We consider the behavior of an ultracold Fermi gas across a narrow Feshbach resonance, where the occupation of the closed channel may not be negligible. While the corrections to the single-channel formulae associated with the nonzero chemical potential and with particle conservation have been considered in the existing literature, there is a further effect, namely the "inter-channel Pauli exclusion principle" associated with the fact that a single hyperfine species may be common to the two channels. We focus on this effect and show that, as intuitively expected, the resulting corrections are of order $E_F/η$, where $E_F$ is the Fermi energy of the gas in the absence of interactions and $η$ is the Zeeman energy difference between the two channels. We also consider the related corrections to the fermionic excitation spectrum, and briefly discuss the collective modes of the system.
We study the impurity problem in a gas of $^{173}$Yb atoms near the recently discovered orbital Feshbach resonance. In an orbital Feshbach resonance, atoms in the electronic ground state $^1S_0$ interact with those in the long-lived excited $^3P_0$ state with magnetically tunable interactions. We consider an impurity atom with a given hyperfine spin in the $^3P_0$ state interacting with a single-component Fermi sea of atoms in the ground $^1S_0$ manifold. Close to the orbital Feshbach resonance, the impurity can induce collective particle-hole excitations out of the Fermi sea, which can be reg…
Starting from weakly bound Feshbach molecules, we demonstrate a two-photon pathway to the dipolar ground state of bi-alkali molecules that involves only singlet-to-singlet optical transitions. This pathway eliminates the search for a suitable intermediate state with sufficient singlet-triplet mixing and the exploration of its hyperfine structure, as is typical for pathways starting from triplet dominated Feshbach molecules. By selecting a Feshbach state with a stretched singlet hyperfine component and controlling the polarization of the excitation laser, we assure coupling to only a single hyp…
We show that the essential properties of a Feshbach resonance in cold atomic gases can be tuned by dressing the atomic states in different scattering channels through inter-channel couplings. Such a scheme can be readily implemented in the orbital Feshbach resonance of alkaline-earth-like atoms by coupling hyperfine states in the clock-state manifolds. Using $^{173}$Yb atoms as an example, we find that both the resonance position and the two-body bound-state energy depend sensitively on the inter-channel coupling strength, which offers control parameters in tuning the inter-atomic interactions…
We report on the experimental observation of a novel inter-orbital Feshbach resonance in ultracold 173-Yb atoms, which opens the possibility of tuning the interactions between the 1S0 and 3P0 metastable state, both possessing vanishing total electronic angular momentum. The resonance is observed at experimentally accessible magnetic field strengths and occurs universally for all hyperfine state combinations. We characterize the resonance in the bulk via inter-orbital cross-thermalization as well as in a three-dimensional lattice using high-resolution clock-line spectroscopy.
Magnetic control of ultra-cold $^6$Li and $^{174}$Yb($^3P_2$) atom mixtures with Feshbach resonances
从理论上研究了在玻色子亚稳$^{174}$ Yb（$^3$ P $_2$）原子与费米$^6$ Li原子碰撞中形成磁调谐Feshbach分子的可行性.与碱金属原子碰撞相比，亚稳原子碰撞具有高度的各向异性。我们的第一原理耦合通道计算这些碰撞揭示了广泛的费什巴赫共振的存在，由于各向异性的分子和原子的超精细相互作用的综合影响。为了使我们的预测符合实验观察到的宽共振结构\cite{Deep2015}的具体位置，我们通过直接最小二乘拟合优化了短程势的形状。这使我们能够确定其领先的角动量量子数的主导共振和描述的作用，碰撞各向异性的创建和扩大这个和其他共振。
The ultracold mixture of \Na and \Rb atoms has become an important system for investigating physics in Bose-Bose atomic mixtures and for forming ultracold ground-state polar molecules. In this work, we provide an improved characterization of the most commonly used Feshbach resonance near 347.64 G between \Na and \Rb in their absolute ground states. We form Feshbach molecules using this resonance and measure their binding energies by dissociating them via magnetic field modulation. We use the binding energies to refine the singlet and triplet potential energy curves, using coupled-channel bound…
