Dark-state polaritons are form-stable coupled excitations of light and matter that arise in Electromagnetically Induced Transparency (EIT). These polaritons are coherent superpositions of photonic and Raman-like matter branches and their group velocity is determined by the mixing angle between light and matter components. The mixing angle can be controlled by an external coherent field, allowing for the deceleration and trapping of light pulses, with their shape and quantum state preserved in metastable collective states of matter. This reversible coherent control technique has potential applications in generating non-classical states of atomic ensembles, reversible quantum memories for light, and high-resolution spectroscopy. It also enables the processing of quantum information stored in collective excitations of matter and the study of quantum scattering phenomena in systems with coherent cold collisions. The study considers a medium of Λ-type 3-level atoms with two metastable lower states. A quantum field couples resonantly between the ground state and an excited state, and is further coupled to a stable state via a coherent control field. The propagation of the quantum field is governed by a set of Heisenberg-Langevin equations, and the evolution of the optical field is described by a propagation equation. Under adiabatic conditions, the Rabi-frequency of the quantum field is much smaller than the control field, allowing for a perturbative treatment of the atomic equations. The propagation equations simplify under these conditions, leading to a modified group velocity of the quantum field. A canonical transformation is introduced to define a new quantum field, which obeys a shape-preserving propagation equation. This new field has bosonic commutation relations and can be associated with bosonic quasi-particles (polaritons). These polaritons are dark-states, immune to spontaneous emission and eigenstates of the interaction Hamiltonian with zero eigenvalue. The quantum states of light can be coherently transferred to collective atomic states and vice versa, enabling the generation of non-classical atomic ensembles and high-precision spectroscopy. The technique is complementary to earlier studies on quantum state mapping in EIT media and offers advantages in terms of simplicity and flexibility. The analysis involves perturbation expansion, adiabatic approximation, and neglects Raman coherence decay. The validity of these approximations is discussed, showing that the adiabatic condition is easier to implement in optically dense media. The study also considers the effects of Raman coherence decay and the practical aspects of trapping light pulses in the medium. The results demonstrate the potential of dark-state polaritons for quantum information processing and quantum optics applications.Dark-state polaritons are form-stable coupled excitations of light and matter that arise in Electromagnetically Induced Transparency (EIT). These polaritons are coherent superpositions of photonic and Raman-like matter branches and their group velocity is determined by the mixing angle between light and matter components. The mixing angle can be controlled by an external coherent field, allowing for the deceleration and trapping of light pulses, with their shape and quantum state preserved in metastable collective states of matter. This reversible coherent control technique has potential applications in generating non-classical states of atomic ensembles, reversible quantum memories for light, and high-resolution spectroscopy. It also enables the processing of quantum information stored in collective excitations of matter and the study of quantum scattering phenomena in systems with coherent cold collisions. The study considers a medium of Λ-type 3-level atoms with two metastable lower states. A quantum field couples resonantly between the ground state and an excited state, and is further coupled to a stable state via a coherent control field. The propagation of the quantum field is governed by a set of Heisenberg-Langevin equations, and the evolution of the optical field is described by a propagation equation. Under adiabatic conditions, the Rabi-frequency of the quantum field is much smaller than the control field, allowing for a perturbative treatment of the atomic equations. The propagation equations simplify under these conditions, leading to a modified group velocity of the quantum field. A canonical transformation is introduced to define a new quantum field, which obeys a shape-preserving propagation equation. This new field has bosonic commutation relations and can be associated with bosonic quasi-particles (polaritons). These polaritons are dark-states, immune to spontaneous emission and eigenstates of the interaction Hamiltonian with zero eigenvalue. The quantum states of light can be coherently transferred to collective atomic states and vice versa, enabling the generation of non-classical atomic ensembles and high-precision spectroscopy. The technique is complementary to earlier studies on quantum state mapping in EIT media and offers advantages in terms of simplicity and flexibility. The analysis involves perturbation expansion, adiabatic approximation, and neglects Raman coherence decay. The validity of these approximations is discussed, showing that the adiabatic condition is easier to implement in optically dense media. The study also considers the effects of Raman coherence decay and the practical aspects of trapping light pulses in the medium. The results demonstrate the potential of dark-state polaritons for quantum information processing and quantum optics applications.