  We have identified a novel mechanism for the birth of Strange Nonchaotic
Attractor (SNA) in a quasiperiodically forced Chua's circuit. In this study the
amplitude of one of the external driving forces is considered as the control
parameter. By varying this control parameter, we find that bubbles appear in
the strands of the torus. These bubbles start to double in number as the
control parameter is increased. On increasing the parameter continuously,
successive doubling of the bubbles occurs, leading to the birth of SNAs. We
call this mechanism as the bubble doubling mechanism. The formation of SNA
through this bubble doubling route is confirmed numerically, using Poincar\'e
maps, maximal Lyapunov exponent and its variance and the distribution of
finite-time Lyapunov exponents. Also a quantitative confirmation of the strange
nonchaotic dynamics is carried out with the help of singular continuous
spectrum analysis.

Chaotic Dynamics