Dynamics of atomic and molecular bright solitons in a hybrid atom-molecular BEC (Bose Einstein Condensate) system of 85Rb coupled through Magnetic Feshbach Resonance (MFR) has been investigated. By solving the time independent atom-molecular coupled equations, the initial atomic and molecular wavefunctions were obtained and the dynamics of the initial atomic and molecular waves in a spherical one-dimensional trap were studied by solving the time-dependent atom-molecular coupled equations. During evolution two types of induced or stimulated decays of the feshbach molecules were switched on. The…
We theoretically show that a two-band system with very different masses harbors a resonant pair scattering that leads to novel pairing properties, as highlighted by the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) crossover. Most importantly, the interband pair-exchange coupling induces an effective intraband attraction in each band, enhancing the superfluidity/superconductivity. The effect, a kind of Suhl-Kondo mechanism, is specifically enhanced when the second band has a heavy mass and is incipient (lying close to, but just above, the chemical potential, $μ$), which w…
Observation of high partial-wave Feshbach resonances in $^{39}$K Bose-Einstein condensates
State Key Laboratory of Quantum Optics Technologies and Devices, Institute of Opto-electronics, Shanxi University（山西大学光电研究所量子光学技术与器件国家重点实验室）；Collaborative Innovation Center of Extreme Optics, Shanxi University（山西大学极端光学协同创新中心）
We theoretically investigate normal-state properties of an ultracold Fermi gas with an orbital Feshbach resonance (OFR). Recently, OFR has attracted much attention as a promising pairing mechanism to realize a superfluid 173Yb Fermi gas. Including pairing fluctuations within a T-matrix approximation, and removing effects of an experimentally inaccessible deep bound state, we evaluate strong-coupling corrections to single-particle excitations. With increasing the strength of an OFR-induced tunable pairing interaction, the open channel is shown to exhibit the pseudogap phenomenon in the BCS-BEC …
By including the effect of a trap with characteristic energy given by the Fermi temperature $T_F$ in a two-body two-channel model for Feshbach resonances, we reproduce the experimental closed-channel fraction $Z$ across the BEC-BCS crossover and into the BCS regime of a $^6$Li atomic Fermi gas. We obtain the expected behavior $Z \propto \sqrt{T_F}$ at unitarity, together with the recently measured proportionality constant. Our results are also in agreement with recent measurements of the $Z$ dependency on $T_F$ on the BCS side, where a significant discrepancy between experiments and theory has…
We theoretically investigate strong-coupling properties of an ultracold Fermi gas with an orbital Feshbach resonance (OFR). Including tunable pairing interaction associated with an OFR within the framework of the strong-coupling theory developed by Nozières and Schmitt-Rink (NSR), we examine the occupation of the closed channel. We show that, although the importance of the closed channel is characteristic of the system with an OFR, the occupation number of the closed channel is found to actually be very small at the superfluid phase transition temperature $T_{\rm c}$, in the whole BCS (Bardeen…
Paraexcitons, the lowest energy exciton states in Cu$_{2}$O, have been considered a good system for realizing exciton Bose-Einstein condensation (BEC). The fact that their BEC has not been attained so far is attributed to a collision-induced loss, whose nature remains unclear. To understand collisional properties of cold paraexcitons governing their BEC, we perform here a microscopic consideration of the s-wave paraexciton-paraexciton scattering. We show its two-channel character with incoming paraexcitons coupled to a biexciton, which is a Feshbach resonance producing a paraexciton loss and a…
Controlling the group velocity of colliding atomic Bose-Einstein condensates with Feshbach resonances
