Tunneling Time Research Articles

Trap dynamics of hot electrons in metal–insulator–metal plasmonic structures for ultra-fast optoelectronics

We have calculated the time constants of the electron dynamics in traps in a metal–insulator–metal (MIM) plasmonic structure. Because of electron relaxation in metal, the surface plasmon polaritons decays into hot electrons near the surface of the metal, which facilitates the trap of electrons in the interfacial layer of the dielectric. We have calculated the capture and emission times separately as the electron does not follow the same mechanisms with the capture process when it is emitted from a trap at the metal/oxide interface. We have developed a quasi-two-dimensional treatment that has been modified from a previously used semiconductor/oxide junction by using Bardeen’s function to calculate the capture time. Various parameters including trap’s distance from the interface, temperature, voltage bias, and spectral nature of the hot electrons’ energy distribution influence the interaction between a plasmonic hot electron and a neutral near-interface trap in the capture process. On the one hand, the emission time is independent of the capture time, and it is determined by the tunneling time to the metal depending on the temperature and the energy difference between the trap energy levels (ground and excited states). We have showed that a wide range of capture times from seconds to picoseconds is possible for an interfacial trap at the room temperature due to the spectral energy distribution of hot electrons and dependence of the capture process on the losses in metals. On the other hand, the temperature plays the dominant role in the emission time. For the trap with 250 meV energy difference between its levels, the emission time is in the range of picosecond at room temperature. Therefore, the MIM plasmonic device can respond to a wide range of ac voltage frequencies including the ultra-fast domain. These interesting findings are useful to understand the ac response of the MIM plasmonic devices with applications in integrated photonics and ultra-fast optoelectronics.

A-Variant Design of Hypersonic Ludwieg Tube Wind Tunnel

To improve the operation efficiency of conventional Ludwieg tube tunnel, a fast-acting valve is usually deployed between the storage tube and Laval nozzle in order to separate the high- and low-pressure air. However, the disturbance produced by the fast-acting valve as well as the nonuniform heating of storage tube affects the flow quality of the hypersonic Ludwieg tube. Stimulated by the motivation of overcoming the mentioned problems, the feasibility of a novel configuration of hypersonic Ludwieg tube is explored in this research. Upon this study, we introduced an additional Laval nozzle and settling chamber to the conventional Ludwieg tube tunnel, while the cross-section area of the main Laval nozzle is smaller than that of the introduced Laval nozzle. To begin with, the flow evolution along the dual-throat Ludwieg tube was analyzed theoretically; subsequently, numerical simulations were conducted to study the starting process of the dual-throat Ludwieg tube tunnel, and emphasis was placed on the influence of different throat area ratios and settling chamber lengths upon the startup time of wind tunnel. Lastly, the flowfield of the dual-throat Ludwieg tunnel was characterized by measuring the Mach number distribution and pitot pressure fluctuation in the test section as well as the pressures along the overall tunnel. The results show that this novel configuration of Ludwieg tube is applicable and it offers the opportunity for flow quality improvement for conventional Ludwieg tubes with small penalty of reducing the tunnel’s efficient running time.

Proposal for a solid-state magnetoresistive Larmor quantum clock

We propose a solid-state implementation of the Larmor clock that exploits tunnel magnetoresistance to distill information on how long itinerant spins take to traverse a barrier embedded in it. Keeping in mind that the tunnelling time innately involves pristine pre-selection and post-selection, our proposal takes into account the detrimental aspects of multiple reflections by incorporating multiple contacts, multiple current measurements and suitably defined magnetoresistance signals. Our analysis provides a direct mapping between the magnetoresistance signals and the tunneling times and aligns well with the interpretation in terms of generalized quantum measurements and quantum weak values. By means of an engineered pre-selection in one of the ferromagnetic contacts, we also elucidate how one can make the measurement "weak" by minimizing the back-action, while keeping the tunneling time unchanged. We then analyze the resulting interpretations of the tunneling time and the measurement back action in the presence of phase breaking effects that are intrinsic to solid state systems. We unravel that while the time-keeping aspect of the Larmor clock is reasonably undeterred due to momentum and phase relaxation processes, it degrades significantly in the presence of spin-dephasing. We believe that the ideas presented here also open up a fructuous solid state platform to encompass emerging ideas in quantum technology such as quantum weak values and its applications, that are currently exclusive to quantum optics and cold atoms.

