Atomic qubits protected from decoherence by strong coupling to a fiber-based optical cavity

Controlling and characterizing entanglement in large quantum systems is an exciting challenge of modern physics, and a necessary milestone to fulfill the promises of the second quantum revolution. Along this line, we have built a platform where ultracold rubidium atoms are strongly coupled to a fiber-based Fabry-Perot cavity under a quantum gas microscope. Here, the cavity is used to create collective interactions between the atoms, while the microscope is meant to allow for single-qubit manipulation and readout. To maximize the overlap between the atomic distribution and the 780nm cavity mode to which they are coupled, we use an intracavity far off-resonance lattice trap at 1560nm in a configuration where the antinodes of the 1560nm standing wave coincide with antinodes of the 780nm standing wave, which is possible because the two wavelength are commensurate. With this device, we have observed vacuum Rabi frequencies on the order of 60MHz, corresponding to a single-atom cooperativity of about 40, deep into the strong coupling regime.