Quantum non-demolition measurements play an important role in quantum theory and many of its applications. In theory they are the most fundamental quantum measurements, but in practice their realization can be chal- lenging due to realistic constraints. In optics for example, most measurements are destructive since photons get absorbed by the detector. While some simple single particle non-demolition measurements are routinely done in optical setups by using a second degree of freedom to encode the results at an intermediate stage, measurements of degenerate non-local observables involving multiple photons remain challenging, especially when these are done at intermediate measurement strengths. Here we present an optical setup for performing variable strength non-demolition measurements of non-local observables in a pre and postselected setting. At the heart of the setup is an apparatus that can be used to turn a strong (projective) measurement into an arbitrary strength measurement by using a quantum eraser. We present our initial calibration results for this apparatus.
Monolithic photonics architectures which enable the generation and processing of quantum states of light will be discussed. Some architectures are shown to exhibit characteristics that are unique to integrated architectures over their bulk-optics counterparts.
If we use on-chip quantum interference as an example, one find it is often assumed that the 2x2 mode coupler maintains a 50:50 splitting ratio over the twin-photons’ entire joint spectrum. However, this is not necessarily the only case possible for integrated devices. For some designs the interferometer behaves as an ideal 50:50 beamsplitter (BS), while for others it behaves as an ideal wavelength de-multiplexer (WD). This interesting ramifications for two-photon interference, where dispersion can allow integrated 2x2 couplers to play a far more versatile role in quantum circuits than their bulk-optics counterparts.