Quantum Tunneling Research Articles

Quantum Tunnelling – What, Where and Whatnot

Quantum Tunnelling – What, Where and Whatnot

Quantum Dynamics Framework with Quantum Tunneling Effect for Numerical Optimization

In recent years, optimization algorithms have developed rapidly, especially those which introduce quantum ideas, which perform excellently. Inspired by quantum thought, this paper proposes a quantum dynamics framework (QDF) which converts optimization problems into the problem of the constrained ground state of the quantum system and analyzes optimization algorithms by simulating the dynamic evolution process of physical optimization systems in the ground state. Potential energy equivalence and Taylor expansion are performed on the objective function to obtain the basic iterative operations of optimization algorithms. Furthermore, a quantum dynamics framework based on the quantum tunneling effect (QDF-TE) is proposed which adopts dynamic multiple group collaborative sampling to improve the quantum tunneling effect of the QDF, thereby increasing the population diversity and improving algorithm performance. The probability distribution of solutions can be visually observed through the evolution of the wave function, which also indicates that the QDF-TE can strengthen the tunneling effect. The QDF-TE was evaluated on the CEC 2017 test suite and shown to be competitive with other heuristic optimization algorithms. The experimental results reveal the effectiveness of introducing a quantum mechanism to analyze and improve optimization algorithms.

Dynamical system description of quantum tunneling in a double well potential

Dynamical system description of quantum tunneling in a double well potential

Directed Evolution's Selective Use of Quantum Tunneling in Designed Enzymes─A Combined Theoretical and Experimental Study.

Natural enzymes are powerful catalysts, reducing the apparent activation energy for reactions and enabling chemistry to proceed as much as 1015 times faster than the corresponding solution reaction. It has been suggested for some time that, in some cases, quantum tunneling can contribute to this rate enhancement by offering pathways through a barrier inaccessible to activated events. A central question of interest to both physical chemists and biochemists is the extent to which evolution introduces mechanisms below the barrier, or tunneling mechanisms. In view of the rapidly expanding chemistries for which artificial enzymes have been created, it is of interest to see how quantum tunneling has been used in these reactions. In this paper, we study the evolution of possible proton tunneling during C-H bond cleavage in enzymes that catalyze the Morita-Baylis-Hillman (MBH) reaction. The enzymes were generated by theoretical design, followed by laboratory evolution. We employ classical and centroid molecular dynamics approaches in path sampling computations to determine whether there is a quantum contribution to lowering the free energy of the proton transfer for various experimentally generated protein and substrate combinations. These data are compared to experiments reporting on the observed kinetic isotope effect (KIE) for the relevant reactions. Our results indicate the modest involvement of tunneling when laboratory evolution has resulted in a system with a higher classical free energy barrier to chemistry (that is, when optimization of processes other than chemistry results in a higher chemical barrier).

Photochemistry of Microsolvated Nitrous Acid: Observation of the Water-Separated Complex of Nitric Oxide and Hydroxyl Radical.

The photochemistry of nitrous acid (HONO) plays a crucial role in atmospheric chemistry as it serves as a key source of hydroxyl radicals (OH) in the atmosphere; however, our comprehension of the underlying mechanism for the photochemistry of HONO especially in the presence of water is far from being complete as the transient intermediates in the photoreactions have not been observed. Herein, we report the photochemistry of microsolvated HONO by water in a cryogenic N2 matrix. Specifically, the 1:1 hydrogen-bonded water complex of HONO was facially prepared in the matrix through stepwise photolytic O2 oxidation of the water complex of imidogen (NH-H2O) via the intermediacy of the elusive water complex of peroxyl isomer HNOO. Upon photolysis at 193 nm, the matrix-isolated HONO-H2O complex decomposes by yielding the ternary water complex of OH and NO due to the matrix cage effect. The identification of this rare water-separated radical pair (OH-H2O-NO) with matrix-isolation infrared and ultraviolet-visible spectroscopy is aided by D, 15N, and 18O isotope labeling and quantum chemical calculations at the (U)CCSD/AVTZ level of theory, and its most stable structure exhibits separate hydrogen bonding interactions of the OH and NO radicals with H2O via OH···OH2 and ON···HOH contacts, respectively. This ternary complex is extremely unstable, as it undergoes spontaneous radical recombination to reform the HONO-H2O complex in the temperature range of 4-12 K through quantum-mechanical tunneling with 16/18O, H/D, 14/15N kinetic isotopic effects of 1.43, 2.33, and 0.91, respectively. At increased temperatures from 15 to 21 K, the recombination proceeds predominantly by overcoming the activation barrier with an estimated height of 0.12(1) kcal/mol.