Analysis of mechanized tunneling parameters to determine the overcutting characteristics

Tunneling in urban conditions requires costly measures, in order to ensure the safety of existing buildings. On average, there are up to 17–20 buildings per 1 km of Moscow Subway Lines under construction. Analysis and comparison of geotechnical monitoring data and results of geotechnical estimations for underground construction using cut-and-cover and tunneling methods in conditions of high-density urban area shows an unsatisfactory correlation between estimated and actual data. This can be described in the following way: insufficient geotechnical survey data; discrepancy between the accepted estimation model and the actual behavior of soil under load; insufficient qualification of the construction workers; and overcutting. The study was aimed at solving the urgent scientific and engineering problem of determining the characteristics of overcutting during mechanized tunnel boring. At the first stage, the investigations were aimed at identifying the key reasons and factors which determine the quantitative parameters of overcutting in urban underground construction by tunneling. These factors include the following: mismatch between the cutting diameter and the outer lining diameter; displacement of the soil mass in front of the face; incomplete grouting of voids beyond the lining; incomplete filling of beyond-shield voids with clay mortar or slow-curing grouting mortar or no filling at all; and human factor (low qualifications of personnel). The overcutting coefficient was determined on the basis of the proposed empirical dependence of its values with regard to the depth of tunneling. The experimental data allowed the depth dependence of the overcutting coefficient for different tunneling depths to be defined, as well as for tunnel diameters from 4 to 10 meters in the case of mechanized tunnel boring machine (TBM) using the earth pressure balanced tunneling method. The practical importance of the studies consists in determining the range of the empirical overcutting coefficient variation from 0.5 % (for TBMs with nominal diameter of 10 m) up to 5 % (for TBMs with nominal diameter of 4 m). The development of organizational measures and justification of process solutions, aimed at ensuring the safety of the existing buildings in conjunction with the scientific and technical support of underground construction has led to a shortening of tunneling time between the Okskaya and Nizhegorodskaya stations of Nekrasovskaya Line of Moscow Subway by about six months. It has also provided savings of about 2.5 billion rubles.

Prediction of Final Displacement of Tunnels in Time-Dependent Rock Mass Based on the Nonequidistant Grey Verhulst Model

Time-dependent deformations of rock are important factors for the design and construction of tunnels in the rock masses with time-dependent strength and deformation properties. Therefore, determination displacement and stable time of tunnel are an indispensable task in geotechnical engineering, especially during the design and construction of underground structures. However, in some types of rock masses, the tunnel displacement may increase for months or years after the excavation owing to the rheological behavior of the surrounding rock masses, which greatly influences the selection of the initial tunnel support system, the excavation layout, and the determination of its load-carrying capacity. In this paper, we present a method to quickly predict the final displacement and stable time of tunnels in time-dependent rock mass using the improved nonequidistant grey Verhulst model (INGVM) with Fourier series, which is used to reduce the periodic residual error. The proposed method is validated fairly via a test for a newly excavated roadway of −600 m level in a coal mine, Democratic People’s Republic of Korea. These results are useful references for similar projects in the future.

