  In recent quantum optical continuous-variable experiments, the number of
fully inseparable light modes has drastically increased by introducing a
multiplexing scheme either in the time domain or in the frequency domain. Here,
modifying the time-domain multiplexing experiment reported in Nature Photonics
7, 982 (2013), we demonstrate successive generation of fully inseparable light
modes for more than one million modes. The resulting multi-mode state is useful
as a dual-rail CV cluster state. We circumvent the previous problem of optical
phase drifts, which has limited the number of fully inseparable light modes to
around ten thousands, by continuous feedback control of the optical system.