Exploring low barrier quantum tunneling and structural planarity in 3-methylstyrene conformers: Insights from microwave spectroscopy.

The first ground-state rotational spectrum of 3-methylstyrene (3MS) was measured by Fourier transform microwave spectroscopy under supersonic jet-cooled conditions. Transitions were assigned for two conformers: cis-3MS and trans-3MS. In the cis conformer, the vinyl group is oriented toward the methyl group, while in the trans conformer, it is positioned away from the methyl. The energy difference between the two conformers was calculated to be only 2.1cm-1, with the cis conformer having lower energy. Significant tunneling splitting, caused by the low-barrier internal rotation of the methyl group, was observed and analyzed using the XIAM and BELGI-Cs codes. The BELGI results show that the V3 barrier is 30.6688(87) cm-1 for the cis conformer and 11.0388(88) cm-1 for the trans conformer. The experimental rotational and torsional parameters are compared to their density functional theory counterparts. The planarity of the molecular geometry of cis- and trans-3MS is discussed, contributing to the long-standing topic of discussion about the planarity of styrene derivatives.

Study on the Influence of External Electric Field Control and Vibrational Quantum Effect on the Charge Separation Mechanism in Fullerene-Based Systems.

Based on the DCV-C60 system of fullerene acceptor organic solar cell active materials, the charge transfer process of D-A type molecular materials under the action of an external electric field (Fext) was explored. Within the range of electric field application, the excited state characteristics exhibit certain regular changes. Based on reducing the excitation energy, the excitation mode shows a trend of developing toward low excited states. The effect of solvent polarity on the stability and reorganization energy of the charge transfer state was investigated. The dependence of charge separation parameters on specific molecular structures within the electric field range was studied, proving that the electric field set along the electron transfer direction can indeed accelerate charge separation. The influence of vibrational modes on the charge separation process was studied, and the results showed that the vibrational quantum tunneling effect significantly promoted the charge separation. Therefore, considering the vibrational excitation effect and the perturbation of the nuclear-electron interaction is crucial for more accurate simulation of the electron-vibration coupling process in the excited state.

Evaluation of Nanocrystalline Magnetic ErFeO3 Composite for the Sorptive Removal of Cesium and Cobalt Ion from Aqueous Solution

Abstract The effect of nano-scale size in the magnetic semiconductor rare earth ferrite system, ErFeO3, has been studied. The orthorhombic crystal structure in the nano-scale was found for ErFeO3 prepared by the sol-gel method to be 8 nm. Fe-O stretching vibration was identified in the IR band at around 561 cm-1, whereas the O-Fe-O deformation vibration was identified in the band at about 437 cm-1. The semiconducting behavior of ErFeO3 was found, and its energy gap equals 1.75eV. As the frequency increases, the charge transport mechanism showed transition from the small polaron model, dominated by thermally activated hopping, to a quantum mechanical tunneling model, where charge carriers move through the material by tunneling between localized states without trapping. This transition is driven by the charge carriers having less time to become localized at higher frequencies, allowing for more direct tunneling transport. The new application of nano-crystalline ErFeO3 to remove hazardous elements was evaluated. The adsorption isotherm of Cs(I) and Co(II) by ErFeO3 nanocomposite was studied. The findings of the present studies highlight the potential use of ErFeO3 as a new, efficacious sorbent for removing Cs(I) and Co(II) from the waste stream, providing a reliable and efficient solution to environmental pollution

Unveiling the Werner-Type Cluster Chemistry of Heterometallic 4f/Post-Transition Metals: A {Dy3Bi8} Complex Exhibiting Quantum Tunneling Steps in the Hysteresis Loops and its 1-D Congener.

