The photonic echo is a fundamental tool for the manipulation of electromagnetic fields. An inevitable spontaneous emission noise is generated in this process due to the strong rephasing pulse. This limits the achievable signal-to-noise ratio and represents a fundamental obstacle to their applications in the quantum regime.
However, the intense spontaneous noise emission generated has the same frequency as the signal; it is impossible to separate them in principle.
Previous protocols, such as atomic frequency comb and silent echo reactivation, failed to eliminate spontaneous noise emission as much as needed.
In a new study, Professor LI Chuanfeng and Professor Zhou Zongquan of the China University of Science and Technology (USTC) of the Chinese Academy of Sciences (CAS) innovatively developed and performed the Photon Echo Protocol noiseless (NLPE). They served the optical quantum memory protocol in the Eu3 + crystal: Y2SiO5. They also applied a four-level atomic system to suppress noise.
By rephasing the pulse twice in the four-level atomic system, scientists could manipulate the spontaneous noise emission to have a different frequency from the signal. This made it easy to separate the signal from the noise emission.
The experiments showed that the noise was 0.0015 photons, 670 times less than the previous results. In addition, the effectiveness of NLPE was more than three times that of previous protocols.
- You-Zhi Ma et al., Noise elimination in echoes of optically rephased photons, Nature Communications (2021). DOI: 10.1038 / s41467-021-24679-4