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In this work, we theoretically explore whether a parity-violating/chiral light–matter interaction is required to capture all relevant aspects of chiral polaritonics or if a parity-conserving/achiral theory is sufficient (e.g., long-wavelength/dipole approximation). This question is non-trivial to answer since achiral theories (Hamiltonians) still possess chiral solutions. To elucidate this fundamental theoretical question, a simple GaAs quantum ring model is coupled to an effective chiral mode of a single-handedness optical cavity in dipole approximation. The bare matter GaAs quantum ring possesses a non-degenerate ground state and a doubly degenerate first excited state. The chiral or achiral nature (superpositions) of the degenerate excited states remains undetermined for an isolated matter system. However, inside our parity-conserving description of a chiral cavity, we find that the dressed eigenstates automatically (ab initio) attain chiral character and become energetically discriminated based on the handedness of the cavity. In contrast, the non-degenerate bare matter state (ground state) does not show energetic discrimination inside a chiral cavity within a dipole approximation. Nevertheless, our results suggest that the handedness of the cavity can still be imprinted onto these states (e.g., angular momentum and chiral current densities). Overall, the above findings highlight the relevance of degenerate states in chiral polaritonics. In particular, because recent theoretical results for linearly polarized cavities indicate the formation of a frustrated and highly degenerate electronic ground state under collective strong coupling conditions, which, likewise, is expected to form in chiral polaritonics and, thus, could be prone to chiral symmetry breaking effects. [ABSTRACT FROM AUTHOR]

The molecular dynamics with electronic friction (MDEF) approach can accurately describe nonadiabatic effects at metal surfaces in the weakly nonadiabatic limit. That being said, the MDEF approach treats nuclear motion classically such that the nuclear quantum effects are completely missing in the approach. To address this limitation, we combine Electronic Friction with Ring Polymer Molecular Dynamics (EF-RPMD). In particular, we apply the averaged electronic friction from the metal surface to the centroid mode of the ring polymer. We benchmark our approach against quantum dynamics to show that EF-RPMD can accurately capture zero-point energy as well as transition dynamics. In addition, we show that EF-RPMD can correctly predict the electronic transfer rate near metal surfaces in the tunneling limit as well as the barrier crossing limit. We expect that our approach will be very useful to study nonadiabatic dynamics near metal surfaces when nuclear quantum effects become essential. [ABSTRACT FROM AUTHOR]

Within the framework of the macroscopic dielectric continuum model, the dispersive spectra of polar optical phonon modes of III-nitride based nanostructures with different inner and outer dielectric media are investigated in this paper. The dielectric and quantum size effects on the dispersive frequencies of phonon modes are focused and emphasized. In the case of GaN quantum rings (QRs), we found that the dielectric constant of the inner/outer medium could significantly influence the dispersive spectra of the surface optical (SO) phonon mode as the high/low-frequency SO phonon modes are mainly localized at the inner/outer surface of QRs, respectively. Moreover, such effects associated with different crystallographic structures of GaN, i.e., the wurtzite (WZ) and zinc blende (ZB) crystal structures, are also studied in detail, showing the different degenerating behavior and electron–phonon coupling strength. The results obtained in this study provide a beneficial opportunity to independently adjust dispersive spectra of the two branches of SO modes in GaN nanostructures; thus, it could be used to design and develop phonon-based detectors and sensors. [ABSTRACT FROM AUTHOR]

The magnetic properties of the lattice formed by noninteracting semiconductor quantum rings in a longitudinal magnetic field are investigated. It was shown that when the value of the Rashba parameter ξ = 1.5, the magnetization varies from positive to negative with changes in the Aharonov–Bohm flux and amplitude oscillations decrease. [ABSTRACT FROM AUTHOR]

We study the effect of the magnetic and Aharonov–Bohm (AB) flux fields on the two-photon absorption (2PA) in a quantum ring (QR) system. The expression of 2PA coefficient is expressed through the two-photon transition probability including both intraband and interband transitions. The effect of the polarization orientation of the incident light breaks the symmetry from the contribution between the AB flux field and the azimuthal quantum number. Magnetic and AB flux fields have a significant effect on the electronic properties of the QR. The 2PA spectra for intraband transitions are in the THz range and have a much higher magnitude compared to those for interband transitions, which are located in the near-infrared range. The increase in the magnetic field results in a blue-shift of the 2PA spectra for both intraband and interband transitions, whereas changes in the azimuthal quantum number only affect the spectra for interband transitions. [ABSTRACT FROM AUTHOR]

