Enhanced laboratory searches for variation of fundamental constants

We report on recent progress in finding new reference transitions for atomic clocks that exhibit enhanced sensitivity to a potential variation of fundamental constants. High sensitivity to variation of the fine structure constant can come from comparison of heavy near-neutral ions (such as mercury, ytterbium, thorium), or from comparing two near-degenerate levels in dysprosium. Exceptionally strong sensitivity could be provided by optical transitions in highly charged ions. Other constants such as electron-to-proton mass ratio can be probed using microwave clocks or molecular transitions. Nuclear clocks may provide unparalleled sensitivity to variation of constants that parameterize both the electromagnetic and strong nuclear forces. Measurement of variations in the constants of nature will provide insights into some of the deepest questions in physics and cosmology.