Are there quantum beats from vacuum-induced coherence?

Hao‐Sheng Zeng, Ming-Jie Liao

Zhiming Wu, Jiahua Li, Ying Wu

Vacuum-induced coupling (VIC), arising from the quantum interference between the spontaneous emission pathways from the excited doublet to a common ground state, has attracted significant research interest and has been observed in recent experiments. Here, we present an alternative route to probe the existence of VIC by means of the coherence statistics of photon antibunching and show that, under realistic experimental conditions, the vacuum-induced quantum beat (VIQB) can enable strong photon antibunching with high brightness in an optical nanofiber (ONF) cavity quantum electrodynamics (CQED) system. We find that the occurrence of the photon antibunching corresponds to the existence of the VIC, indicating that the photon antibunching can be an important witness for VIC. In addition, a strong photon antibunching effect appears in the weak-coupling regime of light-atom interactions when the VIQB is present, as a result of the destructive quantum interference between the different paths for two-photon excitation. Furthermore, we find that strong photon antibunching can be generated within a certain driving frequency range in the present system, which can relax the requirement for the driving frequency in the ONF CQED system. Also, we compare the analytical and numerical results of the second-order intensity correlation function, and they are in good agreement. The present study builds a bridge between the photon antibunching and the VIC and VIQB, which is useful for well understanding and researching a tunable single-photon source, as well as enabling potential applications in quantum information processing and quantum communications.

Fam Le Kien

Kariman I. Osman

Effect of the relative control phase as well as the squeezed phase parameter on the optical switching process of the optical bi-multistable behaviour are investigated in detail for a four-level Y-type atomic system; in the presence of a control field (coherent + dc fields) with squeezed vacuum field and quantum interference from spontaneous emission. The results indicated that (a) the quantum interference assists to decrease the rate of switching via the relative phase of the control field and makes the switching on/off points more rapid in squeezed vacuum compared to a normal vacuum case, and (b) the phase switching effects between the output field and the relative control phase increases the switching on/off processes in normal vacuum more than the squeezed vacuum case. In addition, we have demonstrated the possibility of displaying quantum beats with a novel type of bi-multistable behaviour in the cooperative switching diagram.

Hyok Sang Han, Ahreum Lee, Kanu Sinha +2 more

Hyok Sang Han, Ahreum Lee, Kanu Sinha +2 more

We demonstrate collectively enhanced vacuum-induced quantum beat dynamics from a three-level V-type atomic system. Exciting a dilute atomic gas of magneto-optically trapped ^{85}Rb atoms with a weak drive resonant on one of the transitions, we observe the forward-scattered field after a sudden shut-off of the laser. The subsequent radiative dynamics, measured for various optical depths of the atomic cloud, exhibits superradiant decay rates, as well as collectively enhanced quantum beats. Our work is also the first experimental illustration of quantum beats arising from atoms initially prepared in a single excited level as a result of the vacuum-induced coupling between excited levels.