Feynman-Vernon influence functional approach to quantum transport in interacting nanojunctions: An analytical hierarchical study

We present a nonperturbative and formally exact approach for the charge transport in interacting nanojunctions based on a real-time path-integral formulation of the reduced system dynamics. For reservoirs of noninteracting fermions, the exact trace over the leads' degrees of freedom results in the time-nonlocal Feynman-Vernon influence functional, a functional of the Grassmann-valued paths of the nanojunction, which induces correlations among the tunneling transitions in and out of the nanojunction. An expansion of the influence functional in terms of the number of tunneling transitions, and integration of the Grassmann variables between the tunneling times, allows us to obtain a still exact generalized master equation for the populations of the reduced density matrix in the occupation-number representation, as well as a formally exact expression for the current. By borrowing the nomenclature of the famous spin-boson model, we parametrize the two-state dynamics of each single-particle fermionic degree of freedom, in the occupation-number representation, in terms of blips and sojourns. We apply our formalism to the exactly solvable resonant level model (RLM) and to the single-impurity Anderson model (SIAM), the latter being a prototype system for studying strong correlations. For both systems, we demonstrate a hierarchical diagrammatic structure. While the hierarchy closes at the second tier for the RLM, this is not the case for the interacting SIAM. Upon inspection of the current kernel, known results from various perturbative and nonperturbative approximation schemes to quantum transport in the SIAM are recovered. Finally, a noncrossing approximation for the hierarchical kernel is developed, which enables us to systematically decrease temperature at each next level of the approximation. Analytical results for a simplified fourth-tier scheme are presented both in equilibrium and nonequilibrium and with an applied magnetic field.

Resonant Activation of Resistance Switching in Memristors Based on YSZ Films with Au Nanoparticles

The resonant activation of resistance switching (RS) of a memristor based on an yttria stabilized zirconia (YSZ) film with embedded Au nanoparticles (NPs) was investigated. The switching was made by triangular pulses with high frequency (HF) sinusoid added. A non-monotonous dependence a ratio of the electric current through the memristor in the low resistive state to the current in the high resistive one on the HF sinusoid frequency was found. The effect was explained by a finite electron tunneling time between the Pt electrode and Au NPs. This conclusion was supported by measuring a dependence of HF memristor capacitance on the probing signal frequency.

Carrier dynamics of AlGaAs/AlAs asymmetric double quantum wells with different barrier thickness

Optical properties and carrier dynamics of AlGaAs/AlAs asymmetric double quantum wells (ADQWs) with varied barrier thickness are studied by excitation-power-dependent photoluminescence (PL) and temperature-dependent time-resolved PL (TRPL) experiments. The origin of the transition energies derived from the time-integrated spectra is confirmed by theoretical calculation using the Schrödinger equation. The carrier kinetics and the temporal behavior of the emission in the narrow well (NW) and wide well (WW) are physically revealed with varying barrier thicknesses by the TRPL measurements. For a better understanding of the carrier transport mechanism, the electron tunneling times for the ADQWs are theoretically estimated based on a rate-equation model. The calculation indicates that the electron tunneling time decreases with increasing temperature, which may be induced by enhanced phonon-assisted scattering.

Efficient computations of continuous action densities of states for lattice models

The Logarithmic Linear Relaxation (LLR) algorithm is an efficient method for computing densities of states for systems with a continuous spectrum. A key feature of this method is exponential error reduction, which allows us to evaluate the density of states of a system over hundreds of thousands of orders of magnitude with a fixed level of relative accuracy. As a consequence of exponential error reduction, the LLR method provides a robust alternative to traditional Monte Carlo calculations in cases in which states suppressed by the Boltzmann weight play nevertheless a relevant role, e.g., as transition regions between dominant configuration sets. After reviewing the algorithm, we will show an application in U(1) Lattice Gauge Theory that has enabled us to obtain the most accurate estimate of the critical coupling with modest computational resources, defeating exponential tunneling times between metastable vacua. As a further showcase, we will then present an application of the LLR method to the decorrelation of the topological charge in SU(3) Lattice Gauge Theory near the continuum limit. Finally, we will review in general applications of the LLR algorithm to systems affected by a strong sign problem and discuss the case of the Bose gas at finite chemical potential.

Mid-IR quantum dot cascade VCSEL: feasibility study and feature extraction.

