Virtual-State Spectroscopy with Frequency-Tailored Intense Entangled Beams

TL;DR

This paper analyzes virtual-state spectroscopy using intense entangled beams with tunable spectral correlations, revealing its potential for high-sensitivity detection of virtual states in two-photon absorption processes.

Contribution

It provides a detailed theoretical analysis of the two-photon absorption signal, including classical and quantum contributions, and establishes the feasibility of using high-photon-number entangled beams for virtual-state spectroscopy.

Findings

Spectroscopy can be performed with entangled twin beams carrying up to 10^4 photon pairs.

Two-photon absorption signals could be up to 10,000 times larger than previous reports.

The results suggest the first experimental realization of virtual-state spectroscopy is feasible.

Abstract

In this contribution we analyze virtual-state spectroscopy --- a unique tool for extracting information about the virtual states that contribute to the two-photon excitation of an absorbing medium --- as implemented by means of intense entangled beams with tunable spectral correlations. We provide a thorough description of all contributing terms (classical and quantum) in the two-photon absorption signal, as well as the limits imposed by the power of the pump that produces the entangled beams on the observability of the spectral lines of the virtual transitions. We find that virtual-state spectroscopy may be implemented with entangled twin beams carrying up to $10^4$ photon pairs. This implies that, in principle, one might be able to detect two-photon absorption signals up to four orders of magnitude larger than previously reported, thus paving the way towards the first experimental realization of the virtual-state spectroscopy technique.