We present a unified model to describe the dynamics of optical frequency combs in quantum cascade lasers (QCLs), incorporating both ring and Fabry–Pérot (FP) cavity configurations. The model derives a modified complex Ginzburg–Landau equation (CGLE), leveraging an order parameter approach, and is capable of capturing the dynamics of both configurations, thus enabling a comparative analysis. This result demonstrates that FP QCLs, in addition to ring QCLs, belong to the same universality class of physical systems described by the CGLE, which includes, among others, systems in the fields of superconductivity and hydrodynamics. In the modified CGLE, a nonlinear integral term appears that is associated with the coupling between counterpropagating fields in the FP cavity and whose suppression yields the ring model, which is known to be properly described by a conventional CGLE. We show that this crucial term holds a key role in inhibiting the formation of harmonic frequency combs (HFCs), associated with multi-peaked localized structures, due to its anti-patterning effect. We provide support for a comprehensive campaign of numerical simulations in which we observe a higher occurrence of HFCs in the ring configuration compared to the FP case. Furthermore, the simulations demonstrate the model's capability to reproduce experimental observations, including the coexistence of amplitude and frequency modulation, linear chirp, and typical dynamic scenarios observed in QCLs. Finally, we perform a linear stability analysis of the single-mode solution for the ring case, confirming its consistency with numerical simulations and highlighting its predictive power regarding the formation of harmonic combs. [ABSTRACT FROM AUTHOR]

We conducted a joint anion photoelectron spectroscopy and theoretical investigation on hybrid lanthanum-copper oxides clusters, LaCu2On−/0 (n=4, 5). The experimental vertical detachment energies of LaCu2O4− and LaCu2O5− are determined to be 3.70 and 3.79 eV, respectively. Theoretical calculations show that the most stable structures of LaCu2O4,5− are mainly composed of LaCu2O3 six-membered ring, with an additional O atom or O2 unit interacting with the La atom. In LaCu2O4−, covalent interaction is presented between the external O atom and the LaCu2O3 six-membered ring. As for LaCu2O5− anion, a weak interaction dominated by inductive force is presented between the external O2 unit and the LaCu2O3 six-membered ring. [ABSTRACT FROM AUTHOR]

Quantum cascade lasers (QCLs) have emerged as promising candidates for generating chip-scale frequency combs in mid-infrared and terahertz wavelengths. In this work, we demonstrate frequency comb formation in ring terahertz QCLs using the injection of light from a distributed feedback (DFB) laser. The DFB design frequency is chosen to match the modes of the ring cavity (near 3.3 THz), and light from the DFB is injected into the ring QCL via a bus waveguide. By controlling the power and frequency of the optical injection, we show that combs can be selectively formed and controlled in the ring cavity. Numerical modeling suggests that this comb is primarily frequency-modulated in character, with the injection serving to trigger comb formation. We also show that the ring can be used as a filter to control the output of the DFB QCL, potentially being of interest in terahertz photonic integrated circuits. Our work demonstrates that waveguide couplers are a compelling approach for injecting and extracting radiation from ring terahertz combs and offer exciting possibilities for the generation of new comb states in terahertz, such as frequency-modulated waves, solitons, and more. [ABSTRACT FROM AUTHOR]

We report extensive numerical simulations of different models of 2D polymer rings with internal elasticity. We monitor the dynamical behavior of the rings as a function of the packing fraction to address the effects of particle deformation on the collective response of the system. In particular, we compare three different models: (i) a recently investigated model [N. Gnan and E. Zaccarelli, Nat. Phys. 15, 683 (2019)] where an inner Hertzian field providing the internal elasticity acts on the monomers of the ring, (ii) the same model where the effect of such a field on the center of mass is balanced by opposite forces, and (iii) a semi-flexible model where an angular potential between adjacent monomers induces strong particle deformations. By analyzing the dynamics of the three models, we find that in all cases, there exists a direct link between the system fragility and particle asphericity. Among the three, only the first model displays anomalous dynamics in the form of a super-diffusive behavior of the mean-squared displacement and of a compressed exponential relaxation of the density auto-correlation function. We show that this is due to the combination of internal elasticity and the out-of-equilibrium force self-generated by each ring, both of which are necessary ingredients to induce such a peculiar behavior often observed in experiments of colloidal gels. These findings reinforce the role of particle deformation, connected to internal elasticity, in driving the dynamical response of dense soft particles. [ABSTRACT FROM AUTHOR]

Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green's function formalism following the Landauer–Büttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory. [ABSTRACT FROM AUTHOR]

In this paper, we study the optical properties of a two-dimensional quantum ring with a diluted magnetic semiconductors structure. The Volcano model was chosen as the confinement potential of a quantum system. For interband optical transitions, the behavior of the absorption coefficient of a quantum ring as a function of the incident photon energy is numerically studied as a function of various values of such parameters as temperature, magnetic field, ring radius, and inner ring radius. In addition, the change in the threshold frequency as a function of the magnetic field and temperature for an interband optical transition is numerically studied. According to the results obtained, the considered parameters change the optical properties of the quantum ring. [ABSTRACT FROM AUTHOR]

We investigate the energy levels and persistent currents of MoS 2 quantum rings having different shapes and edge types in the presence of a perpendicular magnetic field by means of the tight-binding approach. We find states localized at the inner and outer boundaries of the ring. These energy levels exhibit different magnetic field dependences for the inner and outer ring states due to their different localization properties. They both exhibit the usual Aharanov–Bohm oscillations but with different oscillation periods. In the presence of spin–orbit coupling, we show distinct spin and charge persistent currents for inner and outer ring states. We find well-defined spin currents with negligibly small charge currents. This is because the local currents of spin-up and -down states flow in opposite directions. [ABSTRACT FROM AUTHOR]

To explore the edge deformation effects on the performance of a graphene quantum ring gas sensor, we considered an armchair hexagonal graphene ring connected to two semi-infinite armchair graphene nanoribbons. We calculated the current through the graphene ring upon exposure to CO, NO, CO2, and NH3 gas molecules. It is shown that the behavior of current vs bias voltage depends on the inner and outer radii, and it is independent of the graphene quantum ring width. The effect of temperature resulting from nonequilibrium Green's function (Fermi–Dirac distribution) related to leads has been investigated. The substantial finding is that the current value remains unchanged up to room temperature at a perfect graphene quantum ring and, indeed, the sensor performance is unrelated to temperature. In a deformed graphene quantum ring, the influence of temperature on sensor performance is insignificant so that it is ineffective. Furthermore, the deformation in the edges can be accidental in the formation process, which we have simulated by randomly removing the atoms of the edges, or deformation can be manual, which was simulated by removing successive edge atoms from the ring sides. In the presence of edge deformation at a constant voltage, the difference between current values related to adsorption of NO, CO, and NH3 gas molecules and the pristine ring increases. In fact, the edge deformation improves the selectivity and the sensitivity of the graphene ring gas sensor. Single vacancy and double vacancies decrease the graphene ring sensor's performance. This underlines the importance of precision in the fabrication of nonedge parts of a graphene ring, although edge deformation is worthwhile in the improvement of the gas sensor. [ABSTRACT FROM AUTHOR]

The possibility of tailoring III-V GaAs/Al0.3Ga0.7As concentric double quantum rings (CDQRs) by tuning the central barrier, width, and height of the rings brings out carrier confinement in different regimes, which make them suitable for specific applications. Using variational ansatz, Coulomb interaction and carrier localization in the rings are investigated through calculation of diamagnetism and binding energy of donor for different ring dimensions (both axial and radial). Conspicuous changes occur in the behavior of both binding energy and diamagnetism for different dimensions of the inner and outer rings. Tuning the central barrier below a critical limit favors coupling of the two rings and promotes tunneling. The effect of these modifications on the carrier localization has been investigated, which gives a good insight into selective design of CDQRs for specific applications. [ABSTRACT FROM AUTHOR]

Spin angular momentum (SAM) and orbital angular momentum (OAM) are two important fundamental degrees of freedom of light and play crucial roles in various light–matter interactions. SAM usually makes the microparticle rotate around its axis, while OAM causes orbital motion of the microparticles around the beam axis. For an optical field with only SAM, the spin-to-orbit conversion may occur under the tightly focused condition, leading to the orbital motion of probing particles. However, it is invalid for weakly focused conditions. Here, we generated an annular optical field without intrinsic OAM by weakly focusing (i.e., negligible spin-to-orbit conversion) a circularly polarized light with a linearly varying radial phase and then observed a kind of dual orbital motion of asymmetric probing particles (Janus particles) in the focal plane. The two orbital motions have opposite directions on both sides across the strongest ring of the annular optical field. In addition to the SAM, the local angular momentum (AM) density also depends on the radial intensity gradient. The radial intensity gradient has the opposite signs on both sides across the strongest ring of the annular optical field, which results in the opposite orbital motions of trapped particles. The manipulation of the local AM density and the resulting novel dual orbital effect in the absence of intrinsic OAM provide a new scene to understand the physics underlying the light–matter interaction, paving the way to some new applications involving the sorting and delivery of microparticles. [ABSTRACT FROM AUTHOR]