Quantum cascade lasers with quantum dot (QD) active regions have been developed to overcome the drawbacks of quantum-well-based cascade lasers. Low threshold current and enhanced bandwidth characteristics of QD lasers can be combined with promising energy-efficient features of vertical cavity surface emitting lasers (VCSELs) through introducing the novel, to the best of our knowledge, concept of a QD cascade VCSEL (QDC-VCSEL). Design steps and predicted features of a QDC-VCSEL operating at 4.5 µm wavelength are discussed in this paper, where the cavity and active region are optimized for TE mode using a high contrast grating design. Laser characteristics are investigated by developing rate equations for the cascade scheme. Threshold and L-I characteristics are obtained at different temperatures. Also, the dependency of threshold current, slope efficiency, and modulation bandwidth on design parameters, mainly the carrier tunneling time, is studied. Results exhibit output peak powers of ∼2 and ∼0.5mW at 150 and 273 K, respectively. In addition, threshold current increment and modulation bandwidth reduction are observed with the increase in tunneling time.

Time-dependent Interactions in Tunnelling Dynamics

In this paper, the tunnelling of a particle through a potential barrier is investigated in the presence of a time-dependent perturbation. The latter is attributed to the process of the energy measurement of the scattered particle. The time-dependent Schrödinger equation of the model is exactly solved. The probability density inside the barrier is calculated from the obtained wave function, proving that the tunnelling dynamics is determined not only by the transmitted and reflected waves but also by their interference. Furthermore, the interference term is time-dependent and contribute to the scattering process duration. The tunnelling time is calculated as the time needed to get the probability density inside the barrier to zero. This is the minimum duration of the measurement process before detecting the particle beyond the barrier. Based on this, a new method of estimating the tunnelling time by energy experimental measuring is proposed.

Biexciton and trion dynamics in InP/ZnSe/ZnS quantum dots.

Transient absorption (TA) and time-resolved photoluminescence (PL) spectroscopies have been used to elucidate the hole tunneling and Auger dynamics in biexcitons and negative trions in high-quality InP/ZnSe/ZnS quantum dots (QDs). In a previous paper [Nguyen et al., J. Phys. Chem. C 125, 15405-15414 (2021)], we showed that under high-intensity photoexcitation, two types of biexcitons are formed: those having two conduction band electrons and two valence band holes (designated as an XX state) and those having two conduction band electrons, one valence band hole, and an additional trapped hole (designated as an XT state). In the present paper, we show that both types of biexcitons can undergo Auger processes, with those of the XT state being a factor of four to five slower than those of the XX state. In addition, the trapped holes can undergo tunneling into the valence band, converting an XT state to an XX state. The relative amplitudes of the fast (XX) and slow (XT) components are different in the TA and PL kinetics, and these differences can be quantitatively understood in terms of oscillator strengths and electron-hole overlap integrals of each state. XT to XX hole tunneling rates are obtained from the comparison of the XT state lifetimes with those of the negative trions. This comparison shows that the tunneling times decrease with decreasing core size and shell thickness. These times are about 2ns for the thinnest shell red-emitting QDs and decrease to 330ps for QDs that luminesce in the yellow.

Effect of Strain on Tunneling Time in Graphene Magnetic Barrier

Effect of Strain on Tunneling Time in Graphene Magnetic Barrier

The Transfer Matrix Method and the Theory of Finite Periodic Systems. From Heterostructures to Superlattices

Historically, the physics, energy spectrum, and wave functions of superlattices have had different levels of understanding. Unlike the standard approaches, based on theorems for infinite systems, the theory of finite periodic systems (TFPS) constitutes a genuine quantum approach, with closed analytical results. In this theory the finite number of unit‐cells is an essential condition, while the number of propagating modes, as well as, the potential profiles (or refractive indices) are arbitrary. In this work, the transfer matrix definitions, symmetry properties, group representations, and relations with the scattering amplitudes are reviewed. The derivation of multichannel matrix polynomials (which reduce to Chebyshev polynomials in the one‐propagating mode limit), analytical formulas for resonant states, energy eigenvalues, eigenfunctions, parity symmetries, and discrete dispersion relations for superlattices with different confinement characteristics are reviewed. After showing the inconsistencies and limitations of hybrid approaches that combine the transfer‐matrix method with Floquet's theorem, some applications of the TFPS to multichannel negative resistance, ballistic transistors, coupled channels transport, spintronics, superluminal, and optical antimatter effects are revisited. Two high‐resolution superlattice related experiments are reviewed: the tunneling time in photonic band‐gap and the optical response of blue‐emitting diodes. It is shown that the TFPS accurately predicts the experimental results.

