19-23 September 2022
Perimeter Institute for Theoretical Physics
America/Toronto timezone

Poster Presentations

Chiara Brandenstein, Technical University of Munich

An electrostatic storage ring for fundamental physics measurements

We discuss an electrostatic trap for polarized 30 keV ions or ionic molecules to perform metrology-grade magnetic field measurements through spin precession in a frozen-spin configuration. Depending on the trapped species and the type of spin manipulation used, a range of fundamental effects can be probed, ranging from ultra-light axion-darkmatter to electric dipole moment (EDM) searches. In its ultimate implementation, polarized ions at storage times of several hours under cryogenic conditions can reach magnetic field measurement sensitivities beyond 10-20 T and correspondingly a competitive sensitivity for a dark-matter search. Using molecular ions like ThOH+ in the same setup together with laser spectroscopy for accessing molecular states, new perspectives for EDM could open up due to long trapping times, large statistics and a configuration of independently accessible bunches of trapped particles. The currently being set up implementation will demonstrate the feasibility of such a system at room temperature and respectively much shorter storage times at the order of minutes. With a comparably simple and easy-to-handle ion system, Ba+, we aim initially for operation as a magnetometer to demonstrate the experimental feasibility and set first limits on laboratory axion-electron couplings in the next years. In this presentation the current state of the development of the demonstrator setup and the ion source is shown, as well as a series of experimental details and problems currently under investigation

Hannah Day, University of Illinois at Urbana-Champaign

Stripping away assumptions to measure the Migdal effect

The Migdal effect occurs when a particle collides with an atom, and the lag between the movement of the nucleus and that of the electron cloud results in ionization. It was first predicted in 1939, but to date it has yet to be experimentally observed. In order to measure the effect, one must remove many of the standard assumptions that make calculations easier in order to obtain a result that is realistically measurable. The original calculation was performed assuming a free atom, but most realistic experiments require the use of semiconductors in which atoms are constrained to a lattice. Modern calculations take these lattice effects into account, but they still use the soft-limit assumption that the momentum of the electron cloud will be significantly less than that of the nucleus. This assumption breaks down in key regions of the parameter space where calibration experiments would be most sensitive to a signal. Thus, in order to make an accurate prediction for the signature of the Migdal effect, we determine whether removing the soft-limit assumption significantly changes the result of the calculation.

Adriana Dropulic, Princeton University

Revealing the Milky Way's Most Recent Major Merger with a Gaia EDR3 Catalog of Machine-Learned Line-of-Sight Velocities

Machine learning can play a powerful role in inferring missing line-of-sight velocities from astrometry in surveys such as Gaia. We apply a neural network to Gaia Early Data Release 3 (EDR3) and obtain line-of-sight velocities and associated uncertainties for ~92 million stars. The network, which takes as input a star's parallax, angular coordinates, and proper motions, is trained and validated on ~6.4 million stars in Gaia with complete phase-space information. The network's uncertainty on its velocity prediction is a key aspect of its design; by properly convolving these uncertainties with the inferred velocities, we obtain accurate stellar kinematic distributions. As a first science application, we use the new network-completed catalog to identify candidate stars that belong to the Milky Way's most recent major merger, Gaia-Sausage-Enceladus (GSE). We present the kinematic, energy, angular momentum, and spatial distributions of the ~450,000 GSE candidates in this sample, and also study the chemical abundances of those with cross matches to GALAH and APOGEE. The network's predictive power will only continue to improve with future Gaia data releases as the training set of stars with complete phase-space information grows. This work provides a first demonstration of how to use machine learning to exploit high-dimensional correlations on data to infer line-of-sight velocities, and offers a template for how to train, validate and apply such a neural network when complete observational data is not available.

Yufeng Du, California Institute of Technology

Atom Interferometer Tests of Dark Matter

Direct detection experiments for dark matter are increasingly ruling out large parameter spaces. However, light dark matter models with particle masses < GeV are still largely unconstrained. Here we examine a proposal to use atom interferometers to detect a light dark matter subcomponent at sub-GeV masses. We describe the decoherence and phase shifts caused by dark matter scattering off of one “arm” of an atom interferometer using a generalized dark matter direct detection framework. This allows us to consider multiple channels: nuclear recoils, hidden photon processes, and axion interactions. We apply this framework to several proposed atom interferometer experiments. Because atom interferometers are sensitive to extremely low momentum deposition and their coherent atoms give them a boost in sensitivity, these experiments will be highly competitive and complementary to other direct detection methods.

