  Quantum phase transitions are usually classified into discrete universality
classes that typically only depend on symmetries and spatial dimensionalities.
In this Letter, we demonstrate an opportunity to continuously vary the critical
exponents or universalities by tuning experimental parameters in a given
physical system. Particularly, we show that critical exponents in long-range
spin systems simulated in ion traps can be easily tuned with laser detuning. We
suggest that such experiments also effectively simulate some aspects of
critical phenomena in conventional spin systems but in artificial non-integer
spatial dimensions.
