Coherent control using quantum light incident upon molecules in an optical lattice is shown to give rise to a direct way of writing arbitrary sequences of entangled atom-ion pairs. There is no evident limitation on the length of the word (i.e., the number of qbits) that can be formed.
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.
We consider different ways of engineering quantum states of light and atoms via their interaction. First, we show that with atoms in optical lattices one may induce quantum gates between two photons. Then, I will give some procedures to create entangled states of ions and atoms in optical lattices. Those states have the property that can be mapped into photonic states by using interference, in such a way that one ends up with several entangled photons. The mapping is triggered by a laser pulse, and the emerging photons are collimated even in the absence of a cavity.
We propose a method for producing entangled spin and orbital states in pairs of atoms resulting from the dissociation of diatomic molecules. The method employs the interference between a one-photon and a two-photon process to break the backward-forward symmetry of the dissociation processes. The spin entanglement of distant atom pairs makes use of excited spin-orbit-coupled (molecular) intermediate states. When the dissociating molecules are confined to a one-dimensional optical lattice, the method can be used to generate long sequences of (spin- and orbit-) entangled pairs of atoms.
Laser-cooled atomic ions are standards for quantum information science, acting as qubit memories with unsurpassed levels of quantum coherence while also allowing near-perfect measurement. When qubit state-dependent optical dipole forces are applied to a collection of trapped ions, their Coulomb interaction is modulated in a way that allows the entanglement of the qubits through quantum gates that form the basis of a quantum computer. Similar optical forces allow the simulation of quantum many-body physics, where recent experiments are approaching a level of complexity that cannot be modelled with conventional computers. Scaling to much larger numbers of qubits can be accomplished by coupling trapped ion qubits through optical photons, where entanglement over remote distances can be used for quantum communication and large-scale distributed quantum computers. Laser sources and quantum optical techniques are the workhorse for such quantum networks, and will continue to lead the way as future quantum hardware is developed.
Abstract The demonstration of optical multipath interference from a large number of quantum emitters is essential for the realization of many paradigmatic experiments in quantum optics. However, such interference remains still unexplored as it crucially depends on the sub-wavelength positioning accuracy and stability of all emitters. We present the observation of controlled interference of light scattered from strings of up to 53 trapped ions. The light scattered from ions localized in a harmonic trapping potential is collected along the ion crystal symmetry axis, which guarantees the spatial indistinguishability and allows for an efficient scaling of the contributing ion number. We achieve the preservation of the coherence of scattered light observable for all the measured string sizes and nearly-optimal enhancement of phase sensitivity. The presented results will enable realization and control of directional photon emission, direct detection of enhanced quadrature squeezing of atomic resonance fluorescence, or optical generation of genuine multi-partite entanglement of atoms.