Charged Quantum Research Articles

Charging by Quantum Measurement

We propose a quantum charging scheme fueled by measurements on ancillary qubits serving as disposable chargers. A stream of identical qubits are sequentially coupled to a quantum battery of $N+1$ levels and measured by projective operations after joint unitary evolutions of optimized intervals. If charger qubits are prepared in excited state and measured on ground state, then their excitations (energy) can be near perfectly transferred to battery by iteratively updating the optimized measurement intervals. Starting from its ground state, the battery could be constantly charged to an even higher energy level. Starting from a thermal state, the battery could also achieve a near-unit ratio of ergotropy and energy through less than $N$ measurements, when a population inversion is realized by measurements. If charger qubits are prepared in ground state and measured on excited state, useful work extracted by measurements alone could transform the battery from a thermal state to a high-ergotropy state before the success probability vanishes. Our operations in charging are more efficient than those without measurements and do not invoke the initial coherence in both battery and chargers. Particularly, our finding features quantum measurement in shaping nonequilibrium systems.

Magnetic charge and black hole supersymmetric quantum statistical relation

Magnetic charge and black hole supersymmetric quantum statistical relation

Determining the sequence of charge transport events and their roles on the limit of quantum efficiency of photocatalytic hydrogen production

•A novel method utilizing semi-empirical electrical circuits •Faithfully determine the sequence of charge transport events •Direct correlation between quantum efficiency and charge transport events Quantum efficiency (QE) is a defining parameter to rank the efficiency of a photocatalyst. The QE is governed by the kinetics of recombination and transfer processes of photogenerated charge carriers along with the sequence in which these events occur. However, there are no experimental techniques able to determine the sequence (i.e., series, parallel, or combination of both) of these charge transport events and directly determine the QE from charge transport information and vice versa. To address these gaps, here we report a semi-empirical circuit model to determine the sequence of charge transport events and propose a set of hypotheses to discriminate the deciding role of recombination and charge transfer in predicting the QE in a photocatalytic process. By testing with literature data for photocatalytic water splitting, we demonstrate that this model is able to predict QE when the percentage of recombination is known and the sequence of charge transport events when QE is known. Quantum efficiency (QE) is a defining parameter to rank the efficiency of a photocatalyst. The QE is governed by the kinetics of recombination and transfer processes of photogenerated charge carriers along with the sequence in which these events occur. However, there are no experimental techniques able to determine the sequence (i.e., series, parallel, or combination of both) of these charge transport events and directly determine the QE from charge transport information and vice versa. To address these gaps, here we report a semi-empirical circuit model to determine the sequence of charge transport events and propose a set of hypotheses to discriminate the deciding role of recombination and charge transfer in predicting the QE in a photocatalytic process. By testing with literature data for photocatalytic water splitting, we demonstrate that this model is able to predict QE when the percentage of recombination is known and the sequence of charge transport events when QE is known.

Quantum capacitance of graphene-like/graphene heterostructures for supercapacitor electrodes

The charge storage capacity, quantum capacitance, and atomic structures of transition-metal doped graphene-like/graphene heterostructures were studied by density functional theory (DFT). The impact of transition-metal (TM) doping (Ni, Co, Fe, Mn, Cr, V, Ti, and Sc) on the capacitance capacity of silicene/graphene, phosphorene/graphene, germanene/graphene, WSe2/graphene heterostructures was also examined. The findings showed that doping was more useful compared to vacancy defects to enhance the quantum capacitance of heterostructures. The Sc-doped WSe2/graphene exhibited the highest quantum capacitance (838.24 μF/cm2), which is the most promising positive electrode material for supercapacitors. The findings were supposed to provide the theoretical foundation to produce high-capacitance supercapacitors.

