Hungsoo Kim

Greenberger-Horne-Zeilinger versus W states : Quantum teleportation through noisy channels

Eylee Jung, Mi-Ra Hwang, You Hwan Ju, Min-Soo Kim, Sahng-Kyoon Yoo, Hungsoo Kim, D. K. Park, Jin-Woo Son, S. Tamaryan, Seong-Keuck Cha 1 Department of Physics, Kyungnam University, Masan, 631-701, Korea 2 Department of Mathematics, Kyungnam University, Masan, 631-701, Korea 3 Green University, Hamyang, 676-872, Korea 4 The Institute of Basic Science, Kyungnam University, Masan, 631-701, Korea 5 Theory Department, Yerevan Physics Institute, Yerevan-36, 375036, Armenia 6 Department of Chemistry, Kyungnam University, Masan, 631-701, Korea Abstract 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 (L2,x, L3,x, L4,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, (L2,y, L3,y, L4,y)-type channel the situation becomes completely reversed. In (L2,z, L3,z, L4,z)-type channel W state is more robust than GHZ state when the noisy parameter (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.

Nonvanishing cosmological constant of flat universe in brane world scenario

Abstract The finite temperature effect is examined in Randall–Sundrum brane-world scenario with inclusion of the matter fields on the brane. At zero temperature it is found that the theory on the brane is conformally invariant, which guarantees AdS/CFT. At 4d effective action we derived a temperature-dependent nonvanishing cosmological constant at the flat spacetime limit of brane worldvolume. At the cosmological temperature 3xa0K the cosmological constant is roughly (0.0004xa0eV) 4 which is within the upper bound of the recent experimental value (0.01xa0eV) 4 .

Gross-Ooguri phase transition at zero and finite temperature: two circular Wilson loop case

In the context of AdS/CFT correspondence the two Wilson loop correlator is examined at both zero and finite temperatures. On the basis of an entirely analytical approach we have found for Nambu-Goto strings the functional relation dSc(Reg)/dL = 2πk between Euclidean action Sc and loop separation L with integration constant k, which corresponds to the analogous formula for point-particles. The physical implications of this relation are explored in particular for the Gross-Ooguri phase transition at finite temperature.

Reduced state uniquely defines the Groverian measure of the 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.

Single 3-brane brane-world in six dimension

Abstract The single 3-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’.

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.

Singular Quantum Mechanical Viewpoint of Localized Gravity in Brane-World Scenario

The graviton localized on the 3-brane is examined in Randall–Sundrum brane-world scenario from the viewpoint of one-dimensional singular quantum mechanics. For the Randall–Sundrum single brane scenario the one-parameter family of the fixed-energy amplitude is explicitly computed where the free parameter ξ parametrizes the various boundary conditions at the brane. The general criterion for the localized graviton to be massless is derived when ξ is arbitrary but non-zero. When ξ=0, the massless graviton is obtained via a coupling constant renormalization. For the two branes picture the fixed-energy amplitude is in general dependent on the two free parameters. The numerical test indicates that there is no massless graviton in this picture. For the positive-tension brane, however, the localized graviton becomes massless when the distance between branes are infinitely large, which is essentially identical to the single brane picture. For the negative-tension brane there is no massless graviton regardless of the distance between branes and choice of boundary conditions.

Randall-Sundrum scenario at nonzero temperature

Abstract The effect of temperature is investigated in the Randall–Sundrum brane-world scenario. It is shown that for a spacetime ansatz motivated by similarity with AdS/CFT correspondence several features of the model, such as its Z 2 symmetry, are not maintained at nonzero temperatures.

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 a two-qubit enviroment. The volume ratio is approximately 0.08 which is much smaller than 3/8, the volume ratio for generalized depolarizing channels.