A new [Dy3Bi8O6Cl3(saph)9] (1) Werner-type cluster has been prepared, which is the first DyIII/BiIII polynuclear compound with no metal-metal bond and one of the very few LnIII-BiIII (Ln = lanthanide) heterometallic complexes reported to date. The molecular compound 1 has been deliberately transformed to its 1-D analogue [Dy3Bi8O6(N3)3(saph)9]n (2) via the replacement of the terminal Cl- ions by end-to-end bridging N3- groups. The overall metallic skeleton of 1 (and 2) can be described as consisting of a diamagnetic {Bi8} unit with an elongated trigonal bipyramidal topology, surrounded by a magnetic {Dy3} equilateral triangle, which does not contain μ3-oxo/hydroxo/alkoxo groups. Detailed magnetic studies in a microcrystalline sample and a single crystal of 1 revealed a rare two-step hysteresis loop at various low temperatures and field-sweep rates, with the steps located at zero and ±0.26 T fields providing a measure of intermolecular interactions. Extended ab initio calculations unravel the dominant pathways of magnetization relaxation, as well as the type and magnitude of the magnetic exchange interactions between the DyIII centers and the orientation of their anisotropy axes, thus rendering the {Dy3} unit of 1 as a rare triangle among its congeners with a nontoroidal magnetic state. The combined results demonstrate the potential of heterometallic lanthanide/post-transition metal chemistry to provide molecule-based materials with unprecedented structures and compelling methods to rationalize the obtained magnetic properties.

Quantum-Cognitive Neural Networks: Assessing Confidence and Uncertainty with Human Decision-Making Simulations

Contemporary machine learning (ML) systems excel in recognising and classifying images with remarkable accuracy. However, like many computer software systems, they can fail by generating confusing or erroneous outputs or by deferring to human operators to interpret the results and make final decisions. In this paper, we employ the recently proposed quantum tunnelling neural networks (QT-NNs) inspired by human brain processes alongside quantum cognition theory to classify image datasets while emulating human perception and judgment. Our findings suggest that the QT-NN model provides compelling evidence of its potential to replicate human-like decision-making. We also reveal that the QT-NN model can be trained up to 50 times faster than its classical counterpart.

Uniaxial magnetic anisotropy and weak phonon–spin coupling of a single Ni atom bonded to iridium-doped graphene

We investigate the magnetism and vibrational mode of a single Ni atom bonded to iridium-doped graphene. It is found that the Ni atom exhibits a large magnetic anisotropy energy of 53 meV, and the magnetic anisotropy is perfectly uniaxial. There are no vibrational modes below 40 meV for the Ni atom, which disables the efficient coupling between the spin and phonon at the low magnetic field. The uniaxial magnetic anisotropy combining with the weak phonon–spin coupling effectively resists the quantum tunneling and spin flip, making the Ni atom a viable single atom magnet for information storage.

Efficient Optical Control of Quantum Tunneling Devices Based on Layered Violet Phosphorus

AbstractElectron tunneling devices attract attention due to their potential applications in integrated circuits, memories, and high‐frequency oscillators. However, limited works are devoted to the optical control of electron tunneling processes. The main reason is the low concentration of photogenerated carriers concerning the equilibrium values in heavy‐doped regions. In this work, violet phosphorus (VP) with a unique bilayer tubular structure supplies an excellent platform for investigating the tunneling mechanisms under photo illumination. A VP‐based vertical tunneling diode made of metal‐insulator‐semiconductor (MIS) stacking is presented. The photogenerated carriers increase the tunneling current by ≈4.2 times through photo illumination, leading to a considerable rectification ratio. In addition, a three‐terminal tunneling field‐effect transistor (TFET) made from VP flake with different thicknesses is also presented. The interband tunneling of electrons results in a tunable negative differential transconductance (NDT) at room temperature. The photoillumination can modulate the onset of the NDT region due to the variation of the density of states with Fermi level alignment in the channel and drain region. These results advance the understanding of electron transport mechanisms in VP‐based tunneling devices, showing great potential for exploiting novel 2D multifunctional devices with interactions between light and carriers’ tunneling.

Polyadic Cantor potential of minimum lacunarity: Special case of super periodic generalized unified Cantor potential

Abstract To bridge the fractal and non-fractal potentials we introduce the concept of generalized unified Cantor potential (GUCP) with the key parameter $N$ which represents the potential count at the stage $S=1$. This system is characterized by total span $L$, stages $S$, scaling parameter $\rho$ and two real numbers $\mu$ and $\nu$. Notably, the polyadic Cantor potential (PCP) system with minimal lacunarity is a specific instance within the GUCP paradigm. Employing the super periodic potential (SPP) formalism, we formulated a closed-form expression for transmission probability $T_{S}(k, N)$ using the $q$-Pochhammer symbol and investigated the features of non-relativistic quantum tunneling through this potential configuration. We show that GUCP system exhibits sharp transmission resonances, differing from traditional quantum systems. Our analysis reveals saturation in the transmission profile with evolving stages $S$ and establishes a significant scaling relationship between reflection probability and wave vector $k$
through analytical derivations.

Machine Learning Recognition of Artificial DNA Sequence with Quantum Tunneling Nanogap Junction.

