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Unformatted text preview: PHYS852 Quantum Mechanics II, Spring 2010 HOMEWORK ASSIGNMENT 13 Topics covered: Hilbert-space Frame Transformations, Time-Dependent Perturbation Theory 1. The Hamiltonian for a driven two-level system is H = planckover2pi1 | 2 )( 2 | + planckover2pi1 cos( t ) ( | 1 )( 2 | + | 2 )( 1 | ) , (1) where is the separation between the bare levels, and is the driving frequency. (a) Make a frame transformation generated by the operator G = planckover2pi1 | 2 )( 2 | , and determine the equation of motion for the state-vector in the new frame, defined by | G ( t ) ) = U G ( t ) | ( t ) ) . (b) Make the rotating wave approximation (RWA) by assuming that , and dropping any terms that oscillate at or near 2 . Write, in terms of the detuning = , the effective time-independent Hamiltonian, H G , that then governs the time evolution of | G ( t ) ) . (c) Assume that the system begins at time t = 0 in the ground-state of H G , and calculate | G ( t ) ) . Is this a stationary state in the rotating frame? Now use | S ( t ) ) = U G ( t ) | G ( t ) ) to see what this state looks like in the Scrodinger picture. Is it a stationary state in theto see what this state looks like in the Scrodinger picture....
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This note was uploaded on 12/21/2011 for the course PHYS 852 taught by Professor Moore during the Spring '11 term at Michigan State University.
- Spring '11