess progress and suggest future directions in this field.In this Account, we first outline the characteristic properties, advantages, and challenges for low-dimensional materials, many of which arise as a result of quantum confinement effects. The optoelectronic properties and performance of MDHJs are primarily determined by dynamics of excitons and charge carriers at their interfaces, where these particles tunnel, trap, scatter, and/or recombine on the time scales of tens of femtoseconds to hundreds of nanoseconds. We discuss several photophysical phenomena that deviate from those observed in bulk heterojunctions, as well as factors that can be used to vary, probe, and ultimately control the behavior of excitons and charge carriers in MDHJ systems. We then discuss optoelectronic applications of MDHJs, namely, photodetectors, photovoltaics, and photocatalysts, and identify current performance limits compared to state-of-the-art benchmarks. Finally, we suggest strategies to extend the current understanding of dynamics in MDHJs toward the realization of stimuli-driven responses, particularly with respect to exciton delocalization, quantum emission, interfacial morphology, responsivity to external stimuli, spin selectivity, and usage of chemically reactive materials.

Tunneling of massive vector particles under influence of quantum gravity * * A. Ö. acknowledges financial support provided under the Chilean FONDECYT (3170035)

This study set out to investigate charged vector particles tunneling via horizons of a pair of accelerating rotating charged NUT black holes under the influence of quantum gravity. To this end, we use the modified Proca equation incorporating generalized uncertainty principle. Applying the WKB approximation to the field equation, we obtain a modified tunneling rate and the corresponding corrected Hawking temperature for this black hole. Moreover, we analyze the graphical behavior of the corrected Hawking temperature with respect to the event horizon for the given black hole. By considering quantum gravitational effects on Hawking temperatures, we discuss the stability analysis of this black hole. For a pair of black holes, the temperature increases with the increase in rotation parameters a and , correction parameter , black hole acceleration , and arbitrary parameter k, and decreases with the increase in electric e and magnetic charges g.

Quantum radiation of Kerr black hole in de Sitter background

In this paper, we investigate the tunneling of vector boson particles across the event horizon of Kerr-de Sitter black hole by using Hamilton-Jacobi ansatz to Proca equation and WKB approximation. The surface gravity of KdS black hole has been recovered by using direct calculation and Proca equation. These two different methods give the same Hawking temperature at the event horizon.

Quantum-inspired algorithm for radiotherapy planning optimization.

Modern inverse radiotherapy treatment planning requires nonconvex, large-scale optimizations that must be solved within a clinically feasible timeframe. We have developed and tested a quantum-inspired, stochastic algorithm for intensity-modulated radiotherapy (IMRT): quantum tunnel annealing (QTA). By modeling the likelihood probability of accepting a higher energy solution after a particle tunneling through a potential energy barrier, QTA features an additional degree of freedom (the barrier width, w) not shared by traditional stochastic optimization methods such as Simulated Annealing (SA). This additional degree of freedom can improve convergence rates and achieve a more efficient and, potentially, effective treatment planning process. To analyze the character of the proposed QTA algorithm, we chose two stereotactic body radiation therapy (SBRT) liver cases of variable complexity. The "easy" first case was used to confirm functionality, while the second case, with a more challenging geometry, was used to characterize and evaluate the QTA algorithm performance. Plan quality was assessed using dose-volume histogram-based objectives and dose distributions. Due to the stochastic nature of the solution search space, extensive tests were also conducted to determine the optimal smoothing technique, ensuring balance between plan deliverability and the resulting plan quality. QTA convergence rates were investigated in relation to the chosen barrier width function, and QTA and SA performances were compared regarding sensitivity to the choice of solution initializations, annealing schedules, and complexity of the dose-volume constraints. Finally, we investigated the extension from beamlet intensity optimization to direct aperture optimization (DAO). Influence matrices were calculated using the Eclipse scripting application program interface (API), and the optimizations were run on the University of Michigan's high-performance computing cluster, Flux. Our results indicate that QTA's barrier-width function can be tuned to achieve faster convergence rates. The QTA algorithm reached convergence up to 46.6% faster than SA for beamlet intensity optimization and up to 26.8% faster for DAO. QTA and SA were ultimately found to be equally insensitive to the initialization process, but the convergence rate of QTA was found to be more sensitive to the complexity of the dose-volume constraints. The optimal smoothing technique was found to be a combination of a Laplace-of-Gaussian (LOG) edge-finding filter implemented as a penalty within the objective function and a two-dimensional Savitzky-Golay filter applied to the final iteration; this achieved total monitor units more than 20% smaller than plans optimized by commercial treatment planning software. We have characterized the performance of a stochastic, quantum-inspired optimization algorithm, QTA, for radiotherapy treatment planning. This proof of concept study suggests that QTA can be tuned to achieve faster convergence than SA; therefore, QTA may be a good candidate for future knowledge-based or adaptive radiation therapy applications.