Artificially synthesized DNA holds significant promise in addressing fundamental biochemical questions and driving advancements in biotechnology, genetics, and DNA digital data storage. Rapid and precise electric identification of these artificial DNA strands is crucial for their effective application. Herein, we present a comprehensive investigation into the electric recognition of eight artificial synthesized DNA (xDNA and yDNA) nucleobases using quantum tunneling transport and machine learning (ML) techniques. By embedding these nucleobases within a solid-state nanogap junction, we calculated their fingerprint transmission and current readouts and also analyzed the influence of electronic coupling and molecular orbital delocalization on these properties. The trained ML model achieved a predictive basecalling accuracy of up to 100% for xDNA nucleobases and 99.80% for yDNA transmission readout data sets. ML explainability study revealed that normalized descriptors have a greater impact on nucleobase prediction than the original transmission function, proving more effective in disentangling overlapping artificial DNA nucleobase signals. Quaternary classification results highlighted higher recognition accuracy for xDNA nucleobases than for yDNA nucleobases. Furthermore, precise calling of complementary, purine, and pyrimidine base pair combinations was demonstrated with high sensitivity and an F1 score. Our findings reveal the feasibility of highly sensitive and precise electrical recognition of artificial DNA nucleobases, which can transform genetic research and spur advancements in genetic data storage, synthetic biology, and diagnostics.

Fine-Tuning the Anisotropies of Air-Stable Single-Molecule Magnets Based on Macrocycle Ligands.

Air-stable single-molecule magnets (SMMs) can be obtained by confining DyIII ion in a D6h coordination environment; however, most of the current efforts were focused on modifying the rigidity of the macrocycle ligand. Herein, we attempt to assemble air-stable SMMs based on macrocycles with a replaceable coordination site. By using an in situ 1 + 1 Schiff-base reaction of dialdehyde with diamine, three air-stable SMMs have been obtained in which one of the equatorial coordination sites can be varied from -NH- (for Dy-NH), -O- (for Dy-O), and -NMe- (for Dy-NMe). Complex Dy-NH shows a less distorted D6h symmetry and an anisotropy energy barrier of 1270 K. For complex Dy-O, the coordination site of -O- gives a relatively longer coordination bond but a comparable energy barrier in contrast with that of Dy-NH. In the case of complex Dy-NMe, although the -NMe-group gives a very long coordination bond, the large steric effect on the -NMe- group enforces a larger distortion of the D6h coordination geometry, resulting in the fast quantum tunneling of the magnetization that shortcuts the thermal relaxation process; therefore, Dy-NMe shows a lower energy barrier. This study provides a new strategy for modifying the coordinate site on the equatorial plane of D6h symmetry to fine-tune the structure and magnetic anisotropy of SMMs.

Theoretical Investigations on the Molecular Magnetic Behavior of Actinide Molecules [AnPc2]0/- (An = U, Cf): Prediction of the High Magnetic Blocking Barrier and Magnetic Blocking Temperature in [CfPc2

Searching for single-molecule magnets (SMM) with large effective blocking barriers, long relaxation times, and high magnetic blocking temperatures is vitally important not only for the fundamental research of magnetism at the molecular level but also for the realization of new-generation magnetic memory unit. Actinides (An) atoms possess extremely strong spin-orbit coupling (SOC) due to their 5f orbitals, and their ground multiplets are largely split into several sublevels because of the strong interplay between the SOC of An atoms and the crystal field (CF) formed by ligand atoms. Compared to TM-based SMMs, more dispersed energy level widths of An-based SMMs will give a larger total zero field splitting (ZFS) and thus provide a necessary condition to derive a higher Ueff. In combination of the density functional theory (DFT) as well as the CF model Hamiltonian and ab initio calculation, we have investigated the structural stability and electronic structures as well as the magnetodynamic behavior of [AnPc2]0/- (An = U, Cf) molecules. We find that An atoms can strongly interact with its ligand N atoms in forming An-N ionic bonds, and 5f electrons are more localized in the Cf atom than in the U atom, giving U4+(5f2) and Cf3+(5f9) valence states. Although the UPc2 molecule has a modest value of Ueff = 514 cm-1, it is not a good SMM due to the easy occurrence of quantum tunneling of magnetization (QTM). Based on the consistent results of CF Hamiltonian and ab initio calculations on the [CfPc2]- molecule, we propose that almost prohibited QTM within the Kramers doublets (KDs) as well as very low transition probabilities between different states via hindered spin-flip transitions would result in a high Ueff = 1401 cm-1. The estimated high magnetic blocking temperature (TB) of 58 K renders [CfPc2]- an excellent SMM candidate, implying that magnetic hysteresis could be observed in future experiments.

