Ultrafast Molecular Frame Quantum Tomography

Quantum Tomography is the experimental determination of the quantum state of a system, specifically its density matrix. Using a combination of high-resolution spectroscopic measurements and ultrafast pump-probe measurements on the same pair of resonantly excited electronic states of the ammonia molecule, we determine the time and orientation-angle dependent Lab Frame Density Matrix after resonant excitation. With this density matrix in hand, we construct the time evolving molecular frame electronic probability density for molecules at various orientations. We observe that the electronic probability density rotates around the molecular symmetry axis in different directions for molecules at different orientations, and does not rotate at all in some orientations. We are able to correlate this motion with the behavior of the electronic coherence, the off-diagonal element of the density matrix, at the different orientations. Such a quantum tomography is a perquisite for exploring quantum information processing in isolated molecules; allows studies of entanglement between molecular degrees of freedom; can be used to implement quantum control protocols and can facilitate direct imaging of charge migrating across the molecular frame.