Arbitrary Velocity Volkov States

The evolution of a lepton wavepacket in the fields of an electromagnetic plane wave is described by a superposition of definite-momentum Volkov states. Here, we demonstrate that the peak amplitude of spatiotemporally structured lepton wavepackets can travel through a plane wave at an arbitrary, tailored velocity—independent of the velocity expectation value, classical velocity, and field amplitude. These wavepackets are prepared by imposing correlations between the dressed momenta of the Volkov states. The correlations leave an imprint on the expectation value of the longitudinal momentum or energy, providing a potential observable signature of the arbitrary velocity.