scholarly journals Spin Polarization Oscillations and Coherence Time in the Random Interaction Approach

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
P. Pereyra
Keyword(s):  
Magnetic Field ◽  
Time Evolution ◽  
Spin Polarization ◽  
Energy Levels ◽  
Coherence Time ◽  
Environment Interaction ◽  
Interaction Picture ◽  
Gaussian Orthogonal Ensemble ◽  
Interaction Approach ◽  
The Magnetic Field

We study the time evolution of the survival probability and the spin polarization of a dissipative nondegenerate two-level system in the presence of a magnetic field in the Faraday configuration. We apply the Extended Gaussian Orthogonal Ensemble approach to model the stochastic system-environment interaction and calculate the survival and spin polarization to first and second order of the interaction picture. We present also the time evolution of the thermal average of these quantities as functions of the temperature, the magnetic field, and the energy-levels density, for ρ(ϵ)∝ϵs, in the subohmic, ohmic, and superohmic dissipation forms. We show that the behavior of the spin polarization calculated here agrees rather well with the time evolution of spin polarization observed and calculated, recently, for the electron-nucleus dynamics of Ga centers in dilute (Ga,N)As semiconductors.

scholarly journals Spin-1/2 Particles under the Influence of a Uniform Magnetic Field in the Interior Schwarzschild Solution

Universe ◽  
2021 ◽  
Vol 7 (12) ◽  
pp. 467
Author(s):  
Fayçal Hammad ◽  
Alexandre Landry ◽  
Parvaneh Sadeghi
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Total Mass ◽  
Uniform Magnetic Field ◽  
Energy Levels ◽  
Relativistic Wave Equation ◽  
Relativistic Wave ◽  
Schwarzschild Solution ◽  
Relativistic Regime ◽  
The Magnetic Field

The relativistic wave equation for spin-1/2 particles in the interior Schwarzschild solution in the presence of a uniform magnetic field is obtained. The fully relativistic regime is considered, and the energy levels occupied by the particles are derived as functions of the magnetic field, the radius of the massive sphere and the total mass of the latter. As no assumption is made on the relative strengths of the particles’ interaction with the gravitational and magnetic fields, the relevance of our results to the physics of the interior of neutron stars, where both the gravitational and the magnetic fields are very intense, is discussed.

Effect of temperature on magnetic susceptibility and thermodynamic properties of an asymmetric quantum dot in tilted magnetic field

2015 ◽  
Vol 29 (23) ◽  
pp. 1550127 ◽  
Author(s):  
R. Khordad
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Quantum Dot ◽  
Specific Heat ◽  
Energy Levels ◽  
Effect Of Temperature ◽  
Magnetic Field Direction ◽  
Asymmetric Quantum ◽  
Gaas Quantum Dot ◽  
The Magnetic Field

In this paper, the specific heat, entropy and magnetic susceptibility of an asymmetric GaAs quantum dot (QD) are studied under the influence of temperature and a tilted external magnetic field. We first calculate the analytical wave functions and energy levels using a transformation to simplify the Hamiltonian of the system. Then, we obtain the analytical expressions for specific heat, entropy and magnetic susceptibility as the function of temperature, magnetic field and its direction for various anisotropy of the system. According to the results obtained from the present work, we find that (i) the specific heat and entropy are decreased when the magnetic field increases. (ii) When anisotropy is increased, the specific heat and entropy decrease. (iii) At large magnetic fields, the anisotropy has not important effect on specific heat and entropy. In briefly, the magnetic field, magnetic field direction and anisotropy play important roles in the specific heat, entropy and magnetic susceptibility of an asymmetric QD.

scholarly journals Robust storage qubits in ultracold polar molecules

2021 ◽  
Author(s):  
Philip Gregory ◽  
Jacob Blackmore ◽  
Sarah Bromley ◽  
Jeremy Hutson ◽  
Simon Cornish
Keyword(s):  
Magnetic Field ◽  
Quantum Computation ◽  
Coherence Time ◽  
Magic Angle ◽  
Light Shift ◽  
Ultracold Molecules ◽  
Rotational States ◽  
Ultracold Polar Molecules ◽  
Optically Trapped ◽  
The Magnetic Field

