Wednesday, February 20, 2013

1302.4669 (Ranjith V. et al.)

Quantum First-Passage Time: Exact Solutions for a Class of Tight-Binding
Hamiltonian Systems

Ranjith V., N. Kumar
The Schrodinger integral-equation approach for calculating the classical first-passage time (C-fpt) probability density is extended to the case of quantum first-passage time (Q-fpt). Using this extension, we have calculated analytically the Q-fpt probability density for a class of few-site/state tight-binding Hamiltonian systems, e.g., a qubit, as well as for an infinite 1D lattice. The defining feature of such a quantum system is that the passage across the boundary between a subspace ({\omega}) and its complement ({\omega}') is through a unique pair of door-way sites such that the first departure from (arrival at) {\omega} corresponds to the first arrival at (departure from) {\omega}'. The Q-fpt probability density so derived remains positive over the time interval in which it also normalizes to unity. These conditions of positivity and normalization define the physical time domain for the Q-fpt problem. This time domain is found to remain finite for the few-site/state Hamiltonian systems considered here, which is quite unlike the case for the diffusive C-fpt problems. The door-way sites and the associated Q-fpt probability density derived here should be relevant to the inter-biomolecular/nanostructural electron transport phenomena. Keywords: Quantum First-passage time, arrival time, tunneling time, time in quantum mechanics
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