Alexander Frenett, Harvard University

Zeeman-Sisyphus Decleration of Polyatomic Molecules

Polyatomic molecules can provide improvement over diatomic systems in cold chemistry, precision measurement of fundamental physics, and quantum information. Slowing these species to trappable velocities is a major limitation in realizing these applications. Over the past decade, radiative slowing methods have been successfully applied to diatomic and, recently, triatomic molecules with highly diagonal Frank-Condon factors. Alternative slowing methods are needed for molecules that are less favorable for scattering the ~10,000 photons required for radiative slowing. Here we present a superconducting-magnet-based Zeeman-Sisyphus decelerator that requires fewer than 10 photon scatters to slow molecules to velocities suitable for loading a MOT, magnetic, or electric trap. We describe the design considerations, apparatus construction, and application of the slower to both CaOH and YbOH molecular beams. We also discuss the generalizability of this slowing method to increasingly complex molecular species.

Ting Gao, University of Minnesota

Standard Model prediction for paramagnetic EDMs

Standard Model $CP$ violation associated with the phase of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is known to give small answers for the EDM observables. Moreover, predictions for the EDMs of neutrons and diamagnetic atoms suffer from considerable uncertainties. We point out that the $CP$-violating observables associated with the electron spin (paramagnetic EDMs) are dominated by the combination of the electroweak penguin diagrams and $\Delta I =1/2$ weak transitions in the baryon sector, and are calculable within chiral perturbation theory. The predicted size of the semileptonic operator $C_S$ is $7\times 10^{-16}$ which corresponds to the {\em equivalent} electron EDM $d_e^{\rm eq} = 1.0 \times 10^{-35}e\,{\rm cm}$. While still far from the current observational limits, this result is three orders of magnitude larger than previously believed.

Matheus Hostert, Perimeter Institute

Simulating and exploring dark neutrino sectors

I will present some recent progress on simulating and constraining MeV-scale heavy neutral leptons at neutrino experiments. I will introduce DarkNews, a fast simulation tool for generating dilepton and single photon events in accelerator neutrino experiments, and present new limits derived from the T2K near detector using a novel method to sample multi-dimensional parameter spaces.

Ding Jia, Perimeter Institute

Quantum tunnelling and causal structure fluctuations

Quantum tunnelling processes are often accompanied by enhanced delocalization. For gravity, this could imply enhanced fluctuations for the causal structure of spacetime. I discuss the idea of using analog experiments of cosmological vacuum decay to study causal structure fluctuations.

Giacomo Marocco, University of Oxford

Searching for light dark matter with magnetsv

Dark matter may predominantly couple to Standard Model spins. We propose a method of directional detection of such dark matter candidates using 2d magnetically ordered materials. We forecast the sensitivity of these magnets, improving on previous calculations of dark matter-induced magnon excitations. A gram size target is potentially sensitive to couplings orders of magnitude below existing constraints.

Isabella Oceano, Deutsches Elektronen-Synchrotron

Application of the heterodyne system in ALPS II for the detection of weak fields

Any Light Particle Search II (ALPS II) is a second-generation Light Shining through a Wall experiment that hunts for axion-like particles.  ALPS II plans to discover Axion-Like Particles (ALP) or to improve the upper limit on their coupling strength to two photons by three orders of magnitude. The production of ALP happens via the conversion of a photon under the presence of a strong magnetic field and the detection can be either via Transition-Edge Sensor or via a HETerodyne (HET) system.  In the early science run, the HET sensing scheme will be used for the detection. The principle of heterodyne interferometry requires interfering with two laser fields at a non-zero difference frequency f0 with a consequential production of a time-varying signal, called beat note, having a frequency equal to f0. If the f0 is kept constant, this technique allows the detection of a very weak signal down to a few infrared photons per day. A description of the HET implementation in ALPS II will be described.

Swadha Pandey, Massachusetts Institute of Technology

Axion Dark Matter Birefringent Cavity (ADBC)

We present an experiment to detect the axion-photon coupling using a birefringent bow-tie cavity. Axions behave like coherent classical waves that could couple to electromagnetic fields by introducing a phase difference between right and left circularly polarized light. The bow-tie cavity would be sensitive to this coupling over lower masses of the QCD axion candidate and would scale with cavity length and power.

