arXiv subjects

Hungsoo Kim

Publications and source records attributed to Hungsoo Kim.

At least 19 recordsLinked to original sources

arXiv2013

One and Two-individual Movements of Fish after Chemical Exposure

Movement behavior of an indicator species, zebrafish (Danio rerio), was analyzed with one- and two-individual groups before and after treatment with a toxic chemical, formaldehyde, at a low concentration (1 ppm). After the boundary area had been determined based on experimental data, intermittency was defined as the probability distributions of the shadowing time during which data were above a pre-determined threshold and were obtained from experimental time-series data on forces and the inter-distances for one and two individuals. Overall intermittencies were similar in the boundary and central areas. However, the intermittencies were remarkably different between the one- and the two-individual groups: the single line was used to fit the data for the one-individual group whereas two phases were observed with breakpoints (approximately 10 seconds in logarithm) in the exponential fitting curves for the two-individual group. A difference in the probability distributions of shadowing time was observed "before" and "after" treatment for different areas. Intermittency patterns before and after treatment were contrasted in the center for the one-individual group whereas the difference was observed in the boundary for two-individual group. The intermittencies for the inter-distances of two individuals in the boundary and central areas were markedly different before and after treatment. When the differences between the intermittencies in the boundary and the central areas and between "before" and "after" treatment are considered, the distribution patterns of the shadowing time (scaling behaviors or intermittency patterns) should be a useful means of bio-monitoring to detect contaminants in the environment.

physics.bio-ph↗

arXiv2010

Test of Common Sense in Quantum Copying Process

It is believed that the more we have {\it a priori} information on input states, the better we can make the quality of clones in quantum cloning machines. This common sense idea was confirmed several years ago by analyzing a situation, where the input state is either one of two non-orthogonal states. If the {\it a priori} information is measured by the Shannon entropy, common sense predicts that the quality of the clone becomes poorer with increasing $N$, where $N$ is the number of possible input states. We show, however, that the {\it a priori} information measured by the Shannon entropy does not affect the quality of the clones. Instead the no-cloning theorem and `denseness' of the possible input states play important roles in determining the quality. Specifically, the factor `denseness' plays a more crucial role than the no-cloning theorem when $N \geq 3$.

quant-ph↗

arXiv2010

Difficulties in analytic computation for relative entropy of entanglement

It is known that relative entropy of entanglement for entangled state $ρ$ is defined via its closest separable (or positive partial transpose) state $σ$. Recently, it has been shown how to find $ρ$ provided that $σ$ is given in two-qubit system. In this paper we study on the inverse process, i.e. how to find $σ$ provided that $ρ$ is given. It is shown that if $ρ$ is one of Bell-diagonal, generalized Vedral-Plenio and generalized Horodecki states, one can always find $σ$ from a geometrical point of view. This is possible due to the following two facts: (i) The Bloch vectors of $ρ$ and $σ$ are identical with each other (ii) The qubit-interaction vector of $σ$ can be computed from a crossing point between minimal geometrical object, in which all separable states reside in the presence of Bloch vectors, and a straight line, which connects the point corresponding to the qubit-interaction vector of $ρ$ and the nearest vertex of the maximal tetrahedron, where all two-qubit states reside. It is shown, however, that these nice properties are not maintained for the arbitrary two-qubit states.

quant-ph↗

arXiv2009

Effect of Phase Factor in the Geometric Entanglement Measure of Three-Qubit States

Any pure three-qubit state is uniquely characterized by one phase and four positive parameters. The geometric measure of entanglement as a function of state parameters can have different expressions. Each of expressions has its own applicable domain and thus the whole state parameter space is divided into subspaces that are ranges of definition for corresponding expressions. The purpose of this paper is to examine the applicable domains for the most general qubit-interchange symmetric three-qubit states. First, we compute the eigenvalues of the non-linear eigenvalue equations and the nearest separable states for the permutation invariant three-qubit states with a fixed phase. Next, we compute the geometric entanglement measure, deduce the boundaries of all subspaces, and find allocations of highly and slightly entangled states. It is shown that there are three applicable domains when the phase factor is $π/2$ while other cases have only two domains. The emergence of the three domains is due to the appearance of the additional W-state. We show that most of highly entangled states reside near the boundaries of the domains and states located far from the boundaries become less-entangled and eventually go to the product states. The neighbors of W-state are generally more entangled than the neighbors of Greenberger-Horne-Zeilinger(GHZ) state from the aspect of the geometric measure. However, the range of the GHZ-neighbors is much more wider than the range of the W-neighbors.

quant-ph↗

arXiv2009

Toward an understanding of entanglement for generalized n-qubit W-states

We solve stationarity equations of the geometric measure of entanglement for multi-qubit W-type states. In this way we compute analytically the maximal overlap of one-parameter $n$-qubit and two-parameter four-qubit W-type states and their nearest product states. Possible extensions to arbitrary W-type states and geometrical interpretations of these results are discussed in detail.

