Showing papers on "Stark effect published in 2021"

Single-molecule laser nanospectroscopy with micro-electron volt energy resolution.

Abstract: Ways to characterize and control excited states at the single-molecule and atomic levels are needed to exploit excitation-triggered energy-conversion processes. Here, we present a single-molecule spectroscopic method with micro-electron volt energy and submolecular-spatial resolution using laser driving of nanocavity plasmons to induce molecular luminescence in scanning tunneling microscopy. This tunable and monochromatic nanoprobe allows state-selective characterization of the energy levels and linewidths of individual electronic and vibrational quantum states of a single molecule. Moreover, we demonstrate that the energy levels of the states can be finely tuned by using the Stark effect and plasmon-exciton coupling in the tunneling junction. Our technique and findings open a route to the creation of designed energy-converting functions by using tuned energy levels of molecular systems.

Localization-limited exciton oscillator strength in colloidal CdSe nanoplatelets revealed by the optically induced stark effect.

Abstract: 2D materials are considered for applications that require strong light-matter interaction because of the apparently giant oscillator strength of the exciton transitions in the absorbance spectrum. Nevertheless, the effective oscillator strengths of these transitions have been scarcely reported, nor is there a consistent interpretation of the obtained values. Here, we analyse the transition dipole moment and the ensuing oscillator strength of the exciton transition in 2D CdSe nanoplatelets by means of the optically induced Stark effect (OSE). Intriguingly, we find that the exciton absorption line reacts to a high intensity optical field as a transition with an oscillator strength FStark that is 50 times smaller than expected based on the linear absorption coefficient. We propose that the pronounced exciton absorption line should be seen as the sum of multiple, low oscillator strength transitions, rather than a single high oscillator strength one, a feat we assign to strong exciton center-of-mass localization. Within the quantum mechanical description of excitons, this 50-fold difference between both oscillator strengths corresponds to the ratio between the coherence area of the exciton’s center of mass and the total area, which yields a coherence area of a mere 6.1 nm2. Since we find that the coherence area increases with reducing temperature, we conclude that thermal effects, related to lattice vibrations, contribute to exciton localization. In further support of this localization model, we show that FStark is independent of the nanoplatelet area, correctly predicts the radiative lifetime, and lines up for strongly confined quantum dot systems.

Rashba valleys and quantum Hall states in few-layer black arsenic.

Abstract: Exciting phenomena may emerge in non-centrosymmetric two-dimensional electronic systems when spin-orbit coupling (SOC)1 interplays dynamically with Coulomb interactions2,3, band topology4,5 and external modulating forces6-8. Here we report synergetic effects between SOC and the Stark effect in centrosymmetric few-layer black arsenic, which manifest as particle-hole asymmetric Rashba valley formation and exotic quantum Hall states that are reversibly controlled by electrostatic gating. The unusual findings are rooted in the puckering square lattice of black arsenic, in which heavy 4p orbitals form a Brillouin zone-centred Γ valley with pz symmetry, coexisting with doubly degenerate D valleys of px origin near the time-reversal-invariant momenta of the X points. When a perpendicular electric field breaks the structure inversion symmetry, strong Rashba SOC is activated for the px bands, which produces spin-valley-flavoured D± valleys paired by time-reversal symmetry, whereas Rashba splitting of the Γ valley is constrained by the pz symmetry. Intriguingly, the giant Stark effect shows the same px-orbital selectiveness, collectively shifting the valence band maximum of the D± Rashba valleys to exceed the Γ Rashba top. Such an orchestrating effect allows us to realize gate-tunable Rashba valley manipulations for two-dimensional hole gases, hallmarked by unconventional even-to-odd transitions in quantum Hall states due to the formation of a flavour-dependent Landau level spectrum. For two-dimensional electron gases, the quantization of the Γ Rashba valley is characterized by peculiar density-dependent transitions in the band topology from trivial parabolic pockets to helical Dirac fermions.