Destabilization of Human Islet Amyloid Polypeptide Fibrils by Charged Graphene Quantum Dots: A Molecular Dynamics Investigation with Implications for Nanomedicine

Destabilization of Human Islet Amyloid Polypeptide Fibrils by Charged Graphene Quantum Dots: A Molecular Dynamics Investigation with Implications for Nanomedicine

Pancake-Bonded Dimers of Semiquinone Radical Cations of N,N,N′,N′-Tetramethyl-p-phenylenediamine (Wurster’s Blue)

Pancake bonding in dimers of semiquinoid radical cations in a novel compound, TMPD chloride co-crystal with 2,5-dichlorohydroquinone, is studied by a combination of X-ray charge density and quantum chemical computations. The rings in a pancake-bonded dimer are parallel with a transversal offset, the interplanar separation distance is 3.1191(1) Å, and the centroid distance is 3.2022(2) Å. AIM analysis of experimental charge density revealed four symmetry-independent bonding critical points and a cage critical point between the TMPD cations in a dimer, with a maximum electron density of 0.055 e Å–3. A highest occupied molecular orbital extends between both rings of a dimer. The estimated energy of the covalent component is −3.24 kcal mol–1.

Charge transport, information scrambling and quantum operator-coherence in a many-body system with U(1) symmetry

In this work, we derive an exact hydrodynamical description for the coupled, charge and operator dynamics, in a quantum many-body system with U(1) symmetry. Using an emergent symmetry in the complex Brownian SYK model with charge conservation, we map the operator dynamics in the model to the imaginary-time dynamics of an SU(4) spin-chain. We utilize the emergent SU(4) description to demonstrate that the U(1) symmetry causes quantum-coherence to persist even after disorder-averaging, in sharp contrast to models without symmetries. In line with this property, we write down a ‘restricted’ Fokker-Planck equation for the out-of-time ordered correlator (OTOC) in the large-N limit, which permits a classical probability description strictly in the incoherent sector of the global operator-space. We then exploit this feature to describe the OTOC in terms of a Fisher-Kolmogorov-Petrovsky-Piskun (FKPP)-equation which couples the operator with the charge and is valid at all time-scales and for arbitrary charge-density profiles. The coupled equations obtained belong to a class of models also used to describe the population dynamics of bacteria embedded in a diffusive media. We simulate them to explore operator-dynamics in a background of non-uniform charge configuration, which reveals that the charge transport can strongly affect dynamics of operators, including those that have no overlap with the charge.

Aharonov–Bohm effect with an effective complex-valued vector potential

The interaction between a quantum charge and a dynamic source of a magnetic field is considered in the Aharonov–Bohm (AB) scenario. It is shown that, in weak interactions with a post-selection of the source, the effective vector potential is, generally, complex-valued. This leads to new experimental protocols to detect the AB phase before the source is fully encircled. While this does not necessarily change the nonlocal status of the AB effect, it brings new insights into it. Moreover, we discuss how these results might have consequences for the correspondence principle, making complex vector potentials relevant to the study of classical systems.

Effects of conduction band non-parabolicity and matrix material on THG process in GaAs QD

We investigate theoretically the third harmonic generation (THG) process in the singly charged GaAs quantum dot (QD). The effective mass approximation is used to obtain the energy levels and the wavefunctions. The potential is considered to be of finite type, with and without the effect of non-parabolicity of the conduction band. The effect of the conduction band nonparabolicity is included using the Kane’s model. Within the framework of the density matrix approach, THG nonlinear optical process is investigated in THz region for different dot radii of GaAs QD embedded in three different matrices, viz: Ga1-yAlyAs, Al2O3 and Si3N4.

Metalloids (B, Si) and non-metal (N, P, S) doped graphene nanosheet as a supercapacitor electrode: A density functional theory study

Metalloids [Boron (B), Silicon (Si)] and Non -metals [Nitrogen (N), Phosphorus (P), Sulfur (S)] doped graphene nanosheets were considered for alternative lightweight electrode materials in energy storage device applications. The density functional theory studies were performed to investigate the structural stability, charge density distribution, excessive surface charge density, and quantum capacitance of doped graphene nanosheets. It is found that the structures are stable with negative formation energy, and the graphene nanosheet doped with P and S shows protrusion forming a pyramidal shape along the planar graphene nanosheet to maintain stability. Further, the doping of atoms into the graphene nanosheet introduced a minimal bandgap with a shift in the Fermi level, either into the conduction band or valence band, depending on the dopant type. This appearance of bandgap is attributed to the breaking of the symmetry in the graphene sublattice. Meanwhile, based on the type and concentration of dopant, localized and delocalized states are formed near the Fermi level. It is also found that the formation of a localized state near the Fermi level has profoundly improved the excessive surface charge density and quantum capacitance. The S – doped graphene nanosheet was observed to exhibit an excellent quantum capacitance of 38.88 μFcm−2 compared to all other structures and it can be used as a suitable light-weight electrode for asymmetric supercapacitors.