Numerical investigation of quantum tunneling time and spin-current density in GaAs/GaMnAs/GaAs barriers: Role of an applied bias voltage

In this paper, we have discussed theoretically the effect of an applied bias voltage and the temperature on the spin-tunneling time, spin-dependent polarization and current densities of holes in GaAs/GaMnAs double barriers using the transfer matrix method (TMM). The behavior of the transmission coefficients for different spin orientations (up and down), various applied voltages and different temperatures were calculated. Our findings indicate that the maxima of the spin-up transmission coefficient shift towards the lower energies by increasing the applied bias voltage. Furthermore, our structure is almost transparent for spin-down holes and presents some resonances for spin-up ones. In addition, we have found that the tunneling time decreases progressively by enhancing the applied voltage. It is also shown that the current densities of holes with both spin-up and down orientations present a negative differential resistance (NDR). This (NDR) resistance is more intense for spin-up holes than spin-down ones. Consequently, the obtained results pointed out that we can design and fabricate a high-speed spin-filters and diodes by fixing the appropriate values of applied voltages and temperatures.

Experimental and numerical research on the influence of steel arch frame corrosion on security of supporting system in subsea tunnel

Subjected to high chloride ion content in subsea, underwater structure will be corroded in different degree in the service environment, which will shorten the durability of the structure. Subsea tunnels are often constructed by drilling and blasting method, and microcracks are inevitable in primary support due to blasting impact. The cracks provide channels for chloride ion, sulfate ion in seawater and oxygen in air, which leads to steel arch frame corrosion in primary support. Corrosion will reduce the bond strength and bearing capacity of the supporting system, thus reducing the service time of the subsea tunnel. Based on Xiang'an subsea tunnel, the effect of steel arch frame corrosion on the supporting system was studied. First, the accelerated corrosion test and push-out test were carried out, the bond-slip degradation constitutive model between corroded I-shaped steel and concrete was proposed based on damage variables. Then, the degradation constitutive model was introduced into ANSYS to simulate the influence of corroded I-shaped steel on the overall mechanical behavior and safety of the subsea tunnel. Results of model indicated that with the increase of corrosion ratio, the internal stress of the I-shaped steel, sprayed concrete and secondary lining increased, and the corresponding safety factors all decreased.

Benchmarking a Novel Efficient Numerical Method for Localized 1D Fermi-Hubbard Systems on a Quantum Simulator

Quantum simulators have made a remarkable progress towards exploring the dynamics of many-body systems, many of which offer a formidable challenge to both theoretical and numerical methods. While state-of-the-art quantum simulators are in principle able to simulate quantum dynamics well outside the domain of classical computers, they are noisy and limited in the variability of the initial state of the dynamics and the observables that can be measured. Despite these limitations, here we show that such a quantum simulator can be used to in-effect solve for the dynamics of a many-body system. We develop an efficient numerical technique that facilitates classical simulations in regimes not accessible to exact calculations or other established numerical techniques. The method is based on approximations that are well suited to describe localized one-dimensional Fermi-Hubbard systems. Since this new method does not have an error estimate and the approximations do not hold in general, we use a neutral-atom Fermi-Hubbard quantum simulator with $L_{\text{exp}}\simeq290$ lattice sites to benchmark its performance in terms of accuracy and convergence for evolution times up to $700$ tunnelling times. We then use these approximations in order to derive a simple prediction of the behaviour of interacting Bloch oscillations for spin-imbalanced Fermi-Hubbard systems, which we show to be in quantitative agreement with experimental results. Finally, we demonstrate that the convergence of our method is the slowest when the entanglement depth developed in the many-body system we consider is neither too small nor too large. This represents a promising regime for near-term applications of quantum simulators.