Abstract Quantum states with long-lived coherence are essential for quantum computation, simulation and metrology. The nuclear spin states of ultracold molecules prepared in the singlet rovibrational ground state are an excellent candidate for encoding and storing quantum information. However, it is important to understand all sources of decoherence for these qubits, and then eliminate them, in order to reach the longest possible coherence times. Here, we fully characterise the dominant mechanisms for decoherence of a storage qubit in an optically trapped ultracold gas of RbCs molecules using high-resolution Ramsey spectroscopy. Guided by a detailed understanding of the hyperfine structure of the molecule, we tune the magnetic field to where a pair of hyperfine states have the same magnetic moment. These states form a qubit, which is insensitive to variations in magnetic field. Our experiments reveal an unexpected differential tensor light shift between the states, caused by weak mixing of rotational states. We demonstrate how this light shift can be eliminated by setting the angle between the linearly polarised trap light and the applied magnetic field to a magic angle of arccos(1/√3)≈55°. This leads to a coherence time exceeding 6.9 s (90% confidence level). Our results unlock the potential of ultracold molecules as a platform for quantum computation.

scholarly journals Evolution of quasi-bound states in the circular n–p junction of bilayer graphene under magnetic field

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haijiao Ji ◽  
Yueting Pan ◽  
Haiwen Liu
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Bound States ◽  
Local Density ◽  
Energy Levels ◽  
Bilayer Graphene ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Weak Magnetic Fields ◽  
The Magnetic Field

Abstract Electron in gapless bilayer graphene can form quasi-bound states when a circular symmetric potential is created in bilayer graphene. These quasi-bound states can be adjusted by tuning the radius and strength of the potential barrier. We investigate the evolution of quasi-bound states spectra in the circular n–p junction of bilayer graphene under the magnetic field numerically. The energy levels of opposite angular momentum split and the splitting increases with the magnetic field. Moreover, weak magnetic fields can slightly shift the energy levels of quasi-bound states. While strong magnetic fields induce additional resonances in the local density states, which originates from Landau levels. We demonstrate that these numerical results are consistent with the semiclassical analysis based on Wentzel–Kramers–Brillouin approximation. Our results can be verified experimentally via scanning tunneling microscopy measurements.

REEXAMINATION OF SPIN TRANSPORT THROUGH A DOUBLE-δ MAGNETIC BARRIER WITH SPIN-ORBIT INTERACTIONS

2009 ◽  
Vol 23 (30) ◽  
pp. 3631-3642
Author(s):  
CAIHUA BI ◽  
FENG ZHAI
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Spin Polarization ◽  
Energy Region ◽  
Spin Transport ◽  
Inhomogeneous Magnetic Field ◽  
Pure Spin ◽  
Spin Orbit ◽  
Spin Orbit Interactions ◽  
The Magnetic Field

We revisit the properties of spin transport through a semiconductor 2DEG system subjected to the modulation of both a ferromagnetic metal (FM) stripe on top and the Rashba and Dresselhaus spin-orbit interactions (SOIs). The FM stripe has a magnetization along the transporting direction and generates an inhomogeneous magnetic field in the 2DEG plane which is taken as a double-δ shape. It is found that the spin polarization of this system generated from a spin-unpolarized injection can be remarkable only within a low Fermi energy region and is not more than 30% for the parameters available in current experiments. In this energy region, both the magnitude and the orientation of the spin polarization can be tuned by the Rashba strength, the Dresselhaus strength, and the magnetic field strength. The magnetization reversal of the FM stripe cannot result in a change of the conductance, but can rotate the orientation of the spin polarization. The results are in contrast to those in [ J. Phys.: Condens. Matter15 (2003) L31] where a pure spin state for incident electrons is artificially assumed.

