Neutrinos and Non-Proliferation
What are neutrinos?
Neutrinos are perhaps the least understood fundamental particles in the Standard Model.
Known as "ghost particles", they are extraordinarly difficult to detect due to only interacting with the weak force and gravity.
Their existence was first proposed by Wolfgang Pauli in 1930 as a way to maintain conservation of energy and momentum in beta decay.
At the time Pauli remarked, "I have done something very bad today by proposing a particle that cannot be detected; it is something no theorist should ever do."
In 1956, however, the Cowan–Reines experiment proved the existence of neutrinos.
The experiment used a nuclear reactor as a neutrino source, in which fission products will beta decay and release neutrinos.
A scintillation detector measured neutrino capture events (inverse beta decay), confirmed to originate from neutrinos by shutting off the reactor.
Our understanding of neutrinos has since progressed over the last 70 years.
Their elusiveness has led to 4 Nobel Prizes awarded to new discoveries of neutrino properties, the most of any particle.
Neutrinos have also played a significant role in our understanding of the Standard Model, such as in the discovery of parity violation in the weak force, and electroweak unification.
Despite much progress, many open questions remain to be solved: neutrino mass ordering, a direct mass measurement, Majorana or Dirac in nature, and precise measurements of neutrino mixing, to name a few.
Detecting neutrinos with quantum sensors
In 2017, the COHERENT experiment first observed coherent elastic neutrino-nucleon scattering, or CEvNS (pronounced "sevens").
In CEvNS, the neutrino bounces off an individual nucleus in a manner analogous to classical billiard ball scattering.
Although this interaction was predicted over 40 years earlier, CEvNS only results in a tiny amount of energy deposited in a detector proving to be an experimental challenge.
Despite this, CEvNS will have a relatively high scattering rate compared to inverse beta decay, and does not have a minimum energy threshold required for the incoming neutrino.
This allowed for COHERENT's 15 kg scintillation detector to detect neutrinos, compared to multi-ton detectors needed for measuring inverse beta decay.
Quantum sensors, being compact and sensitive to a larger range of CEvNS energies, are natural neutrino detectors.