Bright squeezed vacuum for two-photon spectroscopy: simultaneously high resolution in time and frequency, space and wavevector

TL;DR

This paper demonstrates that bright squeezed vacuum can achieve high resolution in both time-frequency and space-wavevector domains simultaneously, surpassing classical limits and violating the Mancini criterion of entanglement.

Contribution

It shows that BSV provides high resolution in multiple domains without flux dependence, offering a practical alternative to entangled photons for spectroscopy.

Findings

Measured second-order correlation widths in space, time, frequency, and angle.

Demonstrated violation of the Mancini entanglement criterion.

Compared BSV efficiency with coherent light, showing modest but flux-independent improvements.

Abstract

Entangled photons offer two advantages for two-photon absorption spectroscopy. One of them, the linear scaling of two-photon absorption rate with the input photon flux, is only valid at very low photon fluxes and is therefore impractical. The other is the overcoming of the classical constraints for simultaneous resolution in time-frequency and in space-wavevector. Here we consider bright squeezed vacuum (BSV) as an alternative to entangled photons. The efficiency increase it offers in comparison with coherent light is modest, but it does not depend on the photon flux. Moreover, and this is what we show in this work, BSV also provides simultaneously high resolution in time and frequency, and in space and wavevector. In our experiment, we measure the widths of the second-order correlation functions in space, time, frequency, and angle, and demonstrate the violation of the constraint given by the Fourier transformation, also known as the Mancini criterion of entanglement.