Inverted type-I heterostructure core/crown quantum rings (QRs) are quantum-efficient luminophores, whose spectral characteristics are highly tunable. Here, we study the optoelectronic properties of type-I core/crown CdS/CdSe QRs in the zincblende phase—over contrasting lateral size and crown width. For this, we inspect their strain profiles, transition energies, transition matrix elements, spatial charge densities, electronic bandstructures, band-mixing probabilities, optical gain spectra, maximum optical gains, and differential optical gains. Our framework uses an effective-mass envelope function theory based on the 8-band k · p method employing the valence force field model for calculating the atomic strain distributions. The gain calculations are based on the density-matrix equation and take into consideration the excitonic effects with intraband scattering. Variations in the QR lateral size and relative widths of core and crown (ergo the composition) affect their energy levels, band-mixing probabilities, optical transition matrix elements, emission wavelengths/intensities, etc. The optical gain of QRs is also strongly dimension and composition dependent with further dependency on the injection carrier density causing the band-filling effect. They also affect the maximum and differential gain at varying dimensions and compositions. [ABSTRACT FROM AUTHOR]

Within the framework of the effective-mass approximation, the effect of different static perturbations— lateral electric field, impurity donor, and eccentricity distortion—on the nonlinear optical rectification in a GaAs disc-shaped quantum ring has been investigated. For a concentric ring, the influence of the lateral electric field and off-center impurities on the intraband transitions at two values of temperature was studied in detail. We found that the optical response strongly depends on the incident light polarization and donor position within the structure. Compared with the profile at 4K, the optical rectification spectra exhibit at 77K additional peaks of reduced magnitude in the low-frequency range. The main transition peaks become smaller, while their positions remain almost unchanged with temperature. For eccentric structures, relevant differences between small and large eccentricity regimes can be observed in the electronic properties. In this case, the energy spectra and the nonlinear optical response are very sensitive to the direction of the applied electric field. The effect can be used to identify the eccentricity of the system. [ABSTRACT FROM AUTHOR]

We investigate the spin-polarized electron transport through a quantum ring whose arms are embedded by one protein-like single-helical molecule and one quantum dot, respectively. It is found that the inter-arm quantum interference leads to the enhancement of the spin polarization in this structure. Moreover, when local magnetic flux is applied through the ring, the spin polarization in the electron transport process, including the polarization strength and direction, can be further adjusted. Next in the finite-bias case, the spin polarization is also apparent and can be tuned by changing the magnetic flux or the dot level. This work provides a new scheme to manipulate the spin transport based on the single-helical molecule. [ABSTRACT FROM AUTHOR]

Microstructure evolution of three Al-Ag alloys with different Ag contents (1 wt. % Ag, 5 wt. % Ag, and 15wt. % Ag) was studied by positron annihilation spectroscopy during the aging process. In situ measurements of the positron lifetime and Doppler broadening of annihilation radiation indicate the fast formation of Ag-rich clusters during natural aging of the alloys. The formation of Ag-rich clusters was further confirmed by coincidence Doppler broadening measurements. The Ag signal reflected by the Coincidence Doppler broadening spectrum increases with increasing Ag content and is further enhanced after subsequent artificial aging at 140 °C. This might be due to the increase in the size of Ag clusters. The temperature dependence of the Doppler broadening spectra between 10K and 290K was measured for the Al-Ag alloys after natural and artificial aging. Detrapping of positrons from Ag clusters with increasing temperature was observed for all the three Al-Ag alloys after natural aging and for the Al-1wt. % Ag after artificial aging. This indicates that Ag clusters act as shallow positron trapping centers. The thermal detrapping of positrons becomes ambiguous with increasing Ag content in the alloy and is nearly invisible in the artificially aged Al-5wt. % Ag and Al-15wt. % Ag. The positron binding energy of the Ag cluster is roughly estimated to be about 18.8 meV and 50 meV in the Al-1 wt. % Ag sample after natural aging and artificial aging at 140 °C, respectively, which suggests that the confinement of positrons in the quantum-dot like state depends on the size or chemical composition of clusters. Theoretical calculations confirm positron trapping by Ag nanoclusters, and the confinement of positrons is enhanced with increasing Ag cluster size. [ABSTRACT FROM AUTHOR]

