Artur Widera
Moving in a quantum world – Quantum walks in position space using single neutral atoms
A quantum particle moving on a line can show remarkable
properties, completely different from classical particles. While in the
well-known random walk at each time step a walker moves randomly one
step to the right or to the left, a quantum particle can be brought into
a coherent superposition of right and left. After several steps of such
a quantum walk, the probability to find the particle at a certain
position is dominated by matter wave interference of different partial
wave packets of the walker. A prominent and characteristic consequence
is the linear scaling of the width of the distribution with the number
of time steps in the quantum case, in contrast to the diffusive scaling
of the random walk. This linear scaling forms the basis for applications
in quantum information science, such as fast searching algorithms.
I will report on the experimental realization of a quantum walk using
single neutral atoms trapped in a state-dependent optical lattice.
Site-resolved fluorescence imaging in the lattice allows us to probe and
characterize the delocalized wave function of an atom with local quantum
state tomography. Further, we can perform an effective time-reversal and
refocus a delocalized atom back onto its initial position. This reflects
the highly coherent and deterministic nature of the quantum walk. In
contrast, by destroying the coherence after each time step, we recover
the classical random walk.
