Sympathetic cooling in an optically trapped mixture of alkali and spin-singlet atoms

We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length magnitude |a(6Li-174Yb)|=(13±3)a0 from the rate of interspecies thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction of the 6Li temperature to below the Fermi temperature, purely through interspecies sympathetic cooling.     

Realization of a SU(2)×SU(6) system of fermions in a cold atomic gas

We report the realization of a novel degenerate Fermi mixture with an SU(2)×SU(6) symmetry in a cold atomic gas. We successfully cool the mixture of the two fermionic isotopes of ytterbium 171Yb with the nuclear spin I=1/2 and 173Yb with I=5/2 below the Fermi temperature T_{F} as 0.46TF for 171Yb and 0.54TF for 173Yb. The same scattering lengths for different spin components make this mixture featured with the novel SU(2)×SU(6) symmetry. The nuclear spin components are separately imaged by exploiting an optical Stern-Gerlach effect. In addition, the mixture is loaded into a 3D optical lattice to implement the SU(2)×SU(6) Hubbard model. This mixture will open the door to the study of novel quantum phases such as a spinor Bardeen-Cooper-Schrieffer-like fermionic superfluid.     

Nuclear spin effect on recombination of H₃⁺ ions with electrons at 77 K

Utilizing different ratios of para to ortho H? in normal and para enriched hydrogen, we varied the population of para-H?? in an H?? dominated plasma at 77 K. Absorption spectroscopy was used to measure the densities of the two lowest rotational states of H??. Monitoring plasma decays at different populations of para-H?? allowed us to determine the rate coefficients for binary recombination of para-H?? and ortho-H?? ions: (p)α(bin)(77 K) = (1.9 ± 0.4) × 10?? cm3 s?1 and (o)α(bin)(77 K) = (0.2 ± 0.2) × 10?? cm3 s?1.     

Magnetically tunable Feshbach resonances in ultracold Li-Yb mixtures

We investigate the possibility of forming Li+Yb ultracold molecules by magnetoassociation in mixtures of ultracold atoms. We find that magnetically tunable Feshbach resonances exist, but are extremely narrow for even-mass ytterbium isotopes, which all have zero spin. For odd-mass Yb isotopes, however, there is a new mechanism due to hyperfine coupling between the electron spin and the Yb nuclear magnetic moment. This mechanism produces Feshbach resonances for fermionic Yb isotopes that can be more than 2 orders of magnitude larger than for the bosonic counterparts.     

Ultracold Li + Li2 collisions: bosonic and fermionic cases

We have carried out quantum dynamical calculations of vibrational quenching in Li + Li(2) collisions for both bosonic (7)Li and fermionic (6)Li. These are the first ever such calculations involving fermionic atoms. We find that for the low initial vibrational states considered here (v < or = 3), the quenching rates are not suppressed for fermionic atoms. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.     

Morse Potential in the Momentum Representation

The momentum representation of the Morse potential is presented analytically by hypergeometric function. The properties with respect to the momentum p and potential parameter β are studied. Note that |Ψ(p)| is a nodeless function and the mutual orthogonality of functions is ensured by the phase functions arg[Ψ(p)]. It is interesting to see that the |Ψ(p)| is symmetric with respect to the axis p=0 and the number of wave crest of |Ψ(p)| is equal to n+1. We also study the variation of |Ψ(p)| with respect to β. The amplitude of |Ψ(p)| first increases with the quantum number n and then deceases. Finally, we notice that the discontinuity in phase occurs at some points of the momentum p and the position and momentum probability densities are symmetric with respect to their arguments.     

