Analytical Study of Decoherence in Rydberg Atom Qubits

Individually trapped neutral atoms are a promising candidate for use in quantum computing and simulation applications. Entanglement can be generated between these atoms via strong dipole-dipole interactions by driving them to highly excited Rydberg states (n>20). However, the fidelity of single qubit operations as well as 2 qubit entangling gates is limited by several decoherence channels of which the dominant ones are finite temperature effects, laser frequency noise and intensity noise. Here we present an analytical (perturbative) expression for the effect of these noise sources on the rabi oscillations of a single atom and a pair of atoms in the Rydberg blockade regime. We derive this result in terms of the power spectral density (PSD) of the noise sources and use it to predict the maximum achievable single qubit and 2-qubit gate fidelities. Using this analytical result, we can appropriately adjust the driving laser’s locking parameters in experiments to modify its PSD and increase coherence time as well as gate fidelities. This work provides crucial insight for upcoming experiments aiming to entangle two alkaline-earth atoms for the first time.