Slow terahertz light via resonant-tunneling induced transparency in quantum well heterostructures

We present a theoretical and computational investigation of the possibility of achieving slow terahertz light by exploiting the tunneling induced transparency effect in suitably engineered quantum well heterostructure devices [1]. In our model, we consider a periodic structure consisting of two quantum wells per module, in which the lowest energy eigenstate of module I couples via resonant tunneling to the excited state of the next period, i.e. II, and the resulting triplet |𝑠⟩,|𝑒⟩ and |𝑔⟩ forms a Λ−type system (see Fig. 1a), intimately familiar from the field of electromagnetically induced transparency (EIT) [2]. For our calculations, we couple Schrödinger-Poisson, ensemble Monte-Carlo [3] and Maxwell-Bloch simulation codes, which enables us to self-consistently design and analyze various systems with the desired properties. Fig. 1b-d illustrates preliminary results from Maxwell-Bloch equation simulations for the propagation of a weak 30 picosecond pulse through a 2 mm long active region (shaded area), in the ideal case of vanishing |𝑠⟩↔|𝑔⟩ dephasing. Our calculations reveal a group refractive index of 𝑛𝑔≈11.6, however we believe that higher values can be achieved after a more thorough parameter study. In contrast to the EIT effect [2], the suggested approach offers the possibility to electrically control the coupling between the |𝑠⟩ and |𝑒⟩ states via simply varying the applied bias. Furthermore, given the rapid advances in the growth and processing technologies for quantum well heterostructure devices and fine level of control achieved, especially by the quantum cascade laser research community [4, 5], this technique seems to offer a good alternative for the on-chip integration of optical buffers.     «

We present a theoretical and computational investigation of the possibility of achieving slow terahertz light by exploiting the tunneling induced transparency effect in suitably engineered quantum well heterostructure devices [1]. In our model, we consider a periodic structure consisting of two quantum wells per module, in which the lowest energy eigenstate of module I couples via resonant tunneling to the excited state of the next period, i.e. II, and the resulting triplet |𝑠⟩,|𝑒⟩ and |𝑔⟩ form...     »