Quantum degenerate two-species fermi-fermi mixture coexisting with a bose-einstein condensate

We report on the generation of a quantum degenerate Fermi-Fermi mixture of two different atomic species. The quantum degenerate mixture is realized employing sympathetic cooling of fermionic 6Li and 40K gases by an evaporatively cooled bosonic 87Rb gas. We describe the combination of trapping and cooling methods that proved crucial to successfully cool the mixture. In particular, we study the last part of the cooling process and show that the efficiency of sympathetic cooling of the 6Li gas by 87Rb is increased by the presence of 40K through catalytic cooling. Because of the differing physical properties of the two components, the quantum degenerate 6Li-40K Fermi-Fermi mixture is an excellent candidate for a stable, heteronuclear system allowing the study of several so far unexplored types of quantum matter.     

Near-infrared quantum cutting in Ho3+/Yb3+ codoped nanostructured glass ceramic

A first-order quantum cutting luminescence of Ho3+/Yb3+ couples, which are incorporated in the YF3 nanocrystals embedded in transparent glass ceramic, is reported for the first time, to our knowledge. When Ho3+ is excited with one blue photon, it was experimentally demonstrated that the resonant energy transfer from Ho3+ to Yb3+ occurs, leading to the near-infrared quantum cutting with one Ho3+ photon emitting at 1180?nm and one Yb3+ photon at 980?nm. The theoretical quantum efficiency is evaluated to be 159%.     

矩形弹子球中的量子谱和经典周期轨道

利用SU(2)相干态的表示,我们构造了二维矩形弹子球中与经典周期轨道对应的波函数.经典周期轨道和量子波函数之间的关系可以通过物理图像清晰的表示出来.另外,利用周期轨道理论,我们计算了二维矩形弹子球体系的量子谱的傅立叶变换ρ(L).变换谱|ρN(L)|2对L图像中的峰可以和粒子在二维矩形腔中运动的经典轨迹的长度相比较.量子谱中的每一条峰正好对应一条经典周期轨道的长度,表明量子力学和经典力学的对应关系.     

Precision measurement of the ratio B(t→Wb)/B(t→Wq) and extraction of V(tb)

We present a measurement of the ratio of top quark branching fractions R=B(t→Wb)/B(t→Wq), where q can be a d, s, or b quark, in the lepton+jets and dilepton tt final states. The measurement uses data from 5.4 fb(-1) of pp collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure R=0.90±0.04, and we extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V(tb)| as |V(tb)|=0.95±0.02, assuming unitarity of the 3×3 CKM matrix.     

Explicit Relations of Physical Potentials Through Generalized Hypervirial and Kramers' Recurrence Relations

Based on a Hamiltonian identity,we study one-dimensional generalized hypervirial theorem,Blanchardlike(non-diagonal case) and Kramers'(diagonal case) recurrence relations for arbitrary x~κ which is independent of the central potential V(x).Some significant results in diagonal case are obtained for special κ in x~κ(κ≥ 2).In particular,we find the orthogonal relation(n_1|n_2) = δ_(n_1n_2)(κ = 0),(n_1|V'(x)\n_2) =(E_(n_1)-E_(n_2))~2〈n_1x|n_2)(κ = 1),E_n =(n/V'(x)x/2|n) +(n|V(x)|n)(κ = 2) and-4E_n(n|x|n) +(n|V'(x)x~2\n〉 +4〈n|V(x)x|n〉 = 0(κ = 3).The latter two formulas can be used directly to calculate the energy levels.We present useful explicit relations for some well known physical potentials without requiring the energy spectra of quantum system.     

Determination of the bond length and binding energy of the helium dimer by diffraction from a transmission grating

A molecular beam consisting of small helium clusters is diffracted from a 100 nm period transmission grating. The relative dimer intensities have been measured out to the 7th order and are used to determine the reduction of the effective slit width resulting from the finite size of the dimer. From a theoretical analysis of the data which also takes into account the van der Waals interaction with the grating bars, the bond length (mean internuclear distance) and the binding energy are found to be = 52+/-4 A and |E(b)| = 1. 1+0.3/-0.2 mK.     

