Showing papers on "Stark effect published in 2014"

Electrically driven nuclear spin resonance in single-molecule magnets

Abstract: Recent advances in addressing isolated nuclear spins have opened up a path toward using nuclear-spin–based quantum bits. Local magnetic fields are normally used to coherently manipulate the state of the nuclear spin; however, electrical manipulation would allow for fast switching and spatially confined spin control. Here, we propose and demonstrate coherent single nuclear spin manipulation using electric fields only. Because there is no direct coupling between the spin and the electric field, we make use of the hyperfine Stark effect as a magnetic field transducer at the atomic level. This quantum-mechanical process is present in all nuclear spin systems, such as phosphorus or bismuth atoms in silicon, and offers a general route toward the electrical control of nuclear-spin–based devices.

Ultrafast generation of pseudo-magnetic field for valley excitons in wse2 monolayers

Abstract: The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K' valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications.

Electrically and mechanically tunable electron spins in silicon carbide color centers.

Abstract: The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in 4H-SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10(-6) strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%-36% These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields

Sub-wavelength imaging and field mapping via electromagnetically induced transparency and Autler-Townes splitting in Rydberg atoms

Abstract: We present a technique for measuring radio-frequency (RF) electric field strengths with sub-wavelength resolution. We use Rydberg states of rubidium atoms to probe the RF field. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect, and we detect the splitting via electromagnetically induced transparency (EIT). We use this technique to measure the electric field distribution inside a glass cylinder with applied RF fields at 17.04 GHz and 104.77 GHz. We achieve a spatial resolution of ≈100 μm, limited by the widths of the laser beams utilized for the EIT spectroscopy. We numerically simulate the fields in the glass cylinder and find good agreement with the measured fields. Our results suggest that this technique could be applied to image fields on a small spatial scale over a large range of frequencies, up into the sub-terahertz regime.

Millimeter Wave Detection via Autler-Townes Splitting in Rubidium Rydberg Atoms

Abstract: In this paper, we demonstrate the detection of millimeter waves via Autler-Townes splitting in 85Rb Rydberg atoms This method may provide an independent, atom-based, SI-traceable method for measuring mm-wave electric fields, which addresses a gap in current calibration techniques in the mm-wave regime The electric-field amplitude within a rubidium vapor cell in the WR-10 wave guide band is measured for frequencies of 9371 GHz and 10477 GHz Relevant aspects of Autler-Townes splitting originating from a four-level electromagnetically induced transparency scheme are discussed We measured the E-field generated by an open-ended waveguide using this technique Experimental results are compared to a full-wave finite element simulation

All-Optical Vector Atomic Magnetometer

Abstract: We demonstrate an all-optical magnetometer capable of measuring the magnitude and direction of a magnetic field using nonlinear magneto-optical rotation in cesium vapor. Vector capability is added by effective modulation of the field along orthogonal axes and subsequent demodulation of the magnetic-resonance frequency. This modulation is provided by the ac Stark shift induced by circularly polarized laser beams. The sensor exhibits a demonstrated rms noise floor of ∼65 fT/√[Hz] in measurement of the field magnitude and 0.5 mrad/√[Hz] in the field direction; elimination of technical noise would improve these sensitivities to 12 fT/√[Hz] and 10 μrad/√[Hz], respectively. Applications for this all-optical vector magnetometer would include magnetically sensitive fundamental physics experiments, such as the search for a permanent electric dipole moment of the neutron.

