  Strongly correlated electronic systems can harbor a rich variety of quantum
spin states. Understanding and controlling such spin states in quantum
materials is of great current interest. Focusing on the simple binary system
UPt3 with ultrasound (US) as a probe we identify clear signatures in field
sweeps demarkating new high field spin states. Magnetostriction (MS)
measurements performed up to 65 T also show signatures at the same fields
confirming these state transitions. At the very lowest temperatures (<200 mK)
we also observe magneto-acoustic quantum oscillations which for theta =
90{\deg} and vicinity abruptly become very strong in the 24.8-30 T range. High
resolution magnetization measurements for this same angle reveal a continuous
variation of the magnetization implying the subtle nature of the implied
transitions. With B rotated away from the c-axis, the US signatures occur at
nearly the same field. These state transitions merge with the separate sequence
of the well known metamagnetic transition which commences at 20 T for theta =
0{\deg} but moves to higher fields as 1/cos(\theta). This merge, suggesting a
tricritical behavior, occurs at \theta ~ 51{\deg} from the ab-plane. This is an
unique off-symmetry angle where the length change is precisely zero due to the
anisotropic nature of MS in UPt3 for all magnetic field values.
