Two-qubit Quantum Logic Gates for Neutral Atoms Based on the Spin-Flip Blockade

The strong dipole-dipole interaction between atoms in Rydberg states has emerged as the standard mechanism to induce entanglement between neutral atom qubits. In these protocols, optical/UV lasers that couple qubit states to Rydberg states are modulated to implement entangling gates. Here we present an alternative protocol to implement entangling gates via Rydberg dressing and the spin-flip blockade. An auxiliary state in the ground-hyperfine-manifold is optically dressed so that it acquires partial Rydberg character. It thus acts as a proxy Rydberg state, with a nonlinear light-shift and longer lifetime than the Rydberg state it is coupled to. Hence, a microwave frequency field coupling a qubit state to this dressed auxiliary state can be modulated to implement entangling gates. Many entangling protocols designed for the optical regime can be imported to this microwave regime. Not only is coherent control more mature for microwave than optical fields, but such control can be made more robust to imperfections, such as thermal motion of the atoms. We study various regimes of operations that can yield high-fidelity two-qubit entangling gates.

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