Comparison of single-neutral-atom qubit between in bright trap and in dark trap**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304502) and the National Natural Science Foundation of China (Grant Nos. 11634008, 11674203, 11574187, and 61227902), and the Fund for Shanxi “1331 Project” Key Subjects Construction, Shanxi Province, China.

Abstract

A single neutral atom is one of the most promising candidates to encode a quantum bit (qubit). In a real experiment, a single neutral atom is always confined in a micro-sized far off-resonant optical trap (FORT). There are generally two types of traps: red-detuned trap and blue-detuned trap. We experimentally compare the qubits encoded in “clock states” of single cesium atoms confined separately in either 1064-nm red-detuned (bright) trap or 780-nm blue-detuned (dark) trap: both traps have almost the same trap depth. A longer lifetime of 117 s and a longer coherence time of about 10 ms are achieved in the dark trap. This provides a direct proof of the superiority of the dark trap over the bright trap. The measures to further improve the coherence are discussed.