Tunnelingassisted

Tunneling-assisted refers to processes in which quantum tunneling enables or enhances transitions that would be unlikely under classical energy-barrier assumptions. In these processes, particles or excitations cross barriers by tunneling, and the effect is often shaped by interactions with the environment, vibrational modes, or external fields.

In chemistry and biochemistry, tunneling-assisted reactions are observed when hydrogen or other light atoms transfer through energy barriers at low temperatures or within enzyme active sites. Proton and hydrogen tunneling can set reaction rates that are insensitive to temperature in some regimes and can produce pronounced kinetic isotope effects when hydrogen is substituted with deuterium or tritium.

In solid-state physics and nanotechnology, tunneling-assisted transport appears in tunnel junctions and molecular electronics, where electron flow is modified by interactions with phonons or photons. Phonon-assisted tunneling and photon-assisted tunneling expand the conditions under which charge can move across barriers, enabling or enhancing conduction in systems with weak electronic coupling or strong environmental fluctuations.

Theoretical treatments typically involve semiclassical or quantum-mechanical methods to estimate tunneling rates, including instanton analyses and nonadiabatic transition-state approaches, as well as broader frameworks such as environment-assisted quantum transport (ENAQT) to account for decoherence and dissipation. Experimental signatures of tunneling-assisted processes include unusual temperature dependences of rates, sizable isotope effects, and sensitivity to vibrational or photonic coupling that cannot be explained by classical activation alone.

See also: quantum tunneling, phonon-assisted tunneling, photon-assisted tunneling, electron transfer.