Spin state of spin-crossover complexes: From single molecules to ultrathin films

Abstract: The growth of spin-crossover Fe(1,10-phenanthroline)${}_{2}$(NCS)${}_{2}$ molecules on Cu(100) surfaces in the coverage range from 0.1 to 1.8 molecular layers was studied using a scanning tunneling microscope (STM) operated in ultrahigh vacuum at low temperature ($\ensuremath{\approx}$4 K). STM imaging allowed us to extract the molecular adsorption geometry. While the first-layer molecules point their NCS groups toward the surface and their phenanthroline groups upwards, the adsorption geometry is reversed for the molecules in the second layer. For submonolayer coverages, a coexistence of molecules in the high- and low-spin states was found that is not correlated with the coverage. This coexistence is reduced for second-layer molecules, leading to a dominant spin state at low temperatures. Differential conductance spectra acquired at negative bias voltage on first- and second-layer molecules suggest that second-layer molecules are in the high-spin state and are partially electronically decoupled from the substrate. Furthermore, increasing the tip-to-sample voltage reduces the distance between the two lobes of the molecule. The current dependence of this effect suggests that a smooth spin crossover from a high- to a low-spin state occurs with increasing sample voltage. This analog spin-state switching is well described within a simple transition-state model involving modifications to the energy barriers between low- and high-spin states due to a tip-induced electric field through the Stark effect.

Stark broadening models for plasma diagnostics

Abstract: A review of the models used for the calculation of the Stark broadening spectrum for plasmas is presented. The aim is to provide an overview of the related theories using a simple formalism, useful for an introduction to the study of this phenomenon, which is encountered in plasma diagnostics. A historical development is followed and some of the problems that are currently under investigation are mentioned.

Ester Carbonyl Vibration as a Sensitive Probe of Protein Local Electric Field

Abstract: The ability to quantify the local electrostatic environment of proteins and protein/peptide assemblies is key to gaining a microscopic understanding of many biological interactions and processes. Herein, we show that the ester carbonyl stretching vibration of two non-natural amino acids, l-aspartic acid 4-methyl ester and l-glutamic acid 5-methyl ester, is a convenient and sensitive probe in this regard, since its frequency correlates linearly with the local electrostatic field for both hydrogen-bonding and non-hydrogen-bonding envi- ronments. We expect that the resultant frequency-electric-field map will find use in various applications. Furthermore, we show that, when situated in a non-hydrogen-bonding environ- ment, this probe can also be used to measure the local dielectric constant (e). For example, its application to amyloid fibrils formed by Ab16-22 revealed that the interior of such b-sheet assemblies has an e value of approximately 5.6. Electrostatic interactions are ubiquitous in biological mol- ecules and, in many cases, play a key role in molecular association and enzymatic reactions. (1) However, quantifica- tion of the local electric field or how it changes inside a protein, especially in a site-specific manner and/or as a function of time, still remains a challenging task. One promising method in this regard is vibrational Stark spec- troscopy, (2) which capitalizes on the intrinsic dependence of vibrational transitions on the local electrostatic environment. This method is based on the use of an infrared (IR) probe that has a well-defined, localized vibrational mode to sense the amplitude of the local electric field through the frequency response. (3) For example, the vibrational Stark effect has been used to determine the local electric field at protein interfaces and to monitor protein conformational transitions and dynamics. (4) Although the theoretical underpinning of this

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers

Abstract: InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Measurement of the electron density in Transient Spark discharge

Abstract: This paper presents our measurements of the electron density in a streamer-to-spark transition discharge, which is named transient spark (TS), in atmospheric pressure air. Despite the dc applied voltage, TS has a pulsed character with short (~10–100 ns) high current (>1 A) pulses, with a repetition frequency on the order of kHz. The electron density ne ~ 1017 cm−3 at maximum is reached in TS with repetition frequencies below ~3 kHz, using relatively low power delivered to the plasma (0.2–3 W).The temporal evolution of ne was estimated from the resistance of the plasma discharge, which was obtained by a detailed analysis of the electric circuit representing the TS and the discharge diameter measurements using a fast intensified charge-coupled device (iCCD) camera. This estimate was compared with ne calculated from the measured Stark broadening of several atomic lines: Hα, N at 746 nm, and O triplet at 777 nm. Good agreement was obtained, although the method based on the plasma resistance is sensitive to an accurate determination of the discharge diameter. We have found that this method is also limited for strongly ionized plasmas. On the other hand, a lower ne detection limit can be obtained by this method than from the Stark broadening of atomic lines.

