Quantum Computing Unlocks Neutrino’s Role in Universe’s Large-Scale Structure Formation

Neutrinos, subatomic particles with a finite mass, significantly influence the universe’s large-scale structure (LSS). The existence of massive neutrinos impacts the formation of the LSS, and observations of the LSS can provide constraints on the neutrino mass. However, simulating the LSS formation, which includes massive neutrinos and conventional cold dark matter, is computationally demanding. Researchers propose a quantum algorithm to address this challenge, using quantum computing to speed up numerical tasks. This is the first quantum algorithm for the LSS simulation that outputs the quantity of practical interest with guaranteed accuracy.

What is the Significance of Neutrinos in the Formation of the Universe’s Large-Scale Structure?

The universe’s large-scale structure (LSS) is significantly influenced by neutrinos, subatomic particles with a finite mass. This is a crucial aspect of fundamental physics, as the existence of massive neutrinos impacts the formation of the LSS. Conversely, observations of the LSS can provide constraints on the neutrino mass. The numerical simulation of the LSS formation, which includes massive neutrinos and conventional cold dark matter, is therefore a critical task.

The neutrino distribution in the phase space is calculated by solving the Vlasov equation, a suitable approach for this task. However, this requires solving the partial differential equation (PDE) in a 6+1 dimensional space, which is computationally demanding. The researchers propose a quantum algorithm to address this challenge. By linearizing the Vlasov equation and neglecting the relatively weak self-gravity of the neutrino, they perform a Hamiltonian simulation to produce quantum states that encode the phase-space distribution of neutrinos.

How Does Quantum Computing Aid in the Simulation of the Universe’s Large-Scale Structure?

Quantum computing, an emerging technology, has the potential to speed up numerical tasks that are intractable by classical computers, including supercomputers. With the recent rapid advancement of quantum computing, researchers are exploring its applications in various fields. In this context, the simulation of the LSS of the universe with massive neutrinos is an important task in cosmology.

The researchers propose a method to extract the power spectrum of the neutrino density perturbations as classical data from the quantum state. This is achieved by quantum amplitude estimation with an accuracy of epsilon-1 and a query complexity of order tilde-wideOn grntepsilon-1. The method also reduces the space complexity to Opolylog ngrepsilon-1 in terms of the qubit number while using quantum random access memories with On3 gr entries. This is the first quantum algorithm for the LSS simulation that outputs the quantity of practical interest with guaranteed accuracy.

What is the Role of Neutrinos in the Standard Cosmological Model?

In the standard cosmological model, all the rich structures of the present-day universe formed through gravitational instability of tiny density fluctuations seeded in the early universe. The structure at the largest scale probed by cosmological observations is called the LSS. The evolution and the resultant LSS have been shaped by the nature of the mysterious constituents of the universe.

Interestingly, the major components of the universe are largely unidentified. In terms of the energy fraction, about 69% is contributed by the so-called dark energy, perhaps some unknown form of energy different from matter, and about 26% is dark matter (DM), which is often thought to be unknown elementary particles that are not predicted to exist in the Standard Model (SM) of particle physics. Observations of the cosmic LSS can shed light on the nature of such dark components and eventually provide an important clue on physics beyond the SM.

How Do Neutrinos Contribute to the Understanding of Particle Physics?

An important issue towards a better understanding of particle physics through the LSS is that neutrinos have finite masses. Neutrinos are massless particles in the SM, but the detection of neutrino flavor oscillation has now established that they have nonzero mass. The current constraint from the neutrino oscillation experiments is given as the lower bound on the neutrino mass. Although the estimated mass is much smaller than other SM particles, such as electron with 0.51 MeV, the nonzero neutrino mass is definite evidence that there is physics beyond the SM. Intriguingly, astronomical observations of the cosmic LSS provide independent constraints on the neutrino mass.

How Do Neutrinos Influence the Formation of the Universe’s Large-Scale Structure?

Neutrinos produced in the early universe exist even today as relics and constitute a part of matter component along with cold dark matter (CDM), the conventional picture of DM as particles with much larger mass. In the LSS formation, neutrino behaves differently from CDM and ordinary matter baryons, which we hereafter call CDM collectively since they behave similarly under the action of mutual gravity. Neutrinos have nonrelativistic but extremely large velocities and thus stream almost freely in the gravitational potential of CDM. Hence, neutrinos used to be thought as hot dark matter (HDM), distinguishing from CDM. The distribution and gravitational dynamics of neutrinos affect the formation of LSS differently from the conventional picture with CDM only. This gives hope that by comparing the theoretical prediction on the LSS with massive neutrino to the results of cosmological observations, one can derive constraints on the neutrino mass.