quant-ph↗

arXiv2009

Attack of Many Eavesdroppers via Optimal Strategy in Quantum Cryptography

We examine a situation that $n$ eavesdroppers attack the Bennett-Brassard cryptographic protocol via their own optimal and symmetric strategies. Information gain and mutual information with sender for each eavesdropper are explicitly derived. The receiver's error rate for the case of arbitrary $n$ eavesdroppers can be derived using a recursive relation. Although first eavesdropper can get mutual information without disturbance arising due to other eavesdroppers, subsequent eavesdropping generally increases the receiver's error rate. Other eavesdroppers cannot gain information on the input signal sufficiently. As a result, the information each eavesdropper gains becomes less than optimal one.

quant-ph↗

arXiv2009

Quantum Resonance near Optimal Eavesdropping in Quantum Cryptography

We find a resonance behavior in the disturbance when an eavesdropper chooses a near-optimal strategy intentionally or unintentionally when the usual Bennett-Brassard cryptographic scheme is performed between two trusted parties. This phenomenon tends to disappear when eavesdropping strategy moves far from the optimal one. Therefore, we conjecture that this resonant effect is a characteristic for the eavesdropping strategy near to optimal one. We argue that this effect makes the quantum cryptography more secure against the eavesdropper's attack.

quant-ph↗

arXiv2008

GHZ versus W : Quantum Teleportation through Noisy Channels

Which state does lose less quantum information between GHZ and W states when they are prepared for two-party quantum teleportation through noisy channel? We address this issue by solving analytically a master equation in the Lindbald form with introducing the noisy channels which makes the quantum channels to be mixed states. It is found that the answer of the question is dependent on the type of the noisy channel. If, for example, the noisy channel is ($L_{2,x}$, $L_{3,x}$, $L_{4,x}$)-type where $L's$ denote the Lindbald operators, GHZ state is always more robust than W state, i.e. GHZ state preserves more quantum information. In, however, ($L_{2,y}$, $L_{3,y}$, $L_{4,y}$)-type channel the situation becomes completely reversed. In ($L_{2,z}$, $L_{3,z}$, $L_{4,z}$)-type channel W state is more robust than GHZ state when the noisy paramter ($κ$) is comparatively small while GHZ state becomes more robust when $κ$ is large. In isotropic noisy channel we found that both states preserve equal amount of quantum information. A relation between the average fidelity and entanglement for the mixed state quantum channels are discussed.

quant-ph↗

arXiv2008

Reduced State Uniquely Defines Groverian Measure of Original Pure State

Groverian and Geometric entanglement measures of the n-party pure state are expressed by the (n-1)-party reduced state density operator directly. This main theorem derives several important consequences. First, if two pure n-qudit states have reduced states of (n-1)-qudits, which are equivalent under local unitary(LU) transformations, then they have equal Groverian and Geometric entanglement measures. Second, both measures have an upper bound for pure states. However, this upper bound is reached only for two qubit systems. Third, it converts effectively the nonlinear eigenvalue problem for three qubit Groverian measure into linear eigenvalue equations. Some typical solutions of these linear equations are written explicitly and the features of the general solution are discussed in detail.

quant-ph↗

arXiv2007

Amplitude Damping for single-qubit System with single-qubit mixed-state Environment

We study a generalized amplitude damping channel when environment is initially in the single-qubit mixed state. Representing the affine transformation of the generalized amplitude damping by a three-dimensional volume, we plot explicitly the volume occupied by the channels simulatable by a single-qubit mixed-state environment. As expected, this volume is embedded in the total volume by the channels which is simulated by two-qubit enviroment. The volume ratio is approximately 0.08 which is much smaller than 3/8, the volume ratio for generalized depolarizing channels.

quant-ph↗

arXiv2007

Quantum Teleportation and Von Neumann Entropy

The single qubit quantum teleportation (sender and receiver are Alice and Bob respectively) is analyzed from the aspect of the quantum information theories. The various quantum entropies are computed at each stage, which ensures the emergence of the entangled states in the intermediate step. The mutual information $S(B:C)$ becomes non-zero before performing quantum measurement, which seems to be consistent to the original purpose of the quantum teleportation. It is shown that if the teleported state $|ψ>$ is near the computational basis, the quantum measurement in $C$-system is dominantly responsible for the joint entropy $S(A,C)$ at the final stage. If, however, $|ψ>$ is far from the computational basis, this dominant responsibility is moved into the quantum measurement of system $A$. A possible extension of our results are briefly discussed.

quant-ph↗

arXiv2005

Equation of state for an interacting holographic dark energy model

We investigate a model of the interacting holographic dark energy with cold dark matter (CDM). If the holographic energy density decays into CDM, we find two types of the effective equation of state. In this case we have to use the effective equations of state ($ω^{\rm eff}_{\rm Λ}$) instead of the equation of state ($ω_{\rm Λ})$. For a fixed ratio of two energy densities, their effective equations of state are given by the same negative constant. Actually, the cosmic anti-friction arisen from the vacuum decay process may induce the acceleration with $ω^{\rm eff}_{\rm Λ}<-1/3$. For a variable ratio, their effective equations of state are slightly different, but they approach the same negative constant in the far future. Consequently, we show that such an interacting holographic energy model cannot accommodate a transition from the dark energy with $ω^{\rm eff}_{\rm Λ}\ge-1$ to the phantom regime with $ω^{\rm eff}_{\rm Λ}<-1$.

