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arXiv:1510.04852

A novel technique to achieve atomic macro-coherence as a tool to determine the nature of neutrinos

Roberto Boyero-García, Alicia V. Carpentier, Juan José Gómez-Cadenas, A. Peralta Conde

Published Oct 16, 2015• 2 citations
arXivHTMLPDF

Abstract

The photon spectrum in macrocoherent atomic de-excitation via radiative emission of neutrino pairs (RENP) has been proposed as a sensitive probe of the neutrino mass spectrum, capable of competing with conventional neutrino experiments. In this paper we revisit this intriguing possibility, presenting an alternative method for inducing large coherence in a target based on adiabatic techniques. More concretely, we propose the use of a modified version of Coherent Population Return (CPR), namely double CPR, that turns out to be extremely robust with respect to the experimental parameters, and capable of inducing a coherence close to 100% in the target.

DOI
10.48550/arxiv.1510.04852

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The photon spectrum in macrocoherent atomic de-excitation via radiative emission of neutrino pairs (RENP) has been proposed as a sensitive probe of the neutrino mass spectrum, capable of competing with conventional neutrino experiments. In this paper we revisit this intriguing possibility, presenting an alternative method for inducing large coherence in a target based on adiabatic techniques. More concretely, we propose the use of a modified version of Coherent Population Return (CPR), namely double CPR, that turns out to be extremely robust with respect to the experimental parameters, and capable of inducing a coherence close to 100% in the target.
We discuss a possibility of detecting a coherent photon pair emission and related radiative neutrino pair emission from excited atoms. It is shown that atoms of lambda- and ladder-type three level system placed in a pencil-like cylinder give a back to back emission of two photons of equal energy Δ/2Δ/2Δ/2, sharply peaked with a width $\propto $ 1/(target size) and well collimated along the cylinder axis. This process has a measurable rate ∝\propto∝ (target number density) 2×^2 \times2× target volume, while a broader spectral feature of one-photon distribution separated by (mass sum of a neutrino pair)2/(2Δ)^2/(2Δ)2/(2Δ) from the two photon peak may arise from radiative neutrino pair emission, with a much smaller rate.
We present experimental data on adiabatically driven frequency conversion with ultrashort (picosecond) laser pulses towards the vacuum-ultraviolet regime, enhanced by coherent population return and preparation of maximal atomic coherences. We generate the sum frequency of an intense pump pulse and a probe pulse via a two-photon resonance in xenon. When we slightly detune the pump laser from two-photon resonance, the atomic populations are adiabatically driven forth and back from the atomic ground state to an excited state. This coherent population return (CPR) prepares the medium in a transient state of maximal atomic coherence, which enhances frequency mixing with a probe laser. We thoroughly study the variation of CPR-enhanced frequency conversion with experimental parameters and compare CPR with conventional, resonantly enhanced frequency conversion. In particular, we investigate the temporal evolution of the atomic coherence and the effect of inevitable ac Stark shifts. We find that ac Stark shifts induce an asymmetry in the spectral characteristics of CPR, which nevertheless permits enhanced frequency conversion. For the case of resonantly enhanced frequency conversion, we show that the atomic coherences are maintained for several tens of picoseconds after the pump pulse, which permits time-delayed frequency conversion. Moreover, we analyze the pressure dependence of the atomic coherence' lifetime and observe a free induction decay at the two-photon coherence with the generation of a second harmonic field. These findings shall push applications of adiabatic light-matter interactions also to the regime of nonlinear optics, driven by intense laser pulses.
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We consider atomic system of Λ−Λ-Λ−type 3-level coupled to 2 mode fields, and derive an effective Maxwell-Bloch equation designed for two photon emission between two lower levels. We find axially symmetric, topologically stable soliton solutions made of condensed fields. Immediate implication of soliton formation to radiative neutrino pair emission is to enhance its rate, larger than the usual ∝N2\propto N^2∝N2 factor of target number dependence, along with another merit of increasing the signal to the background photon emission.
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SPAN (Spectroscopy of Atomic Neutrino) project aims to determine the absolute neutrino mass. The process we plan to use is a cooperative de-excitation of atoms in a metastable level emitting a neutrino pair associated with a photon. The photon energy spectrum of this process contains information on the absolute mass of neutrino. Key items of this experiment are a rate amplification using macro-coherence in a target medium in case of plural particles emission and an external triggering of the emission in order to scan the spectrum. We have demonstrated the rate amplification in two-photon emission from para-hydrogen gas which was coherently excited to its first vibrationally excited state. The coherence in the medium was generated by irradiating two driving laser pulses. The emission was stimulated by irradiating a mid-infrared laser pulse. The enhancement factor of more than 10 18 with respect to the spontaneous emission was achieved. This paper briefly summarizes the results.