We study the behavior of weakly bound clusters and their relation to the well-known three-body Efimov states. We adopt a model to describe universal behavior of strongly interacting bosonic systems, and we test its validity by reproducing predictions of three- and four-body universal states. Then, we extend our study to larger systems and identify a series of universal cluster states that can be qualitatively interpreted as adding one particle at a time to an Efimov trimer. The properties of these cluster states and their experimental signatures are discussed.
Universality of weakly bound dimers and Efimov trimers close to Li-Cs Feshbach resonances
研究了超冷Li-Cs混合物在磁场为800 G ~ 1000 G时两个自旋能量最低的通道中的种间散射特性。接近两个广泛的费什巴赫共振，我们创建弱结合的锂离子二聚体的射频协会和测量的结合能对外部磁场强度的依赖性。基于Li-Cs的另外三个s波费什巴赫共振的结合能和互补原子损失谱，我们利用耦合通道计算方法构造了精确的分子单重态和三重态电子基态势。我们提取了Li-Cs物种间散射长度作为外场的函数，并且与我们以前的工作相比，在s波Li-Cs费什巴赫共振的极点位置和宽度的值的精度方面获得了几乎十倍的改进[Pires \textit{et al.}，Phys. Rev. Lett. \textbf{112}，250404（2014）]。我们讨论的Efimov方案和通用的几何缩放LiCsCs三聚体的影响。
Small weakly-bound droplets determine a number of properties of ultracold Bose and Fermi gases. For example, Efimov trimers near the atom-atom-atom and atom-dimer thresholds lead to enhanced losses from bosonic clouds. Generalizations to four- and higher-body systems have also been considered. Moreover, Efimov trimers have been predicted to play a role in the Bose polaron with large boson-impurity scattering length. Motivated by these considerations, the present work provides a detailed theoretical analysis of weakly-bound $N$-body clusters consisting of $N-1$ identical bosons (denoted by "B")…
The Efimov effect, with its ladder of weakly bound three-atomic molecules, poses intriguing questions in the theoretically controversial and experimentally demanding regime of merging of the first excited Efimov energy level with the atom-dimer continuum. Using an original experimental technique, where a coherent superposition state of diatomic and triatomic molecules is utilized, we investigate this regime and reveal a striking behavior: Instead of merging with the atom-dimer continuum the trimer energy level rebounds from it and becomes a deeper bound state again. In addition, instead of a t…
Supersymmetric isospectral formalism for the calculation of near-zero energy states: application to the very weakly bound ${^4}$He trimer excited state
Since the Efimov effect was introduced in 1970, a detailed theoretical understanding of Efimov physics has been developed in the few-body context. However, it has proven to be challenging to describe the role Efimov-type correlations play in many-body systems such as quenched or collapsing Bose-Einstein condensates (BECs). To study the impact the Efimov effect can have in such scenarios, we consider a light impurity immersed in a weakly interacting BEC, forming a Bose polaron. In this case, the higher-order correlations are localized around the impurity, making it more feasible to develop a th…
We investigate the two lowest-lying weakly bound states of $N \leq 8$ bosons as functions of the strength of two-body Gaussian interactions. We observe the limit for validity of Efimov physics. We calculate energies and second radial moments as functions of scattering length. For identical bosons we find that two $(N-1)$-body states appear before the $N$-body ground states become bound. This pattern ceases to exist for $N \geq 7$ where the size of the ground state becomes smaller than the range of the two-body potential. All mean-square-radii for $N \geq 4$ remain finite at the threshold of ze…
Physical systems characterized by a shallow two-body bound or virtual state are governed at large distances by a continuous-scale invariance, which is broken to a discrete one when three or more particles come into play. This symmetry induces a universal behavior for different systems, independent of the details of the underlying interaction, rooted in the smallness of the ratio $\ell/a_B \ll 1$, where the length $a_B$ is associated to the binding energy of the two-body system $E_2=\hbar^2/m a_B^2$ and $\ell$ is the natural length given by the interaction range. Efimov physics refers to this u…
We study three-atom inelastic scattering in ultracold \textsuperscript{39}K near a Feshbach resonance of intermediate coupling strength. The non-universal character of such resonance leads to an abnormally large Efimov absolute length scale and a relatively small effective range $r_e$, allowing the features of the \textsuperscript{39}K Efimov spectrum to be better isolated from the short-range physics. Meticulous characterization of and correction for finite temperature effects ensure high accuracy on the measurements of these features at large-magnitude scattering lengths. For a single Feshba…
Controlling the interactions between atoms with external fields opened up new branches in physics ranging from strongly correlated atomic systems to ideal Bose and Fermi gases and Efimov physics. Such control usually prepares samples that are stationary or evolve adiabatically in time. On the other hand, in molecular physics external ultrashort laser fields are employed to create anisotropic potentials that launch ultrafast rotational wave packets and align molecules in free space. Here we combine these two regimes of ultrafast times and low energies. We apply a short laser pulse to the helium…
We study the quench of a degenerate ultracold Bose gas to the unitary regime, where interactions are as strong as allowed by quantum mechanics. We lay the foundations of a cumulant theory able to capture simultaneously the three-body Efimov effect and ergodic evolution. After an initial period of rapid quantum depletion, a universal prethermal stage is established characterized by a kinetic temperature and an emergent Bogoliubov dispersion law while the microscopic degrees of freedom remain far-from-equilibrium. Integrability is then broken by higher-order interaction terms in the many-body Ha…
Momentum Distribution of a mass-imbalanced three-body system across the Efimov-Unatomic transition
Instituto Tecnológico de Aeronáutica（巴西航空研究院）；Université Paris-Saclay（巴黎萨克雷大学）；CNRS/IN2P3, IJCLab（法国国家科学研究中心/法国国家核物理和粒子物理研究所，IJCLab实验室）；Universidade Estadual Paulista（圣保罗州立大学）
We construct an effective field theory of a two-neutron halo nucleus in the limit where the two-neutron separation energy $B$ and the neutron-neutron two-body virtual energy $ε_n$ are smaller than any other energy scale in the problem, but the scattering between the core and a single neutron is not fine-tuned, and the Efimov effect does not operate. The theory has one dimensionless coupling which formally runs to a Landau pole in the ultraviolet. We show that many properties of the system are universal in the double fine-tuning limit. The ratio of the mean-square matter radius and charge radiu…
It was shown recently that the discrete scaling symmetry, which underlies the Efimov effect in the three identical boson system with two-body short-range interactions, survives when single-particle 1D spin-orbit coupling terms are added to the Hamiltonian. Each three-body energy level in the ordinary Efimov scenario turns into an energy manifold that contains four energy levels in the presence of 1D spin-orbit coupling (equal mixture of Rashba-Dresselhaus coupling). This work provides a detailed characterization of the energy levels in these manifolds. The two-boson energies, which enter into …
The elastic scattering properties of three bosons at low energy enter the many-body description of ultracold Bose gases via the three-body scattering hypervolume $D$. We study this quantity for identical bosons that interact via a pairwise finite-range potential. Our calculations cover the regime from strongly repulsive potentials towards attractive potentials supporting multiple two-body bound states and are consistent with the few existing predictions for $D$. We present the first numerical confirmation of the universal predictions for $D$ in the strongly interacting regime, where Efimov phy…