EPR, optical absorption and superposition model study of Fe³(+) doped strontium nitrate single crystals

Electron paramagnetic resonance (EPR) study of Fe3(+) ions doped strontium nitrate (SN) single crystals is performed at liquid nitrogen temperature and at X band frequency. The spin Hamiltonian (SH) parameters are determined from the resonance lines observed at different angular rotations. The crystal field parameters (CFPs) are evaluated using superposition model of Newman. The Zeeman g-factor and zero-field splitting parameters (ZFSPs) of Fe3(+) ion in SN (truncated SH considered) are: g=1.9989 ± 0.002 and ∣D∣=(338 ± 5) × 10?? cm?1, ∣E∣=(10 ± 5)× 10?? cm?1, a=(458 ± 5)× 10?? cm?1, respectively. The Fe3(+) ion enters the lattice substitutionally replacing the Sr2(+) sites of cubic symmetry. The local site symmetry of Fe3(+) ion in the crystal is orthorhombic (lower than that of the host). The optical absorption study of the crystal is also done at room temperature in the wavelength range 195-925 nm. The energy values of different orbital levels are determined. The observed bands are assigned as transitions from the (6)A?(g)(S) ground state to various excited states of Fe3(+) ion in a cubic crystal field approximation. The observed band positions are fitted with four parameters, the Racah interelectronic repulsion parameters (B and C), the cubic crystal field splitting parameter (Dq) and the Trees correction (α) yielding: B=934, C=2059, Dq=1450, and α=90 (in cm?1). On the basis of EPR and optical data, the nature of metal-ligand bonding in this crystal is discussed. The ZFSPs are also determined theoretically using microscopic SH theory based on perturbation theory and CFPs, B(kq) obtained from superposition model. The values of ZFSPs thus obtained are ∣D∣=(340 ± 5) × 10?? cm?1 and ∣E∣=(15 ± 5) × 10?? cm?1.     

K-Li冷碰撞散射特性的理论研究

本文应用量子方法和半经典方法计算了表征锂(6Li,7Li) 原子和钾(39K,40K,41K) 原子间超冷碰撞特性的散射参数,如s波散射长度,有效力程,p波散射长度等。超冷温度下6Li-39K单重态和三重态原子间的弹性散射截面主要为s波贡献,随着碰撞能量的增加散射截面有丰富的形状共振出现,计算发现单重态和三重态散射截面均存在显著的i波形状共振. 此外,本文应用简并内态近似获得了超精细态相互作用时的s波散射长度.     

Kondo-enhanced Andreev tunneling in InAs nanowire quantum dots

We report measurements of the nonlinear conductance of InAs nanowire quantum dots coupled to superconducting leads. We observe a clear alternation between odd and even occupation of the dot, with subgap peaks at |V(sd)| = Delta/e markedly stronger (weaker) than the quasiparticle tunneling peaks at |V(sd)| = 2Delta/e for odd (even) occupation. We attribute the enhanced Delta peak to an interplay between Kondo correlations and Andreev tunneling in dots with an odd number of spins, and we substantiate this interpretation by a poor man's scaling analysis.     

The Relations Between q-Deformed Oscillator and Fermionic Oscillator

We study the relevance between the statistical property of q-deformed oscillator and thevalue of q. It is shown that there is the consistency condition |q| = 1. When q is not a realnumber. The q-Fock space is reconstructed so that it is applicable to the case in which q is extended to the complex number. And the general expression of q-deformed oscillator b_q and b_q⁺ in the new g-Fock space is given. It is found that q = ±i correspond to fermionic oscillator(the mix of the ordinary proper and improper one). This conclusion implies that q-deformedoscillator relates naturally and inherently the fermionic oscillator with the bosonic oscillatorby choosing the value of q. Actually, the bosonization structure of the single mode of fermioncan also be obtained in the way. Of course, the solution of the fermionic oscillator given inthis paper is a representation of quantum algebra SU_q(2).     

