Highly sensitive displacement transduction of a 1.67 MHz mechanical resonator with a quantum point contact (QPC) formed in a GaAs heterostructure is demonstrated. By positioning the QPC at the point of maximum mechanical strain on the resonator and operating at 80 mK, a displacement responsivity of 3.81 A/m is measured, which represents a two order of magnitude improvement on the previous QPC based devices. By further analyzing the QPC transport characteristics, a sub-Poisson-noise-limited displacement sensitivity of 25 fm/Hz1∕2 is determined which corresponds to a position resolution that is 23 times the standard quantum limit.
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The extra mass and thickness of the Schottky electrodes is negligibly small when compared to the size of the beam and the mechanical resonator can be regarded as a symmetric system.
The quantized conductance at the first two steps is 1.04 G0 and 1.94 G0, respectively. The small deviation from their exact quantized values is due to the limited accuracy of the two-terminal transport measurement setup.
