We present a scheme for non-adiabatically loading a Bose-Einstein condensate into the ground state of a one dimensional optical lattice within a few tens of microseconds typically, i.e. in less than half the Talbot period. This technique of coherent control is based on sequences of pulsed perturbations and experimental results demonstrate its feasibility and effectiveness. As the loading process is much shorter than the traditional adiabatic loading timescale, this method may find many applications.PACS numbers: 32.80. Qk, 37.10.Jk, 02.30.Yy Numerous works related to optical lattice trapping have been published, especially using coherent atoms or Bose-Einstein condensate (BEC) [3], since it has various applications in quantum computation, simulation of basic condensed matter physics, atomic clocks, etc. A common concern to those experiments is how to load a BEC into the lattice without excitation or heating [4][5][6]. In most cases, one chooses to turn on the light field adiabatically and the loading process usually lasts up to tens of milliseconds, during which one tries to avoid excitations to higher states. A long loading may be problematic for quantum computation experiments as it increases the time during which decoherence can occur and reduces speed when atoms stored in optical lattices shall be interrogated and reloaded several times. Furthermore, adiabatic loading is difficult to obtain near the critical point of phase transitions for finite temperatures even well bellow the BEC critical temperature.An alternative idea is to prepare the BEC in the ground state of the lattice, and then turn on the lattice suddenly. This 'preparing' process can be much shorter compared to the adiabatic loading (about 30 µs, as we can see later in this article). One way for realizing this 'preparing' process can stem from nonholonomic coherent control [1,2,7]. In this approach, a sequence of two well chosen Hamiltonians are imposed on the system and the preset duration of each step is modified according to a defined cost function, in order to get the aimed evolution operator as well as the target state.Our proposal for designing and computing the preloading process is reminiscent of this method, but we focus more on the feasibility of its experimental implementation, rather than the stringency or universality of the approach. Experimentally, we achieve the non-adiabatic loading with a very few pulses using directly the results of our computational design. According to our analysis, this method would be valid on many other occasions, such as * Electronic address: xjzhou@pku.edu.cn loading the condensate directly into excited states of the lattice. We first introduce a general method for determining the sequence of steps to be applied to the system before giving an account of our experimental results.Suppose that before the sudden loading at time t 0 of the lattice with optical depth V 0 , m steps have been applied. The ith step corresponds to a HamiltonianĤ i kept constant during t i . The final state |ψ(t 0 ) is given by...

Superradiant Rayleigh scattering in a Bose gas released from an optical lattice is analyzed with incident light pumping at the Bragg angle for resonant light diffraction. We show competition between superradiance scattering into the Bragg mode and into end-fire modes clearly leads to suppression of the latter at even relatively low lattice depths. A quantum light-matter interaction model is proposed for qualitatively explaining this result.PACS numbers: 03.75. Gg; 03.75.Hh; 42.50.Nn; 42.50.Gy The coherent nature of Bose-Einstein condensates has led to new and rapid developments in atom optics and studies on coherent interaction between light and matter waves, with the demonstration of efficient matter wave interferometers, Bragg diffraction, wave mixing, matter wave amplifiers. Superradiant scattering was for the first time analyzed using a Bose-Einstein condensate (BEC) in a seminal experiment by Ketterle et al. [1]. In this experiment the initial matter grating, formed due to Rayleigh scattering of a pumping beam by an elongated Bose-Einstein condensate and subsequent recoil into a moving matter wave, was self amplified by resonant light diffraction in a phenomenon called amplification of matter waves. Absorption of pumping photons and preferential scattering into so-called end-fire modes along the BEC's long axis lead to the observation of patterns of coherently recoiling atoms. Amplification of matter waves was further characterized with the use of an initial matter wave seed formed via Bragg diffraction of a Bose condensate and its coherence nature was demonstrated [2,3].For an elongated BEC, superradiant Rayleigh scattering light is emitted along the long axis because the gain for superradiance is maximum in this direction. However, different superradiant modes can be obtained when a matter wave seed with non-zero momentum is created before pumping since light can then be resonantly diffracted in a different direction [4]. No precise analysis of competition between different superradiant scattering modes has been carried out yet. Such analysis would be useful for calibrating precisely superradiance gains and initial Rayleigh scattering rates if one wants to use quantitatively superradiance for the analysis of coherence in Bose gases [5,6]. Analyzing superradiance with non common configurations is also important as combining early stage superradiance described with quantum theory and long timescale superradiance which is well captured within a semi-classical theory taking into account propagation effects is currently a topic of high interest [7,8] We present in this article an experimental analysis of mode competition in superradiance scattering. Rather than relying on an initial matter wave seed formed via Bragg diffraction of a BEC [2-4] our superradiance experiment is performed after initial adiabatic loading of a BEC along its long axis inside a 1D optical lattice [9]. The choice of contra propagating optical beams (wave vector ± k L ) for the optical lattice loading leads to the formation of a matte...