A unitary operator is a bounded linear operator 
on a complex Hilbert
space satisfying
 |  |  |
(1)
|
 |  |  |
(2)
|
where 
is the adjoint
operator and 1 denotes the identity operator.
Unitary
See also
Antiunitary, Koopman Operator, Unitary TransformationExplore with Wolfram|Alpha
References
Sakurai, J. J. Modern Quantum Mechanics. Menlo Park, CA: Benjamin/Cummings, 1985.Referenced on Wolfram|Alpha
UnitaryCite this as:
Weisstein, Eric W. "Unitary." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Unitary.html