Generating and controlling chains of entangled atoms by coherent control techniques

Abstract

A practical way of writing long sequences of entangled atomic qubits using coherent control with classical light sources is proposed. The method utilizes one-photon vs two-photon interference as a means of controlling the directionality of the motion of valence electrons during molecular dissociation processes. We show that, by dissociating in an optical lattice a one-dimensional array of ultracold diatomic molecules (e.g., ${\mathrm{Na}}_{2}\ensuremath{\rightarrow}\mathrm{Na}+{\mathrm{Na}}^{*}$), using a combination of photoabsorption of two mutually perpendicularly polarized beams at center frequency $\ensuremath{\omega}$ and a coherent Raman transition at frequencies ${\ensuremath{\omega}}_{1}$ and ${\ensuremath{\omega}}_{2}={\ensuremath{\omega}}_{1}\ensuremath{-}\ensuremath{\omega}$, one can craft entangled states composed of arbitrary superpositions of sequences of atomic states, such as $|f\ensuremath{\rangle}|f\ensuremath{\rangle}|b\ensuremath{\rangle}+\ensuremath{\cdots}+|b\ensuremath{\rangle}|b\ensuremath{\rangle}|f\ensuremath{\rangle}+\ensuremath{\cdots},$ where $|f\ensuremath{\rangle}$ designates a dissociation process in which the ground-state Na atom goes in the forwarddirection and the excited-state Na${}^{*}$ goes in the backward direction, while $|b\ensuremath{\rangle}$ designates the reverse process, namely, Na going in the backward direction and Na${}^{*}$ going in the forward direction. The method, which on the basis of past work is expected to be robust against decoherence, would enable the encoding of very long sequences of entangled qubits.