Electric Field Effect on State Energies and Transition Frequency of a Strong-Coupling Polaron in an Asymmetric Quantum Dot

We study the ground and the first excited states’ energies and the corresponding transition frequency of a strong-coupling polaron in an asymmetric quantum dot (AQD). The effects of the electric field, the transverse and the longitudinal effective confinement lengths and the electron-phonon coupling strength are taken into account by using a variational method of the Pekar type. It is found that the ground and the first excited states’ energies and the transition frequency are decreasing functions of the electric field. They will increase rapidly with decreasing the transverse and longitudinal effective confinement lengths. The transition frequency is an increasing function of the electron-phonon coupling strength, whereas the energies are decreasing ones of it.     

Temperature and Impurity Effects of the Polaron in an Anisotropic Quantum Dot

We study the temperature and impurity effects of the ground state energy and the ground state binding energy in an anisotropic quantum dot by using the linear combination operator method. We also discuss the relations of the vibrational frequency and the mean number phonons varying with the Coulomb bound potential at different electron-phonon coupling strength. It is found that the ground state energy and the ground state binding energy will increase with increasing temperature. The ground state energy is a decreasing function of the Coulomb bound potential, whereas the ground state binding energy is an increasing one of it.     

Rashba Effect on the Bound Polaron in an Asymmetric Quantum Dot

By using LLP variational method, the Rashba effect on the bound polaron in an asymmetric quantum dot is investigated and the expression of the bound polaron ground state energy is derived. Considering different Coulomb bound potentials, we discuss the relations between the ground state energy and the electron–phonon coupling strength, the wave vector, the transverse effective confinement length and the longitudsinal effective confinement length, respectively. The results show that the ground state energy is a decreasing function of the Coulomb bound potential, the electron–phonon coupling strength, the transverse effective confinement length and the longitudinal effective confinement length. On the contrary, it is an increasing function of the wave vector. Due to the Rashba effect, the ground state energy splits into two branches.     

Impurity Effect of a Bound Polaron in Quantum Rods

Based on a coordinate transformation, we first change the boundary potential of a quantum rod from the ellipsoidal form into a spherical one. And then the properties of the vibrational frequency and the ground state binding energy of a strongly-coupled impurity bound polaron in it are studied. The effects of the ellipsoid aspect ratio, the electron-phonon coupling strength, the Coulomb bound potential and the transverse and longitudinal effective confinement lengths are taken into consideration by using the linear combination operator method. It is found that the vibrational frequency and the ground state binding energy will increase with increasing Coulomb bound potential and the electron-phonon coupling strength. They are decreasing functions of the ellipsoid aspect ratio and the transverse and longitudinal effective confinement lengths.     

Transition Frequency of Strong-Coupling Magnetopolaron in Quantum Rods

The Hamiltonian of a quantum rod with an ellipsoidal boundary is given after a coordinate transformation, which changes the ellipsoidal boundary into a spherical one. We then study the first excited state energy, the excitation energy and the transition frequency between the first excited and the ground states of the strong-coupling magnetopolaron in it. The effects of the magnetic field cyclotron frequency, the electron-phonon coupling strength, the transverse and longitudinal effective confinement lengths and the aspect ratio of the ellipsoid are taken into consideration by using linear combination operator and the unitary transformation methods. It is found that the first excited state energy, the excitation energy and the transition frequency will increase with increasing the cyclotron frequency. They will increase with decreasing the transverse and longitudinal effective confinement lengths and the aspect ratio of the ellipsoid. The first excited state energy is decreasing functions of the electron-phonon coupling strength, whereas the excitation energy and the transition frequency are increasing functions of the electron-phonon coupling strength.     

Study of Extensive and Nonextensive Entropy of RbCl Quantum Well Qubit in an Asymmetric Gaussian Potential

Journal of Low Temperature Physics - We have presented extensive and nonextensive entropy of RbCl quantum well qubits (QWQ). To this end, we have considered an electron that is coupled to the...     

Temperature Effect on Effective Mass of the Polaron in an Asymmetric Quantum Dot

We investigate the properties of the polaron in an asymmetric quantum dot by using an improved linear combination operator method. The relations between the mean number of phonons, the effective mass and the temperature are derived. It is found that the mean number of phonons and the effective mass are increasing functions of the temperature.     

Temperature Dependence of Strong-Coupled Polaron in a Triangular Potential Quantum Dot

The effect of temperature on the ground-state energy of polaron was obtained with strong electron-LO-phonon coupling by using a variational method of the Pekar type in triangular potential quantum dot (QD). The ground-state energy was expressed as functions of the confinement length of QD, the coupling strength, the polar angle and the temperature. It is found that the ground-state energy decreases with increasing the confinement length of QD and the electron-phonon coupling strength and increases with enhancing the temperature.     

The Rashba Effect on the Bound Polaron in a Parabolic Quantum Dot

The bound polaron ground state energy is calculated by the variational method of Pekar considering the influence of the Rashba SO interaction on the condition of electric?CLO phonon strong coupling in a parabolic quantum dot (QD). The relations on the bound polaron ground state energy with the parallel confinement length, the electron?CLO phonon coupling constant, the perpendicular confinement length and the Coulomb binding parameter are derived for a parabolic quantum dot.     

