Gradient
in B-field
N
S
Lets assume the field gradient is in the z direction.
In the Stern-Gerlach experiment, abeam of atoms(assumeℓ= 1) is sent into a magnet with a
strong field gradient. The atoms come from an oven through some collimator to form a beam. The
beam is said to be unpolarized since the three m states are equally likelyno particular state has
been prepared. An unpolarized,ℓ= 1 beam of atoms will be split into the three beams (of equal
intensity) corresponding to the different eigenvalues ofLz.
S
N
m=1
m=0
m=-1
l=1
atomic
beam
The atoms in the top beam are in them= 1 state. If we put them through another Stern-Gerlach
apparatus, they willallgo into the top beam again. Similarly for the middle beam in them= 0
state and the lower beam in them=−1 state.
We can make afancy Stern-Gerlach apparatuswhich puts the beam back together as shown
below.
NSSSNN
+
0
−
z→
We can represent the apparatus by the symbol to the right.