  Despite much anticipation of valleytronics as a candidate to replace the
ageing CMOS-based information processing, its progress is severely hindered by
the lack of practical ways to manipulate valley polarization all-electrically
in an electrostatic setting. Here we propose a class of all-electric-controlled
valley filter, valve and logic gate based on the valley-contrasting transport
in a merging Dirac cones system. The central mechanism of these devices lies on
the pseudospin-assisted quantum tunneling which effectively quenches the
transport of one valley when its pseudospin configuration mismatches that of a
gate-controlled scattering region. The valley polarization can be abruptly
switched into different states and remains stable over semi-infinite
gate-voltage windows. Colossal tunneling valley-pseudo-magnetoresistance ratio
of over 10,000\% can be achieved in a valley-valve setup. We further propose a
valleytronic-based logic gate capable of covering all 16 types of two-input
Boolean logics. Remarkably, the valley degree of freedom can be harnessed to
resurrect logical-reversibility in two-input universal Boolean gate. The (2+1)
polarization states -- two distinct valleys plus a null polarization --
re-establish one-to-one input-to-output mapping, a crucial requirement for
logical-reversibility, and significantly reduce the complexity of reversible
circuits due to the built-in nature of valley degree of freedom. Our results
suggest that the synergy of valleytronics and digital logics may provide new
paradigms for valleytronic-based information processing and reversible
computing.
