Refine coherent control of atomic qubits via wave-function approach conditioned on no-decay

Abstract: As a fundamental phenomenon in quantum systems, spontaneous emission constitutes an inevitable source of error, which ultimately degrades the fidelity of quantum logic gates. A successful quantum logic gate needs to operate on the condition that no decay event, such as spontaneous emission, occurs. Such successes can be ensured by post-selection based on syndrome extraction according to the theory of quantum error correction or quantum error mitigation. In this case, the wave function of qubits remains a pure state but is subject to additional influences from spontaneous emission, even without actual decay events. Therefore, such a process must be appropriately described by a modified version of Schr\"odinger equation for the dynamics conditioned on no-decay. Calculations reveal that this effect must be seriously taken into consideration for the design of high-fidelity quantum logic gates. With respect to realistic experimental conditions, even if the coherence is well preserved, improving the fidelity of manipulating physical qubits requires careful consideration of the subtle influences of decay processes such as spontaneous emission. Specifically, the gate and readout processes in the atomic qubit platform are discussed.