The interaction of quantum objects lies at the heart of fundamental quantum
physics and is key to a wide range of quantum information technologies.
Photon-quantum-emitter interactions are among the most widely studied.
Two-qubit interactions are generally simplified into two quantum objects in
static well-defined states . In this work we explore a fundamentally new
dynamic type of spin-photon interaction. We demonstrate modulation of a
coherent narrowband wavepacket with another truly quantum object, a quantum dot
with ground state spin degree of freedom. What results is a quantum modulation
of the wavepacket phase (either 0 or {\pi} but no values in between), a new
quantum state of light that cannot be described classically.Comment: Supplementary Information available on reques