Effects of resonance states in barrier region on non-exponential decay of wave-packets scattered by rounded-rectangular potentials

The decay processes of wave-packets scattered by periodically perturbed and unperturbed rounded-rectangular potentials are studied numerically and theoretically, when the widths of the potentials L are very large. For the case of the unperturbed potentials, four different stages successively arise in the decay process of the wave in the potential region: two pre-exponential decays, namely power–law decay of t −3 and oscillating power–law decay, exponential decay and post-exponential decay, which is also power–law decay of t −3. The post-exponential decay is usually extremely small in magnitude. The characteristics of the pre-exponential and exponential decays are explained with the properties of resonance states, i.e. the Gamow states, for the unperturbed system. The rate of the exponential decay is determined by the imaginary part of the eigenenergy of the first resonance state. For the two pre-exponential decays, the ending time of the t −3 decay is a linear function of L and that of the oscillating power-law decay is proportional to L 3. In the limit of L → ∞, the t −3 decay is observed persistently, namely the decay for the rounded-step potential. For the perturbed potentials, even if the average energy of an initial wave-packet is relatively smaller than the oscillating potential, the noninstanton tunnelling, i.e. the multi-quanta absorption tunnelling, raises the tunnelling wave component up to the oscillating top of the rounded-rectangular potential, and the tunnelling probability rapidly increases with the perturbation strength. The properties of the resonance states are almost the same as those of the Gamow states because of the flatness of the potential top. As a result, the decay process after the tunnelling is almost the same as that for the unperturbed system. It is suggested that the tunnelling amplitude and tunnelling time, namely the amplitude and period of the pre-exponential decay, can be controlled by the perturbation strength and the potential width, respectively.

Tunneling dynamics in cosmological bounce models

Quasiclassical methods are used to define dynamical tunneling times in models of quantum cosmological bounces. These methods provide relevant new information compared with the traditional treatment of quantum tunneling by means of tunneling probabilities. As shown here, the quantum dynamics in bounce models is not secure from reaching zero scale factor, re-opening the question of how the classical singularity may be avoided. Moreover, in the examples studied here, tunneling times remain small even for large barriers, highlighting the quantum instability of underlying bounce models.

Navigational tunnel technique for gastric peroral endoscopic pyloromyotomy: getting straight to the point (pylorus).

Background and AimsGastric peroral endoscopic pyloromyotomy (G-POEM) is emerging as a treatment option for patients with gastroparesis. The most technically difficult part of the procedure is creating a submucosal tunnel in the gastric antrum, which can be directionally challenging. We describe a novel navigational tunneling method that guides submucosal dissection in the direction of the pylorus and helps to identify the pyloric landmarks.MethodsConsecutive patients from September to December 2020 who underwent G-POEM for symptomatic gastroparesis were included. All cases were confirmed by prolonged gastric emptying study. The navigational tunnel technique was performed as follows: (1) mucosal cautery markings were made to outline the tunnel starting 3 to 4 cm proximal to the pylorus, (2) submucosal injection was done at the level of the pylorus and extended backward to the incision point, and (3) submucosal dissection was carried out after the prior submucosal injection straight to the pylorus.ResultsSix patients with gastroparesis underwent G-POEM with the navigational tunneling technique. The average time for submucosal injection was 2 minutes and 42 seconds, and the average tunnel time was 15 minutes and 36 seconds. There were no adverse events. All patients reported significant improvement (50%-85%) in symptoms.ConclusionsThis novel navigational tunneling technique appears to guide and facilitate G-POEM by providing a visual path for submucosal dissection straight to the pylorus. It may increase efficiency, decreasing the need to repeatedly exit the tunnel to check direction and preventing nonproductive wandering. It may also help identify the pyloric ring within the tunnel.