This paper presents the study of the electronic and optical properties of multi-layer phosphorene quantum rings (PQRs) by using the tight-binding model. The effects of the hole size and position, along with the number of layers in the PQR on the energy levels and the optical spectrum, are numerically analyzed. The calculations show that the electronic and optical properties can be tuned by the hole size, the hole position, and the number of layers. The coupling of the inner and outer edges depends strongly on the position of the hole. The findings suggest that the layer-dependent optical properties of phosphorene quantum dots and PQRs are related to the parity of the number of layers. [ABSTRACT FROM AUTHOR]

Genuine random numbers can be produced beyond a shadow of doubt through the intrinsic randomness provided by quantum mechanics theories. While many degrees of freedom have been investigated for randomness generation, adequate attention has not been paid to the orbital angular momentum of light. In this work, we present a quantum random number generator based on the intrinsic randomness inherited from the superposition of orbital angular momentum modes caused by the cross talk inside a ring-core fiber. We studied two possible cases: a first one, device-dependent, where the system is trusted, and a second one, semi-device-independent, where the adversary can control the measurements. We experimentally realized the former, extracted randomness, and, after privacy amplification, we achieved a generation rate higher than 10 Mbit/s. In addition, we presented a possible realization of the semi-device-independent protocol using a newly introduced integrated silicon photonic chip. Our work can be considered as a starting point for novel investigation of quantum random number generators based on the orbital angular momentum of light. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the emission of individual GaAs/AlGaAs complex nano-systems composed of two concentric and topologically distinct quantum nanostructures, namely, a quantum dot and a quantum ring. Time resolved, temperature and excitation power density dependence of the photoluminescence from single and ensemble dot/ring structures have been used in order to determine the carrier dynamics. Despite the small spatial separation between the dot and the ring, the exciton dynamics in the two nanostructures is completely decoupled at low temperatures. At higher temperatures, we observe a clear change in the carrier dynamics, which shows the onset of the coupling between the two nanostructures. We attribute such change in carrier dynamics to the breaking of topology induced selection rules which allows the transfer of the carriers between the dot and the ring via an electronic quantum state, common to the two nanostructures. [ABSTRACT FROM AUTHOR]

The influence of Rashba spin orbit interaction on the optical properties of two dimensional mesoscopic ring has been investigated in the presence of uniform perpendicular magnetic field. The Schrodinger equation for the Rashba coupled system is solved by effective mass approximation and diagonalization technique. Using the calculated energies and eigenfunctions, the laser field induced change in refractive index and optical absorption have been studied under the density matrix formalism. It has been found that Rashba spin orbit interaction removes the intersection of energy levels; however, avoided crossings are observed at finite magnetic field. At sufficient high values of Rashba coupling or laser intensity, the optical response of quantum ring is found to be dominated by third order nonlinear term. Also, Rashba interaction shifts the value of magnetic field that is needed to suppress the absorption drastically and to pass the incident light unattenuated. The results reveal that the geometry of the ring plays an important role in determining the magnitude of nonlinear absorption coefficient and change in refractive index which enable us to design the device with optimum efficiency. [ABSTRACT FROM AUTHOR]

Natural orbitals (NOs) are central constituents for evaluating correlation energies through efficient approximations. Here, we report the closed-form expression of the NOs of two-electron quantum rings, which are prototypical finite-extension systems and new starting points for the development of exchange-correlation functionals in density functional theory. We also show that the natural occupation numbers for these two-electron paradigms are in general non-vanishing and follow the same power law decay as atomic and molecular two-electron systems. [ABSTRACT FROM AUTHOR]

We report the results of continuous and time-resolved photoluminescence measurements on type-II GaSb quantum rings embedded within GaAs/AlxGa1-xAs quantum wells. A range of samples were grown with different well widths, compensation-doping concentrations within the wells, and number of quantum-ring layers. We find that each of these variants have no discernible effect on the radiative recombination, except for the very narrowest (5 nm) quantum well. In contrast, single-particle numerical simulations of the sample predict changes in photoluminescence energy of up to 200 meV. This remarkable difference is explained by the strong Coulomb binding of electrons to rings that are multiply charged with holes. The resilience of the emission to compensation doping indicates that multiple hole occupancy of the quantum rings is required for efficient carrier recombination, regardless of whether these holes come from doping or excitation. [ABSTRACT FROM AUTHOR]