gr-qc↗

arXiv2005

Role of the Brans-Dicke scalar in the holographic description of dark energy

We study cosmological application of the holographic energy density in the Brans-Dicke theory. Considering the holographic energy density as a dynamical cosmological constant, it is more natural to study it in the Brans-Dicke theory than in general relativity. Solving the Friedmann and Brans-Dicke field equations numerically, we clarify the role of Brans-Dicke field during evolution of the universe. When the Hubble horizon is taken as the IR cutoff, the equation of state ($w_{\Lmd}$) for the holographic energy density is determined to be 5/3 when the Brans-Dicke parameter $\omg$ goes infinity. This means that the Brans-Dicke field plays a crucial role in determining the equation of state. For the particle horizon IR cutoff, the Brans-Dicke scalar mediates a transition from $w_{\Lmd} = -1/3$ (past) to $w_{\Lmd} = 1/3$ (future). If a dust matter is present, it determines future equation of state. In the case of future event horizon cutoff, the role of the Brans-Dicke scalar and dust matter are turned out to be trivial, whereas the holographic energy density plays an important role as a dark energy candidate with $w_{\Lmd} =-1$.

gr-qc↗

arXiv2005

Holographic energy density in the Brans-Dicke teory

We study cosmological applications of the holographic energy density. Considering the holographic energy density as a dynamical cosmological constant, we need the Brans-Dicke theory as a dynamical framework instead of general relativity. In this case we use the Bianchi identity as a consistency relation to obtain physical solutions. It is shown that the future event horizon as the IR cutoff provides the dark energy in the Brans-Dicke theory. Furthermore the role of the Brans-Dicke scalar is clarified in the dark energy-dominated universe by calculating its equation of state.

hep-th↗

arXiv2005

Inflation parameters from Gauss-Bonnet braneworld

We calculate the spectral index and tensor-to-scalar ratio for patch inflation arisen from the Gauss-Bonnet braneworld scenario. The patch cosmological models consist of Gauss-Bonnet (GB), Randall-Sundrum (RS), and 4D general relativistic (GR) cases. In order to compare with the observation data, we perform leading-order calculations for all patch models by choosing large-field, small-field, and hybrid potentials. We show that the large-field potentials are sensitive to a given patch model, while the small-field and hybrid potentials are insensitive to a given patch model. It is easier to discriminates between quadratic potential and quartic potential in the GB model rather than RS and GR models. Irrespective of patch models, it turns out that the small-field potentials are the promising models in view of the observation.

astro-ph↗

arXiv2004

Second-order corrections to noncommutative spacetime inflation

We investigate how the uncertainty of noncommutative spacetime affects on inflation. For this purpose, the noncommutative parameter $μ_0$ is taken to be a zeroth order slow-roll parameter. We calculate the noncommutative power spectrum up to second order using the slow-roll expansion. We find corrections arisen from a change of the pivot scale and the presence of a variable noncommutative parameter, when comparing with the commutative power spectrum. The power-law inflation is chosen to obtain explicit forms for the power spectrum, spectral index, and running spectral index. In cases of the power spectrum and spectral index, the noncommutative effect of higher-order corrections compensates for a loss of higher-order corrections in the commutative case. However, for the running spectral index, all higher-order corrections to the commutative case always provide negative spectral indexes, which could explain the recent WMAP data.

hep-th↗

arXiv2004

Noncommutative spacetime effect on the slow-roll period of inflation

We study how the noncommutative spacetime affects on inflation. First we obtain the noncommutative power spectrum of the curvature perturbations produced during inflation in the slow-roll approximation. This is the explicit $k$-dependent power spectrum up to first order in slow-roll parameters $ε_1 δ_1$ including the noncommutative parameter $μ$. In order to test the role of $μ$ further, we calculate the noncommutative power spectrum using the slow-roll expansion. We find corrections which arise from the change of pivot scale and a noncommutative parameter with $μ\not=$ constant. It turns out that the noncommutative parameter $μ$ could be considered as a zeroth order slow-roll parameter and the noncommutative spacetime effect suppresses the power spectrum.

hep-th↗

arXiv2002

Single 3-Brane Brane-World in Six Dimension

The single 3-brane brane world at six dimension is examined when the extra dimensions are not compact. Although the warp factor diverges at the asymptotic region of the extra dimension, the normalizable zero mode and higher KK spectrum exist in the gravitational fluctuation. We compute the zero mode analytically and KK spectrum numerically. It is explicitly proven that our solution does not obey `brane world sum rule'.

hep-th↗