  Tunable metasurfaces have demonstrated the potential for dramatically
enhanced functionality for applications including sensing, ranging and imaging.
Liquid crystals (LCs) have fast switching speeds, low cost, and mature
technological development, offering a versatile platform for electrical
tunability. However, to date, electrically tunable metasurfaces are typically
designed at a single operational state using physical intuition, without
controlling alternate states and thus leading to limited switching efficiencies
($<30\%$) and small angular steering ($<$25$^\circ$). Here, we use large-scale
computational 'inverse design' to discover high-performance designs through
adjoint-based local-optimization design iterations within a global-optimization
search. We study and explain the physics of these devices, which heavily rely
on sophisticated resonator design to fully utilize the very small permittivity
change incurred by switching the liquid-crystal voltage. The optimal devices
show tunable steering angles ranging from 12$^\circ$ to 144$^\circ$ and
switching efficiencies above 80%, exhibiting 6X angular improvements and 6X
efficiency improvements compared to the current state-of-the-art.
