Bound state in continuum: Proposal for realization in cold atoms

A bound state in continuum (BIC) is a counter-intuitive concept first introduced by von Neumann and Wigner more than 80 years ago [1], showing that a BIC can exist due to destructive interference of the outgoing Schroedinger waves scattered by an appropriately designed potential. Over the years, the theoretical approach of von Neumann and Wigner has undergone extensions and modifications [2–4]. In recent times, it has attracted renewed research interests [5] with possible experimental realization [6]. In this colloquium, firstly we will introduce the concept of BIC with a historical perspective; and then show that it is possible to generate BIC in cold atoms with lasers in the presence of a magnetic Feshbach resonance [7]. The proposed cold-atom BIC can be realized by forming an appropriate coherent superposition of molecular bound states above the threshold of two-atom collisional continuum. The BIC state becomes effectively decoupled from the continuum, and hence in the absence of other damping processes this state is non-decaying. We will discuss possible experimental signatures of cold-atom BIC and its potential applications in continuum-bound coherent spectroscopy. References [1] J. von Neumann and E. Wigner, Phys. Z. 30, 465 (1929). [2] L. Fonda and R. G. Newton, Ann. Phys. (NY) 10, 490 (1960). [3] F. H. Stillinger and D. R. Herrick, Phys. Rev. A 11, 446 (1975). [4] H. Friedrich and D. Wintgen, Phys. Rev. A 32, 3231 (1985). [5] A. G. Smart, Phys. Today 66, 14 (2013). [6] C. W. Hsu et al., Nature (London) 499, 188 (2013). [7] B. Deb and G. S. Agarwal, Phys. Rev. A 90, 063417 (2014) [Editors' suggestion].