Measurement and control of the streamer head electric field in an atmospheric pressure dielectric barrier plasma jet

Abstract: The propagation dynamics of an atmospheric-pressure plasma jet resemble that of a cathode-directed streamer and are determined, in part, by the high localized electric field at the streamer head. This contribution employs an optical spectroscopy technique based on the polarization-dependent Stark splitting and shifting of visible helium lines to non-invasively measure the streamer head electric field. It is demonstrated that the streamer head is comprised of a high-field region with a peak magnitude of ~24 kV cm−1, which is followed by a low-field region, ~9 kV cm−1, identified as the streamer tail. The application of varying polarity voltage pulses to supplementary electrodes situated along the axis of streamer propagation is shown to influence the streamer head electric field and affords a level of control over the propagation dynamics of the plasma jet, a finding that has considerable application potential.

Nanoscale spin rectifiers controlled by the Stark effect

Abstract: The Stark effect can be used to address two qubits independently that are represented by semiconductor quantum dots, placed only a few nanometres apart.

Entropy squeezing and atomic inversion in the $k$-photon Jaynes-Cummings model in the presence of Stark shift and Kerr medium: full nonlinear approach

Abstract: In this paper the interaction between a two-level atom and a single-mode field in the $k$-photon Jaynes-Cummings model (JCM) in the presence of Stark shift and Kerr medium is studied All terms in the respected Hamiltonian, such as the single-mode field, its interaction with the atom, the contribution of the Stark shift and the Kerr medium effects are considered to be $f$-deformed In particular, the effect of the initial state of radiation field on the dynamical evolution of some physical properties such as atomic inversion and entropy squeezing are investigated by considering different initial field states To achieve this purpose, coherent, squeezed and thermal states as initial field states are considered

Hyperfine Stark effect of shallow donors in silicon

Abstract: We present a complete theoretical treatment of Stark effects in bulk doped silicon, whose predictions are supported by experimental measurements. A multivalley effective mass theory, dealing nonperturbatively with valley-orbit interactions induced by a donor-dependent central cell potential, allows us to obtain a very reliable picture of the donor wave function within a relatively simple framework. Variational optimization of the $1s$ donor binding energies calculated with a new trial wave function, in a pseudopotential with two fitting parameters, allows an accurate match of the experimentally determined donor energy levels, while the correct limiting behavior for the electronic density, both close to and far from each impurity nucleus, is captured by fitting the measured contact hyperfine coupling between the donor nuclear and electron spin. We go on to include an external uniform electric field in order to model Stark physics: with no extra ad hoc parameters, variational minimization of the complete donor ground energy allows a quantitative description of the field-induced reduction of electronic density at each impurity nucleus. Detailed comparisons with experimental values for the shifts of the contact hyperfine coupling reveal very close agreement for all the donors measured (P, As, Sb, and Bi). Finally, we estimate field ionization thresholds for the donor ground states, thus setting upper limits to the gate manipulation times for single qubit operations in Kane-like architectures: the Si:Bi system is shown to allow for $A$ gates as fast as $\ensuremath{\approx}10$ MHz.

Entropy squeezing and atomic inversion in the k-photon Jaynes—Cummings model in the presence of the Stark shift and a Kerr medium: A full nonlinear approach

Abstract: The interaction between a two-level atom and a single-mode field in the k-photon Jaynes—Cummings model (JCM) in the presence of the Stark shift and a Kerr medium is studied. All terms in the Hamiltonian, such as the single-mode field, its interaction with the atom, the contribution of the Stark shift and the Kerr medium effects are considered to be f-deformed. In particular, the effect of the initial state of the radiation field on the dynamical evolution of some physical properties such as atomic inversion and entropy squeezing are investigated by considering different initial field states (coherent, squeezed and thermal states).

Theoretical and experimental investigation of the light shift in Ramsey coherent population trapping

Abstract: The ac Stark shift (or light shift) of the 6$^{2}$S$_{1/2}$ (F $=$ 3 $\leftrightarrow $ 4) transition in $^{133}$Cs, as observed through coherent population trapping under pulsed excitation, is measured using a $^{133}$Cs gas cell and the $D_1$-line vertical-cavity surface-emitting laser. This light shift can be calculated using density-matrix analysis. We derive an expression for this shift as a function of light intensity, showing that it varies linearly with respect to light intensity only with intensities higher than 1.0~mW/cm$^2$. For pulsed excitation of high laser intensity, the variation in light shift is 20 times lower than that when using a continuous wave. The differences between the results of theory and experiment are discussed, taking into account the difference in conditions assumed; the results from theoretical analysis, taking the attenuation of the first-order sideband into account, approximately agree with the experimental results. The light shift is reduced by shortening the observation times.