The Effects of Electric Field on a Triangular Bound Potential Quantum Dot Qubit

On the condition of electron-LO-phonon strong coupling in a triangular bound potential quantum dot, we obtain the eigenenergy and eigenfuctions of the ground state and the first-excited state by using the Pekar type of variational method. This two-level system in a quantum dot can be employed as a qubit, which is a basic unit for quantum information operation and storage. Our numerical results indicate that the oscillation period of this qubit is an increasing function of the confinement length and the electric field. The influence of electric field on the period of oscillation becomes greater when the confinement length is increased. The electron probability density of the qubit is an increasing function of the electron-LO-phonon coupling constant. On the contrary, it is a decreasing function of the electric field. Meanwhile, the electron probability density varies periodically with the polar angle.     

The Effective Mass of Impurity–bound Polaron in a Two- and Three-Dimensional Quantum Dot

Within the framework of the Landau–Pekar variational method we have derived an analytical expression for the ground-state binding energies and the effective mass of an electron bound to a Coulomb impurity in a polar semiconductor quantum dot (QD) with parabolic confinement in both two and three dimensions. We have also calculated the number of phonons in the cloud of this bound polaron. It is found that the effective mass increase with increasing the Coulomb binding parameter and increase with the decrease in size of the QD. The results also indicate that this effect becomes much more pronounced with decreasing dimensionality.     

Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots     

The Effects of Electric Field on Oscillation Period of Triangular Bound Potential Quantum Dot Qubit

This paper calculates the oscillation period of an electron by using variational method of Pekar type on the condition of electric-LO-phonon strong coupling in a triangular bound potential quantum dot. It obtains the eigenenergies of the ground state and the first excited state, the eigenfunctions of the ground state and the first excited state. This system in a quantum dot may be employed as a two-level quantum system qubit. The superposition state electron density oscillates in the quantum dot with a period when the electron is in the superposition state of the ground and the first-excited state. It studies the influence of the electric field on the period of oscillation at different electron-LO-phonon coupling strength, different polar angle and different confinement length.     

Superfluid Phase Transition and Strong-Coupling Effects in an Ultracold Fermi Gas with Mass Imbalance

We investigate the superfluid phase transition and effects of mass imbalance in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an cold Fermi gas. We point out that the Gaussian fluctuation theory developed by Nozières and Schmitt-Rink and the T-matrix theory, that are now widely used to study strong-coupling physics of cold Fermi gases, give unphysical results in the presence of mass imbalance. To overcome this problem, we extend the T-matrix theory to include higher-order pairing fluctuations. Using this, we examine how the mass imbalance affects the superfluid phase transition. Since the mass imbalance is an important key in various Fermi superfluids, such as ⁴⁰K-⁶Li Fermi gas mixture, exciton condensate, and color superconductivity in a dense quark matter, our results would be useful for the study of these recently developing superfluid systems.     

The Properties of the Polaron Ground State in a Parabolic Quantum Dot and Ring

The polaron ground state energy is obtained by using variational method of Pekar type on the condition of electric-LO phonon strong coupling in a quantum dot and ring. The relations of the polaron ground state energy on the inner confinement strength, the outer confinement strength, the inner and outer radius of quantum dot and ring are derived.     

Influence of Magnetic Field and LO Phonon Effects on the Spin Polarization State Energy of Strong-Coupling Bipolaron in a Quantum Dot

On the basis of Lee–Low–Pines unitary transformation, the influence of magnetic field and LO phonon effects on the energy of spin polarization states of strong-coupling bipolarons in a quantum dot (QD) is studied by using the variational method of Pekar type. The variations of the ground state energy $E_0$ and the first excited state the energy $E_1$ of bipolarons in a two-dimensional QD with the confinement strength of QDs $\omega _0$ , dielectric constant ratio $\eta $ , electron–phonon coupling strength $\alpha $ and cyclotron resonance frequency of the magnetic field $\omega _{c}$ are derived when the influence of the spin and external magnetic field is taken into account. The results show that both energies of the ground and first excited states ( $E_0$ and $E_1)$ consist of four parts: the single-particle energy of electrons $E_\mathrm{e}$ , Coulomb interaction energy between two electrons $E_\mathrm{c}$ , interaction energy between the electron spin and magnetic field $E_\mathrm{S}$ and interaction energy between the electron and phonon $E_{\mathrm{e-ph}}$ ; the energy level of the first excited state $E_1$ splits into two lines as $E_1^{(1+1)}$ and $E_1^{(1-1)}$ due to the interaction between the single-particle “orbital” motion and magnetic field, and each energy level of the ground and first excited states splits into three “fine structures” caused by the interaction between the electron spin and magnetic field; the value of $E_{\mathrm{e-ph}}$ is always less than zero and its absolute value increases with increasing $\omega _0$ , $\alpha $ and $\omega _c$ ; the effect of the interaction between the electron and phonon is favorable to forming the binding bipolaron, but the existence of the confinement potential and Coulomb repulsive energy between electrons goes against that; the bipolaron with energy $E_1^{(1-1)}$ is easier and more stable in the binding state than that with $E_1^{(1+1)}$ .