First-excited State Research Articles

Temperature Effects of Electric Field on the First Excited State of Strong Coupling Polaron in a CsI Quantum Pseudodot**Supported by the National Natural Science Foundation of China under Grant No. 11464033

Employing variational method of Pekar type (VMPT), this paper investigates the first-excited state energy (FESE), excitation energy and transition frequency of the strongly-coupled polaron in the CsI quantum pseudodot (QPD) with electric field. The temperature effects on the strong-coupling polaron in electric field are calculated by using the quantum statistical theory (QST). The results from the present investigation show that the FESE, excitation energy and transition frequency increase (decrease) firstly and then at lower (higher) temperature regions. They are decreasing functions of the electric field strength.

Application of different entropies to study of bound magnetopolaron in an asymmetric quantum dot

An electron strongly coupled to the LO-phonon in an asymmetric quantum dot has been considered. The system has a central impurity and it is under electric and magnetic fields. The eigenenergies and eigenfunctions of the ground and the first-excited states of the electron have been calculated using the Pekar variational method. Entropy of the system for different values of Coulomb impurity parameter, electron-LO phonon coupling strength, dispersion coefficient and electric field have been studied. Two entropies, Shannon and Gaussian entropy have been employed. It is found that the entropy has the oscillatory periodic evolution as function of the time due to the confinement form. It is deduced that the entropies increase with enhancing Coulomb impurity parameter, electron-LO phonon coupling strength and dispersion coefficient. With increasing electron-LO phonon coupling strength, the entropies decrease. The control of the coherence of the system can be done with the modulation of the electric field, the Coulomb bound potential, dispersion coefficient and electron-LO phonon coupling strength.

Nonlinear optical rectification in laterally-coupled quantum well wires with applied electric field

Nonlinear optical rectification coefficientχ0(2) in laterally-coupled AlxGa1−xAs/GaAs quantum well wires with an applied electric field is theoretically investigated using the effective mass approximation as well as the numerical energy levels and wavefunctions of electrons. We find that χ0(2) is greatly influenced by the electric field as well as both the distance and the radius of the coupled system. A blue shift of χ0(2) with increasing electric field is exhibited while a red shift followed by a blue shift with increasing distance or radius is exhibited. A nonmonotonic behavior can be found in the resonant peak values of χ0(2) along with the increase of the electric field, the distance or the radius. One or two of the following physical mechanisms: the increased localization of the ground and first-excited states, the reduced coupling and the reduced quantum confinement effect are applied to elucidate the results above. Our results play a potential role in infrared photodetectors based on the coupled system.

Effect of phonons on optical properties of RbCl quantum pseudodot qubits

In this work, an electron which is strongly coupled to the strong electron-longitudinal optical (LO) phonon in RbCl quantum pseudodot qubits is considered. First, we employ the Pekar variational method and obtain the eigenenergies and eigenfunctions of the ground and the first-excited states of the system. Then, we have studied optical properties of the system under strong electron-LO phonon coupling. In this regard, the refractive index changes and absorption coefficient of the system are obtained using compact-density-matrix approach and iterative method. It is found that the absorption coefficients show saturation in the presence of phonon effect. This behavior occurs at small quantum size and for different potential height. Our results show that both the structure parameters and phonon effect have a great effect on the total absorption and refractive index changes.

Studies of X-ray burst reactions with radioactive ion beams from RESOLUT

Reactions on certain proton-rich, radioactive nuclei have been shown to have a significant influence on X-ray bursts. We provide an overview of two recent measurements of important X-ray burst reactions using in-flight radioactive ion beams from the RESOLUT facility at the J. D. Fox Superconducting Accelerator Laboratory at Florida State University. The 17 F(d,n) 18 Ne reaction was measured, and Asymptotic Normalization Coefficients were extracted for bound states in 18 Ne that determine the direct-capture cross section dominating the 17 F(p, γ ) 18 Ne reaction rate for T≲ 0.45 GK. Unbound resonant states were also studied, and the single-particle strength for the 4.523-MeV (3 + ) state was found to be consistent with previous results. The 19 Ne(d,n) 20 Na proton transfer reaction was used to study resonances in the 19 Ne(p, γ ) 20 Na reaction. The most important 2.65-MeV state in 20 Na was observed to decay by proton emission to both the ground and first-excited states in 19 Ne, providing strong evidence for a 3 + spin assignment and indicating that proton capture on the thermally-populated first-excited state in 19 Ne is an important contributor to the 19 Ne(p, γ ) 20 Na reaction rate.

