Energy spectroscopy of controlled coupled quantum-wire states

Abstract

Quantum ballistic transport in electron waveguides (EWGs)1,2 is based on coherent quantum states arising from the one-dimensional (1D) confinement in nanometre-scale constrictions. Semiconductor EWGs have received considerable renewed interest for quantum logic devices3,4,5,6,7 and theoretical concepts8,9,10,11 in the context of solid-state quantum information processing12. Implementation in real-world quantum circuits requires the unambiguous experimental distinction between all involved energy levels. However, such knowledge of EWGs investigated for wavefunction hybridization13,14,15 is solely based on estimates. Here, we present coupled EWGs that allow single-mode control and manipulation of mode coupling at temperatures as high as that of liquid-helium (4.2 K) and above. We demonstrate high-resolution energy spectroscopy of each EWG subband ladder and the 1D coupled states involved. The results verify the power of advanced nanolithography and its ability to open the door to the scalable semiconductor quantum circuits envisaged today.