Photon retention in coherently excited nitrogen ions

TL;DR

This paper demonstrates photon retention and re-emission in coherently excited nitrogen ions, revealing quantum coherence effects that could enable optical information storage in atmospheric conditions.

Contribution

It introduces a novel method of photon retention in N2+ ions using quantum coherence, with experimental validation of re-emission triggered by a delayed femtosecond pulse.

Findings

Photon retention lasts for tens of picoseconds.

Re-emission occurs at 329.3 nm via two-photon resonance.

Excited-state population is crucial for photon transmission.

Abstract

Quantum coherence in quantum optics is an essential part of optical information processing and light manipulation. Alkali metal vapors, despite the numerous shortcomings, are traditionally used in quantum optics as a working medium due to convenient near-infrared excitation, strong dipole transitions and long-lived coherence. Here, we proposed and experimentally demonstrated photon retention and subsequent re-emittance with the quantum coherence in a system of coherently excited molecular nitrogen ions (N2+) which are produced using a strong 800 nm femtosecond laser pulse. Such photon retention, facilitated by quantum coherence, keeps releasing directly-unmeasurable coherent photons for tens of picoseconds, but is able to be read-out by a time-delayed femtosecond pulse centered at 1580 nm via two-photon resonant absorption, resulting in a strong radiation at 329.3 nm. We reveal a pivotal role of the excited-state population to transmit such extremely weak re-emitted photons in this system. This new finding unveils the nature of the coherent quantum control in N2+ for the potential platform for optical information storage in the remote atmosphere, and facilitates further exploration of fundamental interactions in the quantum optical platform with strong-field ionized molecules.