Stark shift and exciton binding energy in parabolic quantum dots: hydrostatic pressure, temperature, and electric field effects

Abstract: The temperature, hydrostatic pressure, and external electric field effects on the confined exciton in cylindrical quantum dots by considering a parabolic confining potential are investigated. The effects of these external perturbations on the binding energy and interband emission energy are calculated numerically by adopting the variational method within the effective mass approximation. Our findings indicate that the exciton binding energy and interband emission energy depend significantly on decreasing electric field, diminishing temperature, and enhancing the hydrostatic pressure. The contribution of the electric field on the binding energy becomes more important for wide axial parabolic quantum well. We have also shown that the Stark effect of exciton diminishes almost linearly with increasing hydrostatic pressure. Furthermore, the electric field and the quantum dot height lead to enhancing the Stark shift. The behaviour of the excitonic Stark shift as a function of the applied electric field proves the existence of a dipole moment. This physical parameter becomes important for the weak confinement regime.

Interlayer exciton mediated second harmonic generation in bilayer MoS2.

Abstract: Second-harmonic generation (SHG) is a non-linear optical process, where two photons coherently combine into one photon of twice their energy. Efficient SHG occurs for crystals with broken inversion symmetry, such as transition metal dichalcogenide monolayers. Here we show tuning of non-linear optical processes in an inversion symmetric crystal. This tunability is based on the unique properties of bilayer MoS2, that shows strong optical oscillator strength for the intra- but also interlayer exciton resonances. As we tune the SHG signal onto these resonances by varying the laser energy, the SHG amplitude is enhanced by several orders of magnitude. In the resonant case the bilayer SHG signal reaches amplitudes comparable to the off-resonant signal from a monolayer. In applied electric fields the interlayer exciton energies can be tuned due to their in-built electric dipole via the Stark effect. As a result the interlayer exciton degeneracy is lifted and the bilayer SHG response is further enhanced by an additional two orders of magnitude, well reproduced by our model calculations. Since interlayer exciton transitions are highly tunable also by choosing twist angle and material combination our results open up new approaches for designing the SHG response of layered materials. Efficient second-harmonic generation (SHG) occurs for crystals with broken inversion symmetry, such as transition metal dichalcogenide monolayers. Here the authors show SHG tuning in bilayer MoS2 - an inversion-symmetric crystal - mediated by interlayer excitons.

Optical control of the valley Zeeman effect through many-exciton interactions

Abstract: Charge carriers in two-dimensional transition metal dichalcogenides (TMDs), such as WSe2, have their spin and valley-pseudospin locked into an optically addressable index that is proposed as a basis for future information processing1,2. The manipulation of this spin–valley index, which carries a magnetic moment3, requires tuning its energy. This is typically achieved through an external magnetic field (B), which is practically cumbersome. However, the valley-contrasting optical Stark effect achieves valley control without B, but requires large incident powers4,5. Thus, other efficient routes to control the spin–valley index are desirable. Here we show that many-body interactions among interlayer excitons (IXs) in a WSe2/MoSe2 heterobilayer (HBL) induce a steady-state valley Zeeman splitting that corresponds to B ≈ 6 T. This anomalous splitting, present at incident powers as low as microwatts, increases with power and is able to enhance, suppress or even flip the sign of a B-induced splitting. Moreover, the g-factor of valley Zeeman splitting can be tuned by ~30% with incident power. In addition to valleytronics, our results could prove helpful to achieve optical non-reciprocity using two-dimensional materials. Many-body interactions amongst interlayer excitons in a WSe2/MoSe2 heterobilayer give rise to a strong and tunable effective magnetic field enabling the control of the valley pseudospin.

Continuous radio-frequency electric-field detection through adjacent Rydberg resonance tuning

Abstract: We demonstrate the use of multiple atomic-level Rydberg-atom schemes for continuous frequency detection of radio-frequency (RF) fields. Resonant detection of RF fields by electromagnetically induced transparency and Autler-Townes (AT) splitting in Rydberg atoms is typically limited to frequencies within the narrow bandwidth of a Rydberg transition. By applying a second field resonant with an adjacent Rydberg transition, far-detuned fields can be detected through a two-photon resonance AT splitting. This two-photon AT splitting method is several orders of magnitude more sensitive than off-resonant detection using the Stark shift. We present the results of various experimental configurations and a theoretical analysis to illustrate the effectiveness of this multiple level scheme. These results show that this approach allows for the detection of frequencies in a continuous band between resonances with adjacent Rydberg states.

