A quantum memory device for storing one or more modes of electromagnetic radiation, the quantum memory device comprising: an atomic ensemble comprising atomic valence electrons having a first state, a second state and a third state, wherein the second state has a higher energy than, and is linked to, the first state by an atomic transition, and the third state has a higher energy than, and is linked to, the second state by one or more atomic transitions; a signal source of electromagnetic radiation arranged to generate one or more modes of electromagnetic radiation to be stored having a frequency corresponding to an off-resonant atomic transition between the first state and the second state of atomic valence electrons in the atomic ensemble, wherein the one or more modes of electromagnetic radiation from the signal source are arranged to be incident upon the atomic ensemble to stimulate off-resonant transitions of the atomic valence electrons in the atomic ensemble between the first state and the second state; one or more control sources of electromagnetic radiation each arranged to generate electromagnetic radiation having a frequency corresponding to an off-resonant atomic transition from the one or more atomic transitions linking the second state and the third state of atomic valence electrons in the atomic ensemble, wherein the electromagnetic radiation from the one or more control sources is arranged to be incident upon the atomic ensemble to stimulate off-resonant transitions of the atomic valence electrons in the atomic ensemble between the second state and the third state; wherein the quantum memory device is arranged such that on incidence of one or more modes of electromagnetic radiation from the signal source and electromagnetic radiation from each of the one or more control sources to the atomic ensemble, a coherent excitation of the transition between the first state and the third state is created that stores the one or more modes of electromagnetic radiation from the signal source in the atomic ensemble, and subsequent incidence of electromagnetic radiation from each of the one or more control sources upon the atomic ensemble stimulates emission of the one or more stored modes of electromagnetic radiation from the atomic ensemble; and wherein the inverse of the residual Doppler linewidth owing to the incidence of the electromagnetic radiation generated by the signal source and the one or more control sources on the atomic valence electrons in the atomic ensemble is greater than half the lifetime of the coherent excitation of the transition between the first state and the third state. an atomic ensemble comprising atomic valence electrons having a first state, a second state and a third state, wherein the second state has a higher energy than, and is linked to, the first state by an atomic transition, and the third state has a higher energy than, and is linked to, the second state by one or more atomic transitions; a signal source of electromagnetic radiation arranged to generate one or more modes of electromagnetic radiation to be stored having a frequency corresponding to an off-resonant atomic transition between the first state and the second state of atomic valence electrons in the atomic ensemble, wherein the one or more modes of electromagnetic radiation from the signal source are arranged to be incident upon the atomic ensemble to stimulate off-resonant transitions of the atomic valence electrons in the atomic ensemble between the first state and the second state; one or more control sources of electromagnetic radiation each arranged to generate electromagnetic radiation having a frequency corresponding to an off-resonant atomic transition from the one or more atomic transitions linking the second state and the third state of atomic valence electrons in the atomic ensemble, wherein the electromagnetic radiation from the one or more control sources is arranged to be incident upon the atomic ensemble to stimulate off-resonant transitions of the atomic valence electrons in the atomic ensemble between the second state and the third state; wherein the quantum memory device is arranged such that on incidence of one or more modes of electromagnetic radiation from the signal source and electromagnetic radiation from each of the one or more control sources to the atomic ensemble, a coherent excitation of the transition between the first state and the third state is created that stores the one or more modes of electromagnetic radiation from the signal source in the atomic ensemble, and subsequent incidence of electromagnetic radiation from each of the one or more control sources upon the atomic ensemble stimulates emission of the one or more stored modes of electromagnetic radiation from the atomic ensemble; and wherein the inverse of the residual Doppler linewidth owing to the incidence of the electromagnetic radiation generated by the signal source and the one or more control sources on the atomic valence electrons in the atomic ensemble is greater than half the lifetime of the coherent excitation of the transition between the first state and the third state.