Soliton Atom Laser with Quantum State Transfer Property

We propose a scheme to obtain soliton atom laser with nonclassical atoms based on quantum state transfer process from light to matter waves in nonlinear case, which may find novel applications in, e.g., an atom interferometer. The dynamics of the atomic gray solitons and the accompanied frequency chirp effect are discussed. PACS numbers: 03.75.-b, 42.50.Gy, 03.65.Ta, 03.67.-a Since the first pulsed atom laser was created in 1997 through RF output coupling of a trapped atomic Bose-Einstein condensate [1], there have been many interests in preparing a continuous atom laser and exploring its potential applications in, e.g., gravity measurements through atom interferometry [2]. Although a sub-quantum-noise atom laser is expected to be crucial to improve the interferometer sensitivities, the difficulties for the atomic beam to propagate over a long distance heavily restrict its actual performance [3]. Some time ago Drummond et al. proposed to use mode-locking technique to stabilize the atom laser based on the generation of a dark soliton in a ring-shaped condensate [4]. Other related works are the atomic soliton formation and its stationary transmission in a travelling optical laser beam [5] or a waveguide [6] for a dense atomic flow. While optical techniques are by now well developed to make and control a soliton laser [7] (even using an interferometer [8]), less progress has been made for ultracold atoms. We here propose a novel scheme to obtain a soliton atom laser with nonclassical characteristic via the versatile quantum state transfer technique [10, 11, 12, 13]. Recently, by manipulating two external lights for an ensemble of 3-level Λ type atoms, the physical mechanism of Electromagnetically Induced Transparency (EIT) [14] has attracted much attention in both experimental and theoretical aspects [10, 11, 12], especially after the dark-states polaritons (DSPs) theory [13] was proposed and thereby the rapid developments of quantum memory technique, i.e., transferring the quantum states of photon wave-packet to collective Raman excitations in a lossfree and reversible manner. By extending the transfer technique to matter waves, a wonderful scheme was proposed to make a continuous atomic beam with nonclassical or entangled states [15], which was later confirmed also for double-Λ 4-level atoms [16]. Nonetheless, in these pioneering works the role of nonlinear atomic interactions in the quantum state transfer process was neglected [15, 16]. In this paper, by studying the quantum states transfer technique from photons to atomic beam in the nonlinear case, we propose a scheme to obtain a soliton atom laser with nonclassical atoms. The dynamics of present gray-solitons is shown to be free of the atomic frequency chirp effect occurring in state transfer process. Essentially being different from output couplings of atomic solitons formed in a trapped condensate [4, 17, 18, 19], this scheme should be realizable in the next generation of experiments. The development herein is outlined as follows. Firstly, we study the role of nonlinear atomic interactions in the transfer process of quantum states from probe field to matter waves in adiabatic condition. For present purpose, the collisions between the initial-state atoms (Φ1) are omitted by, e.g., applying the recently developed novel technique of magnetic-field-induced Feshbach resonance [9], while nonlinear interaction between the generated atoms (Φ2) is well considered. The quantum transfer Electronic address: [email protected] Electronic address:[email protected]