Non-equilibrium band broadening, gap renormalization and band inversion in black phosphorus

Abstract: Black phosphorous (BP) is a layered semiconductor with high carrier mobility, anisotropic optical response and wide bandgap tunability. In view of its application in optoelectronic devices, understanding transient photo-induced effects is crucial. Here, we investigate by time- and angle-resolved photoemission spectroscopy BP in its pristine state and in the presence of Stark splitting, chemically induced by Cs ad-sorption. We show that photo-injected carriers trigger bandgap renormalization and a concurrent valence band attening caused by Pauli blocking. In the biased sample, photoexcitation leads to a long-lived (ns) surface photovoltage of few hundreds mV that counterbalances the Cs-induced surface band bending. This allows us to disentangle bulk from surface electronic states and to clarify the mechanism underlying the band inversion observed in bulk samples.

Nondipole modification of the ac Stark effect in above-threshold ionization

Abstract: Above-threshold ionization (ATI) of atoms in intense laser pulses produces photoelectron momentum distributions that exhibit discrete concentric circles related to the absorption of more photons than required to exceed the ionization threshold. Using numerical solutions of the one-electron time-dependent Schr\"odinger equation beyond the electric dipole approximation for circularly polarized laser pulses, we show that the geometric centers of ATI rings are counterintuitively shifted against the propagation direction of the light, i.e., in the direction opposite to the on-average transferred photon momentum. From a comparison with a simple model based on energy considerations, we identify a nondipole modification of the ac Stark effect for electron continuum states as the origin of our observation.

Measurement of electron density in transient spark discharge by simple interferometry

Abstract: In this work, the electron density in an atmospheric-pressure Ar transient spark (TS) discharge was measured using an interferometric method. The discharge was operated in a pin-to-plate electrode configuration by applying DC voltages of 7–10 kV. The TS discharge current occurred within a short duration of less than 100 ns, and the peak current was as high as ~ 3 A. Below 8 kV, the TS discharge had weak, irregular emission, making it difficult to measure the electron density using Stark broadening. Here, we developed a simple He–Ne laser Michelson interferogram method for estimating the electron density of unstable TS discharge. Above 8 kV, the electron density values obtained from Stark broadening and the Michelson interferogram were similar and proportional to the dissipated energy. This interferogram method could be adopted to measure the electron density of unstable discharge plasmas, which was measured to be 1 × 1016 cm−3 at 7.0 kV in this experiment.

Investigation of the Stark Effect on a Centrosymmetric Quantum Emitter in Diamond

Abstract: Quantum emitters in diamond are leading optically accessible solid-state qubits. Among these, Group IV-vacancy defect centers have attracted great interest as coherent and stable optical interfaces to long-lived spin states. Theory indicates that their inversion symmetry provides first-order insensitivity to stray electric fields, a common limitation for optical coherence in any host material. Here we experimentally quantify this electric field dependence via an external electric field applied to individual tin-vacancy (SnV) centers in diamond. These measurements reveal that the permanent electric dipole moment and polarizability are at least 4 orders of magnitude smaller than for the diamond nitrogen vacancy (NV) centers, representing the first direct measurement of the inversion symmetry protection of a Group IV defect in diamond. Moreover, we show that by modulating the electric-field-induced dipole we can use the SnV as a nanoscale probe of local electric field noise, and we employ this technique to highlight the effect of spectral diffusion on the SnV.

Valley-selective optical Stark effect of exciton-polaritons in a monolayer semiconductor

Abstract: Selective breaking of degenerate energy levels is a well-known tool for coherent manipulation of spin states. Though most simply achieved with magnetic fields, polarization-sensitive optical methods provide high-speed alternatives. Exploiting the optical selection rules of transition metal dichalcogenide monolayers, the optical Stark effect allows for ultrafast manipulation of valley-coherent excitons. Compared to excitons in these materials, microcavity exciton-polaritons offer a promising alternative for valley manipulation, with longer lifetimes, enhanced valley coherence, and operation across wider temperature ranges. Here, we show valley-selective control of polariton energies in WS2 using the optical Stark effect, extending coherent valley manipulation to the hybrid light-matter regime. Ultrafast pump-probe measurements reveal polariton spectra with strong polarization contrast originating from valley-selective energy shifts. This demonstration of valley degeneracy breaking at picosecond timescales establishes a method for coherent control of valley phenomena in exciton-polaritons. Microcavity exciton-polaritons in atomically thin semiconductors are a promising platform for valley manipulation. Here, the authors show valley-selective control of polariton energies in monolayer WS2 using the optical Stark effect, thereby extending coherent valley manipulation to a hybrid light-matter regime

Tunable photon blockade with a single atom in a cavity under electromagnetically induced transparency

