Rydberg Qubits

Phase matching refers to a process in which atom-field interactions lead to the creation of an output field that propagates coherently through the interaction volume. By confining cold 87Rb single atoms in an array formed by holographic optical microtraps, we observe the phase-matched scattering that occurs when changing the dimensionality of the system. Such scattering can be used for mapping collective states within an array of neutral atoms onto propagating light fields and for establishing quantum links between separated arrays. We will further investigate the radiative profiles using EMCCD by exciting these atoms to Rydberg levels to study the collective emissions. 

Homodyne detection is used to measure the (collective) atomic dipole moment for an atomic ensemble that is prepared in a superposition of spatially phased Dicke states having at most two excitations (a so-called “superatom”). Homodyne detection allows one to isolate the contributions to the radiated intensity that depend linearly on the average value of the collective atomic dipole moment operator. Depending on whether the atom-reference field interference is constructive or destructive, either super-Poisson or sub-Poisson statistics for the combined field is observed.

Collective qubits between atomic ground and Rydberg states can be converted, on-demand, into single photons, making them well-suited for scalable quantum network-type protocols. We demonstrate a collective alkali-metal Rydberg qubit held in a state-insensitive optical lattice trap, in which the lifetime of the ground-Rydberg-state coherence is increased to 30 𝜇𝑠, an order of magnitude improvement over previous experiments using freely diffusing atoms. We observe many-body Rabi oscillations with the collective Rabi frequency enhanced by a factor of √N, and obtain 12 fast Rabi oscillations within 6 𝜇𝑠 and 8 Rabi oscillations within 10 𝜇𝑠. Multi-particle entanglement of the 𝑊-state within our ensemble is determined, verifying that at most one excitation blockade sites exist. We also measure the Ramsey interferometry with the dressing field, confirming no relative collective light shift between the two levels. These results provide new evidence that collective Rydberg qubits can be used to create high-fidelity photon-photon gates, deterministic single photons, and multiple qubits for scalable quantum networking.