Mitigating the interfacial concentration gradient by negatively charged quantum dots toward dendrite-free Zn anodes

Aqueous zinc (Zn) batteries have shown great promise in energy storage systems as an intrinsically safe battery configuration. However, Zn dendrite and side reactions may impede their practical application. Here, we propose to mitigate interfacial concentration gradient by introducing N, S-doped carbon quantum dots (NSQDs) as an additive to achieve uniform Zn deposition. The dangling oxygen-containing groups of the NSQDs would be reduced by a Zn foil, thus interacting with the oxidized Zn2+ to form Zn-O bonds on the Zn surface. The formed NSQD layer provides abundant nucleation sites for Zn ions pre-seeding. Meantime, the NSQD layer in negative charge decreases the ion concentration gradient and uniformizes the electric field distribution near the Zn-electrolyte interfaces, facilitating dendrite-free Zn deposition, which is well evidenced by finite simulation results. Together with a decreased interfacial concentration gradient, the Zn metal anode exhibits good rate performances (20 mA cm−2 for nearly 6000 cycles). In addition, the assembled pouch full cell exhibits excellent cycling stability, and 81% of capacity retention is achieved after 250 cycles. This work not only offers a simple approach to modulate the interfacial concentration gradient for uniform Zn deposition but also paves the way for a practical dendrite-free aqueous Zn battery.

Anyonic defect branes and conformal blocks in twisted equivariant differential (TED) K-theory

We demonstrate that twisted equivariant differential K-theory of transverse complex curves accommodates exotic charges of the form expected of codimension[Formula: see text]2 defect branes, such as of [Formula: see text]-branes in IIB/F-theory on [Formula: see text]-type orbifold singularities, but also of their dual 3-brane defects of class-S theories on M5-branes. These branes have been argued, within F-theory and the AGT correspondence, to carry special [Formula: see text]-monodromy charges not seen for other branes, at least partially reflected in conformal blocks of the [Formula: see text]-WZW model over their transverse punctured complex curve. Indeed, it has been argued that all “exotic” branes of string theory are defect branes carrying such U-duality monodromy charges — but none of these had previously been identified in the expected brane charge quantization law given by K-theory. Here we observe that it is the subtle (and previously somewhat neglected) twisting of equivariant K-theory by flat complex line bundles appearing inside orbi-singularities (“inner local systems”) that makes the secondary Chern character on a punctured plane inside an [Formula: see text]-type singularity evaluate to the twisted holomorphic de Rham cohomology which Feigin, Schechtman and Varchenko showed realizes [Formula: see text]-conformal blocks, here in degree 1 — in fact it gives the direct sum of these over all admissible fractional levels [Formula: see text]. The remaining higher-degree [Formula: see text]-conformal blocks appear similarly if we assume our previously discussed “Hypothesis H” about brane charge quantization in M-theory. Since conformal blocks — and hence these twisted equivariant secondary Chern characters — solve the Knizhnik–Zamolodchikov equation and thus constitute representations of the braid group of motions of defect branes inside their transverse space, this provides a concrete first-principles realization of anyon statistics of — and hence of topological quantum computation on — defect branes in string/M-theory.

Anomaly cancellation in the lattice effective electroweak theory

The anomaly cancellation is at the basis of the perturbative consistence of the Standard Model, and it provides a partial explanation of charge quantization. We consider an effective electroweak theory on a lattice, with a quartic interaction describing the weak forces and an interaction with the e.m. field. We prove the validity of the anomaly cancellation at a non-perturbative level and with a finite lattice cutoff, even if the lattice breaks some important symmetries, on which perturbative arguments for the cancellation are based. The method of the proof has analogies with the one adopted for establishing the universality in transport of quantum materials.