Abstract: We present an experimental proposal to achieve a strong photon blockade by employing electromagnetically induced transparency (EIT) with a single alkaline-earth-metal atom trapped in an optical cavity. In the presence of optical Stark shift, both the second-order correlation function and cavity transmission exhibit asymmetric structures between the red and blue sidebands of the cavity. For a weak control field, the photon quantum statistics for the coherent transparency window (i.e., atomic quasi-dark-state resonance) are insensitive to the Stark shift, which should also be immune to the spontaneous emission of the excited state by taking advantage of the intrinsic dark-state polariton of EIT. Interestingly, by exploiting the interplay between the Stark shift and control field, the strong photon blockade at atomic quasi-dark-state resonance has an optimal second-order correlation function g(2)(0)∼10−4 and a high cavity transmission simultaneously. The underlying physical mechanism is ascribed to the Stark shift enhanced spectrum anharmonicity and the EIT hosted strong nonlinearity with loss-insensitive atomic quasi-dark-state resonance, which is essentially different from the conventional proposal with emerging Kerr nonlinearity in cavity-EIT. Our results reveal a new strategy to realize high-quality single photon sources, which could open up a new avenue for engineering nonclassical quantum states in cavity quantum electrodynamics.

Quantum-confined Stark effect and mechanisms of its screening in InGaN/GaN light-emitting diodes with a tunnel junction.

Abstract: Nitride-based light-emitting diodes (LEDs) are well known to suffer from a high built-in electric field in the quantum wells (QWs). In this paper we determined to what extent the electric field is screened by injected current. In our approach we used high pressure to study this evolution. In LEDs with a narrow QW (2.6 nm) we found that even at a high injection current a large portion of built-in field remains. In LEDs with very wide QWs (15 and 25 nm) the electric field is fully screened even at the lowest currents. Furthermore, we examined LEDs with a tunnel junction in two locations – above and below the active region. This allowed us to study the cases of parallel and antiparallel fields in the well and in the barriers.

Molecular Origin of the Asymmetric Photoluminescence Spectra of CsPbBr3 at Low Temperature.

Abstract: CsPbBr3 has received wide attention due to its superior emission yield and better thermal stability compared to other organic-inorganic lead halide perovskites. In this study, through an interplay of theory and experiments, we investigate the molecular origin of the asymmetric low-temperature photoluminescence spectra of CsPbBr3. We conclude that the origin of this phenomenon lies in a local dipole moment (and the induced Stark effect) due to the preferential localization of Cs+ in either of two off-center positions of the empty space between the surrounding PbBr6 octahedra. With increasing temperature, Cs+ ions are gradually occupying positions closer and closer to the center of the cavities. The gradual loss of ordering in the Cs+ position with increasing temperature is the driving force for the formation of tetragonal-like arrangements within the orthorhombic lattice.

Anomalous Stark shift of excitonic complexes in monolayer WS 2

Abstract: Monolayer transition-metal dichalcogenide (TMDC) semiconductors host strongly bound two-dimensional excitonic complexes, and form an excellent platform for probing many-body physics through manipulation of Coulomb interaction. The quantum confined Stark effect is one of the routes to dynamically tune the emission line of these excitonic complexes. In this paper, using a high-quality graphene/hexagonal boron nitride $(\mathrm{hBN})/{\mathrm{WS}}_{2}/\mathrm{hBN}/\mathrm{Au}$ vertical heterojunction, we demonstrate an out-of-plane electric-field driven change in the sign of the Stark shift from blue to red for four different excitonic species, namely, the neutral exciton, the charged exciton (trion), the charged biexciton, and the defect-bound exciton. Such universal nonmonotonic Stark shift with electric field arises from a competition between the conventional quantum confined Stark effect driven redshift and a suppressed binding-energy driven anomalous blueshift of the emission lines, with the latter dominating in the low-field regime. We also find that the encapsulating environment of the monolayer TMDC plays an important role in wave-function spreading, and hence in determining the magnitude of the blue Stark shift. The results for neutral and charged excitonic species are in excellent agreement with calculations from the Bethe-Salpeter equation that use a seven-band per spin tight-binding Hamiltonian. The findings have important implications in probing many-body interaction in two dimensions as well as in developing layered semiconductor based tunable optoelectronic devices.