Thomas Penny, Yale University

Measuring the momentum recoil from nuclear decays using levitated sensors

After more than a century of study, nuclear decays remain an active area of research in fundamental physics. Many experiments rely on detecting the energy of emitted particles and, as a result, can be limited by background signals and broadening of emission lines due to secondary particles . Additionally, such methods cannot fully reconstruct the energy of undetected particles created by the decay. A complimentary approach is to measure the momentum of the daughter nucleus to reconstruct the momentum of the emitted particles. This significantly reduces the impact of low or zero mass backgrounds and secondary emissions, and has the potential to detect new invisible particles created by the decay process. We present initial results to measure the momentum recoil of an optically levitated silica microsphere due to an alpha decay. The nanogram mass spheres used demonstrate sufficient momentum sensitivity to resolve the expected decays and we present a method to load radioactive emitters onto the surface of a trapped microsphere. Additionally, we show that, if this method is extended to nanospheres, the momentum sensitivity will be substantially enhanced with the potential for searching for sterile neutrinos in the 100 keV-10 MeV mass range.

Mario Reig, University of Oxford

Axion couplings in grand unified theories

Axion couplings to gauge bosons are highly restricted in Grand Unified Theories where the Standard Model is embedded in a simple 4D gauge group. The topological nature of these couplings allows them to be matched from the UV to the IR, and the ratio of the anomaly with photons and gluons for any axion is fixed by unification. This implies that there is a single axion, the QCD axion, with an anomalous coupling to photons. Other light axion-like particles can couple to photons by mixing through the QCD axion portal and lie to the right of the QCD line in the mass-coupling plane. Axions which break the unification relation between gluon and photon couplings are necessarily charged under the GUT gauge group and become heavy from perturbative mass contributions. A discovery of an axion to the left of the QCD line can rule out simple Grand Unified models. Axion searches are therefore tabletop and astrophysical probes of Grand Unification.

Elizabeth Ruddy, University of Colorado

Mode entanglement and swapping used for enhanced detection of a weak axion-like signal

Cavity-based axion detectors search for a weak narrow-band signal at unknown frequency that is expected to arise due to the axion’s hypothesized coupling to electromagnetism. Quantum fluctuations intrinsic to the measurement of a cavity’s electromagnetic field quadratures constitute the primary noise barrier limiting these detectors. A comprehensive search of the axion parameter space at the quantum limit is prohibitively resource-intensive with current technology. Here, we present results from an experiment designed to mimic a real axion search in which we employ a quantum-enhanced sensing technique based on mode entanglement and swapping to demonstrate a 5.6-fold acceleration in the search for a weak axion-like signal relative to a quantum-limited search for the same signal. Employing swapping and entanglement simultaneously results in a quantum non-demolition interaction between two modes which amplifies the signal relative to the noise induced by measurement, widening the bandwidth over which the detector is sensitive.

Benjamin Siegel, Yale University

Creating an Array of Levitated Nanogram Spheres as a Dark Matter Detector

Optically levitated masses have many applications in precision measurement, including tests of the neutrality of matter, millicharged particle searches, and dark matter detection. For such searches in which sensitivities scale with the mass or number of neutrons in the test particle, using larger, heavier spheres extends their reach. To capitalize upon this, we have used spheres with diameters on the micrometer scale in past experiments. Further improvements in sensitivity to rare events and rejection of correlated noise sources can be achieved using an array of levitated microspheres. We present a system using an acousto-optic deflector to levitate a two dimensional array of microspheres in vacuum. This array is composed of time-shared traps with independent control of each sphere’s position and feedback. We outline the methods for creating such an array and discuss studies of intersphere interactions and couplings in addition to an array’s application for dark matter searches.

Rajashik Tarafder, California Institute of Technology

Quantum Precision Limits of Displacement-Noise Free Interferometers

Current laser interferometric gravitational wave detectors suffer from a fundamental limit to their precision due to the displacement noise of the mirrors contributed by various sources. Several schemes for noise reduction in Interferometers have been proposed to mitigate their effects. The idea behind these schemes is similar to decoherence-free subspaces in quantum sensing i.e. certain modes contain information about the gravitational waves but are insensitive to the displacement of the mirrors. In our poster, we would present a Displacement-Noise Free Interferometry (DFI) scheme, study its performance and compare it to conventional interferometry methods. We further perform a quantum Fisher information analysis and optimize it over the different parameters and squeezing strategies.

