Physics

The DAMIC experiment exploits the exceptional energy and spatial resolution of charge coupled devices (CCDs) to search for dark matter particles. We present the latest results from the 11 kg-day
exposure collected with the DAMIC detector at SNOLAB. We build on previous analyses to distinguish between bulk and surface backgrounds to construct a robust radioactive background model down to energies as low as 50 eV. We compare the observed spectrum of events to the background-model prediction to search for an excess bulk signal, as would be expected from dark matter.

The EDELWEISS direct detection experiment uses cryogenic Ge semiconductor detectors to search for sub-GeV dark matter (DM) particles. With its low gap energy, germanium is an excellent target to explore DM particles interactions with nucleons in the sub-GeV range, and DM-electron interactions in the MeV range, as well as search for the absorption of eV-scale dark photons. The collaboration has recently obtained the first Ge-based constraints on sub-MeV dark DM particles interacting with electrons using a 33.4 g Ge cryogenic detector prototype with a 0.53 electron-hole pair (rms) resolution, operated underground at the Laboratoire Souterrain de Modane.
These results will be presented, as well as the EDELWEISS-SubGeV plans to achieve lower threshold and more efficient particle identification at low energy.

A dark matter candidate lighter than about 30 eV exhibits wave behavior in a typical galactic environment. Examples include the QCD axion as well as other axion-like-particles. We review the particle physics motivations, and discuss experimental and observational implications of the wave dynamics, including interference substructures, vortices, soliton condensation and black hole hair.

Gravitational waves provide a unique way to study the universe. From the initial direct detection of coalescing black holes in 2015, to the ground-breaking multimessenger observations of coalescing neutron stars in 2017, and continuing with the now routine detection of merging stellar remnants, gravitational wave astronomy has quickly matured into a key aspect of modern physics. After briefly discussing what we've begun to learn from the new gravitational-wave transient catalog published by the LIGO, Virgo, and KAGRA collaborations (GWTC-2), I will discuss novel tests of fundamental physics GWs enable. In particular, I will focus on our current understanding of matter effects during the inspiral of compact binaries and matter at supranuclear densities, including possible phase transitions, through tests of neutron star structure. Detailed knowledge of dynamical interactions between coalescing stars, observations of extreme relativistic astrophysical systems, terrestrial experiments, and nuclear theory provide complementary views of fundamental physics. I will show how combining aspects from all these will improve our understanding of dense matter through the example of how we can determine whether newly observed objects are neutron stars or black holes.

Neutrino oscillations have been probed during the last few decades using multiple neutrino sources and experimental set-ups. In recent years, very large volume neutrino telescopes have started contributing to the field. These large and sparsely instrumented detectors observe atmospheric neutrinos for combinations of baselines and energies inaccessible to other experiments. IceCube, the largest neutrino telescope in operation, has used this to measure standard oscillations and place limits on exotic proposals, such as sterile neutrinos. In this talk, I will go over the newest results from IceCube as well as the improvements expected thanks to a new detector upgrade to be deployed in the near future.

A standard account of the measurement chain in quantum mechanics involves a probe (itself a quantum system) coupled temporarily to the system of interest. Once the coupling is removed, the probe is measured and the results are interpreted as the measurement of a system observable. Measurement schemes of this type have been studied extensively in Quantum Measurement Theory, but they are rarely discussed in the context of quantum fields and still less on curved spacetimes. 

In this talk I will describe how measurement schemes may be formulated for quantum fields on curved spacetime within the general setting of algebraic QFT. This allows the discussion of the localisation and properties of the system observable induced by a probe measurement, and the way in which a system state can be updated thereafter. The framework is local and fully covariant, allowing the consistent description of measurements made in spacelike separated regions. Furthermore, specific models can be given in which the framework may be exemplified by concrete calculations.

I will also explain how this framework can shed light on an old problem due to Sorkin concerning "impossible measurements" in which measurement apparently conflicts with causality.

The talk is based on work with Rainer Verch [Leipzig], (Comm. Math. Phys. 378, 851–889(2020), arXiv:1810.06512; see also arXiv:1904.06944 for a summary) and a recent preprint arXiv:2003.04660 with Henning Bostelmann and Maximilian H. Ruep [York].

We present a quantum architecture based on a linear chain of trapped 171Yb+ ions with individual laser beam addressing and readout. The collective modes of motion in the chain are used to efficiently produce entangling gates between any qubit pair. In combination with a classical software stack, this becomes in effect an arbitrarily programmable and fully connected quantum computer. The system compares favorably to commercially available alternatives [2].
We use this versatile setup to perform a quantum walk algorithm that realizes a simulation of the free Dirac equation where the quantum coin determines the particle mass [3]. We are also pursuing digital simulations towards models relevant in high-energy physics among other applications. Recent results from these efforts, and concepts for expanding and scaling up the architecture will be discussed.
[1] S. Debnath et al., Nature 563:63 (2016); P. Murali et al., IEEE Micro, 40:3 (2020); [3] C. Huerta Alderete et al., Nat. Communs. 11:3720 (2020).

Standard descriptions of the Milky Way dark matter halo and the WIMP-nucleus scattering may be oversimplified. As a result, direct detection experiments like DEAP-3600 can miss important features in case of a future signal. Therefore, it is important to have detailed analysis of the diverse dark matter interactions, in addition to the standard spin-independent and -dependent couplings. In this study we made use of a Non-Relativistic Effective Field Theory which is a suitable framework for such purpose since it considers a palette of dark matternucleon interactions expressed in terms of effective operators. This research also examined how current DEAP-3600 limits are modified due to the presence of substructures in the solar neighborhood; such stellar debris have recently been observed by astronomical surveys like the Gaia satellite and they were assumed with some fraction of dark matter. The most important aspect our study reveals is that both particle physics and astrophysics uncertainties need to be treated together since non-linear effects manifest in exclusion curves.

The idea that structure in the Universe was created from quantum mechanical vacuum fluctuations during inflation is very compelling, but unproven. Finding a test of this proposal has been challenging because the universe we observe is effectively classical. I will explain how quantum fluctuations can give rise to the density fluctuations we observe and will show that we can test this hypothesis using the statistical properties of maps of the universe.