Optical amplifiers are essential in optical communication systems that serve as the backbone of the Internet. Conventional amplifiers suffer from the addition of noise, thus degrading the signals to be detected. There is only one known exception to this, which is in principle capable of noiseless amplification, so-called phase-sensitive amplifiers. While relatively complicated to implement, recent experiments have shown a noise figure well below the conventional quantum limit. Their benefit has subsequently been demonstrated in fiber optic transmission systems by e.g. showing a reach extension of a factor of four compared to traditional approaches.
The potential of PSAs, however, goes beyond amplification in optical communication links, especially since they, in principle, are scalable to any operating wavelength. In any situation where a very weak level of light is to be detected, an ultralow noise optical preamplifier would naturally be valuable. What are the potential uses of noiseless amplifiers in for example spectroscopy, biology, space, sensing? What implementations are viable at various wavelengths of light including visible and infrared?