Fast and slow excited-state intramolecular proton transfer in 3-hydroxychromone: a two-state story?

The photodynamics of 3-hydroxychromone in its first-excited singlet electronic state (bright state of ππ* character) is investigated with special emphasis given to two types of reaction pathways: the excited-state intramolecular-proton-transfer coordinate and the hydrogen-torsion coordinate linking the excited cis and trans isomers. A newly-found conical intersection with the second-excited singlet electronic state (dark state of nπ* character) is suspected to be, to some extent, the reason for the slower rate constant. This hypothesis based on quantum-chemistry calculations is supported by quantum-dynamics simulations in full dimensionality. They show significant transfer of electronic population and provide consistently a vibronic interpretation for the forbidden band in the UV absorption spectrum.

Temperature and hydrogen-like impurity effects on the excited state of the strong coupling bound polaron in a CsI quantum pseudodot**Project supported by the National Natural Science Foundation of China (Grant No. 11464033).

With hydrogen-like impurity (HLI) located in the center of CsI quantum pseudodot (QPD) and by using the variational method of Pekar type (VMPT), we investigate the first-excited state energy (FESE), excitation energy and transition frequency of the strongly-coupled bound polaron in the present paper. Temperature effects on bound polaron properties are calculated by employing the quantum statistical theory (QST). According to the present work’s numerical results, the FESE, excitation energy and transition frequency decay (amplify) with raising temperature in the regime of lower (higher) temperature. They are decreasing functions of Coulomb impurity potential strength.

Accurate theoretical study on the ground and first-excited states of Na2: potential energy curves, spectroscopic parameters, and vibrational energy levels

Potential energy curves (PECs) for the ground and first-excited electronic states of Na2 are obtained by fitting the ab initio energies calculated at the MRCI(Q)/aug-cc-pVXZ (X = T, Q, 5) level of theory, which are subsequently extrapolated to the complete basis set limit. The relativistic effect and core–valence correlation are also considered. The PECs are accurate at both short and long internuclear distances with the root-mean-squared deviations being 0.72 cm−1 for Na2 [Formula: see text] and 0.36 cm−1 for Na2 [Formula: see text]. Utilizing the obtained PECs, we calculate the spectroscopic parameters, vibrational energy levels, classical turning points, inertial rotation, and centrifugal distortion constants, which are in good agreement with other theoretical and experimental work.

Direct spin–phonon coupling of spin-flip relaxation in quantum dots**Project supported by the National Natural Science Foundation of China (Grant No. 11264001) and the Natural Science Foundation of Inner Mongolia, China (Grant No. 2012MS0116).

Within the frame of the Pavlov–Firsov spin–phonon coupling model, we study the spin-flip assisted by the acoustical phonon scattering between the first-excited state and the ground state in quantum dots. We analyze the behaviors of the spin relaxation rates as a function of an external magnetic field and lateral radius of quantum dot. The different trends of the relaxation rates depending on the magnetic field and lateral radius are obtained, which may serve as a channel to distinguish the relaxation processes and thus control the spin state effectively.

Multiple-output microwave single-photon source using superconducting circuits with longitudinal and transverse couplings

Single-photon devices at microwave frequencies are important for applications in quantum information processing and communication in the microwave regime. In this work, we describe a proposal of a multi-output single-photon device. We consider two superconducting resonators coupled to a gap-tunable qubit via both its longitudinal and transverse degrees of freedom. Thus, this qubit-resonator coupling differs from the coupling in standard circuit quantum-electrodynamic systems described by the Jaynes-Cummings model. We demonstrate that an effective quadratic coupling between one of the normal modes and the qubit can be induced, and this induced second-order nonlinearity is much larger than that for conventional Kerr-type systems exhibiting photon blockade. Assuming that a coupled normal mode is resonantly driven, we observe that the output fields from the resonators exhibit strong sub-Poissonian photon-number statistics and photon antibunching. Contrary to previous studies on resonant photon blockade, the first-excited state of our device is a pure single-photon Fock state rather than a polariton state, i.e., a highly hybridized qubit-photon state. In addition, it is found that the optical state truncation caused by the strong qubit-induced nonlinearity can lead to an entanglement between the two resonators, even in their steady state under the Markov approximation.