The origin of anomalous current-carrying edge states in quasi-two-dimensional quantum samples with an insulating interior is currently mysterious. We propose to address this issue using a hybrid setup, an interferometric phase-sensitive configuration of two independent scanning probe tips, normal and superconducting, able to realize the quantum interference effect of quasiparticle currents moving in different directions along the metallic-like one-dimensional near-boundary channels. To simulate the dissipationless edge currents, we consider a quantum material with a simple Corbino disk geometry and analyze how the differential conductance spectrum depends on the distance between the two tips, the applied voltage bias, and the presence of a magnetic field. An essential difference between classical and quantum expectations should clarify the enigmatic origin of the long-range conducting modes observed in different materials at low temperatures. Strong dependence on the applied magnetic field can be useful for practical implementation of the quantum effects associated with the phase difference of electron wave functions in the ring geometry. [ABSTRACT FROM AUTHOR]

Using first-principles computations, we study the effect of epitaxial strains on electronic structure variations across ZnSe/ZnTe nano-heterostructures. Epitaxial strains of various types are modeled using pseudomorphic ZnSe/ZnTe heterostructures. We find that a wide range of band gaps (spanning the visible solar spectrum) and band offsets (0-1.5 eV) is accessible across the heterostructures in a controllable manner via reasonable levels of epitaxial strain. In addition to quantum confinement effects, strain in ZnSe/ZnTe heterostructures may thus be viewed as a powerful degree of freedom that can enable the rational design of optoelectronic devices. [ABSTRACT FROM AUTHOR]

The interplay between structural properties and charge transfer in self-assembled quantum ring (QR) chains grown by molecular beam epitaxy on top of an InGaAs/GaAs quantum dot (QD) superlattice template is analyzed and characterized. The QDs and QRs are vertically stacked and laterally coupled as well as aligned within each layer due to the strain field distributions that governs the ordering. The strong interdot coupling influences the carrier transfer both along as well as between chains in the ring layer and dot template structures. A qualitative contrast between different dynamic models has been developed. By combining temperature and excitation intensity effects, the tuning of the photoluminescence gain for either the QR or the QD mode is attained. The information obtained here about relaxation parameters, energy scheme, interlayer and interdot coupling resulting in creation of 1D structures is very important for the usage of such specific QR-QD systems for applied purposes such as lasing, detection, and energy-harvesting technology of future solar panels. [ABSTRACT FROM AUTHOR]

Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics. [ABSTRACT FROM AUTHOR]

The influence of Rashba spin-orbit interaction on the transport properties of the two-dimensional quantum ring with finite width has been investigated in the presence of the uniform perpendicular magnetic field. The dependence of magnetoresistance on the magnetic field and Rashba spin-orbit coupling parameter in quantum ring with finite width are investigated. It was shown that in the presence Rashba spin-orbit interaction that the beating pattern is destroyed. [ABSTRACT FROM AUTHOR]

We introduce a superconducting coplanar waveguide, in the form of a ring resonator, as a quantum bus for circuit quantum electrodynamics (circuit QED). Due to its unique symmetry, the amplitude of the electromagnetic field inside is uniform along the resonator, which in principle leads to a location independent coupling between qubits and the resonator. For an experimental demonstration, we designed and fabricated a ring resonator capacitively coupled to two tunable Xmon superconducting qubits. We showed that nearly identical coupling was achieved between individual qubits and the resonator. In addition, the resonator was also used as a high quality quantum bus for generating Bell states between the qubits with a fidelity of F = 98.6 % , although an interference effect must be included for understanding the effective coupling between the two qubits. Our results suggest that ring resonators can be a useful addition to the toolbox of circuit QED. [ABSTRACT FROM AUTHOR]