Multipole-moment effects in ion-molecule reactions at low temperatures: part I - ion-dipole enhancement of the rate coefficients of the He+ + NH3 and He+ + ND3 reactions at collisional energies Ecoll/kB near 0 K.

Abstract: The energy dependence of the rates of the reactions between He+ and ammonia (NY3, Y = {H,D}), forming NY2+, Y and He as well as NY+, Y2 and He, and the corresponding product branching ratios have been measured at low collision energies Ecoll between 0 and kB·40 K using a recently developed merged-beam technique [Allmendinger et al., ChemPhysChem, 2016, 17, 3596]. To avoid heating of the ions by stray electric fields, the reactions are observed within the large orbit of a highly excited Rydberg electron. A beam of He Rydberg atoms was merged with a supersonic beam of ammonia using a curved surface-electrode Rydberg–Stark deflector, which is also used for adjusting the final velocity of the He Rydberg atoms, and thus the collision energy. A collision-energy resolution of about 200 mK was reached at the lowest Ecoll values. The reaction rate coefficients exhibit a sharp increase at collision energies below ∼kB·5 K and pronounced deviations from Langevin-capture behaviour. The experimental results are interpreted in terms of an adiabatic capture model describing the rotational-state-dependent orientation of the ammonia molecules by the electric field of the He+ atom. The model faithfully describes the experimental observations and enables the identification of three classes of |JKMp〉 rotational states of the ammonia molecules showing different low-energy capture behaviour: (A) high-field-seeking states with |KM| ≥ 1 correlating to the lower component of the umbrella-motion tunnelling doublet at low fields. These states undergo a negative linear Stark shift, which leads to strongly enhanced rate coefficients; (B) high-field-seeking states subject to a quadratic Stark shift at low fields and which exhibit only weak rate enhancements; and (C) low-field-seeking states with |KM| ≥ 1. These states exhibit a positive Stark shift at low fields, which completely suppresses the reactions at low collision energies. Marked differences in the low-energy reactivity of NH3 and ND3—the rate enhancements in ND3 are more pronounced than in NH3—are quantitatively explained by the model. They result from the reduced magnitudes of the tunnelling splitting and rotational intervals in ND3 and the different occupations of the rotational levels in the supersonic beam caused by the different nuclear-spin statistical weights. Thermal capture rate constants are derived from the model for the temperature range between 0 and 10 K relevant for astrochemistry. Comparison of the calculated thermal capture rate coefficients with the absolute reaction rates measured above 27 K by Marquette et al. (Chem. Phys. Lett., 1985, 122, 431) suggests that only 40% of the close collisions are reactive.

Strong spin-orbit coupling inducing Autler-Townes effect in lead halide perovskite nanocrystals.

Abstract: Manipulation of excitons via coherent light-matter interaction is a promising approach for quantum state engineering and ultrafast optical modulation. Various excitation pathways in the excitonic multilevel systems provide controllability more efficient than that in the two-level system. However, these control schemes have been restricted to limited control-light wavelengths and cryogenic temperatures. Here, we report that lead halide perovskites can lift these restrictions owing to their multiband structure induced by strong spin-orbit coupling. Using CsPbBr3 perovskite nanocrystals, we observe an anomalous enhancement of the exciton energy shift at room temperature with increasing control-light wavelength from the visible to near-infrared region. The enhancement occurs because the interconduction band transitions between spin-orbit split states have large dipole moments and induce a crossover from the two-level optical Stark effect to the three-level Autler-Townes effect. Our finding establishes a basis for efficient coherent optical manipulation of excitons utilizing energy states with large spin-orbit splitting.

Testing the Limitations of MD-Based Local Electric Fields Using the Vibrational Stark Effect in Solution: Penicillin G as a Test Case

Abstract: Noncovalent interactions underlie nearly all molecular processes in the condensed phase from solvation to catalysis. Their quantification within a physically consistent framework remains challenging. Experimental vibrational Stark effect (VSE)-based solvatochromism can be combined with molecular dynamics (MD) simulations to quantify the electrostatic forces in solute-solvent interactions for small rigid molecules and, by extension, when these solutes bind in enzyme active sites. While generalizing this approach toward more complex (bio)molecules, such as the conformationally flexible and charged penicillin G (PenG), we were surprised to observe inconsistencies in MD-based electric fields. Combining synthesis, VSE spectroscopy, and computational methods, we provide an intimate view on the origins of these discrepancies. We observe that the electric fields are correlated to conformation-dependent effects of the flexible PenG side chain, including both the local solvation structure and solute conformational sampling in MD. Additionally, we identified that MD-based electric fields are consistently overestimated in three-point water models in the vicinity of charged groups; this cannot be entirely ameliorated using polarizable force fields (AMOEBA) or advanced water models. This work demonstrates the value of the VSE as a direct method for experiment-guided refinements of MD force fields and establishes a general reductionist approach to calibrating vibrational probes for complex (bio)molecules.

