Quantum Droplet Meta-Materials*

The quantum droplets in binary mixtures of Bose-Einstein Condensates [1,2,3] are dramatic demonstrations of the effects of quantum fluctuations at macroscopic level. It was pointed out by D. Petrov [4] that these fluctuations (of the kind of Lee-Huang-Yang [5]) are able to prevent the collapse of a binary mixture with attractive mean-field mutual interaction, and stabilize the system in a self-bound droplet. This self-bound property immediate accommodates elastic deformations. Here, we show that this elasticity will lead to a whole host of new self-bound structures when a quantum droplet interacts with another quantum gas or is acted on by various optical and magnetic potentials [6]. These new structures include media of various connectivity (i.e. genus), new super-solids, and devices for measuring the equation of state of other quantum gases. They are the solutions of the generalized Gross-Pitaevskii equation of these systems, which contain many new topological excitations and macroscopic quantum phenomena. The creation of new self-bound structures with increasingly complexity from quantum droplets is similar to the creation of meta-materials from simple solid-state units. 

1. G. Semeghini, G. Ferioli, L. Masi, C. Mazzinghi, L. Wolswijk, F. Minardi, M. Modugno, G. Modugno, M. Inguscio, and M. Fattori,  Phys. Rev. Letts. 120,  235301 (2018).

2. C. D'Errico, A. Burchianti, M. Prevedelli, L. Salasnich, F. Ancilotto, M. Modugno, F. Minardi, and C. Fort, Phys. Rev. Research 1, 033155 (2019).

3. Z. Guo, F. Jia, L. Li, Y. Ma, J. M. Hutson, X. Cui, and D. Wang, Phys. Rev. Research 3, 033247 (2021).

4.   D.S. Petrov, Phys. Rev. Letts. 115,  155302 (2015).

5.   T.D. Lee, K. Huang, and C.N. Yang, Phys. Rev. 106,  1135 (1957).

6. T.L. Ho, “Professor C.N.Yang, Quantum Gas Droplets, and Cold Atom Meta-Materials”, p.207, A Festschrift in Honor of the CN Yang Centenary, Scientific Papers, World Scientific (2022); and to be published.