  We consider a quantum state interacting with a short intense linearly
polarized laser pulse. Using the two-dimensional time representation and
Floquet picture we establish a straightforward connection between the laser
carrier-envelope phase (CEP) and the wave function. This connection is revealed
as a unitary transformation in the space of Floquet components. It allows any
CEP effect to be interpreted as an interference between the components and to
put limits on using the CEP in coherent control. A 2-level system is used to
illustrate the theory. On this example we demonstrate strong intensity
sensitivity of the CEP effects and predict an effect for pulses much longer
than the oscillation period of the carrier.
