Session K05: Searches for Dark Matter and Dark Energy

Quantum sensing methods for directional dark matter detection

Detectors searching for weakly interacting massive particle (WIMP) dark matter (DM), which have traditionally grown more sensitive with increasing mass and better background reduction, will soon face an irreducible background: detection of solar neutrinos, or the "neutrino floor". Directional detectors would surpass this "floor" by differentiating particles originating from the sun or the galactic halo. We are developing methods for directional detection in diamond, an attractive detector material because of its favorable sensitivity profile and good semiconductor properties. Nuclear recoils in such a detector would leave "tracks" of crystal damage and lattice strain, serving as a durable record of the initiating particle's direction; detecting and mapping these sub-micron tracks is one of the central challenges of such a detector. Over the past two years, we have demonstrated quantum sensing protocols using nitrogen-vacancy centers to measure diamond crystal strain with the sensitivity required to identify such tracks, as well as x-ray microscopy methods with the resolution required to extract their direction once identified. In this talk, we will present these recently published results, as well as prospects for a next-generation three-dimensional strain microscope.   

Fundamental Physics Searches using Atomic Magnetometers

In this talk, I will present the recent activities on fundamental physics searches using atomic magnetometers (AMs) at Los Alamos National Laboratory. AMs based on lasers and alkali-metal vapor cells are currently the most sensitive non-cryogenic magnetic-field sensor. Our researches have a potential to address some of the most profound physics puzzles–the matter-antimatter asymmetry of the Universe and the existence of dark matter making up ~25% of the Universe. Our experiments aim to search for new fundamental bosonic particles, such as axions, using new detection concepts based on AMs via observable effects induced by new couplings of new bosonic particles with ordinary particles. Due to the use of AMs, our experiments are relatively small projects at low cost.   

Progress toward detection of ultralight dark matter with cryogenic optical cavities

Virialized ultralight fields (VULFs), ϕ, form a category of dark matter (DM) candidates where their coupling (d_e and d_me) to baryonic matter is expected to result in the oscillation of fundamental constants, such as the fine-structure constant (δα/α ∝ d_eϕ) and electron mass (δm_e/m_e ∝ d_meϕ), at the DM Compton frequency (f_ϕ = mc²/(2πħ)). This implies that the Bohr radius (a₀ = ħ/(m_ecα)), and hence the size of atoms, would also oscillate at frequency f_ϕ. Here c & ħ are the speed of light & the reduced Planck's constant respectively.

In this talk, I will present progress toward experimental implementation of a VULF detection scheme, with f_ϕ ⊆ [100 Hz, 10 kHz], involving measurement of differential length change of 2 cryogenic optical cavities using a common laser. One of the cavities has its mirrors attached to a rigid spacer; the latter is expected to oscillate at f_ϕ. The second (non-rigid) cavity has its mirrors separated by vacuum. Moreover, the non-rigid cavity will be isolated, using a pendulum system, such that the effect on the cavity length due to oscillation of the suspension points (at f_ϕ) is suppressed by almost 10 orders of magnitude. This apparatus is projected to extend the exploration of d_e and d_me by 2 orders of magnitude compared to bounds set by other experiments.   

Optical fiber-based detector for scalar ultralight dark matter

We discuss a potential broadband search for scalar ultralight dark matter (ULDM) with an optical fiber-based detector. ULDM that couples to electrons and/or photons would cause oscillations in the electron mass and fine structure constant, both of which produce measurable signals: isotropic strains and varying optical refractive indices. These signals are approximately monochromatic, with an unknown frequency determined by the ULDM particle mass. Both strains and refractive index modulation induce phase shifts in light propagating through optical fibers, which can be read out interferometrically. We show that optical fibers can be used to perform a laboratory-scale, broadband search for scalar ULDM in the relatively unexplored sub-Hz frequency regime (corresponding to $\sim 10^{-16}-10^{-15}$ eV/c$^2$ particle mass).    

Quantum metrology algorithms for dark matter searches with 229Th3+

Quantum metrology aims to apply algorithms from quantum information science to improve the sensitivity of a quantum sensor while minimizing susceptibility to noise. Among the most sensitive quantum sensors are quantum clocks, which have been shown to be ideal devices for searches for local ultralight scalar dark matter. While current atomic clocks reach unprecedented stability, nuclear clocks based on Thorium-229m isomer have been proposed which not only allow for an improvement of the clock stability, but also offer increased sensitivity to possible dark matter signals by many orders of magnitude. Here we explore different quantum metrology algorithms in the context of dark matter searches using nuclear clocks. We propose a new quantum algorithm and compare it to previously explored quantum metrology protocols. We develop numerical simulations taking into account dark matter decoherence, laser noise and quantum projection noise and report improved sensitivity of nuclear clocks to dark matter.

    

Constructing a Levitated Microsphere Array and its Application to Dark Matter Searches

Arrays of optically levitated micron-sized, nanogram-mass spheres have many applications in precision measurements. For example, an array of levitated microspheres can enable improved searches for dark matter using mechanical oscillators. By monitoring the motion of the spheres for impulses of imparted momentum, we can search for composite dark matter particles. Arrays can also be utilized to improve background rejection for millicharged particle searches. We present a system which uses 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 study optically and electrically mediated intersphere interactions to better understand backgrounds inherent with this new tool.   

Quantum-enhanced Measurement using Optomechanical Sensors for Gravitational Direct Detection of Dark Matter

Recent advances in mechanical sensing technologies have recently led to the suggestion that heavy dark matter candidates — around the Planck mass range — could be detected through their gravitational interaction alone. With this ultimate goal on the horizon, the Windchime collaboration is involved in developing the necessary techniques, systems, and experimental apparatus using arrays of optomechanical sensors. These can also be used to investigate non- gravitational signals from other dark matter candidates in the near-term. However, to achieve Planck-scale detection, measurements of these devices much exceed the standard quantum limit. Hence we need to employ quantum-enhanced readout techniques for detecting the extremely weak impulse transfers from the gravitational interaction of dark matter. Here we discuss the different techniques of achieving such quantum-enhanced measurements including an optomechanical measurement combining backaction evasion and squeezing. This would help us in reducing the measurement-added noise floor in experimentally relevant parameter regimes in order to reach our desired sensitivity.   

Searching for Chameleon Dark Energy with Mechanical Systems

A light scalar field framework of dark energy, sometimes referred to as quintessence, introduces a fifth forcebetween normal matter objects. Screening mechanisms, such as the chameleon model, allow the scalar field to be almost massless on cosmological scales while simultaneously evading laboratory constraints. We explore the ability of mechanical systems available in the near term to directly detect the fifth force associated with chameleon dark energy. We provide analytical expressions for the weakest accessible chameleon model parameters in terms of experimentally tunable variables and apply our analysis to two mechanical systems: levitated microspheres and torsion balances, showing that the current generation of these experiments have the sensitivity to rule out a significant portion of the proposed chameleon parameter space. We also indicate regions of theoretically well motivated chameleon parameter space to guide future experimental work.