Plasma density effects can cause an exponential change in charge particle nuclear reaction rates important in stellar evolution. Reaction rates in dense plasmas, with emphasis on quantum aspects, are examined here using path integral Monte Carlo. Quantum mechanics cause a reduction in the many body enhancement of the reaction rate compared to the value for a classical system. This can be attributed to the "quantum smearing" of the short range Coulomb interaction resulting in reduced repulsion between the reacting pair and surrounding particles. Electron screening and ion exchange effects are also examined, with screening reducing and exchange slightly increasing the many body enhancement.

Accepted for publication in Physical Review Letters, November, 2003.