Energy Tunneling: A Way to Achieve Highly Sensitive Material Detection With Sub-Wavelength Resolution

The phenomenon of microwave energy tunneling (ET) has been reported in guided microwave structures loaded with either epsilon-near-zero (ENZ) materials or resonant metallic wires [1]-[14]. A bit of confusion sometimes can arise over the term tunneling, which is often used by physicists, so it seems appropriate here to point out the difference between ET and the well-known particle tunneling encountered in quantum mechanics (Figure 1).

Tunneling of massive vector particles from types of BTZ-like black holes

In this paper, we analyze the Hawking radiation phenomenon for types of Banados-Teitelboim-Zanelli-like (BTZ-like) black holes. For this purpose, using the Hamilton-Jacobi method, we consider semi-classical WKB approximation to calculate the tunneling probabilities of massive boson particles. For these particles, we use the equation of motion for the Glashow-Weinberg-Salam model. Using quantum tunneling process of charged massive bossons, we compute the corresponding Hawking temperatures. Furthermore, we discuss the effects of rotation parameter on tunneling probability and temperature.

Quantum gravity effect on the Hawking radiation of spinning dilaton black hole

The quantum gravity correction to the Hawking temperature of the 2+1 dimensional spinning dilaton black hole is studied by using the Hamilton-Jacobi approach in the context of the Generalized Uncertainty Principle (GUP). It is observed that the modified Hawking temperature of the black hole depends on both black hole and the tunnelling particle properties. Moreover, it is observed that the mass and the angular momentum of the scalar particle have the same effect on the Hawking temperature of the black hole, while the mass and total angular momentum (orbital+spin) of Dirac particle have different effect. Furthermore, the mass and total angular momentum (orbital+spin) of vector boson particle have a similar effect that of Dirac particle. Also, thermodynamical stability and phase transition of the black hole are discussed for scalar, Dirac and vector boson in the context of GUP, respectively. And, it is observed that the scalar particle probes the black hole as stable whereas, as for Dirac and vector boson particles, it might undergoes second-type phase transition to become stable while in the absence of the quantum gravity effect all of these particle probes the black hole as stable.

Multiband superconductivity and possible nodal gap in RbCr3As3 revealed by Andreev reflection and single-particle tunneling measurements

By measuring point-contact Andreev reflection (PCAR) spectra in the newly discovered chromium-based quasi-one-dimensional superconductor RbCr$_{3}$As$_{3}$, we find clear evidence of two superconducting components, i.e., one having a gap value of about 1.8 meV and another with a gap value of about 5 meV. Since the current injection may have components in both the direction parallel and perpendicular to the [(Cr$_{3}$As$_{3}$)$^{-}$]$_\infty$ chains in the PCAR measurements, it naturally explains the two-component feature observed in this multi-band superconductor. Detailed analysis shows that the larger gap may have an $s$-wave nature. We then carry out the single-particle tunneling measurements based on a scanning tunneling spectroscope by using the needle-like sample as the tip, and in this case the measured current is mainly parallel to the [(Cr$_{3}$As$_{3}$)$^{-}$]$_\infty$ chains. The single-particle tunneling spectra show only one gap feature with a gap value of about 1.8 meV. Fitting to the single particle tunneling spectra indicates that the gap should have a large anisotropy or even node(s). We argue that the absence of the larger gap may be related to the direction of the injecting current. Therefore, our combined experiments show the multiband superconductivity with one gap being nodal or highly anisotropic.

Generalized Klein\u2013Gordon equation and quantum gravity corrections to tunneling of scalar particles from Kerr\u2013Newman black hole

In this article we deduce the generalized Klein–Gordon Equation in curved spacetime in the presence of an electromagnetic field from first principles, using the generalized uncertainty principle. Using this equation we study the tunneling of scalar particles from a Kerr–Newman black hole. Corrections to the Hawking temperature and entropy of the black hole due to quantum gravity effects are discussed.