Magnetic Field Effects on Electron Eigenstates in a Concentric Triple Quantum Ring

2010 ◽  
Vol 10 ◽  
pp. 121-130 ◽  
Author(s):  
Hojjatollah K. Salehani ◽  
Mahdi Esmaeilzadeh ◽  
Khosrow Shakouri
Keyword(s):  
Magnetic Field ◽  
Energy Levels ◽  
Quantum Ring ◽  
Dimensional System ◽  
Magnetic Field Effects ◽  
Donor Impurity ◽  
Quantum Rings ◽  
Hydrogenic Donor Impurity ◽  
Hydrogenic Donor ◽  
The Magnetic Field

In this paper, the electronic eigenstates and energy spectra of a two-dimensional system formed by three concentric, coupled, semiconductor quantum rings with a perpendicular magnetic field in the presence and the absence of a single ionized hydrogenic donor impurity are studied. It is found that the magnetic field localizes the electron wave function in the inner rings. The effects of hydrogenic donor on the electronic structure of concentric triple quantum rings are investigated in the both on- and off-center configurations. It is shown that as the donor moves away from the center of the system, the ground state energy decreases monotonically, the degeneracy is lifted and the gap between the energy levels increases. Also, the binding energy of donor impurity increases with increasing magnetic field.

GROUND STATE RESONANCES OF A HYDROGEN ATOM IN AN INTENSE MAGNETIC FIELD

1995 ◽  
Vol 07 (03) ◽  
pp. 311-361 ◽  
Author(s):  
RICHARD FROESE ◽  
ROGER WAXLER
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Hydrogen Atom ◽  
Time Evolution ◽  
Complex Plane ◽  
Exponential Decay ◽  
Ground State ◽  
Stationary States ◽  
Intense Magnetic Field ◽  
The Magnetic Field

We consider a hydrogen atom in a constant and very large magnetic field. For bounded angular momentum about the direction of the magnetic field we consider resonances in the sense of dilation analyticity. We find a class of resonances corresponding to quasi-stationary states which behave in a certain sense like ground states. The position of these resonances in the complex plane is estimated. Further it is shown that under the time evolution generated by the Hamiltonian for this system these quasi-stationary states exhibit exponential decay in time.

scholarly journals Magnetic Quantum Otto Engine for the Single-Particle Landau Problem

2017 ◽  
Author(s):  
Francisco J. Peña ◽  
Alejandro González ◽  
A.S. Nunez ◽  
Pedro Orellana ◽  
René G. Rojas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Field Intensity ◽  
Compression Ratio ◽  
Single Particle ◽  
Magnetic Field Intensity ◽  
Energy Levels ◽  
Adiabatic Process ◽  
Adiabatic Processes ◽  
The Magnetic Field

We study the effect of the degeneracy factor in the energy levels of the well-known Landau problem for a magnetic quantum Otto engine. The scheme of the cycle is composed of two quantum adiabatic processes and two quantum isomagnetic processes driven by a quasi-static modulation of external magnetic field intensity. We derive the analytical expression of the relation between the magnetic field and temperature along the adiabatic process and, in particular, reproduce the expression for the efficiency as a function of the compression ratio.

The effect of a magnetic field on the thermal conductivity of paramagnetic crystals: cerium ethylsulphate

1968 ◽  
Vol 302 (1470) ◽  
pp. 419-436 ◽  
Keyword(s):  
Magnetic Field ◽  
Thermal Conductivity ◽  
Energy Levels ◽  
Thermal Resistivity ◽  
Zero Field ◽  
Coupling Constant ◽  
Spin Lattice ◽  
Spin Interactions ◽  
The Mean ◽  
The Magnetic Field

The thermal conductivity of crystals of concentrated cerium ethylsulphate has been measured in the range 1 to 4·58°K and in magnetic fields of up to 53 kG. In zero field there is a marked anomaly at 2·5°K in the variation of conductivity with temperature. Owing to the anisotropy of the g -values the magnetic field dependence of the thermal resistivity at constant temperature depends on the field direction; with the field parallel to the hexagonal axis, a maximum occurs in the resistivity which moves roughly linearly with temperature, and in very high fields it is always less than in zero field; with the field applied in the perpendicular direction a resistivity maximum is only observed above 2°K, and in the highest available field it is always much greater than in zero field. These results are explained by assuming that direct process phonon-spin interactions scatter certain bands of phonons whose frequency depends on the separation of the energy levels produced by the applied magnetic field. A statistical theory is used to determine the relative populations of the energy levels in the calculation of the thermal resistivity. It is assumed that the spin-phonon absorption lineshape is Gaussian. By fitting the theory to the experimental data, approximate values of the spin-lattice coupling constant, the linewidth of the transitions and the mean free paths for boundary and point-defect scattering are obtained.

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