Effects of Quantum Recoil Forces in Resistive Switching in Memristors

Memristive devices, whose resistance can be controlled by applying a voltage and further retained, are attractive as possible circuit elements for neuromorphic computing. This new type of devices poses a number of both technological and theoretical challenges. Even the physics of the key process of resistive switching, usually associated with formation or breakage of conductive filaments in the memristor, is not completely understood yet. This work proposes a new resistive switching mechanism, which should be important in the thin-filament regime and take place due to the back reaction, or recoil, of quantum charge carriers – independently of the conventional electrostatically-driven ion migration. Since thinnest conductive filaments are in question, which are only several atoms thick and allow for a quasi-ballistic, quantized conductance, we use a mean-field theory and the framework of nonequilibrium Green’s functions to discuss the electron recoil effect for a quantum current through a nanofilament on its geometry and compare it with the transmission probability of charge carriers. Namely, we first study an analytically tractable toy model of a 1D atomic chain, to qualitatively demonstrate the importance of the charge-carrier recoil, and further proceed with a realistic molecular-dynamics simulation of the recoil-driven ion migration along a copper filament and the resulting resistive switching. The results obtained are expected to add to the understanding of resistive switching mechanisms at the nanoscale and to help downscale high-retention memristive devices.

Finite temperature energy–momentum tensor in compactified cosmic string spacetime

In this paper we analyze the expectation value of the field squared and the energy–momentum tensor associated with a massive charged scalar quantum field with a nonzero chemical potential propagating in a high-dimensional compactified cosmic string spacetime in thermal equilibrium at finite temperature T. Moreover, we assume that the charged quantum field interacts with a very thin magnetic flux running along the core of the idealized cosmic string, and with a magnetic flux enclosed by the compact dimension. These observables are expressed as the vacuum expectation values and the finite temperature contributions coming from the particles and antiparticles excitations. Due to the compactification, the thermal corrections can be decomposed in a part induced by the cosmic string spacetime without compactification, plus a contribution induced by the compactification. This decompositions explicitly follows from the Abel–Plana formula used to proceed the summation over the discrete quantum number associated with the quasiperiodic condition imposed on the quantum field along the compact dimension. The expectations values of the field squared and the energy–momentum tensor are even periodic functions of the magnetic flux with period being the quantum flux, and also even functions of the chemical potential. Our main objectives in this paper concern in the investigation of the thermal corrections only. In this way we explicitly calculate the behavior of these observables in the limits of low and high temperature. We show that the temperature enhance the induced densities. In addition some graphs are also included in order to exhibit these behaviors.

Hall Droplet Sheets in Holographic QCD

In single-flavor QCD, the low energy description of baryons as Skyrmions is not available. In this case, it has been proposed by Komargodski that baryons can be viewed as kinds of charged quantum Hall droplets, or “sheets”. In this paper we propose a string theory description of the sheets in single-flavor holographic QCD, focusing on the Witten-Sakai-Sugimoto model. The sheets have a “hard” gluonic core, described by D6-branes, and a “soft” mesonic shell, dual to non-trivial D8-brane gauge field configurations. We first provide the description of an infinitely extended sheet with massless or moderately massive quarks. Then, we construct a semi-infinite sheet ending on a one-dimensional boundary, a “vortex string”. The holographic description allows for the precise calculation of sheet observables. In particular, we compute the tension and thickness of the sheet and the vortex string, and provide their four dimensional effective actions.

How Do Quantum Effects Influence the Capacitance and Carrier Density of Monolayer MoS2 Transistors?

