Microscopic Theory of Energy Dissipation and Decoherence in Solid-State Quantum Devices: Need for Nonlocal Scattering Models

Abstract

Energy dissipation and decoherence in state-of-the-art quantum nanomaterials and related nanodevices are routinely described and simulated via local scattering models, namely relaxation-time and Boltzmann-like schemes. The incorporation of such local scattering approaches within the Wigner-function formalism may lead to anomalous results, such as suppression of intersubband relaxation, incorrect thermalization dynamics, and violation of probability-density positivity. The primary goal of this article is to investigate a recently proposed quantum-mechanical (nonlocal) generalization (Phys. Rev. B 2017, 96, 115420) of semiclassical (local) scattering models, extending such treatment to carrier-carrier interaction, and focusing in particular on the nonlocal character of Pauli-blocking contributions. In order to concretely show the intrinsic limitations of local scattering models, a few simulated experiments of energy dissipation and decoherence in a prototypical quantum-well semiconductor nanostructure are also presented.

Simulation of Electronic Quantum Devices: Failure of Semiclassical Models

“…As a final remark, we notice that the unphysical features of the low-density Boltzmann-type simulations just reviewed come out to be further amplified in the presence of high carrier concentrations. As discussed in detail in [64], in high-density conditions, the Wigner function may still be negative, but also greater than unity. This implies that, for high carrier concentrations, the role played by the Pauli factor (1 − f (r, k)) in Equation (11) may deviate significantly with respect to the conventional semiclassical scenario (where it is always bounded between 0 and 1), leading to highly counter-intuitive effects such as a sort of "negative dissipation".…”

“…In particular, comparing Equation (37) with its semiclassical counterpart in Equation (11), it is evident that the action of the Pauli exclusion principle within the Wigner phase-space is itself nonlocal: the generalized in and out scattering rates for a given transition r, k → r , k depend on the value of the Wigner function in any other phase-space point r , k via the Pauli factor 1 − f (r , k ). A detailed investigation of such Pauli-blocking nonlocality is outside the scope of the present work and can be found in [64].…”

“…Such a local description is, however, intrinsically incompatible with the fully quantum-mechanical (i.e., non-local) nature of the dissipation-free carrier dynamics within the device active region. Indeed, during the last decades the intrinsic limitations of such hybrid treatments have been repeatedly pointed out, both for the case of thermalization models based on the conventional inflow-boundary-condition scheme [34,37,[45][46][47]67] and for the case of dissipation versus decoherence treatments based on the relaxation-time approximation as well as on Boltzmann-like scattering models [61,64].…”

Quantum Nonlocality

“…Another work showing the need for quantum nonlocality to explain observed behavior was presented by Iotti and Rossi in [ 29 ] “Microscopic Theory of Energy Dissipation and Decoherence in Solid-State Quantum Devices: Need for Nonlocal Scattering Models”. Here, nonlocal generalization of semiclassical (local) scattering models [ 30 ] was successful, whereas numeral calculations based on local models failed.…”

Generalized nonequilibrium quantum transport of spin and pseudospins: Entanglements and topological phases

“…There are indeed theoretical and experimental works which support this assertion, the effect is related to what is often referred to in the literature as weak localization due to Dresselhaus and Rashba spin-orbit couplings15 and weak antilocalization or supression of scattering rates due to the Dyakonov-Perel and Elliott-Yafet scattering mechanisms16,17 or entanglement of spin-orbit couplings with another torque (spin) degrees of freedom. Delocalization or nonlocal scattering terms may also occur where the scattering centers have a pseudo-spin character, such as the two-level dependence of the scattering in Wigner-function quantum transport formalism recently studied by Rossi et al36,37…”