The influences of the dispersion, the impurity and the electron–phonon coupling (EPC) on the properties of the Gaussian confining (GC) potential qubit with magnetic field were studied by Pekar-type variation method. Results show that the decoherence time will increase with increasing the dielectric constant (DC) ratio, the dispersion coefficient and the EPC strength, respectively. The phase rotation quality factor increases with increasing the dielectric constant ratio, the dispersion coefficient and EPC strength, respectively. The magnetic field has a regulatory effect on the decoherence time and the phase rotation quality factor.
The influences of the dispersion, the impurity and the electron–phonon coupling (EPC) on the properties of the Gaussian confining (GC) potential qubit with magnetic field were studied by Pekar-type variation method. Results show that the decoherence time will increase with increasing the dielectric constant (DC) ratio, the dispersion coefficient and the EPC strength, respectively. The phase rotation quality factor increases with increasing the dielectric constant ratio, the dispersion coefficient and EPC strength, respectively. The magnetic field has a regulatory effect on the decoherence time and the phase rotation quality factor.
Selecting the double-parameter asymmetric Gaussian (AG) potential to describe the confinement effect of electrons in a quantum dot, the ground state and the first excited state energy eigenvalues and eigenfunctions of the three-body interaction system that are composed of the electrons, the impurity and the longitudinal optical phonon are derived by using the Lee-Low-Pines unitary transformation and the Pekar-type variational method, and the two-level structure required for a qubit is constructed. The influences of material parameters such as the dispersion coefficient, dielectric constant (DC) ratio, and electron-phonon coupling (EPC) constant on the probability density and the oscillation period of electron in the AG potential qubit are investigated. Based on the Fermi gold rule and the even-order approximation, the effects of the DC ratio, the dispersion coefficient and the EPC constant on the qubit decoherence are studied. And then the influences of the dispersion coefficient, the DC ratio and the EPC constant on the phase rotation manipulation of the qubit sphere are discussed. Numerical results show that the dispersion coefficient, the DC ratio and EPC constant of the medium have both advantages and disadvantages for the formation and information storage of qubits. The probability density of electrons in quantum dot qubits decreases with DC ratio increasing and exhibits significant oscillations as the well width of the AG potential decreases; the oscillation period of the qubit decreases with the well depth of the AG potential or the DC ratio increasing; the decoherence time increases with DC ratio or dispersion coefficient increasing; the phase rotation quality factor increases with DC ratio or dispersion coefficient increasing. Using the double-parameter AG potential to describe the confinement of electrons in quantum dot will better reflect the quantization properties of qubit. Increasing the dispersion coefficient or the DC ratio of the material is beneficial to not only the phase rotation manipulation of the qubit sphere, but also improving the coherence of the quantum dot qubit. The results of this paper can be used for reference in the experimental work on the constructing and manipulating of the quantum dot qubits.
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 ω c , confinement strength of the quantum dot ω 0 , 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 φ 2 , 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 electromagnetic-field dependence of the ground and the first excited-state (GFES) energy eigenvalues and eigenfunctions of the strong-coupling polaron in a quantum dot (QD) was studied for various QD thicknesses by using the variational method of the Pekar type (VMPT). On this basis, we construct a qubit in the quantum dot (QQD) by taking a two-level structure of the polaron as the carrier. The results of numerical calculations indicate that the oscillation period of the qubit, {itT}{in0}, increases with increasing the thickness of the quantum dot (TQD) {itL}, but decreases with increasing the cyclotron frequency of the magnetic field (CFMF) ω{in{itc}}, electric-field strength {itF}, and electron-phonon coupling strength (EPCS) α. The probability density of the qubit |Ψ({itρ}, {itz}, {itt})|{su2} presents a normal distribution of the electronic transverse coordinate ρ, significantly influenced by the TQD and effective radius of the quantum dot (ERQD) {itR}{in0}, and shows a periodic oscillation with variations in the electronic longitudinal coordinate {itz}, polar angle φ and time {itt}. The decoherence time τ and the quality factor {itQ} of the free rotation increase with increasing the CFMF ω{in{itc}}, dispersion coefficient η, and EPCS α, but decrease with increasing the electric-field strength {itF}, TQD {itL}, and ERQD {itR}{in0}. The TQD is an important parameter of the qubit. Theoretically, the target, which is to regulate the oscillation period, decoherence time and quality factor of the free rotation of the qubit, can be achieved by designing different TQDs and regulating the strength of the electromagnetic field.
In order to protect coherence of quantum states and reduce the impact of environment on quantum information, we investigate decoherence and relaxation time of magnetopolaron in the presence of three dimensional impurity under strong parabolic potential. The first states energies have been evaluated using the Lee Low Pine transformation and Pekar-type variational method. Parameters such as: decoherence time, transition frequency, spontaneous emission, Shannon entropy, relaxation time and probability density, have been evaluated. It has been seen that the impurity and electron-phonon coupling constant have a considerable effect on formation, protection of quantum qubit and quantum transport. The information exchange measured by the rate of Shannon entropy, has a great dependence on impurity and with its interaction with electrons. The relaxation time τr exhibits increasing behavior as a function of, α, β, and ωc. The electron-phonon coupling constant, impurity and cyclotron frequency are useful parameters to prevent decoherence phenomena. This study paves the way to prolong quantum effect in nanostructure and favor the realization of the future quantum computer.
In the condition of electron-LO phonon strong coupling in a three-dimention parabolic quantum dot,we obtain the eigenenergy of the ground state and the first excited state,the eigenfunction of the ground state and the first excited state by using variational method of pekar type.This system in quantum dot may be employed as a two-level quantum system-qubit,we obtain the quality factors of free rotation of qubit.It is shown that the quality factors of free rotation decrease with increasing confined length and the quality factors of free rotation increase with increasing strength coupling.
We study the eigenenergies and the eigenfunctions of the ground and the first excited states of an electron, which is strongly coupled to the LO-phonon in a quantum dot with triangular bound potential by using the Pekar variational method. This system may be used as a two-level qubit. Our numerical results indicate that the decoherence rate will decrease with increasing the confinement length of the quantum dot (QD) and decrease with increasing electron-LO-phonon coupling constant. The influences of the polar angle on the decoherence rate are dominant when the coupling constant increases, while the effects of the polar angle on that are strong when the confinement length increases. Meanwhile, the decoherence rate varies periodically with respect to the polar angle.