Determining Absolute Neutrino Mass using Quantum Technologies

TL;DR

The paper argues that determining the absolute neutrino mass $m_\beta$ requires moving beyond molecular tritium beta spectroscopy and towards cyclotron radiation emission spectroscopy (CRES) using atomic Tritium. The proposed QTNM program combines high-density atomic-tritium sources, atomic quantum sensors (notably circular Rydberg states) for precise magnetic and electric-field mapping, and quantum-noise-limited microwave amplifiers to realize a scalable, large-volume CRES spectrometer. By incorporating a modular magnetic storage-ring design, supersonic atomic beams, REMPI detection, and advanced readout technologies, the approach targets sensitivities down to the ~10 meV/$c^2$ scale, potentially probing normal-ordering neutrino masses and sterile-neutrino scenarios. The work outlines a concrete development path (CRESDA prototype, field-mapping protocols, and multi-channel GHz receivers) and situates QTNM within a broader landscape of Project 8, KATRIN, and PTOLEMY, emphasizing a terrestrial, model-agnostic probe of neutrino mass and new quantum technologies. The significance lies in achieving a direct, laboratory-based measurement with competitive or superior precision to cosmology, while simultaneously advancing quantum sensing and superconducting microwave technologies.

Abstract

Next generation tritium decay experiments to determine the absolute neutrino mass require high-precision measurements of $β$-decay electron energies close to the kinematic end point. To achieve this, the development of high phase-space density sources of atomic tritium is required, along with the implementation of methods to control the motion of these atoms to allow extended observation times. A promising approach to efficiently and accurately measure the kinetic energies of individual $β$-decay electrons generated in these dilute atomic gases, is to determine the frequency of the cyclotron radiation they emit in a precisely characterised magnetic field. This cyclotron radiation emission spectroscopy technique can benefit from recent developments in quantum technologies. Absolute static-field magnetometry and electrometry, which is essential for the precise determination of the electron kinetic energies from the frequency of their emitted cyclotron radiation, can be performed using atoms in superpositions of circular Rydberg states. Quantum-limited microwave amplifiers will allow precise cyclotron frequency measurements to be made with maximal signal-to-noise ratios and minimal observation times. Exploiting the opportunities offered by quantum technologies in these key areas, represents the core activity of the Quantum Technologies for Neutrino Mass project. Its goal is to develop a new experimental apparatus that can enable a determination of the absolute neutrino mass with a sensitivity on the order of 10~meV/$c^2$.

Figures (12)

• Figure 1: Dependence of the effective $\beta$-decay mass of the neutrino, $m_\beta$, on (a) the lightest neutrino mass $m_\text{lightest}$, (b) the sum of neutrino masses $\Sigma m_\nu$, and (c) the effective neutrinoless double $\beta$-decay mass $m_{\beta\beta}$. Neutrino oscillation parameters are taken from nufit5.2 for NO (blue) and IO (red) with the bands indicating $1\sigma$ uncertainties.
• Figure 2: (a) Tritium decay spectrum $\rmd\Gamma/\rmd E_e$ with respect to the emitted electron kinetic energy $E_e$. The solid black curve ($m_\nu = 0$) indicates the spectrum for a single, massless antineutrino. (b) Kurie plot of $C^{-1}\sqrt{\rmd\Gamma/\rmd E_e}$ near the endpoint for a single massless electron-antineutrino (continuous grey curve), and three active neutrinos in NO (continuous blue curve) and IO (continuous red curve) with a massless lightest neutrino. The dashed curves in (b) represent spectra in which the three neutrino mass contributions are replaced by $m_\beta$.
• Figure 3: Dependence of the sensitivity of a CRES experiment to measure $m_\beta$, on the T atom number density in the measurement volume. The set of volumes considered are indicated. In each case, the coloured bands represent the range of sensitivities expected from a frequency measurement precision set by the Cramér-Rao bound (equation \ref{['eq:fVar']}, continuous curve) to that set by $t_\text{obs}^{-1}$ (dashed-dotted curve). In all cases, the magnetic field strength was chosen to be 1 T (see text for details). Horizontal lines denoting the current, and ultimate projected limit of the KATRIN experiment with T$_2$ molecules katrin2024, and the minimally allowed value of $m_\beta$ for IO neutrinos, i.e., $m_\beta^{\mathrm{min}}(\mathrm{IO})$, are also shown.
• Figure 4: Conceptual layout of the QTNM apparatus. This comprises: (I) A high density source of T atoms produced by dissociation of T$_2$. (II) A CRES region in which the cyclotron radiation from electrons generated by $\beta$-decay of T atoms in a homogeneous magnetic field is collected. The magnetic field is measured with atoms in superpositions of Rydberg states. (III) A receiver chain, containing quantum-noise-limited amplifiers, in which the cyclotron radiation will be amplified and measured.
• Figure 5: (a) Schematic diagram of a pulsed supersonic beam source of H atoms (adapted from hogan12a). (b) Calculated longitudinal speed distributions of supersonic beams of H$_2$, D$_2$ and T$_2$ emanating from a source operated at 30 K. H, D or T atoms with similar speed distributions can be generated in these beams by dissociation in an electric discharge.