Quantum-degenerate mixture of fermionic lithium and bosonic rubidium gases

We report on the observation of sympathetic cooling of a cloud of fermionic 6Li atoms which are thermally coupled to evaporatively cooled bosonic 87Rb. Using this technique we obtain a mixture of quantum-degenerate gases, where the Rb cloud is colder than the critical temperature for Bose-Einstein condensation and the Li cloud is colder than the Fermi temperature. From measurements of the thermalization velocity we estimate the interspecies s-wave triplet scattering length |amx|=20(+9)(-6)aB. We found that the presence of residual rubidium atoms in the |2, 1> and the |1, -1> Zeeman substates gives rise to important losses due to inelastic collisions.     

Off-resonance saturation MRI of superparamagnetic nanoprobes: theoretical models and experimental validations

Off-resonance saturation (ORS) is a new magnetic resonance imaging (MRI) method that has shown greatly improved contrast sensitivity for the detection of cancer-specific biomarkers by superparamagnetic nanoprobes in vivo. However, quantitative understanding of the ORS contrast mechanism and its dependence on the structural parameters of superparamagnetic nanoprobes are still lacking. Here we propose a quantitative model of ORS contrast and its experimental validation by superparamagnetic polymeric micelles (SPPM) with precisely controlled structural properties. Size selected, monodisperse Fe?O? nanoparticles (6.1 ± 0.2 nm) were used to form a series of SPPM nanoprobes with specifically controlled corona thickness using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxypoly(ethylene glycol) (DSPE-PEG) with different PEG molecular weights. Transmission electron microscopy and dynamic light scattering showed that SPPM were uniform in size. The average hydrodynamic diameters of SPPM with PEG lengths of 0.55, 1, 2, and 5 kD were 16.6 ± 2.8, 18.4 ± 2.9, 24.1 ± 3.4, and 28.9 ± 3.4 nm, respectively. MRI experiments at 7 T determined that r? values of SPPM with 0.55, 1, 2, and 5 kD PEG as corona were 201 ± 3, 136 ± 8, 107 ± 5, and 108 ± 8 FemM?1s?1, respectively. ORS intensity from Z-spectra of SPPM showed a significant correlation with the inverse of T? relaxation rates (1/T?, s?1) of the SPPM nanoprobes regardless of the PEG corona thickness. These data provide the fundamental understanding of the structure-property relationships between the SPPM nanostructures and ORS sensitivity, which offers useful mechanistic insights for the future improvement of SPPM nanoprobes in cancer molecular imaging applications.     

Laser locking to the ¹⁹⁹Hg ¹S₀ - ³P₀ clock transition with 5.4 × 10^-15/✓τ fractional frequency instability

With Hg199 atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is ?15??Hz. Here we lock an ultrastable laser to this ultranarrow S₀1?P₀3 clock transition and achieve a fractional frequency instability of 5.4×10^?15/? for ??400??s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of ?6.0×10^?17??s^?1 (?16.9??mHz?s^?1 at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4×10^?16 per cavity.     

Ce~(3+)-Yb~(3+)共掺YAG荧光粉量子剪裁发光的浓度及温度特性

采用高温固相法制备了不同掺杂浓度的YAG∶1%Ce~(3+),x%Yb~(3+)(x=5,10,15,20,25)系列荧光粉。在450 nm蓝光激发下,测试了样品的发射光谱,得到了中心波长在550 nm的可见宽带发射(Ce~(3+):5d→4f)和1 030 nm的近红外发射(Yb~(3+):2F_(5/2)→2F_(7/2))。可见和近红外发射强度随Yb~(3+)掺杂浓度的变化表明Ce~(3+)到Yb~(3+)存在能量传递过程,并得到Yb~(3+)的猝灭浓度为15%。在低温条件下(80~300 K)测试YAG∶1%Ce~(3+),15%Yb~(3+)样品的发射光谱和拉曼光谱,通过对其量子剪裁发光温度特性的分析,描述了基质声子在Ce~(3+)到Yb~(3+)的能量传递过程中起到的重要作用。