Electron density determination in the divertor volume of ASDEX Upgrade via Stark broadening of the Balmer lines

Abstract: In this article we present the development of a new diagnostic capable of determining the electron density in the divertor volume of ASDEX Upgrade (AUG). It is based on the spectroscopic measurement of the Stark broadening of the Balmer lines. In this work two approaches of calculating the Stark broadening, i.e. the unified theory and the model microfield method, are compared. It will be shown that both approaches yield similar results in the case of Balmer lines with high upper principal quantum numbers n. In addition, for typical AUG parameters the influence of the Zeeman splitting on the high n Balmer lines is found to be negligible. Moreover, an assumption for the Doppler broadening of Tn = 5 eV, which is the maximum Frank–Condon dissociation energy of recycled neutrals, is sufficient. The initial electron density measurements performed using this method are found to be consistent with both Langmuir probe and pressure gauge data.

Conditional control of donor nuclear spins in silicon using stark shifts.

Abstract: Electric fields can be used to tune donor spins in silicon using the Stark shift, whereby the donor electron wave function is displaced by an electric field, modifying the hyperfine coupling between the electron spin and the donor nuclear spin. We present a technique based on dynamic decoupling of the electron spin to accurately determine the Stark shift, and illustrate this using antimony donors in isotopically purified silicon-28. We then demonstrate two different methods to use a dc electric field combined with an applied resonant radio-frequency (rf) field to conditionally control donor nuclear spins. The first method combines an electric-field induced conditional phase gate with standard rf pulses, and the second one simply detunes the spins off resonance. Finally, we consider different strategies to reduce the effect of electric field inhomogeneities and obtain above 90% process fidelities.

Ion Dynamics Effect on Stark-Broadened Line Shapes: A Cross-Comparison of Various Models

Abstract: Modeling the Stark broadening of spectral lines in plasmas is a complex problem. The problem has a long history, since it plays a crucial role in the interpretation of the observed spectral lines in laboratories and astrophysical plasmas. One difficulty is the characterization of the emitter's environment. Although several models have been proposed over the years, there have been no systematic studies of the results, until now. Here, calculations from stochastic models and numerical simulations are compared for the Atoms 2014, 2 300 Lyman-α and -β lines in neutral hydrogen. Also discussed are results from the Helium-α and -β lines of Ar XVII.

Electron density measurements of atmospheric-pressure non-thermal N2 plasma jet by Stark broadening and irradiance intensity methods

Abstract: An atmospheric-pressure non-thermal plasma jet excited by high frequency alternating current using nitrogen is developed and the electron density in the active region of this plasma jet is investigated by two different methods using optical emission spectroscopy, Stark broadening, and irradiance intensity method. The irradiance intensity method shows that the average electron density is about 1020/m3 which is slightly smaller than that by the Stark broadening method. However, the trend of the change in the electron density with input power obtained by these two methods is consistent.

Deep-ultraviolet light emission properties of nonpolar M-plane AlGaN quantum wells

Abstract: Deep-ultraviolet (deep-UV) light emissions from nonpolar (10-10) M-plane AlxGa1−xN/AlyGa1−yN multiple quantum wells (MQWs) were studied by photoluminescence spectroscopy. The nonpolar M-plane AlGaN MQWs showed shorter emission wavelength than the polar (0001) C-plane ones, mainly because of the absence of the quantum-confined Stark effect. The deep-UV light emissions from the M-plane AlGaN MQWs showed stronger polarization with electric field E parallel to the c-axis (E||c) than the C-plane ones. The different polarization properties between the M- and C-plane AlGaN MQWs can be explained in terms of in-plane lattice strain and anisotropy of the effective hole mass.

