Coherent control of a classical nanomechanical two-level system

• Published in: Nature physics 2013-08, Vol.9 (8), p.485-488
• Main Authors: Faust, T., Rieger, J., Seitner, M. J., Kotthaus, J. P., Weig, E. M.
• Format: Article
• Language: English
• Subjects: 639/766/1130; 639/925/927/359; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Control systems; Dielectric properties; Dynamical systems; Dynamics; Electromagnetic fields; Electromagnetics; Energy; letter; Magnetic fields; Mathematical analysis; Mathematical and Computational Physics; Molecular; Nanocomposites; Nanomaterials; Nanostructure; Optical and Plasma Physics; Physics; Quantum physics; Relaxation time; Superconductivity; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys2666

Coherent control of two flexural modes of a nanoscale oscillator using radiofrequency signals is now demonstrated. This oscillator is analogous to quantum two-level systems such as superconducting circuits and quantum dots, and therefore this technique raises the possibility of information processing using nanomechanical resonators. The Bloch sphere is a generic picture describing the coherent dynamics of coupled classical or quantum-mechanical two-level systems under the control of electromagnetic fields 1 , 2 . It is commonly applied to systems such as spin ensembles 3 , atoms 4 , quantum dots 5 and superconducting circuits 6 . The underlying Bloch equations 7 describe the state evolution of the two-level system and allow the characterization of both energy and phase relaxation processes 3 , 8 , 9 . Here we realize a classical nanomechanical two-level system 2 driven by radiofrequency signals. It is based on the two orthogonal fundamental flexural modes of a high-quality-factor nanostring resonator that are strongly coupled by dielectric gradient fields 10 . Full Bloch sphere control is demonstrated by means of Rabi 11 , Ramsey 12 and Hahn echo 13 experiments. Furthermore, we determine the energy relaxation time T 1 and phase relaxation times T 2 and T 2 *, and find them all to be equal. Thus decoherence is dominated by energy relaxation, implying that not only T 1 but also T 2 can be increased by engineering larger mechanical quality factors.