A cloud of 40Ca+is successfully trapped and cooled using the radiation of a red-detuned 397 nm laser beam and a resonant 866 nm laser beam in our prototype linear ion trap,which was designed and constructed for studying quantum information processing.We have characterized the size of the ion cloud,estimating the temperature to be in the order of milli-Kelvins.
By using Faraday optical filter combined with four-wave mixing （FWM） amplifier, a narrow bandwidth optical amplifying atomic filter with switchable dual-passband is demonstrated experimentally. The two transmission peaks of the filter correspond to the Stokes and anti-Stokes frequencies, exhibiting a Raman gain in 13- and 17-fold, respectively, with bandwidth of ～120 MHz. By properly setting pump laser detuning, switching between filter passbands is realized. We also investigate the dependence of peak transmission on both pump laser intensity and Rb cell temperature. This atomic filter can find practical applications in long-distance laser communications and laser remote-sensing systems.
We report the experimental demonstration of an ultranarrow bandwidth atomic filter by optically induced polarization rotation in multilevel electromagnetically induced transparency systems in hot Rb vapor. With a coupling intensity of 2.3 W/cm^2, the filter shows a peak transmission of 33.2% and a bandwidth of 10 MHz. By altering the coupling frequency, a broad tuning range of several Doppler linewidths of the D1 line transitions of STRb atoms can be obtained. The presented atomic filter has useful features of ultranarrow bandwidth, and the operating frequency can be tuned resonance with the atomic transition. Such narrowband tunable atomic filter can be used as an efficient noise rejection tool in classical and quantum optical applications.
Following a recent proposal by Dhar et al （2006 Phys. Rev. Lett. 96 100405）, we demonstrate experimentally the preservation of quantum states in a two-qubit system based on a super-Zeno effect using liquid-state nuclear magnetic resonance techniques. Using inverting radiofrequency pulses and delicately selecting time intervals between two pulses, we suppress the effect of decoherence of quantum states. We observe that preservation of the quantum state ｜11〉 with the super-Zeno effect is three times more efficient than the ordinary one with the standard Zeno effect.
A potential scheme is proposed for generating cluster states of many atoms in cavity quantum electradynamics （QED）, in which an unorthodox encoding is employed with the ground state being qubit [0〉 while two closely spaced upper states being qubit ｜1〉. Throughout the scheme the cavities can be in thermal states but axe only virtually excited. We show how to create the cluster states by performing a two-step hut no single-qubit operation. Discussion is also carried out on the experimental feasibility of our scheme.
The interaction between polychromatic fields and atoms is an important subject in quantum optics.Frequency locking for small frequency interval multi-field is usually required in some experiments.In this letter,we experimentally demonstrate a holistic scheme for bichromatic laser frequency stabilization.Compared with traditional saturation absorption methods and complicated frequency shift schemes,offset locking for bichromatic fields is simply achieved using polarization spectroscopy and Doppler effect.Frequency locking with a wide-range asymmetry of the detuning is also shown.Our scheme makes laser spectroscopy experiments with polychromatic fields more convenient.
Squeezing via the interaction between the cavity light field and the Bose Einstein Condensate （BEC） in a doublewell potential is considered within the context of the two-mode approximation. For the cavity light field initially in a coherent state, it is shown that by choosing appropriate parameters, quadrature squeezing of the cavity light field can be achieved and it exhibits periodic oscillation. We also study the case in which BEC is tuned to resonance by periodically modulating the trapping potentiaL and the quadrature squeezing of the cavity field exhibits periodic collapse and revival effect. Both analytic and numerical calculations are performed, and they are found to be in good agreement with each other. The result shows that the quantum statistical properties of the cavity light field can be manipulated by its coupling with the condensates in the double-well potential. On the other hand, dynamical properties of the condensates in the double-well potential will be reflected by the quadrature squeezing of the light field.
