Velocity selection for ultracold atoms using mazer action in a bimodal cavity

In this paper, we discuss the velocity selection of ultracold three-level atoms in Λ configuration using a mazer. Our model is the same as discussed by Arun et al. [R. Arun, G.S. Agarwal, M.O. Scully, H. Walther, Phys. Rev. A 62 (2000) 023809] for mazer action in a bimodal cavity. We show that the initial Maxwellian velocity distribution of ultracold atoms can be narrowed due to the presence of resonances in the transmission through dressed-state potential. When the atoms are initially prepared in one of the two lower atomic states then significantly better velocity selectivity is obtained due to the presence of dark states.     

Transmission of ultracold atoms through a micromaser: detuning effects

The transmission probability of ultracold atoms through a micromaser is studied in the general case where a detuning between the cavity mode and the atomic transition frequencies is present. We generalize previous results established in the resonant case (zero detuning) for the mesa mode function. In particular, it is shown that the velocity selection of cold atoms passing through the micromaser can be very easily tuned and enhanced using a non-resonant field inside the cavity. Also, the transmission probability exhibits with respect to the detuning very sharp resonances that could define single cavity devices for high accuracy metrology purposes (atomic clocks).Received: 25 March 2003, Published online: 17 February 2004PACS: 42.50.-p Quantum optics - 32.80.-t Photon interactions with atoms - 32.80.Lg Mechanical effects of light on atoms, molecules, and ions     

Scattering models for ultracold atoms

We present a review of scattering models that can be used to describe the low-energy behavior of identical bosonic atoms. In the simplest models, the only degrees of freedom are atoms in the same spin state. More elaborate models have other degrees of freedom, such as atoms in other spin states or diatomic molecules. The parameters of the scattering models are specified by giving the S-wave phase shifts for scattering of atoms in the spin state of primary interest. The models are formulated as local quantum field theories and the renormalization of their coupling constants is determined. Some of the parameters can be constrained by renormalizability or by the absence of negative-norm states. The Green’s functions that describe the evolution of two-atom states are determined analytically. They are used to determine the T-matrix elements for atom-atom scattering and the binding energies of diatomic molecules. The scattering models all exhibit universal behavior as the scattering length in a specific spin state becomes large.     

Functional integral for ultracold fermionic atoms

We develop a functional integral formalism for ultracold gases of fermionic atoms. It describes the BEC–BCS crossover and involves both atom and molecule fields. Beyond mean field theory we include the fluctuations of the molecule field by the solution of gap equations. In the BEC limit, we find that the low temperature behavior is described by a Bogoliubov theory for bosons. For a narrow Feshbach resonance these bosons can be associated with microscopic molecules. In contrast, for a broad resonance the interaction between the atoms is approximately pointlike and microscopic molecules are irrelevant. The bosons represent now correlated atom pairs or composite “dressed molecules”. The low temperature results agree with quantum Monte Carlo simulations. Our formalism can treat with general inhomogeneous situations in a trap. For not too strong inhomogeneities the detailed properties of the trap are not needed for the computation of the fluctuation effects—they enter only in the solutions of the field equations.     

Laser based accelerator for ultracold atoms

We present our first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams, and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F=2, m(F)=2] state, but the scheme is not restricted to atoms in any particular magnetic substates and can readily be extended to other atomic species as well.     

Low-noise detection of ultracold atoms

We have demonstrated a new technique for detecting ultracold atoms. A balanced detection technique was used to reduce laser-induced detection noise in conjunction with modulation-transfer spectroscopy to distinguish cold atoms from a thermal cloud. Using this technique, we have achieved signal-to-noise ratios in excess of 2000:1.     

失谐对冷原子介质中光脉冲信息存储的影响

通过对电磁感应透明模型的理论推导和数值模拟，讨论了光场和原子能级间有失谐 的光脉冲信息的存储过程. 结果表明：只有在光场和原子能级共振时，光和原子相互作用系 统的存储态才能最终演化到暗态. 随着失谐量的增大，只有部分信号光脉冲存储于冷原子介质中，并且光脉冲负群速度的绝对值逐渐增大，导致在介质中“读出”信号光相对于“读入”信号光的位置有明显的倒退现象. 对于能级上下对称相同失谐的情况，存储过程中系统各 物理量的演化过程几乎相同. 关键词： 光存储 失谐 暗态 电磁感应透明     

Magnetic trapping of ultracold Rydberg atoms

We investigate the quantum dynamics of ultracold Rydberg atoms being exposed to a magnetic quadrupole field. A Hamiltonian describing the coupled dynamics of the electronic and center of mass motion is derived. Employing an adiabatic approach, the potential energy surfaces for intra-n-manifold mixing are computed. By determining the quantum states of the center of mass motion, we demonstrate that trapped states can be achieved if the total angular momentum of the atom is sufficiently large. This holds even if the extension of the electronic Rydberg state becomes equal to or even exceeds that of the ultracold center of mass motion.     

