Direct absolute spectrometer for direct absolute spectrometry

A direct absolute spectrometer to perform direct absolute spectrometry, the direct absolute spectrometer comprising:

• a first light source that provides single photon light;
• a second light source that provides pump light;
• an optical combiner in optical communication with the first light source and in optical communication with the second light source and that:
• receives the single photon light from the first light source;
• receives the pump light from the second light source;
• combines the single photon light and the pump light;
• and
• produces dual light that comprises the single photon light and the pump light;
• an optical cell that receives the dual light from the optical combiner;
• an electromagnetically induced transparent (EIT) medium disposed in the optical cell, the EIT medium being:
• optically transparent to the single photon light in a presence of the pump light, such that the EIT medium produces output light comprising:
• the pump light;
• and
• an EIT light;
• and
• optically opaque to the single photon light in an absence of the pump light, such that the EIT medium does not produce the output light;
• and
• a filter in optical communication with the EIT medium and that:
• receives the output light from the optical cell when output light is produced by EIT medium;
• and
• filters the pump light from the output light;
• and
• provides EIT light free from pump light,
• wherein EIT light is a direct and absolute metric of a linewidth and a wavelength of the single photon light such that direct absolute spectrometer provides direct and absolute determination of the linewidth of the single photon light and direct and absolute determination of wavelength at a maximum of intensity of the single photon light.