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Quantum Evolution of Cosmological Constant after Reheating
Jeong Ryeol Choi,Sang Pyo Kim,Chung In Um 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
The energy density of the in aton vacuum uctuation is interpreted as the cosmological constant. The vacuum uctuation provides a lower bound on the energy density. The cosmological constant evolved from the reheating period shows a good agreement with the recent data on cosmic microwave background radiation for a universe expanding according to the matter-dominated power-law.
Choi, Jeong Ryeol,Ju, Sanghyun Springer US 2019 Nanoscale research letters Vol.14 No.1
<P>The geometric phase is an extra phase evolution in the wave function of vibrations that is potentially applicable in a broad range of science and technology. The characteristics of the geometric phase in the squeezed state for a carbon-nanotube-based nanowire resonator have been investigated by means of the invariant operator method. The introduction of a linear invariant operator, which is useful for treating a complicated time-dependent Hamiltonian system, enabled us to derive the analytical formula of the geometric phase. By making use of this, we have analyzed the time behavior of the geometric phase based on relevant illustrations. The influence of squeezing parameters on the evolution of the geometric phase has been investigated. The geometric phase, in large, oscillates, and the envelope of such oscillation increases over time. The rate of the increase of the geometric phase is large when the parameters, such as the classical amplitude of the oscillation, the damping factor, and the amplitude of the driving force, are large. We have confirmed a very sharp increase of the geometric phase over time in the case that the angular frequency of the system reaches near the resonance angular frequency. Our development regarding the characteristics of the geometric phase is crucial for understanding the topological features in nanowire oscillations.</P>
Investigation of the coherent wave packet for atime-dependent damped harmonic oscillator
Jeong-Ryeol Choi,S. S. Choi 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.17 No.1-2
We investigated both classical and quantum properties of a damped harmonic oscillator with a time-variable elastic coefficient using invariant operator method. We acquired the energy eigenvalues, uncertainties and probability densities for several types of wave packet. The probability density corresponding to the displaced minimum wave packet expressed in terms of the time-dependent Gaussian function. The displaced minimum wave packet not only be attenuated but also oscillates about ˆx = 0. We confirmed that there exist correspondence between quantum and classical behaviors for the time-dependent damped harmonic oscillator.
Squeezed states for the general time-dependent harmonic oscillator with and without singularity
Jeong Ryeol Choi,Dae-Wook KIM 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
We investigated squeezed states for the general time-dependent harmonic oscillator with and without a singularity by using the minimum uncertainty method. We also derived the even and odd squeezed states of the system by introducing lowering and raising operators. We applied our theory to the periodically driven Caldirola-Kanai oscillator. The graphs of the probability densities in squeezed states exhibited an explicit squeezing eect on the system. As the time-dependency of the Hamiltonian vanishes, our results agree with those of previous reports.
INVESTIGATION OF THE COHERENT WAVE PACKET FOR A TIME-DEPENDENT DAMPED HARMONIC OSCILLATOR
CHOI, JEONG RYEOL,CHOI, S. S. 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.17 No.1
We investigated both classical and quantum properties of a damped harmonic oscillator with a time-variable elastic coefficient using invariant operator method. We acquired the energy eigenvalues, uncertainties and probability densities for several types of wave packet. The probability density corresponding to the displaced minimum wave packet expressed in terms of the time-dependent Gaussian function. The displaced minimum wave packet not only be attenuated but also oscillates about x = 0. We confirmed that there exist correspondence between quantum and classical behaviors for the time-dependent damped harmonic oscillator.
Thermal state for time-dependent oscillator with a singular term
Jeong-Ryeol Choi 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.44 No.2
We investigated the thermal states for a time-dependent harmonic oscillator with a singular potential by introducing the density operator that satised the Liouville-von Neumann equation. We supposed that an ensemble of harmonic oscillator particles, which was initially in equilibrium at a certain temperature, followed Bose-Einstein distribution statistics. The expectation values of ^ql(l = 1; 2; 3; ) in the thermal state were evaluated using the diagonal elements of the density operator, and we conrmed that the time dependency for l = 1 was exactly the same as the expectation value in the number state.
Squeezing effects applied in nonclassical superposition states for quantum nanoelectronic circuits
Choi Jeong Ryeol 나노기술연구협의회 2017 Nano Convergence Vol.4 No.17
Quantum characteristics of a driven series RLC nanoelectronic circuit whose capacitance varies with time are studied using an invariant operator method together with a unitary transformation approach. In particular, squeezing effects and nonclassical properties of a superposition state composed of two displaced squeezed number states of equal amplitude, but 180° out of phase, are investigated in detail. We applied our developments to a solvable specific case obtained from a suitable choice of time-dependent parameters. The pattern of mechanical oscillation of the amount of charges stored in the capacitor, which are initially displaced, has exhibited more or less distortion due to the influence of the time-varying parameters of the system. We have analyzed squeezing effects of the system from diverse different angles and such effects are illustrated for better understanding. It has been confirmed that the degree of squeezing is not constant, but varies with time depending on specific situations. We have found that quantum interference occurs whenever the two components of the superposition meet together during the time evolution of the probability density. This outcome signifies the appearance of nonclassical features of the system. Nonclassicality of dynamical systems can be a potential resource necessary for realizing quantum information technique. Indeed, such nonclassical features of superposition states are expected to play a key role in upcoming information science which has attracted renewed attention recently.