We propose a quantum optical implementation of a class of dissipative spin systems, including the XXZ and Ising model, with ultra-cold atoms in optical lattices. Employing the motional degree of freedom of the atoms and detuned Raman transitions we show how to obtain engineerable dissipation and a tunable transversal magnetic field, enabling the study of the dynamics and steady-states of dissipative spin models. As an example of effects made accessible this way, we consider small spin chains and weak dissipation and show by numerical simulation that steady-state expectation values display pronounced peaks at certain critical system parameters. We show that this effect is related to degeneracies in the Hamiltonian and derive a sufficient condition for its occurrence.

The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum dot strongly coupled to a high-finesse optical cavity. By adiabatically eliminating the electron a direct effective coupling is achieved. Depending on the laser field applied, interactions that enable either write-in or read-out are obtained.

We show how to realize a quantum interface between optical fields and the polarized nuclear spins in a singly charged quantum dot, which is strongly coupled to a high-finesse optical cavity. An effective direct coupling between cavity and nuclear spins is obtained by adiabatically eliminating the (far detuned) excitonic and electronic states. The requirements needed to map qubit and continuous variable states of cavity or traveling-wave fields to the collective nuclear spin are investigated: For cavity fields, we consider adiabatic passage processes to transfer the states. It is seen that a significant improvement in cavity lifetimes beyond present-day technology would be required for a quantum interface. We then turn to a scheme which couples the nuclei to the output field of the cavity and can tolerate significantly shorter cavity lifetimes. We show that the lifetimes reported in the literature and the recently achieved nuclear polarization of ∼ 90% allow both high-fidelity read-out and write-in of quantum information between the nuclear spins and the output field. We discuss the performance of the scheme and provide a convenient description of the dipolar dynamics of the nuclei for highly polarized spins, demonstrating that this process does not affect the performance of our protocol.

Highly asymmetric dynamic nuclear spin pumping is observed in a single self-assembled InGaAs quantum dot subject to resonant optical excitation of the neutral exciton transition. A large maximum polarization of 54% is observed and the effect is found to be much stronger upon pumping of the higher energy Zeeman level. Time-resolved measurements allow us to directly monitor the buildup of the nuclear spin polarization in real time and to quantitatively study the dynamics of the process. A strong dependence of the observed dynamic nuclear polarization on the applied magnetic field is found, with resonances in the pumping efficiency observed for particular magnetic fields. We develop a model that accounts for the observed behavior, where the pumping of the nuclear spin system is due to hyperfine-mediated spin-flip transitions between the states of the neutral exciton manifold.