Strongly pumped parametric down-conversion: bright squeezed vacuum and parametric amplification

Spontaneous parametric down-conversion is the workhorse of quantum optics. It is used to generate entangled photon pairs and heralded single photons. When strongly pumped, spontaneous parametric down-conversion generates so many photon pairs that they overlap and form radiation with almost laser brightness. Nevertheless, this radiation manifests nonclassical effects: quadrature squeezing, photon-number correlations, and macroscopic entanglement. It has no coherent component and can be considered as amplified vacuum noise; it is therefore often called bright squeezed vacuum. In addition, strong photon-number fluctuations of bright squeezed vacuum make it extremely efficient for pumping multiphoton effects.

In my talk I will describe the quantum features of bright squeezed vacuum, and our recent experiments where we use it to pump multiphoton effects: optical harmonic generation and multiphoton photoelectron emission from nanotips. Further, I will speak about nonlinear interferometry, where two sources of parametric down-conversion are placed one after another to measure phase disturbances or absorption in between. Finally, I will show how a strongly pumped parametric amplifier can be used for the tomography of a quantum state, with immunity to loss and imperfect photodetection.