We address generic behavior of quantum dislocations in almost ideal crystals. It is proven that the combination of arbitrary small Peierls potential and Coulomb-type elastic interaction between dislocation kinks prevents quantum roughening of dislocations. Thermally created kinks induce classical roughening which leads to softening of crystal shear modulus at temperatures comparable to the kink energy. This effect is discussed in the context of the shear modulus softening observed by Day & Beamish in solid 4 He.

Glide and climb of quantum dislocations under finite external stress, variation of chemical potential and bias (geometrical slanting) in Peierls potential are studied by Monte Carlo simulations of the effective string model. We treat on unified ground quantum effects at finite temperatures T . Climb at low T is assisted by superflow along dislocation coresuperclimb. Above some critical stress avalanche-type creation of kinks is found. It is characterized by hysteretic behavior at low T . At finite biases gliding dislocation remains rough even at lowest T -the behavior opposite to non-slanted dislocations. In contrast to glide, superclimb is characterized by quantum smooth state at low temperatures even for finite bias. In some intermediate T -range giant values of the compressibility as well as non-Luttinger type behavior of the core superfluid are observed.