We demonstrate the potential of a Ramsey spectroscopic scheme based on high-order harmonics to reach a resolving power >10^5 in the XUV. This is done by measuring clear quantum interferences in the excitation of an Argon transition at 87 nm for XUV pulse delays larger than 100 ps.

Dec 31 2009

## OSA “Best of 2009” in Optics and Photonics News

Oct 18 2009

## First direct test of quantum commutation rules

Arbitrary superpositions of quantum operators demonstrated: first direct quantitative test of quantum commutation rules. We designed a scheme for conditionally generating arbitrary coherent superpositions of quantum operators. The general scheme was later applied to an experiment for implementing the commutator of the creation and annihilation operators. We quantitatively verified the well-known commutation rules in a direct experiment for the first time.

Jan 18 2009

## “The nature of light: What is a photon?”

Dec 31 2008

## “Best of 2008” in New Journal of Physics

Dec 18 2008

## Playing with photon subtraction

We implemented a reliable scheme for single photon subtraction and tested its effects on paradigmatic light states: Fock, thermal, and coherent. When applied to coherent states, the annihilation operator does not modify the state itself. Experimentally verified that coherent states are eigenstates of the photon annihilation operator.