The effect of shape and size anisotropy on unipolar intraband transitions of holes in quantum dots (QDs) is studied. The optical matrix elements are calculated for transitions of holes in valence band. To get the optical matrix elements, energy eigenvalues and eigenvectors are calculated using 4×4 Luttinger Hamiltonian in the effective mass approximation. The formulation is applied to InGaAs/GaAs QD with parabolic confinement potential in xy-plane. The optical matrix elements for intraband hole transitions are calculated for x and y polarised light. The transitions are considered from ground state to other excited states. The effect of In concentration on optical matrix elements is also investigated. It is important to note that the transitions of holes are governed by the character of initial and final states for different light polarisations that give specific transition selection rules. It is found that the polarisation is strongly dependent on the in-plane anisotropy of the QDs. [ABSTRACT FROM AUTHOR]

We investigate the electric field tuning of the phonon-assisted hole spin relaxation in single self-assembled In1-xGaxAs/GaAs quantum dots (QDs), using an atomistic empirical pseudopotential method. We find that the electric field along the growth direction can tune the hole spin relaxation time for more than one order of magnitude. The electric field can prolong or shorten the hole spin lifetime and the tuning shows an asymmetry in terms of the field direction. The asymmetry is more pronounced for the taller dot. The results show that the electric field is an effective way to tune the hole spin-relaxation in self-assembled QDs. [ABSTRACT FROM AUTHOR]

The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga0.7Al0.3As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring. [ABSTRACT FROM AUTHOR]

We extend a special kind of localized state trapped at the intersection due to the geometric confinement, first proposed in a three-terminal-opening T-shaped structure [L. A. Openov, Europhys. Lett. 55, 539 (2001)], into a ring geometry with a tangent connection to the wire. In this ring geometry, there exists one localized state trapped at the intersection with energy lying inside the lowest subband. We systematically study this localized state and the resulting Fano-type interference due to the coupling between this localized state and the continuum ones. It is found that the increase of inner radius of the ring weakens the coupling to the continuum ones and the asymmetric Fano dip fades away. A wide energy gap in transmission appears due to the interplay of two types of antiresonances: the Fano-type antiresonance and the structure antiresonance. The size of this antiresonance gap can be modulated by adjusting the magnetic flux. Moreover, a large transmission amplitude can be obtained in the same gap area. The strong robustness of the antiresonance gap is demonstrated and shows the feasibility of the proposed geometry for a real application. [ABSTRACT FROM AUTHOR]

The optical parameters describing the sub-bandgap response of GaSb/GaAs quantum rings solar cells have been obtained from photocurrent measurements using a modulated pseudomonochromatic light source in combination with a second, continuous photo-filling source. By controlling the charge state of the quantum rings, the photoemission cross-sections describing the two-photon sub-bandgap transitions could be determined independently. Temperature dependent photo-response measurements also revealed that the barrier for thermal hole emission from the quantum rings is significantly below the quantum ring localisation energy. The temperature dependence of the sub-bandgap photo-response of the solar cell is also described in terms of the photo- and thermal-emission characteristics of the quantum rings. [ABSTRACT FROM AUTHOR]

Isotropic spin analysis is a key step in spintronics and could be useful in quantum information, which usually requires light as an essential component. It has not yet been realized in a solid-state device. Here, we propose an isotropic all electrical spin analyzer designed from a quantum ring with spin–orbit couplings by analytically and numerically modeling how the charge transmission rate depends on the polarization of the incident spin. The spin transport features are also demonstrated to be robust against ring structure defects, disorder, and a bias between the two leads at finite temperature in the nanoscale ring. Similar to the light polarizer/analyzer, this interesting two-dimensional electron system can be designed as a spin filter, spin polarizer, and a general spin analyzer with high resolution by simply tuning the spin–orbit couplings, which paves the way for realizing the tunable and integrable spintronics devices. [ABSTRACT FROM AUTHOR]

We have employed a variable stripe length method in order to measure the optical gain of GaAs/AlGaAs quantum rings. Although the large lateral diameter of quantum rings (∼ 50 nm) with a few nm size distribution is expected to cause a small spectral inhomogeneity (∼ 1 %), a broad gain width (∼ 300 meV) was observed. This result was attributed to a variation of the vertical heights and variations in localized states that exhibit crescent shaped wavefunctions, whereby the energy levels are distributed over a broad spectral range. When the excitation intensity is decreased, irregular peaks appear in the gain spectrum gradually. Similar phenomena were also observed as the temperature increased. We conclude that excited carriers in quantum rings are distributed stochastically at various localized states and that the population inversion is sensitive to both excitation intensity and temperature. [ABSTRACT FROM AUTHOR]

