Rydberg quantum computation with nuclear spins in two-electron neutral atoms

Abstract

Alkaline-earth-like (AEL) atoms with two valence electrons and a nonzero nuclear spin can be excited to Rydberg state for quantum computing. Typical AEL ground states possess no hyperfine splitting, but unfortunately a GHz-scale splitting seems necessary for Rydberg excitation. Though strong magnetic fields can induce a GHz-scale splitting, weak fields are desirable to avoid noise in experiments. Here, we provide two solutions to this outstanding challenge with realistic data of wellstudied AEL isotopes. In the first theory, the two nuclear spin qubit states |0 and |1 are excited to Rydberg states |r with detuning ∆ and 0, respectively, where a MHz-scale detuning ∆ arises from a weak magnetic field on the order of 1 G. With a proper ratio between ∆ and Ω, the qubit state |1 can be fully excited to the Rydberg state while |0 remains there. In the second theory, we show that by choosing appropriate intermediate states a two-photon Rydberg excitation can proceed with only one nuclear spin qubit state. The second theory is applicable whatever the magnitude of the magnetic field is. These theories bring a versatile means for quantum computation by combining the broad applicability of Rydberg blockade and the incomparable advantages of nuclear-spin quantum memory in two-electron neutral atoms.