我们报告的建议，以改变群速度的一个小的玻色-爱因斯坦凝聚体（BEC）碰撞后，与另一个BEC类似的光通过色散介质的减慢。我们利用超冷碰撞附近的磁费什巴赫共振，这引起了急剧变化的散射长度与碰撞能量，从而改变群速度。一个广义Gross-Pitchkii方程推导出一个小的BEC通过一个较大的静态BEC运动。我们分别用激光和介质BEC来表示这两种凝聚体，以突出激光脉冲穿过介质的类比。我们推导出一个表达式的群速度在均匀介质中，以及在距离的差异，$δ$，所覆盖的激光BEC的存在和不存在的有限大小的介质BEC与一个E-Fermi密度分布。对于相同同位素种类的介质和激光器，位移$δ$的上限为介质的费米半径的两倍。对于典型的窄费什巴赫共振和具有数密度$10^{15}$ cm $^{-3}$的介质，可以实现高达上限的85%，使得效果在实验上可观察到。我们还得到我们的建议的实验实现的限制。
We theoretically investigate normal-state properties of a gas mixture of single-component bosons and fermions with a hetero-nuclear Feshbach resonance. Including strong hetero-pairing fluctuations associated with the Feshbach resonance, we calculate single-particle density of states, as well as the spectral weight at various interaction strengths. For this purpose, we employ an improved T-matrix approximation (TMA), where the bare Bose Green's function in the non-selfconsistent TMA self-energy is modified so as to satisfy the Hugenholtz-Pines relation at the Bose-Einstein condensation (BEC) te…
Characterization of Feshbach resonances in $^6\mathrm{Li}{-}^7\mathrm{Li}$ using improved interaction potentials
University of Maryland（马里兰大学）；Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology (NIST)（马里兰大学与美国国家标准与技术研究院联合量子研究所）
通过改进的势能曲线和耦合通道散射计算，预测并表征了 $^6\mathrm{Li}{-}^7\mathrm{Li}$ 同位素中的 s 波 Feshbach 共振，发现其窄且以三重态为主，为超冷 Li$_2$ 分子的拉曼光转移路径设计提供基础。
Feshbach resonances are among the essential control tools used in ultracold atom experiments. However, for complex atomic species the theoretical characterization of resonances becomes challenging. For closely spaced resonances, the measurement of three-body losses does not provide sufficient resolution to discriminate them. For this reason, resonance spectroscopy of trapped isolated atoms is becoming the state of the art. Here we show that trapping the atoms in a double well potential such as an optical lattice or a pair of optical tweezers enables precise characterization of not only the res…
We present two simple designs of matter-wave beam splitters in a trapped Bose-Einstein Condensate (BEC). In our scheme, identical pairs of atomic solitons are produced by an adequate control --- in time and/or space --- of the scattering length. Our analysis is performed by numerical integration of the Gross-Pitaevskii equation and supported by several analytic estimates. Our results show that these devices can be implemented in the frame of current BEC experiments. The system has potential applications for the construction of a soliton interferometer.
We demonstrate the coherent creation of a single NaCs molecule in its rotational, vibrational, and electronic (rovibronic) ground state in an optical tweezer. Starting with a weakly bound Feshbach molecule, we locate a two-photon transition via the $|{c^3Σ,v'=26}\rangle$ excited state and drive coherent Rabi oscillations between the Feshbach state and a single hyperfine level of the NaCs rovibronic ground state $|{X^1Σ,v''=0,N''=0}\rangle$ with a binding energy of $D_0 = h \times 147038.30(2)$ GHz. We measure a lifetime of $3.4\pm1.6$ s for the rovibronic ground-state molecule, which possesses…
We first show that the many-body Hamiltonian governing the physical properties of an alkaline-earth Yb-173 Fermi gas across the recently-realized orbital Feshbach resonance is exactly analogous to that of two-band s-wave superconductors with contact interactions: i.e., even though the free-particle bands have a tunable energy offset in between and are coupled by a Josephson-type attractive inter-band pair scattering, the intra-band interactions have exactly the same strength. We then introduce two intra-band order parameters within the BCS mean-field approximation, and investigate the competit…
Condensate of spin-1 atoms frozen in a unique spatial mode may possess large internal degrees of freedom. The scattering amplitudes of polarized cold atoms scattered by the condensate are obtained with the method of fractional parentage coefficients that treats the spin degrees of freedom rigorously. Channels with scattering cross sections enhanced by square of atom number of the condensate are found. Entanglement between the condensate and the propagating atom can be established by the scattering. The entanglement entropy is analytically obtained for arbitrary initial states. Our results also…
