Quantum Nanomechanics

Quantum Nanomechanics is the emerging field which pertains to the mechanical behavior of nanoscale systems in the quantum domain. Unlike the conventional studies of vibration of molecules and phonons in solids, quantum nanomechanics is defined as the quantum behavior of the entire mechanical structure, including all of its constituents—the atoms, the molecules, the ions, the electrons as well as other excitations. The relevant degrees of freedom of the system are described by macroscopic variables and quantum mechanics in these variables is the essential aspect of quantum nanomechanics. In spite of its obvious importance, however, quantum nanomechanics still awaits proper and complete physical realization. In this article, I provide a conceptual framework for defining quantum nanomechanical systems and their characteristic behaviors, and chart out possible avenues for the experimental realization of bona fide quantum nanomechanical systems. 1 Why Quantum Nanomechanics A Quantum Nano-Mechanical (QnM) system is defined as a structure which demonstrates quantum effects in its mechanical motion. This mechanical degrees of freedom involve physical movement of the entire structure. In its current physical realizations, a typical nanomechanical system may consist of 100 million to 100 billion atoms. The mechanical degrees of freedom are therefore described by macroscopic variables. Experimental access to the quantum realm is crudely defined as the regime in which the quantum of energy h f in a resonant mode with frequency f is larger than the thermal energy kBT . The motivation behind this crude definition of the quantum regime is simple. The motion of a QnM system can be described by a harmonic oscillator potential. In the quantum regime, the harmonic oscillator potential energy Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, MA 02215 email: [email protected] 1 ar X iv :0 80 2. 41 16 v1 [ co nd -m at .m es -h al l] 2 8 Fe b 20 08