When transistor gate insulators have nanometer-scale equivalent oxide thickness (EOT), the gate capacitance (CG) becomes smaller than the oxide capacitance (Cox) due to the quantum capacitance and charge centroid capacitance of the channel. Here, we study the capacitance of monolayer MoS2 as a prototypical two-dimensional (2D) channel while considering spatial variations in the potential, charge density, and density of states. At 0.5 nm EOT, the monolayer MoS2 capacitance is smaller than its quantum capacitance, limiting the single-gated CG of an n-type channel to between 63% and 78% of Cox, for gate overdrive voltages between 0.5 and 1 V. Despite these limitations, for dual-gated devices, the on-state CG of monolayer MoS2 is 50% greater than that of silicon at 0.5 nm EOT and more than three times that of InGaAs at 1 nm EOT, indicating that such 2D semiconductors are promising for improved gate control of nanoscale transistors at future technology nodes.

Aptasensor-based assay for dual-readout determination of aflatoxin B1 in corn and wheat via an electrostatic force-mediated FRET strategy.

Arapid and sensitive aptasensor was established for the dual-readout determination of aflatoxin B1 (AFB1) utilizing an electrostatically mediated fluorescence resonance energy transfer (FRET) signal amplification strategy. In the presence of AFB1, the aptamer preferentially bound to AFB1, resulting in the aggregation of bare gold nanoparticles (AuNPs) induced by NaCl, accompanied by a change of AuNP solution from wine-red to purple. This color change was used for colorimetric channel analysis. Then, the positively charged quantum dots were introduced into reaction system and interacted with negatively charged AuNPs, which successfully converted the color signal into a more sensitive fluorescence signal through FRET. The fluorescence quenching efficiency decreased with increasing concentrations of AFB1, and the fluorescence of aptasensor gradually recovered. Thevariation of fluorescence intensity was employed for fluorometric channel analysis. Under the optimal conditions, the color and fluorescence signals exhibited excellent response to AFB1 concentration within the ranges 10-320 ng·mL-1 and 3-320 ng·mL-1,respectively, and the limit of detection was as low as 7.32 ng·mL-1 and 1.48 ng·mL-1, respectively. The proposed aptasensor exhibited favorable selectivity, good recovery (85.3-113.4% in spiked corn and wheat samples), stable reproducibility (RSD<13.3%), and satisfactory correlation with commercial kits (R2=0.998). The aptasensor developed integrates advantages of modification-free, dual-readout, self-calibration, easy operation, and cost-effectiveness, while providing a simple and universal strategy for rapid and sensitive detection of mycotoxins in foodstuffs.

Z 3 scalar dark matter with strong positron fluxes

We explore a class of simplified extensions to the Standard Model containing a complex singlet scalar as a dark matter candidate accompanied by a vector-like lepton as a mediator, both charged under a new Z 3 symmetry. In its simplest form, the new physics couples only to right-handed electrons, and the model is able to accommodate the correct dark matter relic abundance around the electroweak scale up to several TeV evading the strongest constraints from perturbativity, collider and dark matter searches. Furthermore, the model is capable to enhance naturally positron fluxes by several orders of magnitude presenting a box-shape spectra. This framework opens up a lot of phenomenological possibilities depending on the quantum charge assignments of the new fields.

Effect of Synthesis Method on Reaction Mechanism for Hydrogen Evolution over CuxOy/TiO2 Photocatalysts: A Kinetic Analysis.

The existing literature survey reports rare and conflicting studies on the effect of the preparation method of metal-based semiconductor photocatalysts on structural/morphological features, electronic properties, and kinetics regulating the photocatalytic H2 generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H2 generation synthesized via distinct methods (i.e., photodeposition and impregnation). Our study aims to establish a stringent correlation between physicochemical/electronic properties and photocatalytic performances for H2 generation based on material characterization and kinetic modeling of the experimental outcomes. Estimating unknown kinetic parameters, such as charge recombination rate and quantum yield, suggests a mechanism regulating charge carrier lifetime depending on copper distribution on the TiO2 surface. We demonstrate that H2 generation photoefficiency recorded over impregnated CuxOy/TiO2 is related to an even distribution of Cu(0)/Cu(I) on TiO2, and the formation of an Ohmic junction concertedly extended charge carrier lifetime and separation. The outcomes of the kinetic analysis and the related modeling investigation underpin photocatalyst physicochemical and electronic properties. Overall, the present study lays the groundwork for the future design of metal-based semiconductor photocatalysts with high photoefficiencies for H2 evolution.