A quantum Rosetta stone for interferometry

Heisenberg-limited measurement protocols can be used to gain an increase in measurement precision over classical protocols. Such measurements can be implemented using, for example, optical Mach—Zehnder interferometers and Ramsey spectroscopes. We address the formal equivalence between the Mach—Zehnder interferometer, the Ramsey spectroscope and a generic quantum logic circuit. Based on this equivalence we introduce the 'quantum Rosetta stone', and we describe a projective-measurement scheme for generating the desired correlations between the interferometric input states in order to achieve Heisenberg-limited sensitivity. The Rosetta stone then tells us that the same method should work in atom spectroscopy.