Entanglement analysis of a two-atom nonlinear Jaynes–Cummings model with nondegenerate two-photon transition, Kerr nonlinearity, and two-mode Stark shift

Abstract: An entangled state, as an essential tool in quantum information processing, may be generated through the interaction between light and matter in cavity quantum electrodynamics. In this paper, we study the interaction between two two-level atoms and a two-mode field in an optical cavity enclosed by a medium with Kerr nonlinearity in the presence of a detuning parameter and Stark effect. It is assumed that the atom–field coupling and third-order susceptibility of the Kerr medium depend on the intensity of the light. In order to investigate the dynamics of the introduced system, we obtain the exact analytical form of the state vector of the considered atom–field system under initial conditions which may be prepared for the atoms (in a coherent superposition of their ground and upper states) and the fields (in a standard coherent state). Then, in order to evaluate the degree of entanglement between the subsystems, we investigate the dynamics of the entanglement by employing the entanglement of formation. Finally, we analyze in detail the influences of the Stark shift, the deformed Kerr medium, the intensity-dependent coupling, and also the detuning parameter on the behavior of this measure for different subsystems. The numerical results show that the amount of entanglement between the different subsystems can be controlled by choosing the evolved parameters appropriately.

Spectroscopy of atom and nucleus in a strong laser field: Stark effect and multiphoton resonances

Abstract: The consistent relativistic energy approach to atoms in a strong realistic laser field, based on the Gell-Mann and Low S-matrix formalism, is applied in the study of resonant multiphoton ionization of krypton by intense uv laser radiation and for the computation of the resonance shift and width in krypton. The approach to the treatment of the multiphoton resonances in nuclei is outlined for the 57Fe nucleus.

Static and dynamic polarizability and the Stark and blackbody-radiation frequency shifts of the molecular hydrogen ions H 2 + , HD + , and D 2 +

Abstract: We calculate the DC Stark effect for three molecular hydrogen ions in the non-relativistic approximation. The effect is calculated both in dependence on the rovibrational state and in dependence on the hyperfine state. We discuss special cases and approximations. We also calculate the AC polarisabilities for several rovibrational levels, and therefrom evaluate accurately the black-body radiation shift, including the effects of excited electronic states. The results enable the detailed evaluation of certain systematic shifts of the transitions frequencies for the purpose of ultra-high-precision optical, microwave or radio-frequency spectroscopy in ion traps.

Stark broadening measurement of Al II lines in a laser-induced plasma

Abstract: Laser induced plasma was a light source for the study of Stark broadening parameters of singly charged aluminum ion lines. Plasma electron number density in the range (0.3-2.3) � 10 23 m � 3 was measured from the Stark width of the hydrogen Hα impurity line, while the electron temperature between 6500 and 17,500 K was determined from relative intensities of Fe II, Mg I and Al II spectral lines using the Boltzmann plot technique. The experimental Stark widths were compared with other experiments and theories, which include semiclassical results and data evaluated from the modified semiempirical formula.

Temperature effect on the optical emission intensity in laser induced breakdown spectroscopy of super alloys

Abstract: In this paper, the influence of heating and cooling samples on the optical emission spectra and plasma parameters of laser-induced breakdown spectroscopy for Titanium 64, Inconel 718 super alloys, and Aluminum 6061 alloy is investigated. Samples are uniformly heated up to approximately 200°C and cooled down to -78°C by an external heater and liquid nitrogen, respectively. Variations of plasma parameters like electron temperature and electron density with sample temperature are determined by using Boltzmann plot and Stark broadening methods, respectively. Heating the samples improves LIBS signal strength and broadens the width of the spectrum. On the other hand, cooling alloys causes fluctuations in the LIBS signal and decrease it to some extent, and some of the spectral peaks diminish. In addition, our results show that electron temperature and electron density depend on the sample temperature variations.

Stark effect of excitons in individual air-suspended carbon nanotubes

Abstract: We investigate electric-field induced redshifts of photoluminescence from individual single-walled carbon nanotubes. The shifts scale quadratically with field, while measurements with different excitation powers and energies show that effects from heating and relaxation pathways are small. We attribute the shifts to the Stark effect and characterize nanotubes with different chiralities. By taking into account exciton binding energies for air-suspended tubes, we find that theoretical predictions are in quantitative agreement.