Atomic mixture of dysprosium and potassium in mixed dimensions – Mix2Dim
Atomic mixture of dysprosium and potassium in mixed dimensions
The Mix2Dim relies on a new experimental setup on which I intend to: (i) study stable Efimov-like trimers, thus decoupling the enhancement of three-body correlations from three-body losses; (ii) explore new many- body phases that can emerge in the case of strongly-interacting bilayer systems. For that purpose, we will manipulate a cold atomic mixture, potassium and dysprosium, evolving in mixed dimensions.
Production of stable Efimov trimers.
Interactions play a crucial role in our understanding of physical systems. Since the 19th century, initial modeling<br />of two-particle interactions and their contribution to large ensembles led to new theoretical descriptions of gases and liquids. In particular, J. D. van der Waals showed that as two particles approach each other, repulsive forces lead to the presence of molecules that have non-zero incompressible volume, which modifies the equation of state of an ideal gas. Later on, stimulated by the observation, in 1937, of superfluidity in liquid helium, N. N. Bogoliubov developed a theoretical framework for weakly-interacting quantum systems. In that case, a simple quantity, the scattering length, a, which characterizes binary collisions at low energy, suffices to accurately describe the macroscopic modifications induced by the microscopic two-body interactions. Although his work could not be straightforwardly applied to liquid helium, this theoretical framework is crucial to describe the bulk properties of gaseous Bose-Einstein condensates and remains a cornerstone of our understanding of weakly-interacting cold atom experiments. Nonetheless, as the complexity of the system grows, new phases of matter emerge that cannot be solely reduced to an extension of few-body mechanisms. The system is then not only “more” complex, but “different” as famously stated by P. W. Anderson.<br />Cold atom experiments are, in that sense, pristine setups in which to both understand the building blocks of the system and to study the emergence of new phases of matter. Indeed, these experiments allow us to progressively increase system’s complexity, in an isolated environment, and to test the limits of several theoretical models. <br />Of particular interest is the “unitary”<br />regime, where a ? 8. In this regime, the energy of the two-body molecular bound state approaches the dissociation threshold, and the interactions are said to be nearly-resonant, thus reaching their<br />maximum value allowed by the unitarity of quantum mechanics.<br />As introduced by Efimov in 1970 [11], for Bose or mass-imbalanced Fermi gases, three-particles can form a three-body bound state even in the absence of two-body bound<br />states, which introduces a new length-scale of interaction. This new scattering parameter is often referred as the scattering hypervolume which possess both a real part, associated to long-range correlations, and an imaginary part linked to short-ranged inelastic losses. So far, the observation of Efimov trimers has always been performed through the observation of a resonance of both real and imaginary parts of the scattering hypervolume, and therefore the resulting long-range interactions are always associated to short-range losses.<br />We will solve this issue by imposing a minimal distance between the three particles forming these trimers, and study the consequences of strong (truly) long-range interactions in dilute gases.
In three dimensions, Efimov trimers are always associated with three-body loss mechanisms, related to the probability of finding all three particles at a distance smaller than the van der Waals length. In this case, two particles tend to bind into a much deeper dimer state after occupying a loosely bound trimer state. The potential energy of the bound state is then imparted on the kinetic energy of the third particle. This process implies losses, and, after re-thermalization, heating. Although Efimov trimers at unitarity exhibit universal scaling properties, the losses are species dependent.
To bypass the loss mechanism, we intend to confine the dysprosium atoms in layers. In our project, the only possible arrangement of Efimov trimers is composed of two spin-polarized (dysprosium) atoms trapped in independent layers and a freely propagating potassium atom which mediates the interlayer interaction. In this case, the trimer is stable and can be probed at equilibrium. We will also ensure that the trimer binding energy is large compared to the kinetic energy of the sample. For cold atom experiments, this implies a binding energy on the order of a few tens of nano-Kelvin, and thus a distance between layers of typically 50 nm. We will engineer this bilayer configuration by combining a sub-wavelength optical barrier and an optical lattice. The sub-wavelength optical barrier results from a Lambda optical scheme between two ground states and an excited state. One of the couplings is spatially dependent, such that the spin-composition of the resulting dark state changes spatially. Non-adiabatic correction lead to an effective repulsive barrier felt by the dark state.
We will probe the binding energy of this stable Efimov trimer as a function of the interspecies scattering length through radio-frequency spin injection. This technique will also allow us to probe the lifetime of the trimers and their energy.
The completion of this project will culminate in the study of a stable Efimov trimer extending over two layers. We will measure the trimer binding energy at equilibrium, its lifetime and the universal scaling factor regarding the energy between different excited states. This study will pave the way towards a better understanding of Efimov physics and the possibility to investigate many-body phases of matter in which two and three-body interaction length scales coexist. For instance the emergence of a superfluid Efimov trimer phase constitutes a new and exciting many-body phase in which both two and three-body interaction length-scales are at play. More generally, this project will provide a new toolkit to the cold atom community, namely the possibility to manipulate three-body interactions without the burden of inelastic losses.
Interactions are the cornerstone of the most spectacular phenomena in many-body quantum physics. At the microscopic level, interactions may result in the formation of bound-states that affect the response of a system drastically. For dilute gases, one could naively expect that the problem reduces to the presence of two-body bound states. Surprisingly, even for such dilute gases, three-body bound states can emerge even in the absence of dimers. These Efimov trimers are always unstable, and it thus remains elusive to investigate their impact on new phases of matter. In the Mix2Dim project, we will combine cutting-edge cold atom experimental techniques to realize stable Efimov trimers. For that purpose, we will study an atomic mixture, dysprosium and potassium, in mixed dimensions. Turning from few-body to many-body systems, the Mix2Dim project will also explore new many-body phases of matter such as superfluid Efimov liquids, and the emergence of a Fulde-Ferrell-Larkin-Ovchinnikov phase.
Project coordination
Raphael Lopes (Raphael Lopes)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partnership
LKB Raphael Lopes
Help of the ANR 486,144 euros
Beginning and duration of the scientific project:
March 2021
- 48 Months
