ABSTRACT

We have learnt in Chapter 5 how to reduce fluctuations of an

electromagnetic (EM) field below the quantum (Heisenberg) limit

imposed by the quantum nature of light. It has been shown that

the quantum limit can be beaten using non-classical squeezed light

of reduced fluctuations. Another issue of significant interest in

quantum optics is to beat the diffraction limit imposed on the

resolution of measured objects by the wave nature of light. In this

chapter, we will illustrate how one can beat the diffraction limit by

using the quantumnature of entangled light beams.We shall see that

entangled light can lead us to a new domain of quantum optics in

which detectors can resolve two closely spaced objects or spectral

lines with the minimal resolvable limit significantly reduced or even

completely suppressed. This subject is generally known as quantum

optical lithography and could be described in short as the ability to

print patterns onto certain materials using non-classical light. The

developments in this area are of fundamental interest, and they hold

promise for advances in optical interferometry and in applications

such as quantummetrology and gravitational wave studies.