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Schematic of heterodyne measurement setup. The quantum dots can be resonantly excited through the side of the chip into the planar waveguide. This minimizes the amount of scattered resonant pump light entering the collection optics. By modulating the QD resonance frequency at rf frequencies using a SAW, however, we can use the heterodyne technique to extract the resonant QD signal even when exciting the QD and extracting the fluorescence perpendicular to the surface of the chip using the same optics.
Shot-noise limited S/N ratio for heterodyne signal from a single quantum emitter with for the cases (left, green) , (middle, blue) , (right, red) ; different heterodyne frequencies are taken for clarity. In all cases, it is assumed that all of the scattered light is captured and the detector has unit quantum efficiency. The inelastic part of the spectrum falls below the noise floor.
Typical heterodyne signal measured on spectrum analyzer. The local oscillator is offset from the excitation laser by 80 MHz, the QD energy levels are modulated using a SAW at 92 MHz, and the sidebands generate beat notes at 12 MHz and 172 MHz. Red curve: Signal at 172 MHz, offset by . The spectrum analyzer resolution bandwidth is set to 100 Hz. Blue curve: Background signal when the QD emission is “switched off” by extinguishing the repumper.
(a) Mollow triplet measured using a scanning FP interferometer for three different resonant drive powers. Elastic emission is visible at low pump powers (blue curve), but not distinguishable from inelastic emission at high pump powers (green and red curves). Inset: Result of fitting 18 such curves to the Mollow expression to extract . (b) Heterodyne signal power versus input optical pump power for the same QD. The red curve is a fit to Eq. (2) .
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