The Future: From Q‐demonstrations to Q‐technologies

A significant consequence of the quantum nature of light in optical instruments is the presence of quantum noise in optical measurements. This noise limits the range of signals that can be used and signal‐to‐noise ratios that can be achieved. In addition, the performance of the system is different for very large signals, or modulations, and for small signals close to the quantum noise level. Some of the limitations introduced by quantum noise can be avoided by using non‐classical, or squeezed, states of light. Technology has now advanced to the point where fundamental quantum effects such as the fluctuations of the vacuum field and the discreteness of light can be demonstrated in undergraduate teaching laboratories, and there are a growing number of applications for quantum light, in particular in precision metrology and applications ranging from large‐scale gravitational‐wave detectors to imaging and precision clocks.