Suppressing deleterious effects of spontaneous emission in creating bound states in cold atom continuum

Abstract

In a previous paper [Deb and Agarwal 2014 Phys. Rev. A 90 063417], it was theoretically shown that, magneto-optical manipulation of low energy scattering resonances and atom-molecule transitions could lead to the formation of a bound state in continuum (BIC), provided there is no spontaneous emission. We find that even an exceedingly small spontaneous decay from exited molecular states can spoil the BIC. In this paper, we show how to circumvent the detrimental effect of spontaneous emission by making use of vacuum-induced coherence (VIC) which results in the cancellation or suppression of spontaneous emission. VIC occurs due to the destructive interference between two spontaneous decay pathways. An essential condition for VIC is the non-orthogonality of two transition dipole moments associated with the radiative decays form two excited states. Furthermore, the interference between two decay pathways requires that the spacing between the two decaying states must be comparable to or smaller than the square root of the product of the two spontaneous linewidths. We demonstrate that these conditions can be fulfilled by optically manipulating appropriately chosen molecular excited states, opening a promising prospect for the experimental realization of BIC of cold atoms.