Rigorous derivation of coherent resonant tunneling time and velocity in finite periodic systems

The velocity $v_{res}$ of resonant tunneling electrons in finite periodic structures is analytically calculated in two ways. The first method is based on the fact that a transmission of unity leads to a coincidence of all still competing tunneling time definitions. Thus, having an indisputable resonant tunneling time $\tau_{res},$ we apply the natural definition $v_{res}=L/\tau_{res}$ to calculate the velocity. For the second method we combine Bloch's theorem with the transfer matrix approach to decompose the wave function into two Bloch waves. Then the expectation value of the velocity is calculated. Both different approaches lead to the same result, showing their physical equivalence. The obtained resonant tunneling velocity $v_{res}$ is smaller or equal to the group velocity times the magnitude of the complex transmission amplitude of the unit cell. Only at energies where the unit cell of the periodic structure has a transmission of unity $v_{res}$ equals the group velocity. Numerical calculations for a GaAs/AlGaAs superlattice are performed. For typical parameters the resonant velocity is below one third of the group velocity.Comment: 12 pages, 3 figures, LaTe

Deterministic fabrication of nanostructures for plasmonic lens by focused ion beam

Plasmonic lens is a key component in the development of sub-wavelength resolution optical system for bio-imaging and nanolithography applications. In order to develop a deterministic fabrication capability for nanostructures on plasmonic lens by using focused ion beam, this paper presents a highly robust and accurate surface topography model based on level set method. Sputtered atom distribution and angular dependence of sputter yield are calculated by Monte Carlo simulation programs SRIM/TRIM and TRIDYN, respectively. Redeposition effect is included in the physical model and successfully embedded into a topography simulation program by applying the level set method. The proposed model is validated and evaluated in the focused ion beam fabrication experiments. Simulation error of less than 7% is obtained. Two types of nanostructures for plasmonic lens were fabricated using the machining parameters approved by this simulation model. Simulation errors of 7 and 2 nm were found in a nanodots array and a spiral Bragg grating, respectively. The results clearly demonstrate the effectiveness of the modelling approach developed for deterministic fabrication of nanostructure

The SECOQC quantum key distribution network in Vienna

International audienceThe paper presents the architecture and functionality of the principal networking agent—the SECOQC node module, which enables the authentic classical communication required for key distillation, manages the generated key material, determines a communication path between any destinations in the network, and realizes end-to-end secure transport of key material between these destinations. The paper also illustrates the operation of the network in a number of typical exploitation regimes and gives an initial estimate of the network transmission capacity, defined as the maximum amount of key that can be exchanged, or alternatively the amount of information that can be transmitted with information theoretic security, between two arbitrary nodes