Boris L. Glebov, Jingyun Fan, Alan L. Migdall


In recent years, there has been a significant amount of research showing the potential advantage of quantum-enhanced techniques applicable in the fields of imaging, sensing, and metrology. Using quantum photonic states, these techniques allow increases in spatial and phase resolution well beyond the classical Shot limit, referred to as “the Standard Quantum Limit” (SQL). The resolution of these quantum-enhanced systems scales not only with the wavelength of light, but also with the number of photons. To achieve this quantum enhancement one needs a source of light whose uncertainty in the photon number has been reduced below that of Poissonian statistics.

Currently, quantum photonic states are produced using processes such as Spontaneous Parametric Down-Conversion (SPDC). These sources are fundamentally random in their nature, following a distribution with an uncertainty that is at least Poissonian. If the generated photons are restricted to a single mode (a necessary condition for many applications), the number distribution becomes thermal, which has even more uncertainty than the Poisson distribution. In both cases, the width of the distribution scales unfavorably with the mean – the probability of obtaining a photon state with a specific number of photons drops off rapidly for increasing photon numbers. To beat this problem, a photon generation scheme is needed in which the numbers of photons created are distributed more narrowly.

The proposed device uses multiple-pass SPDC to build up a desired state in a series of steps. Since SPDC produces pairs of separable photons, it is possible to monitor the number of photons generated at each step, and the process can be stopped once the targeted number has been reached. Photons already present in the cavity seed subsequent PDC processes, greatly accelerating photon generation. This makes it possible to reach high number states quickly. The system uses active feedback to modulate system gain and know when to release the final state, thus achieving high number photon states quickly and with a sub-Poissonian distribution.

This presentation discusses the proposed device, specifics of accumulation strategies, and compares theoretical performance limits of the feedback-based device to traditional single-pass schemes.