Dr. Igor Dotsenko

Laboratoire Kastler Brossel, Collège de France, Paris

“Quantum state reconstruction of a single photon shared by two cavities”

Our two ‘photon boxes’, i.e. microwave cavities made of two high-quality mirrors, are capable of storing quanta of light for very long time. Individual, highly excited atoms in circular Rydberg states, passing through the boxes one by one, serve us to prepare, manipulate and measure the photons’ quantum state in real time.

In this talk I will present the way we prepare a single photon coherently shared by two cavities. Then, I describe two methods to sensor this state, either with resonant or dispersive atom-cavity interaction. After accumulating enough statistics on many copies of this state, its density matrix is then estimated by maximizing the probability of all observed measurements.

The proposed and realized optimization algorithm not only allows us to merge into the same analysis the measurement results different by their type of interaction, but also to take into account any known measurement imperfections as well as additional coherent and non-unitary system evolution. The algorithm is a combination of two approaches in quantum state estimation: maximum likelihood reconstruction and past quantum state analysis, followed by the optimized maximization algorithm. We believe that it can be very useful in other quantum systems where different measurements and imperfections have to be considered simultaneously.