QUANTUM NANOMECHANICS
Nanomechanics involves structures in the nanometer scale, capable of mechanical motion with three-dimensional relief. These structures, often engineered in laboratories by advanced fabrication techniques, enable studies of phenomena of both fundamental and technological interests. Because of their size nanomechanical elements such as cantilevers and beams can be extremely sensitive to small forces. Therefore, they can be used as devices for detection of small forces. Of particular interest are fundamental weak forces such as gravitational force in micron distance scales or forces generated by quantum effects at low temperatures. Advanced techniques for fabricating complex nanomechanical structures and ultra-sensitive measurement techniques in low temperature environment make it possible to study a host of fundamental phenomena.
Consider, for example, a nanomechanical structure such as a beam with three-dimensional relief. Because of its size, its normal-mode frequency lies in the range of hundreds of megahertz to a few gigahertz . Since the vibration of such a structure can be closely approximated by a weakly-damped harmonic oscillator, its study at temperatures low enough to be smaller than the quantum of energy contained within each mode, hf > kT, will be essentially equivalent to that of a quantum mechanical harmonic oscillator. Experimental realization of such a structure and its low temperature measurement will therefore undoubtedly enable the study of a host of problems with mechanical systems, ranging from quantum dissipation and quantum jumps to macroscopic quantum coherence and tunneling. From a technological point of view, mechanical structures capable of resonating at high frequencies will have a broad range of applications. Filters and passive devices in cell phones, gyroscopes and accelerometers, switches in telecommunication, and highly parallel biomolecular sensors are some of the obvious examples, and not surprisingly, somewhat larger versions of these conceptual devices in the micron range are already commercially available.
PROJECTS
Quantum Dissipation in Nanomechanical Oscillators
(G. Zolfagharkhani, A. Gaidarzhy, R.L. Badzey, P. Mohanty)
Dissipation or energy relaxation of a resonant mode in a nanomechanical device occurs by its coupling to environment degrees of freedom, which also acquire quantum mechanical correlations at millikelvin temperatures. We report measurements of temperature and magnetic field dependence of dissipation in single crystal silicon nanobeams in MHz up to 1 GHz frequency range. We extend our measurements down to temperatures of 20 millikelvin and up to fields of 16 tesla. The fabrication of our Nano-Electro-Mechanical Systems (NEMS) involves e-beam lithography, as well as various deposition and plasma etching processes.
Towards the Quantum Mechanical Regime in Nanoscale Oscillators
(A. Gaidarzhy, G. Zolfagharkhani, R.L. Badzey, P. Mohanty)
Nanomechanical oscillators at millikelvin temperatures enter the quantum mechanical regime as the quantum of energy stored in a single mode hf becomes comparable or larger than the average thermal energy kT such that hf/kT is greater than 1. The corresponding temperature for 1 GHz range oscillator is 48 millikelvin. We report measurements of suspended silicon nano-electro-mechanical systems (NEMS) in the high MHz up to a GHz resonant frequency range at temperatures below 20 millikelvin. We discuss various techniques for ultra-sensitive measurement of femtometer-level displacements.
Mechanical Signal Processing with Nano-Electro-Mechanical Systems (NEMS)
(R.L. Badzey, A. Gaidarzhy, G. Zolfagharkhani, P. Mohanty)
We report extensive measurements of linear and nonlinear response of Nano-Electro-Mechanical Systems (NEMS) at millikelvin temperatures. Our structures are suspended single-crystal silicon beams with three-dimensional relief fabricated by electron-beam lithography and nanomachining. Excited via a magnetomotive technique and measured by a variety of methods, the dynamics of these beams is known to become nonlinear with sufficient excitation. We have performed comprehensive characterization of nonlinearity in a wide range of frequencies, temperatures, and driving amplitudes. We discuss our approach to mechanical signal processing in these structures, in both the frequency and time domains. Understanding the nature of the nonlinear behavior of these systems will have significant impact on signal processing with nanomechanical systems.