Quadrature Squeezing in Extended Two-Site Bose–Hubbard Model with Pair Tunneling

We analytically and numerically investigate quadrature squeezing in an extended two-site Bose–Hubbard model with pair tunneling by using the rotating-wave approximation. It is shown that single particle tunneling and the density-dependent tunneling have no influence on quadrature squeezing; the onsite interaction and the inter-well particle interactions effect the regime of squeezing under some conditions.

Inner-shell ionization duringαdecay of superheavy isotopes from the tennessineTs117293and oganessonOg118294chains

Presented here are calculations of probabilities of the $K$-, $L$-, and $M$-shell ionization during $\ensuremath{\alpha}$ decay of superheavy isotopes $_{117}^{293}\mathrm{Ts}$, $_{115}^{289}\mathrm{Mc}$, and $_{113}^{285}\mathrm{Nh}$ involved in the tennessine decay chain as well as $_{118}^{294}\mathrm{Og}$, $_{116}^{290}\mathrm{Lv}$, and $_{114}^{286}\mathrm{Fl}$ involved in the new oganesson decay chain. The ionization probabilities are of importance for handling data obtained by methods of the combined $\ensuremath{\alpha}$, $\ensuremath{\gamma}$, and conversion-electron spectroscopy used in the superheavy element synthesis analysis. Relativistic calculations are based on the quantum mechanical model. Electron wave functions are determined by the Dirac-Fock method. The $\ensuremath{\alpha}$-particle tunneling through the atomic Coulomb barrier is taken into account. Peculiarities of the $K$-, $L$-, and $M$-shell ionization are considered. Results demonstrate that the effect of tunneling through the Coulomb barrier for the $L$ and $M$ shells is of no significance as distinct from the $K$ shell, where the inclusion of the tunneling leads to a considerable decrease of the ionization probability. The probability of ionization from higher shells is larger than that from inner shells. However, the change from the $K$ shell to $L$ shell is much more significant than the change from the $L$ shell to $M$ shell. It has been found that only monopole and dipole terms of the radiative field $L=0,1$ make a contribution to the $K$- and ${L}_{1}$-shell ionization probabilities while contributions of all multipoles $L\ensuremath{\le}4$ may be important for the ${L}_{2}$, ${L}_{3}$, and particularly for ${M}_{1}\ensuremath{-}{M}_{5}$ subshells.

Simulating the Klein tunneling of pseudospin-one Maxwell particles with trapped ions

We propose an experimental scheme to simulate and observe the Klein tunneling of relativistic Maxwell particles with trapped ions. We explore the scattering dynamics of the pseudospin-one Maxwell particles and demonstrate that the scattered state should be a superposition of a reflection state, a localization state, and a transmission state. The probabilities of these states can be analytically obtained by the approach of Landau-Zener transition. We further show that the Maxwell Hamiltonian and the associated scattering dynamics can be mimicked with two trapped ions. The Maxwell spinors are encoded by three internal states of the first ion, the position and momentum are described by those of the motional modes, and the desired linear potential barrier is built by the second ion.

Dry transfer method for suspended graphene on lift-off-resist: simple ballistic devices with Fabry–Pérot interference

We demonstrate a fabrication scheme for clean suspended structures using chemical-vapor-deposition-grown graphene and a dry transfer method on lift-off-resist-coated substrates to facilitate suspended graphene nanoelectronic devices for technological applications. It encompasses the demands for scalable fabrication as well as for ultra-fast response due to weak coupling to environment. The fabricated devices exhibited initially a weak field-effect response with substantial positive (p) doping which transformed into weak negative (n) doping upon current annealing at the temperature of 4 K. With increased annealing current, n-doping gradually decreased while the Dirac peak position approached zero in gate voltage. An ultra-low residual charge density of 9 × 108 cm−2 and a mobility of 1.9 × 105 cm2 V−1 s−1 were observed. Our samples display clear Fabry–Pérot (FP) conductance oscillation which indicates ballistic electron transport. The spacings of the FP oscillations are found to depend on the charge density in a manner that agrees with theoretical modeling based on Klein tunneling of Dirac particles. The ultra-low residual charge, the FP oscillations with density dependent period, and the high mobility prove the excellent quality of our suspended graphene devices. Owing to its simplicity, scalability and robustness, this fabrication scheme enhances possibilities for production of suspended, high-quality, two-dimensional-material structures for novel electronic applications.