Recombination of three ultracold fermionic atoms

Three-body recombination of identical, spin-polarized fermionic atoms in the ultracold limit is investigated using model interactions. The mechanisms for recombination are parametrized by the "scattering volume" V(p) and described in the framework of the adiabatic hyperspherical representation. We have calculated the recombination rate K3 as a function of V(p) and have found K3 proportional, variant |V(p)|(8/3) for small |V(p)|. Recombination near a two-body Feshbach resonance can thus be significant.     

High-resolution laser spectroscopy of ultracold ytterbium atoms using spin-forbidden electric quadrupole transition

We have successfully observed high-resolution spectra of spin-forbidden electric quadrupole transition (¹ S ₀→³ D ₂) in ytterbium (¹⁷⁴Yb) atoms. The differential light shifts between the ¹ S ₀ and the ³ D ₂ states in a far-off resonant trap at 532 nm are also measured. For the spectroscopy, we developed simple, narrow-linewidth, and long-term frequency stabilized violet diode laser systems. Long-term drifts of the excitation laser (404 nm) is suppressed by locking the laser to a length stabilized optical cavity. The optical path length of the cavity is stabilized to another diode laser whose frequency is locked to a strong ¹ S ₀→¹ P ₁ transition (399 nm) of Yb. Both lasers are standard extended-cavity diode lasers (ECDLs) in the Littrow configuration. Since the linewidth of a violet ECDL (～10 MHz) is broader than a typical value of a red or near infra-red ECDL (<1 MHz), we employ optical feedback from a narrow-band Fabry–Perot cavity to reduce the linewidth. The linewidth is expected to be <20 kHz for 1 ms averaging time, and the long-term frequency stability is estimated to be ～200 kHz/h.     

High-resolution photoassociation spectroscopy of ultracold ytterbium atoms by using the intercombination transition

We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested.     

Manipulation of ultracold Rb atoms using a single linearly chirped laser pulse

At ultracold temperatures, atoms are free from thermal motion, which makes them ideal objects of investigations aiming to advance high-precision spectroscopy, metrology, quantum computation, producing Bose condensates, etc. The quantum state of ultracold atoms may be created and manipulated by making use of quantum control methods employing low-intensity pulses. We theoretically investigate population dynamics of ultracold Rb vapor induced by nanosecond linearly chirped pulses having kW/cm2 beam intensity and show a possibility of controllable population transfer between hyperfine (HpF) levels of 5(2)/S(1/2) state through Raman transitions. Satisfying the one-photon resonance condition with the lowest of the HpF states of 5(2)/P(1/2) or 5(2)/P(3/2) state allows us to enter the adiabatic region of population transfer at very low field intensities, such that corresponding Rabi frequencies are less than or equal to the HpF splitting. This methodology provides a robust way to create a specifically designed superposition state in Rb in the basis of HpF levels and perform state manipulation controllable on the picosecond-to-nanosecond time scale.     

Collision properties of ultracold 133Cs atoms

We present a theoretical analysis of numerous magnetically tunable Feshbach resonances measured by Chin et al. [preceding Letter, Phys. Rev. Lett. 85, 2717 (2000)] at fields of up to 25 mT. This analysis provides the most accurate characterization of the collisional properties of ground state Cs atoms currently available and clearly shows, in contrast to previous work, that Bose-Einstein condensation of 133Cs cannot be ruled out. The X1Sigma(+)(g) and a(3)Sigma(u) scattering lengths are constrained to (280+/-10)a(0) and (2400+/-100)a(0), respectively ( 1a(0) = 0.052 917 7 nm), and the van der Waals C6 coefficient to 6890+/-35 a.u.(1 a.u. = 0.095 734 5 x10(-24) &Jdot;nm(6)).     

Spin gradient demagnetization cooling of ultracold atoms

We demonstrate a new cooling method in which a time-varying magnetic field gradient is applied to an ultracold spin mixture. This enables preparation of isolated spin distributions at positive and negative effective spin temperatures of ±50 pK. The spin system can also be used to cool other degrees of freedom, and we have used this coupling to cool an apparently equilibrated Mott insulator of rubidium atoms to 350?pK. These are the lowest temperatures ever measured in any system. The entropy of the spin mixture is in the regime where magnetic ordering is expected.     

转动冷原子研究的前沿介绍

环流的宏观量子化是超流体最引人瞩目的性质之一．1995年玻色一爱因斯坦凝聚的实现为超流提供了一个新的研究对象，使得人们可以对转动的超流体进行深入的研究．实验上在BEC中产生了涡旋激发，并进一步观测到了涡旋晶格．理论研究表明当冷原子的转速进一步增大，涡旋品格会融解成一种新的强关联系统——量子霍尔液体．文章主要介绍近年在转动冷原子方向上理论和实验的进展．     

转动冷原子研究的前沿介绍

环流的宏观量子化是超流体最引人瞩目的性质之一.1995年玻色－爱因斯坦凝聚的实现为超流提供了一个新的研究对象,使得人们可以对转动的超流体进行深入的研究.实验上在BEC中产生了涡旋激发,并进一步观测到了涡旋晶格.理论研究表明当冷原子的转速进一步增大,涡旋晶格会融解成一种新的强关联系统——量子霍尔液体.文章主要介绍近年在转动冷原子方向上理论和实验的进展.