  We describe the off-diagonal spin basis for observing angular correlations in
top quark pair production events at the Fermilab Tevatron. For events initiated
by quark-antiquark annihilation, the top and antitop quark spins are 100%
correlated in this basis: a spin-up top quark is always accompanied by a
spin-down antitop quark and vice versa. Inclusion of the gluon-gluon initial
state lowers the fraction of unlike spin events to 92%. Nevertheless, the
angular correlations between the top and antitop quark decay products are twice
as large in the off-diagonal basis as those in the more traditional helicity
basis. We give two brief examples of how the presence of new physics would
alter these correlations.
