Resumen de Transport quàntic en dispositius d'estat sòlid per a aplicacions de freqüència de terahertzs
The work presented in this thesis is dedicated to the understanding of practical and conceptual challenges in simulating dynamical properties beyond the quasi-static approximation, in solid-state quantum devices in scenarios where a full quantum mechanical treatment is necessary. The results of this thesis are particularly relevant for the computation of the fluctuations of the electric current in the THz regime which aids in determining the correlations, the evaluation of tunnelling times that define the cut-off frequency of high-frequency operated devices, or the assessment of thermodynamic work to realize quantum thermal engines.The above mentioned dynamical properties involve multi-time measurements and hence are sensitive to quantum backaction. In the context of Orthodox quantum mechanics, the definition of these dynamical properties cannot be detached from the specification of the measurement apparatus. That is, defining apparatus-independent or intrinsic dynamical properties of quantum systems is incompatible with the postulates of Orthodox quantum mechanics.
All in all, a device engineer like me, working on practical problems related with the present and future solid-state devices, is forced to delve into the foundations of quantum mechanics if I really want to properly understand the high-frequency performance of solid-state devices. In this regard, I will show that the difficulties associated to the understanding of dynamical properties can be solved by looking beyond Orthodox quantum mechanics. In particular, I have explored the modal interpretation of quantum mechanics, which is a mathematically precise quantum theory that reproduces all quantum mechanical phenomena. I will show that intrinsic properties can be easily defined in this new (non-orthodox) context. Importantly, I will prove that intrinsic properties can be identified with weak values and hence that they can be measured! Focused on a particular modal theory, viz., Bohmian mechanics, an electron transport simulator will be discussed and applied to address both methodological and practical issues related to the simulation of quantum electron transport. The ontology of Bohmian mechanics naturally enables describing continuously monitored open quantum systems with a precise description of the conditional states for Markovian and non-Markovian regimes. This helps to provide an alternate to density matrix approach in the description of open quantum systems, which scales poorly computationally with the number of degrees of freedom.
Thus the Bohmian conditional state strategy, which has led to the development of an electron transport simulator, BITLLES will be shown to compute the dwell times for electrons in a two-terminal graphene barrier. It will be demonstrated that Bohmian trajectories are very appropriate to provide an unambiguous description of transit (tunnelling) times and its relation to the cut-off frequencies in practical electron devices. Finally, a protocol incorporating collective-like measurements to evade the current measurement uncertainty in the classical and quantum computing electron devices will be discussed.