Yu-Han Tseng, Yale University

Toward Doppler Cooling a Microsphere using Whispering Gallery Mode Resonances

Optically levitated microspheres have applications including dark matter searches and nuclear recoil measurements. To effectively mitigate the impact of external noise, it is essential to cool down the mechanical degrees of freedom in the system. We present our ongoing study of the whispering gallery mode resonances (WGMs) in a microsphere. The effort is motivated by previous studies that suggest that it is possible to use the WGMs to Doppler cool the center-of-mass motion of a levitated microsphere down to a sub-mK effective temperature. We use in-house fabricated evanescent couplers, including tapered and angle-polished fibers, to investigate the excitation of WGMs. We experimentally measure the Q-factors and coupling efficiencies of the resonance modes and compare them to theoretical expectations. Finally, we discuss the prospect and challenges toward experimentally realizing the Doppler cooling scheme in a levitated microsphere system.

Sean  Vanbergen, TRIUMF/UBC

The TUCAN EDM Experiment

The TUCAN EDM experiment will attempt to improve the current upper limit on the neutron electric dipole moment, by an order of magnitude, to 10-27 ecm. This will be achieved through the combination of a spallation-based superfluid-helium ultracold-neutron source, currently under construction at TRIUMF, with a specialized Ramsey interferometer. In this measurement, spin-polarized neutrons undergo precession in a small magnetic field while also being subjected to a large electric field, which produces a small shift in the precession frequency in the case of a non-zero electric dipole moment. Achieving the target sensitivity requires precise control and understanding of systematic effects, which primarily arise due to non-uniformity in the 1 μT measurement field. To control these effects, the TUCAN EDM experiment will use a multi-layer passive magnetic shield and active compensation coils to produce a low-background environment, and the combination of a cohabiting mercury-gas magnetometer and an external array of cesium magnetometers to monitor the applied magnetic field and gradients.

Molly Watts, Yale University

Discharging microspheres for optomechanical dark matter searches

Levitated optomechanical systems can be used as ultra-sensitive directional force sensors that provide a novel way to search for dark matter in the 1 – 100 TeV range. To create such precision force sensors, we utilize a high vacuum environment that mechanically, thermally, and electrically isolates the system. We require complete control of charge to neutralize our spheres to provide the sensitivity to study zeptonewton forces. Our previous search for composite DM “nuggets” employed a single optically levitated microsphere, where we controlled the charge state of the sphere by removing or adding electrons in ±1 e precision steps that acted globally within the chamber. Currently, we are working to scale to a microspheres array which would increase our cross section for greater sensitivity and would enable better background rejection. To achieve an n x n array, we cannot employ the global stochastic discharging methodology used previously as we must eliminate the monopole coulomb force between spheres to trap successive spheres individually. We present a method for creating a guided single site UV device that can discharge individual spheres in situ.

Michael Wentzel, University of Illinois at Urbana-Champaign

Search for Dark Matter and Gravitational Waves with SRF Cavities

Advancements in superconducting radiofrequency (SRF) cavity design have the potential to enable searches for previously unobserved physics with weak coupling to photons. To motivate the use of SRF cavities as particle detectors, we discuss the generic properties of SRF cavities in the context of detecting small photon couplings. We describe two dark matter models that could be probed with SRF cavities, axion-like particles (ALPs) and primordial black holes (PBHs). Examining the resonant sensitivity of a single cavity to axion-mediated light-by-light scattering, we show that with feasible cavity parameters, future experiments can probe previously unexplored axion parameter space. Additionally, we discuss the potential for indirect detection of PBHs using cavities as gravitational wave detectors and argue that for models of PBHs which favor inspirals, PBH mergers can emit gravitational waves potentially detectable by future cavity experiments. We also discuss other gravitational wave sources that could be probed with SRF cavities.

Samuel Wong, Stanford University

One-Electron Quantum Cyclotron as a Milli-eV Dark Photon  Detector

We propose the use of charged particle traps for detection of dark photon dark matter.  In particular, we show that a one-electron quantum cyclotron is a promising detector at frequencies around 100 GHz. The trapped electron acts as a high-$Q$ resonator.  When the mass (frequency) of the dark photon matches the energy splitting of the cyclotron levels of the trap, the electron will be resonantly excited.  The resonant frequency can be scanned by sweeping the applied magnetic field, changing the cyclotron frequency and allowing sensitivity to a large dark photon mass range. Further, we carry out a proof-of-principle detection experiment using an existing apparatus tuned to a single frequency.  We demonstrate that this apparatus is background-free for the entire duration of the 7.4 day search.  We thus set a limit on dark photon dark matter at 148 GHz which is around 30 times better than current constraints. Future, purpose-built detectors have the potential to detect dark photon dark matter in the 0.1 -- 1 meV mass range ($\sim 20 - 200 \, \GHz$), an otherwise challenging range to probe.