Time complexity and gate complexity (2009)
Koike, Tatsuhiko, Okudaira, Yosuke
We formulate and investigate the simplest version of time-optimal quantum computation theory (t-QCT), where the computation time is defined by the physical one and the Hamiltonian contains only one-...
Gauge-invariant construction of quantum cosmology (2009)
Amemiya, Fumitoshi, Koike, Tatsuhiko
We present and analyze a gauge-invariant quantum theory of the Friedmann-Robertson-Walker universe with dust. We construct the reduced phase space spanned by gauge-invariant quantities by using the...
Exactly solvable strings in the Minkowski spacetime (2009)
Kozaki, Hiroshi, Koike, Tatsuhiko, Ishihara, Hideki
We study the integrability of the equations of motion for the Nambu-Goto strings with a cohomogeneity-one symmetry in the Minkowski spacetime. A cohomogeneity-one string has a world surface which is...
Strings in five-dimensional anti-de Sitter space with a symmetry (2008)
Koike, Tatsuhiko, Kozaki, Hiroshi, Ishihara, Hideki
The equation of motion of an extended object in spacetime reduces to an ordinary differential equation in the presence of symmetry. By properly defining of the symmetry with notion of cohomogeneity,...
Time Optimal Quantum Operartion for Mixed States(Micro-Macro Duality in Quantum Analysis) (2007)
Carlini, Alberto, Hosoya, Akio, Koike, Tatsuhiko, Okudaira, Yosuke
Time Optimal Unitary Operations (2006)
Carlini, Alberto, Hosoya, Akio, Koike, Tatsuhiko, Okudaira, Yosuke
Extending our previous work on time optimal quantum state evolution, we formulate a variational principle for the time optimal unitary operation, which has direct relevance to quantum computation. We...
Quantum Brachistochrone (2005)
Carlini, Alberto, Hosoya, Akio, Koike, Tatsuhiko, Okudaira, Yosuke
We present a general framework for finding the time-optimal evolution and the optimal Hamiltonian for a quantum system with a given set of initial and final states. Our formulation is based on the...
Topological classification of black Hole: Generic Maxwell set and crease set of horizon (2004)
Siino, Masaru, Koike, Tatsuhiko
The crease set of an event horizon or a Cauchy horizon is an important object which determines qualitative properties of the horizon. In particular, it determines the possible topologies of the...
Black hole and baby universe in a thin film of 3He-A (2002)
Jacobson, Ted, Koike, Tatsuhiko
Condensed matter black hole analogues may provide guidance in grappling with difficult questions about the role of short distance physics in the Hawking effect. These questions bear on the very...
Thurston's Geometrization Conjecture and cosmological models (2000)
Yasuno, Katsuhito, Koike, Tatsuhiko, Siino, Masaru
We investigate a class of spatially compact inhomogeneous spacetimes. Motivated by Thurston's Geometrization Conjecture, we give a formulation for constructing spatially compact composite spacetimes...
Hamiltonians for Compact Homogeneous Universes (1997)
Tanimoto, Masayuki, Koike, Tatsuhiko, Hosoya, Akio
We briefly show how we can obtain Hamiltonians for spatially compact locally homogeneous vacuum spacetimes. The dynamical variables are categorized into the curvature parameters and the...
Upper bound for entropy in asymptotically de Sitter space-time (1997)
Maeda, Kengo, Koike, Tatsuhiko, Narita, Makoto, Ishibashi, Akihiro
We investigate nature of asymptotically de Sitter space-times containing a black hole. We show that if the matter fields satisfy the dominant energy condition and the cosmic censorship holds in the...
Renormalization Group Approach to Einstein Equation in Cosmology (1997)
Iguchi, Osamu, Hosoya, Akio, Koike, Tatsuhiko
The renormalization group method has been adapted to the analysis of the long-time behavior of non-linear partial differential equation and has demonstrated its power in the study of critical...
Hamiltonian structures for compact homogeneous universes (1997)
Tanimoto, Masayuki, Koike, Tatsuhiko, Hosoya, Akio
Hamiltonian structures for spatially compact locally homogeneous vacuum universes are investigated, provided that the set of dynamical variables contains the \Teich parameters, parameterizing the...
Renormalization group and critical behaviour in gravitational collapse (1996)
Hara, Takashi, Koike, Tatsuhiko, Adachi, Satoshi
We present a general framework for understanding and analyzing critical behaviour in gravitational collapse. We adopt the method of renormalization group, which has the following advantages. (1) It...
Compact hyperbolic universe and singularities (1996)
Ishibashi, Akihiro, Koike, Tatsuhiko, Siino, Masaru, Kojima, Sadayoshi
Recently many people have discussed the possibility that the universe is hyperbolic and was in an inflationary phase in the early stage. Under these assumptions, it is shown that the universe cannot...
Dynamics of compact homogeneous universes (1996)
Tanimoto, Masayuki, Koike, Tatsuhiko, Hosoya, Akio
A complete description of dynamics of compact locally homogeneous universes is given, which, in particular, includes explicit calculations of Teichm\"uller deformations and careful counting of...
Koike, Tatsuhiko, Hara, Takashi, Adachi, Satoshi
A scenario is presented, based on renormalization group (linear perturbation) ideas, which can explain the self-similarity and scaling observed in a numerical study of gravitational collapse of...
An Analytic Model with Critical Behavior in Black Hole Formation (1994)
Koike, Tatsuhiko, Mishima, Takashi
A simple analytic model is presented which exhibits a critical behavior in black hole formation, namely, collapse of a thin shell coupled with outgoing null fluid. It is seen that the critical...
Compact Homogeneous Universes (1994)
Koike, Tatsuhiko, Tanimoto, Masayuki, Hosoya, Akio
A thorough classification of the topologies of compact homogeneous universes is given except for the hyperbolic spaces, and their global degrees of freedom are completely worked out. To obtain...
Causal Feature of Central Singularity and Gravitational Mass (1993)
Koike, Tatsuhiko, Onozawa, Hisashi, Siino, Masaru
Mass of singularity is defined, and its relation to whether the singularity is spacelike, timelike or null is discussed for spherically symmetric spacetimes. It is shown that if the mass of...