  Efficient control of phonons is crucial to energy-information technology, but
limited by the lacking of tunable degrees of freedom like charge or spin. Here
we suggest to utilize crystalline symmetry-protected pseudospins as new quantum
degrees of freedom to manipulate phonons. Remarkably, we reveal a duality
between phonon pseudospins and electron spins by presenting Kramers-like
degeneracy and pseudospin counterparts of spin-orbit coupling, which lays the
foundation for "pseudospin phononics". Furthermore, we report two types of
three-dimensional phononic topological insulators, which give topologically
protected, gapless surface states with linear and quadratic band degeneracies,
respectively. These topological surface states display unconventional phonon
transport behaviors attributed to the unique pseudospin-momentum locking, which
are useful for phononic circuits, transistors, antennas, etc. The emerging
pseudospin physics offers new opportunities to develop future phononics.
