Any scientific instrument, including an electrical amplifier, necessarily adds noise in the process of performing a
measurement. As might be expected from knowledge of Heisenberg's uncertainty principle, quantum mechanics
sets strict limits on how little noise a measurement can add. There is a great deal of current interest in performing
measurements at the quantum limit on such systems as qubits and nanomechanical resonators. Here we introduce
the notion of quantum limited electrical measurement, and discuss recent progress made toward this goal.
By coupling a radio-frequency single-electron transistor (RF-SET) to a quantum dot (QD) in a GaAs/AlGaAs heterostructure, we have succeeded in detecting the tunneling of individual electrons on and off the QD on time scales as short as one microsecond. Using charge detection to probe the state of the QD allows us to nearly isolate the dot from its leads, thereby minimizing decoherence-inducing effects of the environment. We have extended these charge detection techniques to double quantum dots (DQDs) that can simultaneously be used to characterize the backaction of the RF-SET. The combined RF-SET/DQD system is well-suited to the development of charge- or spin-based quantum bits, and to investigation of the quantum measurement problem.
We have demonstrated a method of fabricating long-range arrays of 2D metallic microstructures on glass surfaces and measured the optical resonances of those structures. Gold and silver stripes are fabricated using microcontact printing with PDMS gratings and electroless plating techniques without the use of resist masks or etching. Changing the blaze angle and periodicity of the gratings used to make the PDMS stamps varies the line widths. The optical response of these fabricated transmission gratings was evaluated by measuring the transmission spectra while varying the angle of the incident light.