Mapping Lamb, Stark and Purcell effects at a chromophore-picocavity junction with hyper-resolved fluorescence microscopy

Abstract: The interactions between the excited states of a single chromophore with static and dynamic electric fields confined to a plasmonic cavity of picometer dimensions are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extensions of the confined fields are smaller than the one of the molecular exciton, a property that is used to generate fluorescence maps of the chromophores with intra-molecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the chromophore-picocavity junction are able to reproduce and interpret these hyper-resolved fluorescence maps, and reveal the key role played by subtle variations of Purcell, Lamb and Stark effects at the chromophore-picocavity junction.

Piezoelectric Modulation of Excitonic Properties in Monolayer WSe 2 under Strong Dielectric Screening.

Abstract: We investigate the interaction of excitons in monolayer WSe2 with the piezoelectric field of surface acoustic wave (SAW) at room temperature using photoluminescence (PL) spectroscopy and report a large in-plane exciton polarizability of 8.43 ± 0.18 × 10-6 Dm/V. Such large polarizability arises due to the strong dielectric screening from the piezoelectric substrate. In addition, we show that the exciton-piezoelectric field interaction and population distribution between neutral excitons and trions can be optically manipulated by controlling the field screening using photogenerated free carriers. Finally, we model the broadening of the exciton PL line width and report that the interaction is dominated by type-II band edge modulation, because of the in-plane electric field in the system. The results help understand the interaction of excitons in monolayer transition-metal dichalcogenides that will aid in controlled manipulation of excitonic properties for applications in sensing, detection, and on-chip communication.

Linear Stark effect in Y 3 Al 5 O 12 :Tm 3 + crystal and its application in the addressable quantum memory protocol

Abstract: We report an observation of the linear Stark effect in a ${\mathrm{Tm}}^{3+}:{\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ crystal with the distribution of the Stark coefficient over the ion ensemble. We associate this effect with local lattice distortions near the positions of ${\mathrm{Tm}}^{3+}$ ions. Using this effect, the addressable storage of a series of weak light pulses in a cavity-assisted scheme of the revival of silenced echo quantum memory protocol is implemented. In this memory scheme, we also demonstrate storage of a light pulse on the few photon level. The application of an optical resonator makes it possible to increase the memory efficiency in this crystal and to reduce the minimal number of photons in the input signal pulse to 5.6 for the signal-to-noise ratio of 1 in the retrieved echo pulse. The results are in good agreement with the theoretical analysis. The possible ways of the further improvement of the implemented memory scheme are also discussed.

60Gb/s waveguide-coupled O-band GeSi quantum-confined Stark effect electro-absorption modulator

Abstract: We report O-band GeSi quantum-confined Stark effect waveguide-coupled electro-absorption modulator with 50GHz bandwidth. Static extinction ratio of 5.2dB, insertion loss of 7.6dB and 60Gb/s NRZ-OOK operation are shown for a 2V swing.

The Semiclassical Limit of the Gailitis Formula Applied to Electron Impact Broadening of Spectral Lines of Ionized Atoms

Abstract: The present paper revisits the determination of the semi-classical limit of the Feshbach resonances which play a role in electron impact broadening (the so-called “Stark“ broadening) of isolated spectral lines of ionized atoms. The Gailitis approximation will be used. A few examples of results will be provided, showing the importance of the role of the Feshbach resonances.

Acoustically Driven Stark Effect in Transition Metal Dichalcogenide Monolayers.