Study on the ground states of a square-lattice polymer by using exhaustive enumeration

We exhaustively enumerate the ground-state conformations of polymers with attractive nearest-neighbor interactions on a square lattice. We find that when the ground-state number is considered as a function of the chain length, local minima appear at magic lengths. However, the ground-state entropy per monomer does not vanish in the thermodynamic limit when an extrapolation is performed with the magic-length data, implying that the number of ground-state conformations grows exponentially. We also study the entropy difference between the ground and the first-excited states. The entropy difference per monomer diverges in the thermodynamic limit, indicating that the zero-tail of the specific heat is modified in the thermodynamic limit.

Influences of the Temperature on the Parabolic Quantum Dot Qubit in the Magnetic Field

Using the variational method of the Pekar type, we study the influences of the temperature on the parabolic quantum dot qubit in the magnetic field under the condition of electric–LO-phonon strong coupling. Then we derive the numerical results and formulate the derivative relationships of the oscillation period of the electron in the superposition state of the ground state and the first-excited state with the magnetic field, the electron–LO-phonon coupling constant and the confinement length at different temperatures, respectively.

Application of non-extensive entropy to study of decoherence of RbCl quantum dot qubit: Tsallis entropy

In this work, an electron which is strongly coupled to the LO-phonon in triangular quantum dots with Coulomb impurity is considered. The eigenenergies and eigenfunctions of the ground and the first-excited states of the electron are obtained using the Pekar variational method. We have studied decoherence of RbCl quantum dot qubit using the non-extensive entropy (Tsallis entropy) for different values of Coulomb impurity parameter, polaronic radius and electron-LO phonon coupling strength. Numerical analysis shows that the entropy has the oscillatory periodic evolution as function of the time due to the triangular form of the confinement. It is found that entropy oscillates under a standing wave envelope with increasing the Coulomb impurity parameter, electron-LO phonon coupling strength and polaronic radius. With reducing the non-extensive parameter q, the entropy increases and thereby we can miss information about the system.

Complete kinematical study of the 3 $\alpha$ breakup of the 16.11 MeV state in 12C

The reaction $^{11}B+p$ has been used to populate the $(J^{\pi},T)=(2^+,1)$ state at an excitation energy of 16.11 MeV in $^{12}$C, and the breakup of the state into three $\alpha$ particles has been studied in complete kinematics. A two-step breakup model which includes interference effects is found to provide the most accurate description of the experimental data. The branching ratio to the ground state of $^8$Be is determined to be 5.1(5)% in agreement with previous findings, but more precise by a factor of two, while the decay to the first-excited state in $^8$Be is found to be dominated by $d$-wave emission.

Effects of Temperature and Magnetic Field on the Coherence Time of a RbCl Parabolic Quantum Dot Qubit

Employing the Pekar variational method, quantum statistics theory and the Fermi golden rule, the temperature and magnetic field effects on the qubit in rubidium chloride (RbCl) parabolic quantum dots (PQDs) are investigated. We then obtain the eigenenergies and corresponding eigenfunctions of ground and first-excited states coupled strongly to an electron to bulk longitudinal optical phonons in a RbCl PQD with applied magnetic field. A two-level system of PQDs may be regarded as a single qubit. The spontaneous emission of phonons causes the qubit decoherence. The numerical results indicate that the coherence time decreases with elevating temperature. The coherence increases the effective confinement length, whereas there is a decrease of the magnetic field’s cyclotron frequency.

