Session E03: Focus Session: Using Quantum Sensors to Search for New Physics

Axion Dark Matter and Quantum Measurement: ABRACADABRA to DMRadio

The particle nature of dark matter remains one of the great open questions in physics. The axion has had a renaissance as a dark matter candidate as theoretical studies have improved our understanding of axion cosmology and advances in quantum sensing and cryogenics have opened new opportunities for detection. In this talk, I will review axion physics and motivate searches for < 1 micro-eV axions. I will then present the current results from ABRACADABRA and our vision for the DMRadio program including R&D on quantum sensors to enable a definitive search for axions throughout this < 1 micro-eV space. 

 

Novel quantum sensing techniques for dark matter detection

In this talk, I will cover selected topics in sensing ultraweak forces from passing dark matter using quantum sensors such as superconducting qubits and Rydberg atoms.  These will include quantum non-demolition measurements, stimulated transitions using prepared quantum states, and quasiparticle detection.  I will also discuss challenges in operating quantum sensors in the vicinity of high laboratory magnetic fields needed to induce interactions with the dark matter axion.   

GPS.ELF: Search for emission of exotic low-mass fields from the binary neutron star merger (GW170817) using GPS atomic clocks

Exotic bosonic fields are plausible constituents of dark matter and are potential solutions to the strong-CP and the hierarchy problems. Such fields can be potentially sourced by powerful astrophysical events, such as binary neutron star and binary black hole mergers. This opens an intriguing possibility for a novel, exotic physics, modality in multi-messenger astronomy [Nature Astronomy 5, 150 (2021)]. We present the initial results of our search for such feebly interacting exotic low-mass field (ELFs). We use data from atomic clocks of the Global Positioning System (GPS). The search is carried out by comparing the clock excess noise before and after the LIGO gravitational wave trigger.  Our initial search focuses on the August 17, 2017 GW170817 binary neutron star merger event.   

Optical Trapping of Microdisks for Detection of High Frequency Gravitational Waves with the Levitated Sensor Detector

We present an update on the Levitated Sensor Detector (LSD) project for detection of high frequency (10-100kHz) gravitational waves above the region previously probed by LIGO. Motivated sources of gravitational waves in this frequency range include superradiance from QCD axion clouds around black holes. The experiment will make use of optically-levitated flat dielectric micro-scale particles as force sensors with the advantage of reduced photon recoil heating. We therefore discuss analytical and numerical models of the motional dynamics of dielectric microdisks, as well as initial experimental trapping results of SiO₂ microdisks and NaYF₄ hexagonal prisms. Finally, we examine the experimental progress of the 1-meter LSD prototype that is in construction at Northwestern University.   

Librational feedback cooling with spinning silica microspheres

An optically-levitated, 4.7 μm diameter silica microsphere can be driven into rotation by coupling a rotating electric field of constant magnitude to the permanent electric dipole moment found in microspheres grown via the Stöber process. In the frame co-rotating with the electric field, the microsphere's dipole moment undergoes libration about the instantaneous direction of the electric field. The librational degree of freedom can be cooled by applying a phase modulation to the rotation of the electric field that is proportional to the librational velocity, effectively damping the motion. The degree of cooling is quantified by applying a π/2 shift to the phase of the electric field and observing the resulting exponential decay of the librational motion to infer a damping time. The thermally driven spectrum of librational motion can also be examined to determine an effective temperature. In this prototype demonstration, we tune the damping time over four orders of magnitude, and the effective temperature over two orders of magnitude. Anomalous dissipation observed may shed light on charge multipole moments within the microspheres.

    

A background-free optically levitated charge sensor

Optically levitated macroscopic objects are a powerful tool in the field of force sensing, owing to high sensitivity, absolute force calibration, environmental isolation, and the advanced degree of control over their dynamics that have been achieved. However, limitations arise from the spurious forces caused by electrical polarization effects that, even for nominally neutral objects, affect the force sensing because of the interaction of dipole moments with gradients of external electric fields. In this talk, I will present a new technique to model and eliminate dipole moment interactions limiting the performance of sensors employing levitated objects. This process leads to the first noise-limited measurement of charges with unprecedented sensitivity. As a specific example, we apply the technique to test the observation that the proton charge is equal in magnitude to that of the electron.   

Novel Technique to Measure μm-Scale Forces Using a Non-Linear Attractor

The gravitational force, while well-understood at large distances, has not been measured on scales below a few tens of microns.  Several theoretical arguments suggest the possibility of variations from the inverse square law at such small scales. Recently, the use of optically levitated microspheres has shown promising results as a technique to extend the experimental reach at small distances.

The source of gravitational field for these experiments has, until now, been a reciprocating linear attractor, presenting a density modulation at micron-scale distances from the optical trap.  Some of the background forces observed can be attributed to vibrations induced by the reciprocating motion and the spurious modulation of the light exiting the trap and used for detection of the microsphere position. Such modulation results from the interaction of light halos with the reciprocating attractor. Here we report on the initial efforts to implement a rotary disk attractor system. This system is expected to reduce vibrations and change or possibly improve the scattered light background, thus reducing backgrounds and allowing for a larger signal bandwidth.