Measurements of quantum dot level populations using an optical waveguide

A scheme is proposed for measuring electron level populations in a semiconductor quantum dot embedded in a multimode waveguide. The photon transmittance of the waveguide under steady-state pumping is shown to depend on the presence of an electron in the ground state of the quantum dot. The influence of waveguide, quantum dot, and photon source parameters on the electron detection process is examined. It is shown that, even at a moderate mode Q-factor (10⁴ to 10⁵), the measurement contrast and signalto-noise ratio are rather high (above 10⁴). The feasibility of using the proposed method for probing the state of a charge qubit is discussed.