Influence of temperature on the excited state of the strong coupling polaron in a CsI quantum pseudodot

In the present work, we have considered a polaron confined in a CsI quantum pseudodot (QPD) with the pseudoharmonic potential (PHP). The properties of the first-excited state energy, the excitation energy and the transition frequency of the strong-coupling polaron in the CsI QPD were studied by using variational method of Pekar type (VMPT). By employing a quantum statistical theory (QST), we have calculated the effect of the temperature on the properties of the polaron. The investigated results demonstrate that the absolute value of first-excited state energy, the excitation energy and the transition frequency lift (decay) with raising temperature in lower (higher) temperature regime. The excitation energy and the transition frequency are enhancing functions of the chemical potential of the two-dimensional electron gas, whereas the absolute value of first-excited state energy is a decaying one of it.

Explanations of the g factors for the tetragonal (MoO4)3−clusters inγ-irradiated (MoO4)2−-doped KDP and ADP crystals through the dynamic effect

The electron paramagnetic resonance (EPR) g factors g // and g ┴ for the tetragonally-compressed (MoO 4 ) 3− clusters in the γ -irradiated (MoO 4 ) 2− -doped KH 2 PO 4 (KDP) and NH 4 H 2 PO 4 (ADP) crystals are computed from the high-order perturbation formulas based on the two (crystal-field and charge transfer)-mechanism model for the compressed d 1 tetragonal tetrahedra with the ground state |d z 2 ⟩. From the calculated values and by taking account of the mixing of the first-excited state |d x 2 −y 2 ⟩ to the ground state |d z 2 ⟩ caused by the dynamic effect due to the vibration of ligands (which can result in a twinkling change of tetrahedron from compression to elongation), the computed g // and g ┴ for the two crystals are in good accordance with the experimental values. The large deviations of the observed g // from g e (≈2.0023, the g factor of free electron) in both crystals are therefore explained. The results are discussed.

Properties of strong-coupling magneto-bipolaron qubit in quantum dot under magnetic field**Project supported by the Natural Science Foundation of Hebei Province, China (Grant No. E2013407119) and the Items of Institution of Higher Education Scientific Research of Hebei Province and Inner Mongolia, China (Grant Nos. ZD20131008, Z2015149, Z2015219, and NJZY14189).

Based on the variational method of Pekar type, we study the energies and the wave-functions of the ground and the first-excited states of magneto-bipolaron, which is strongly coupled to the LO phonon in a parabolic potential quantum dot under an applied magnetic field, thus built up a quantum dot magneto-bipolaron qubit. The results show that the oscillation period of the probability density of the two electrons in the qubit decreases with increasing electron–phonon coupling strength α, resonant frequency of the magnetic field ωc, confinement strength of the quantum dot ω0, and dielectric constant ratio of the medium η; the probability density of the two electrons in the qubit oscillates periodically with increasing time t, angular coordinate φ2, and dielectric constant ratio of the medium η; the probability of electron appearing near the center of the quantum dot is larger, and the probability of electron appearing away from the center of the quantum dot is much smaller.

The Effect of Phonons in RbCl Quantum Pseudodot Qubits

By employing the Pekar variational method, the eigenenergies and eigenfunctions of the ground and first-excited states are obtained in a strong electron-longitudinal optical (LO) phonon coupling RbCl quantum pseudodot (QPD). A single qubit can be realized in this two-level quantum system. The electron probability density (EPD) oscillates in the RbCl QPD with a certain period. The investigated results show that the EPD rises with raising the chemical potential of the two-dimensional electron gas and the zero point of the pseudoharmonic potential, whereas it decays with increasing the polaron radius. However, the oscillating period (OP) possesses precisely the opposite characteristics. Through the results and analysis above, we find three ways to adjust the EPD and the OP via changing the chemical potential of the two-dimensional electron gas, the zero point of the pseudoharmonic potential, and the polaron radius.

Temperature, impurity and electromagnetic field effects on the transition of a two-level system in a triangular potential

Using the Pekar variational method, the effects of the temperature, impurity and electromagnetic fields on the transition are investigated through the eigenenergies of the ground and first-excited states of the polaron in a triangular potential quantum dot. Those parameters are essential for the transition of the polaron from the ground state to the first-excited state. This quantum system in nanostructure can be employed as a two-level quantum qubit. The numerical result shows the weak evolution of the probability density with the electron-phonon coupling constant, the cyclotron frequency and the Coulombic potential. It is also noted that this probability increased with the confinement length and electric-field strength. The tunneling of temperature leads to the amplification of the probability density.