  Various new phenomena emerge in quantum materials under elastic deformations,
such as hydrostatic or uniaxial stresses. In particular, using uniaxial strain
or stress can help to tune or uncover specific structural or electronic orders
in materials with multiple coexisting phases. Those phases may be associated
with a quantum phase transition requiring a millikelvin environment combined
with multiple experimental probes. Here, we describe our unique apparatus,
which allows in situ tuning of strain in large samples inside a dilution
refrigerator while the samples are monitored via an optical microscope. We
describe the engineering details and show some typical results of
characterizing superconducting strontium titanate under stress. This letter
should serve as a practical reference for experts in ultra-low temperature
experimental physics involving uniaxial stresses or strains.
