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M-st

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**spin 1/2 placed in a magnetic field at x-direction**

Hello guys

I have been a regular reader of this forum. This is my first thread.

## Homework Statement

A spin-1/2 is place in a magnetic field which points in the x-direction. The Hamiltonian is [tex]\hat{H}[/tex] = - B S

_{x}

where S

_{x}= [STRIKE]h[/STRIKE]/2 * pauli x-matrix. We have absorbed all couplings into an effective magnetic field B>0 so that B has dimension inverse time.

1. Find the energy eigenvalues and corresponding eigenstates of H.

the spin is known to be in its lowest energy state. Then a measurement (M1) of the spin-component in the x-direction is carried out.

2. Calculate the probability of finding the value h-bar /2 in measurement M1.

## The Attempt at a Solution

Many attempts but, don't have a clue where to start from.

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