Cross-correlated noise measurements are performed in etched Al x Ga 1 − x As/GaAs based quantum rings in equilibrium at a bath temperature of T bath = 4.2 K. The measured white noise exceeds the thermal (Johnson–Nyquist) noise expected from the measured electron temperature T e and the electrical resistance R. This excess part of the white noise decreases as T bath increases and vanishes for T bath ≥ 12 K. Excess noise is neither observed if one arm of a quantum ring is depleted of electrons nor in one-dimensional-constrictions that have a length and width comparable to the quantum rings. A model is presented that suggests that the excess noise originates from the correlation of noise sources, mediated by phase-coherent propagation of electrons. [ABSTRACT FROM AUTHOR]

We examine the influence of quantum dot (QD) morphology on the optical properties of two-dimensional (2D) GaSb/GaAs multilayers, with and without three-dimensional nanostructures. Using nanostructure sizes from scanning transmission electron microscopy and local Sb compositions from local-electrode atom-probe tomography as input into self-consistent Schrödinger–Poisson simulations based on 8 × 8 k·p theory, we compute confinement energies for QDs, circular arrangements of smaller QDs, termed QD-rings, and 2D layers on GaAs substrates. The computed confinement energies and the measured photoluminescence emission energies increase from QDs to QD-rings to 2D layers, enabling direct association of nanostructure morphologies with the optical properties of the GaSb/GaAs multilayers. This work opens up opportunities for tailoring near to far infrared optoelectronic devices by varying the QD morphology. [ABSTRACT FROM AUTHOR]

The influence of exchange interaction on the transport properties of a two-dimensional diluted magnetic semiconductor quantum ring with finite width has been investigated in the presence of a uniform perpendicular magnetic field. The dependence of magnetoresistance on the magnetic field, Mn concentration, and quantum ring width are investigated. In the absence of exchange interaction, a typical beating pattern with well-defined node-positions in the oscillating magnetoresistance is observed. It was shown that in the present exchange interactions the beating pattern is destroyed. [ABSTRACT FROM AUTHOR]

Over the past few decades, superconducting circuits have been used to realize various novel electronic devices such as quantum bits, SQUIDs, parametric amplifiers, etc. One domain, however, where superconducting circuits fall short is information storage. Superconducting memories are based on the quantization of magnetic flux in superconducting loops. Standard implementations store information as magnetic flux quanta in a superconducting loop interrupted by two Josephson junctions (i.e., a SQUID). However, due to the large inductance required, the size of the SQUID loop cannot be scaled below several micrometers, resulting in low-density memory chips. Here, we propose a scalable memory consisting of a voltage-biased superconducting ring threaded by a half-quantum flux bias. By numerically solving the time-dependent Ginzburg-Landau equations, we show that applying a time-dependent bias voltage in the microwave range constitutes a writing mechanism to change the number of stored flux quanta within the ring. Since the proposed device does not require a large loop inductance, it can be scaled down, enabling a high-density memory technology. [ABSTRACT FROM AUTHOR]

An alternative strategy is proposed to achieve visible-blind ultraviolet (UV) monitoring. By introducing photochromic spiropyran (SP) molecules into the dielectric as the charge trapping layer, organic field-effect transistor (OFET) memories show a selective response to UV light and are inert to visible light. The photoisomerization of SP from the ring-close to ring-open states under UV illumination modifies its electronic structure, which facilitates electron trapping into the charge trapping layer and accordingly induces the memory effect. UV exposure recording can be realized by cumulative and nonvolatile electron trapping, enabling potential applications of OFET memories for UV monitoring in wearable electronics. [ABSTRACT FROM AUTHOR]

It is shown by numerical simulations within a regularized Biot-Savart law that dynamical systems of two or three leapfrogging coaxial quantum vortex rings having a core width ξ and initially placed near a torus of radii R0 and r0 can be three-dimensionally (quasi-)stable in some regions of parameters Λ = ln(R0/ξ) and W = r0/R0. At fixed Λ, stable bands on W are intervals between non-overlapping main parametric resonances for different (integer) azimuthal wave numbers m. The stable intervals are most wide (ΔW ∼ 0.01–0.05) between m-pairs (1, 2) and (2, 3) at Λ ≈ 4–12, thus corresponding to micro/mesoscopic sizes of vortex rings in the case of superfluid 4He. With four and more rings, at least for W > 0.1, resonances overlap for all Λ and no stable domains exist. [ABSTRACT FROM AUTHOR]