Black Hole and Quantum Information

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We have given a general frame work to find an optimal quantum evolution for given initial final states in quantum mechanics in analogy to brachistochrone in classical mechanics. The formulation is based on variational principle, in which the Hamiltonian is regarded as a dynamical variable as well as the quantum state. The available Hamiltonian is constrained by natural law or experimental set-up etc and taken care of as the constraints. A few simple examples are demonstrated.This method is extended to the case of arbitrary initial state so as to be relevant to quantum computation. We demonstrated it in typical two qubit gates. To scale-up to many qubits, we have developed a powerful numerical methods. The method is extended to mixed state cases by using measurement. In some cases, the quantum trajectory which passes mixed state is more efficient.We hope our method is useful for quantum computation algorithm, quantum control and Making efficient quantum devices.