A device (1, 2) for measuring a quantity (Γ A) representative of a population of cold atoms occupying a predetermined atomic level, said cold atoms being located in a cloud of cold atoms to be analyzed, the device comprising: - a microwave source configured to generate an incident signal (SMWi) at a predetermined signal frequency (fs), - a microwave guide configured to propagate said incident signal and an antenna (Ant) configured to emit said incident signal to said cloud of cold atoms and its environment, Said device being characterized in that: said antenna and said microwave guide also being able to recover an atomic reflected signal (SMWra) resulting from a reflection of the incident signal by said cloud and its environment, and which propagates in the waveguide in the opposite direction to the incident signal, and in that the device comprises: - a splitting device coupled to the microwave guide and configured to extract at least part of the atomic reflected signal, - a detector (Det) configured to detect said atomic reflected signal extracted by the splitting device, said quantity representative of the population of cold atoms of said predetermined atomic level being obtained from a detected value (S A) of the atomic reflected signal (SMWra) and from a detected value (S 0) of a signal reflected by the environment in the absence of said cloud, called reference reflected signal (SMWr0), said representative quantity (Γ A) being called atomic reflection coefficient and defined as follows: Γ A = S A − S 0 S A + S 0 where S A is the detected value of the atomic reflected signal S 0 is the detected value of the reference reflected signal. - a microwave source configured to generate an incident signal (SMWi) at a predetermined signal frequency (fs), - a microwave guide configured to propagate said incident signal and an antenna (Ant) configured to emit said incident signal to said cloud of cold atoms and its environment, said antenna and said microwave guide also being able to recover an atomic reflected signal (SMWra) resulting from a reflection of the incident signal by said cloud and its environment, and which propagates in the waveguide in the opposite direction to the incident signal, and in that the device comprises: - a splitting device coupled to the microwave guide and configured to extract at least part of the atomic reflected signal, - a detector (Det) configured to detect said atomic reflected signal extracted by the splitting device, - a splitting device coupled to the microwave guide and configured to extract at least part of the atomic reflected signal, - a detector (Det) configured to detect said atomic reflected signal extracted by the splitting device, said quantity representative of the population of cold atoms of said predetermined atomic level being obtained from a detected value (S A) of the atomic reflected signal (SMWra) and from a detected value (S 0) of a signal reflected by the environment in the absence of said cloud, called reference reflected signal (SMWr0), said representative quantity (Γ A) being called atomic reflection coefficient and defined as follows: Γ A = S A − S 0 S A + S 0 where S A is the detected value of the atomic reflected signal S 0 is the detected value of the reference reflected signal.