Atomic spatial coherence with spontaneous emission in a strong coupling cavity

Spontaneous Scattering of Raman Photons from Cavity-QED Systems in the Ultrastrong Coupling Regime

We show that spontaneous Raman scattering of incident radiation can be observed in cavity-QED systems without external enhancement or coupling to any vibrational degree of freedom. Raman scattering processes can be evidenced as resonances in the emission spectrum, which become clearly visible as the cavity-QED system approaches the ultrastrong coupling regime. We provide a quantum mechanical description of the effect, and show that ultrastrong light-matter coupling is a necessary condition for the observation of Raman scattering. This effect, and its strong sensitivity to the system parameters…

Efficient quantum memory for heralded single photons generated by cavity-enhanced spontaneous parametric downconversion

We interface a spontaneous parametric down conversion (SPDC) crystal and a cold atomic ensemble and demonstrate a highly efficient quantum memory through polarization-encoded single-photon qubits. Specifically, narrowband heralded single photons from a cavity-enhanced SPDC source is stored using cold atomic ensemble, with ~70% storage-and-retrieval efficiency and ~10$μ$s storage time at 50% efficiency. To prevent the degradation after storage, we also manipulate the single-photon wave profile so that the retrieved non-classical nature of single photon is preserved. On the other hand, the dual-…

Spontaneous creation and persistence of ground-state coherence in a resonantly driven intra-cavity atomic ensemble

The spontaneous creation and persistence of ground-state coherence in an ensemble of intracavity Rb atoms has been observed as a quantum beat. Our system realizes a quantum eraser, where the detection of a first photon prepares a superposition of ground-state Zeeman sublevels, while detection of a second erases the stored information. Beats appear in the time-delayed photon-photon coincidence rate (intensity correlation function). We study the beats theoretically and experimentally as a function of system parameters, and find them remarkably robust against perturbations such as spontaneous emi…

Route from spontaneous decay to complex multimode dynamics in cavity QED

We study the non-Markovian quantum dynamics of an emitter inside an open multimode cavity, focusing on the case where the emitter is resonant with high-frequency cavity modes. Based on a Green's function technique suited for open photonic structures, we study the crossovers between three distinct regimes as the coupling strength is gradually increased: (i) overdamped decay with a time scale given by the Purcell modified decay rate, (ii) underdamped oscillations with a time scale given by the effective vacuum Rabi frequency, and (iii) pulsed revivals. The final multimode strong coupling regime …

Delayed choice experiment using atoms in optical cavity

In this article, we propose a method to realize the "delayed choice experiment" using ultra-cold atoms. Here we attempt to probe the "welcher-Weg" information without collapsing the wavefunction of the atom. This experiment consists of components built around proven techniques that are put together in novel configuration to preserve the coherence of the system during the measurement. The Ramsey interference is used to establish the wave nature of the atom and the particle nature of the atom is probed by detecting its internal state by performing a nondemolition measurement using an ultra-high …

原子蒸气自发噪声光谱中的噪声抑制与超精细能级相干性

Noise reduction and hyperfine level coherence in spontaneous noise spectroscopy of atomic vapor

本研究开发了含噪声抑制方案与激光稳频的透射光强涨落功率谱测量系统，可降低散粒噪声等外来噪声，观测原子蒸气自发噪声光谱及激发态超精细能级相干性，并通过实验验证了系统性能。