Abstract: The Stark effect is one of the most efficient mechanisms to manipulate many-body states in nanostructured systems. In mono- and few-layer transition metal dichalcogenides, it has been successfully induced by optical and electric field means. Here, we tune the optical emission energies and dissociate excitonic states in MoSe2 monolayers employing the 220 MHz in-plane piezoelectric field carried by surface acoustic waves. We transfer the monolayers to high dielectric constant piezoelectric substrates, where the neutral exciton binding energy is reduced, allowing us to efficiently quench (above 90%) and red-shift the excitonic optical emissions. A model for the acoustically induced Stark effect yields neutral exciton and trion in-plane polarizabilities of 530 and 630 × 10-5 meV/(kV/cm)2, respectively, which are considerably larger than those reported for monolayers encapsulated in hexagonal boron nitride. Large in-plane polarizabilities are an attractive ingredient to manipulate and modulate multiexciton interactions in two-dimensional semiconductor nanostructures for optoelectronic applications.

Quantum simulation of the ground-state Stark effect in small molecules: a case study using IBM Q

Abstract: As quantum computing approaches its first commercial implementations, quantum simulation emerges as a potentially ground-breaking technology for several domains, including biology and chemistry. However, taking advantage of quantum algorithms in quantum chemistry raises a number of theoretical and practical challenges at different levels, from the conception to its actual execution. We go through such challenges in a case study of a quantum simulation for the hydrogen (H $$_2$$ ) and lithium hydride (LiH) molecules, at an actual commercially available quantum computer, the IBM Q. The former molecule has always been a playground for testing approximate calculation methods in quantum chemistry, while the latter is just a little bit more complex, lacking the mirror symmetry of the former. Using the variational quantum eigensolver method, we study the molecule’s ground state energy versus interatomic distance, under the action of stationary electric fields (Stark effect). Additionally, we review the necessary calculations of the matrix elements of the second quantization Hamiltonian encompassing the extra terms concerning the action of electric fields, using STO-LG-type atomic orbitals to build the minimal basis sets.

Electrical tuning of tin-vacancy centers in diamond

Abstract: Group-IV color centers in diamond have attracted significant attention as solid-state spin qubits because of their excellent optical and spin properties. Among these color centers, the tin-vacancy (SnV$^{\,\textrm{-}}$) center is of particular interest because its large ground-state splitting enables long spin coherence times at temperatures above 1$\,$K. However, color centers typically suffer from inhomogeneous broadening, which can be exacerbated by nanofabrication-induced strain, hindering the implementation of quantum nodes emitting indistinguishable photons. Although strain and Raman tuning have been investigated as promising techniques to overcome the spectral mismatch between distinct group-IV color centers, other approaches need to be explored to find methods that can offer more localized control without sacrificing emission intensity. Here, we study electrical tuning of SnV$^{\,\textrm{-}}$ centers in diamond via the direct-current Stark effect. We demonstrate a tuning range beyond 1.7$\,$GHz. We observe both quadratic and linear dependence on the applied electric field. We also confirm that the tuning effect we observe is a result of the applied electric field and is distinct from thermal tuning due to Joule heating. Stark tuning is a promising avenue toward overcoming detunings between emitters and enabling the realization of multiple identical quantum nodes.

Coupled Double Optical Stark Effect in CdSe Colloidal Nanoplatelets

Abstract: Optical Stark effect (OSE) is a coherent phenomenon that is in close relation to quantum information science and ultrafast optical modulation. Recent studies have demonstrated strong OSE from emerg...

Monolayer-Scale GaN/AlN Multiple Quantum Wells for High Power e-Beam Pumped UV-Emitters in the 240-270 nm Spectral Range.

Abstract: Monolayer (ML)-scale GaN/AlN multiple quantum well (MQW) structures for electron-beam-pumped ultraviolet (UV) emitters are grown on c-sapphire substrates by using plasma-assisted molecular beam epitaxy under controllable metal-rich conditions, which provides the spiral growth of densely packed atomically smooth hillocks without metal droplets. These structures have ML-stepped terrace-like surface topology in the entire QW thickness range from 0.75–7 ML and absence of stress at the well thickness below 2 ML. Satisfactory quantum confinement and mitigating the quantum-confined Stark effect in the stress-free MQW structures enable one to achieve the relatively bright UV cathodoluminescence with a narrow-line (~15 nm) in the sub-250-nm spectral range. The structures with many QWs (up to 400) exhibit the output optical power of ~1 W at 240 nm, when pumped by a standard thermionic-cathode (LaB6) electron gun at an electron energy of 20 keV and a current of 65 mA. This power is increased up to 11.8 W at an average excitation energy of 5 µJ per pulse, generated by the electron gun with a ferroelectric plasma cathode at an electron-beam energy of 12.5 keV and a current of 450 mA.