Preparation and photoelectric properties of Si:B nanowires with thermal evaporation method.

We have successfully prepared a significant number of nanowires from non-toxic silicon sources. Compared to the SiO silicon source used in most other articles, our preparation method is much safer. It provides a simple and harmless new preparation method for the preparation of silicon nanowires. SiNWs (Silicon nanowires), as a novel type of nanomaterial, exhibit many outstanding properties, including the quantum confinement effect, quantum tunneling, Coulomb blocking effect, and exceptional electrical and optical properties. The study of SiNWs is therefore highly significant. In this paper, non-toxic SiO2 powder, Si powder, and B2O3 powder were utilized as raw materials to prepare SiNWs with diameters ranging from 30-60 nm and lengths from several hundred nanometers to tens of microns. The resulting SiNWs have a uniform morphology, smooth surfaces, and are produced in considerable yield. The morphology and structure of the SiNWs were characterized using XRD, SEM, HRTEM, SAED, EDS, and Raman spectroscopy. The results indicate that the prepared SiNWs are pure, uniform, and have a polycrystalline structure. The PL (photoluminescence) spectra show a pronounced UV emission peak at 346 nm, with the optimal excitation wavelength being 234 nm. Measurements with the Keithley 2601B demonstrate that the resistivity of the SiNWs is 4.292 × 108Ω·cm. Further studies reveal that the PL properties of SiNWs are influenced by their size and surface state. These findings have significant implications for understanding the luminescent mechanism of SiNWs and their potential applications in optoelectronics and biomedicine. This paper serves as a reference for the preparation and characterization of SiNWs, highlighting their PL properties and potential use in various applications, including biomedical imaging, sensors, and optoelectronic devices.

Bi-Josephson effect in a driven-dissipative supersolid

Abstract The Josephson effect is a macroscopic quantum tunneling phenomenon in a system with superfluid property, when it is split into two parts by a barrier. Here, we examine the Josephson effect in a driven-dissipative supersolid realized by coupling Bose-Einstein condensates to an optical ring cavity. We show that the spontaneous breaking of spatial translation symmetry in supersolid makes the location of the splitting barrier have a significant influence on the Josephson effect. Remarkably, for the same splitting barrier, depending on its location, two different types of DC Josephson currents are found in the supersolid phase (compared to only one type found in the superfluid phase). Thus, we term it a bi-Josephson effect. We examine the Josephson relationships and critical Josephson currents in detail, revealing that the emergence of supersolid order affects these two types of DC Josephson currents differently---one is enhanced, while the other is suppressed. The findings of this work unveil unique Josephson physics in the supersolid phase, and show new opportunities to build novel Josephson devices with supersolids.

Cooling of Semiconductor Devices via Quantum Tunneling.

Classical transport of electrons and holes in nanoscale devices leads to heating that severely limits performance, reliability, and efficiency. In contrast, recent theory suggests that interband quantum tunneling and subsequent thermalization of carriers with the lattice results in local cooling of devices. However, internal cooling in nanoscale devices is largely unexplored. Here, using a novel scanning thermal microscopy technique with millikelvin temperature resolution and nanometer spatial resolution, we directly record the cross-sectional temperature in functional InGaAs tunnel diodes. Our measurements reveal large, localized cooling of 2-3 W/cm^{2} at the tunnel junction, which is in quantitative agreement with the bipolar Peltier process associated with interband tunneling. These advances hold significant potential for integration into electronic and energy conversion devices and improving their performance.

Remark on Falaco Soliton as a Tunneling Mechanism in a Navier-Stokes Universe

This paper is a follow up to our previous article [1] suggesting that it is possible to find tunneling time solutions for Schrodinger equation considering quasicrystalline as interstellar matter, by virtue of quasicrystalline potential. The paper also discusses the mapping of these equations to Riccati equations, a class of nonlinear differential equations. This mapping can provide insights into the behavior of the Navier-Stokes equations and may lead to new methods for solving them. The Navier-Stokes equations, a set of nonlinear partial differential equations, are fundamental in fluid mechanics. They describe the motion of viscous fluids. In three dimensions, these equations are particularly complex and often leading to turbulence. The paper also discusses shortly on Falaco soliton as a tunneling mechanism in a Navier-Stokes Universe, which is quite able to fill the gap of realistic mechanism of quantum tunneling which is missing in standard Wave Mechanics. Further investigations are advised.