Cavity quantum electrodynamics (QED) involves the study of atom-field interactions in the region of a confined space, such as an optical cavity, microtoroidal resonator or other different forms of resonators. In the regime of strong atom-field interactions, single atom is coupled so strong to a particular field mode by a single photon leads to an interaction that changes the familiar irreversible processes, such as spontaneous decay. It is being increasingly recognized that the cavity QED systems have applications in the small quantum optical devices, quantum control, quantum state engineering and quantum information science. Currently far off resonance optical dipole trap has been used to control the neutral atoms. Through the low loss micro resonator, the strong interaction between light field and atom can be implemented, thus the cavity QED system can be used as a sensitive single atom and single photon detector to do the measurement on single quanta level. The radiant properties of atom and the quantum entanglement of atom-field or atom-atom, various quantum states based on cavity QED system can be generated and investigated.
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Probing spontaneous wave-function collapse with entangled levitating nanospheres

Jing Zhang, Tiancai Zhang, Jie Li

Wave-function collapse models are considered to be the modified theories of standard quantum mechanics at the macroscopic level. By introducing nonlinear stochastic terms in the Schr¨odinger equation, these models (different from standard quantum mechanics) predict that it is fundamentally impossible to prepare macroscopic systems in macroscopic superpositions. The validity of these models can only be examined by experiments, and hence efficient protocols for these kinds of experiments are greatly needed. Here we provide a protocol that is able to probe the postulated collapse effect by means of the entanglement of the center-of-mass motion of two nanospheres optically trapped in a Fabry-P´erot cavity. We show that the collapse noise results in a large reduction of the steady-state entanglement, and the entanglement, with and without the collapse effect, shows distinguishable scalings with certain system parameters, which can be used to determine unambiguously the effect of these models.

 

PHYSICAL REVIEW A 95, 012141 (2017) PDF

 

 

 

Experimental test of Bohr’s complementarity principle with single neutral atoms

Zhihui Wang, Yali Tian, Chen Yang, Pengfei Zhang, Gang Li,Tiancai Zhang

An experimental test of the quantum complementarity principle based on single neutral atoms trapped in a blue detuned bottle trap was here performed. A Ramsey interferometer was used to assess the wavelike behavior or particlelike behavior with second π/2 rotation on or off. The wavelike behavior or particlelike behavior is characterized by the visibility V of the interference or the predictability P of which-path information, respectively. The measured results fulfill the complementarity relation P2 + V2≤ 1. Imbalance losses were deliberately introduced to the system and we find the complementarity relation is then formally “violated.” All the experimental results can be completely explained theoretically by quantum mechanicswithout considering the interference betweenwave and particle behaviors. This observation complements existing information concerning Bohr’s complementarity principle based on wave-particle duality of a massive quantum system.

 

PHYSICAL REVIEW A 94, 062124 (2016) PDF

 

 

 

 

High-efficiency blue light generation at 426 nm in low pump regime

Jianfeng Tian, Chen Yang1, Jia Xue1, Yuchi Zhang, Gang Li,Tiancai Zhang

We report high-efficiency Ti:sapphire-laser-based frequency doubling at the cesium D2 line 852 nm using a 20 mm-long periodically-poled potassium titanyl phosphate crystal in a bow-tie four-mirror ring enhancement cavity. The relatively complete cavity design procedure is presented. Focusing that is over twice as loose as optimal focusing is used, and both the fundamental frequency wave and second harmonic beam absorption-induced thermal lensing effects are weakened. Blue light of 210mW at 426 nm, where absorption is severe, was obtained with 310mW mode-matched fundamental light, corresponding to conversion efficiency of up to 67%. The blue light beam power showed 1.5% RMS fluctuation over 40 min.

 

J. Opt. 18,055506 (2016) PDF

 

 

Experimental investigation of the statistical distribution of single atoms in cavity quantum electrodynamics

Jin-Jin Du, Wen-Fang Li, Rui-Juan Wen, Gang Li and Tian-Cai Zhang

The Hanbury Brown–Twiss experiment for a beam of photons or atoms can be performed using counting experiments. We present the statistical distribution of single 133Cs atoms detected by a high finesse microcavity, which acts as a point-like single-atom counter. The distribution of the arrival times of the atoms and the correlation between the atoms was obtained based on the full counting statistics of the beam emitted from the cavity. The bunching behavior of the thermal atomic beams is clearly observable using this type of atom–cavity system. The correlation between the cesium atoms depends on the temperature of the atom cloud, and the corresponding parameters may be found by fitting an experimentally measured curve using the theory of multimode thermal light.

 

Laser Phys. Lett., 12, 065501(2015) PDF

 

 

 

Temperature measurement of cold atoms using single-atom transits and Monte Carlo simulation in a strongly coupled atom-cavity system

Wenfang Li, Jinjin Du, Ruijuan Wen, Pengfei Yang, Gang Li, Junjun Liang,

and Tiancai Zhang

We investigate the transmission of single-atom transits based on a strongly coupled quantum electrodynamics system. By superposing the transit transmissions of a considerable number of atoms, we obtain the absorption spectra of the cavity induced by single atoms and obtain the temperature of the cold atom. The number of atoms passing through the microcavity each release is also counted, and this number changes exponentially along with the temperature. Monte Carlo simulations agree closely with the experimental results, and the temperature of the cold atom is determined. Compared with the conventional time-of-flight (TOF method, this approach avoids some uncertainties in the standard TOF and sheds new light on determining temperature of cold atoms by counting atoms individually in a confined space.

 

APPLIED PHYSICS LETTERS 104, 113102 (2014) PDF