  Low-noise, efficient, phase-sensitive time-domain optical detection is
essential for foundational tests of quantum physics based on optical quantum
states and the realization of numerous applications ranging from quantum key
distribution to coherent classical telecommunications. Stability, bandwidth,
efficiency, and signal-to-noise ratio are crucial performance parameters for
effective detector operation. Here we present a high-bandwidth, low-noise,
ultra-stable time-domain coherent measurement scheme based on balanced homodyne
detection ideally suited to characterization of quantum and classical light
fields in well-defined ultrashort optical pulse modes.