We investigate a thermodynamic cycle using a Bose-Einstein condensate with nonlinear interactions as the working medium. Exploiting Feshbach resonances to change the interaction strength of the BEC allows us to produce work by expanding and compressing the gas. To ensure a large power output from this engine these strokes must be performed on a short timescale, however such non-adiabatic strokes can create irreversible work which degrades the engine's efficiency. To combat this, we design a shortcut to adiabaticity which can achieve an adiabatic-like evolution within a finite time, therefore s…
We theoretically investigate superfluid properties of a two-band gas of $^{173}$Yb Fermi atoms with an orbital Feshbach resonance (OFR). To describe the BCS-BEC crossover region, we include superfluid fluctuations caused by inter-band and intra-band pairing interactions associated with OFR, by extending the strong-coupling theory developed by Nozières and Schmitt-Rink to the two-band case below the superfluid phase transition temperature; however, effects of an experimentally inaccessible deep bound state are removed, to model a real $^{173}$Yb Fermi gas near OFR. We show that the condensate f…
The recently discovered Orbital Feshbach Resonance (OFR) offers the possibility of tuning the interaction between alkaline earth(-like) metal atoms with magnetic field. Here, we introduce a single-manifold Raman scheme to dress the OFR, which allows us to tune the interaction with the optical field and it is readily realizable in experiment. We demonstrate the scattering resonance could be shifted by the dressing Raman laser using few-body and many-body mean-field calculation, which give rise to an optical dependent two-body bound state and Raman coupling induced BCS-BEC crossover in the BCS-t…
Effective Field Theory for Atom-Molecule Systems III: Dynamic Effects of a Feshbach Resonance on Bragg scattering from a Bose-Einstein Condensate
我们提出了一个在磁费什巴赫共振附近的玻色-爱因斯坦凝聚体（BEC）的布拉格散射的理论模型，采用两个c场的形式，一个c场用于原子，另一个用于由两个原子组成的分子.我们使用这个模型数值模拟最近的实验[S. B. Papp等人，物理学评论快报，101（13）：135301，2008年9月]研究强相互作用对来自85 Rb BEC的布拉格光谱的影响。从这些模拟的结果是在非常好的定量协议与实验结果，确认的重要性的共振束缚态的凝聚物的动力学快速实验，如布拉格散射。
We present precise measurements of the optical Feshbach resonances (OFRs) of $^{174}$Yb atoms for the intercombination transition. We measure the photoassociation (PA) spectra of a pure $^{174}$Yb Bose-Einstein condensate, and determine the dependence of OFRs to PA laser intensities and frequencies for four least bound vibrational levels near the intercombination transition. We confirm that our measurements are consistent with the temporal decay of a BEC subjected to a PA beam in the vicinity of the fourth vibrational level from the dissociation limit.
We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms. Being a metastable quasiparticle excitation at the positive energy, the repulsive polaron is induced by the interaction between an impurity atom and a Fermi sea. By analyzing in detail the energy, the polaron residue, the effective mass, and the decay rate of the repulsive polaron, we reveal interesting features that are intimately related to the two-channel nature of the orbital Feshbach resonance. In particular, we find that the life time of …
Ultracold Dipolar Gas of Fermionic $^{23}$Na$^{40}$K Molecules in their Absolute Ground State
我们报告创建一个超冷偶极气体的费米子$^{23}$ Na $^{40}$ K分子在其绝对振转和超精细基态。从弱结合Feshbach分子，我们证明了超精细分辨双光子转移到单重态${\rm X}^1Σ^+ |v{=}0,J{=}0\rangle$基态，相干桥接的结合能差为0.65 eV通过受激快速绝热通道。自旋极化，近量子简并分子气体显示寿命超过2.5秒，突出了NaK对两体化学反应的稳定性。施加均匀电场以诱导高达0.8德拜的偶极矩。随着这些进展，对$^{23}$ Na $^{40}$ K分子的强偶极费米气体的多体物理探索已进入实验阶段。
We theoretically investigate dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance with random phase approximation, and find their dynamical characters during the phase transition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid and a polarized Sarma superfluid by continuously varying the chemical potential difference of two spin components. In a BEC-like regime of the BCS superfluid, dynamic structure factors can do help to distinguish the in-phase ground state from the out-of-phase metastable state by the relative location…
