Session X09: Axions I

Recent Results from the ADMX Axion Dark Matter Search Experiment

We present recent results from the ADMX haloscope search for dark matter axions in the mass range $\rm{2.66-2.81\,\mu eV}$. In this mass range, assuming an axion dominated dark matter halo, we will exclude at 90\% confidence or discover axion-photon couplings predicted a range of plausible phenomenological axion models, including for the first time those predicted in the Dine-Fischler-Sredniki-Zhitnitsky (DFSZ) model. Ongoing searches will provide nearly definitive tests of the invisible axion model over a wide range of axion masses.   

Design of the ADMX Gen2 Axion Search

Axions are hypothetical elementary particles that may help provide the answer as to why QCD preserves the discrete symmetries P and CP. Light axions also have properties that make them ideal dark-matter candidates. The Axion Dark Matter eXperiment (ADMX), has been at the forefront of the search for dark-matter axions for over a decade, and over the past few years has undergone upgrades to dramatically improve its sensitivity. 2017 was a particularly exciting year for ADMX as we collected our first science data for Generation 2 of the experiment, and has sensitivity to the entire axion-photon coupling range for invisible QCD axions over a range of axion masses. I will discuss the unique design of the ADMX experiment that has allowed us to reach this unprecedented level of sensitivity.   

Quantum Amplifiers for the ADMX experiment

The nature of dark matter is one of the largest open questions in particle physics and cosmology. One leading candidate is the axion particle, a light neutral pseudoscalar boson that would be produced in copious amounts in the early universe. Though extremely weakly interacting they may be detected by their conversion to photons in the microwave resonator immersed in a strong magnetic field. This is the basis of the Axion Dark Matter Experiment (ADMX) which recently completed its first data run at unprecedented sensitivity. This experiment was enabled by superconducting quantum amplifiers including the Microstrip SQUID amplifier (MSA) and the Josephson Parameteric Amplifier (JPA). Here I will describe how these amplifiers work and how they will be applied in ADMX moving forward.   

Axion Dark Matter Detection using Superconducting Qubits

A transmon qubit can be operated in a resonant cavity as a sensor of a single microwave photon produced by the interaction between axion dark matter and a laboratory magnetic field. The axion is an extremely attractive dark matter candidate postulated to solve the strong CP problem in QCD. The interaction of axion field with applied magnetic field sources a current in the cavity which can be harnessed to drive a resonant cavity to single photon occupation. When weakly coupled to the detection cavity through a dipole interaction, the qubit transition frequency shift is used to measure the cavity photon number. The use of a direct dispersive quantum non-demolition measurement of the photon number decouples the measurement induced back action from the experimental uncertainties.   

Reaching the 5--9 $\mu$eV Range with ADMX: Multi-Cavity Array

Axions are particles that arise from the Peccei-Quinn solution to the strong charge-parity problem in quantum chromodynamics. Axions with a few $\mu$eV mass are a prominent cold dark matter (CDM) candidate. The aim of the Axion Dark Matter eXperiment (ADMX) is to detect CDM axions in the halo of our Galaxy. ADMX seeks to detect axions by observing the conversion of axions to microwave photons in a high-$Q$ resonant cavity in a strong magnetic field (an Axion haloscope). ADMX recently has completed successfully a search over the 2.66--2.81 $\mu$eV mass range with unprecedented sensitivity. For higher mass range searches, ADMX has developed multi-cavity arrays as the heart of a haloscope for axion masses in the 5--9 $\mu$eV range. We will present design aspects and preliminary study results of a 4-cavity array prototype. We will also discuss the performance of a Pound locking method adapted to synchronize the resonant frequencies of the multiple cavities.   

The First data of axion mass range around 2.5 GHz at CAPP in Korea

The flagship axion experiment of CAPP (Center for Axion and Precision Physics Research) of IBS in Korea, CULTASK (CAPP's Ultra Low Temperature Axion Search in Korea) has been built on a low vibration facility at Munji campus of KAIST (Korea Advanced Institute for Science and Technology). We have prepared one complete direct-search axion experiment with a powerful dilution refrigerator and a 8T superconducting magnet, ready to explore an axion mass range of 2\textasciitilde 2.5 GHz. A resonant cavity (10 cm OD) with a sapphire tuning rod driven by a piezoelectric actuator system was successfully cooled down below 40 mK and showed a very high unloaded Q-factor (\textasciitilde 130,000) even under 8T magnetic field. The RF receiver employs a 1K HEMT amplifier out of the cavity, but the design is flexible enough to replace it with SQUID amplifier when R{\&}D is completed soon. I will present the results of physics data runs in this mass range and our future plans.   

Improving axion dark matter search at IBS/CAPP in Korea

The axion is an excellent dark matter candidate motivated by the Peccei-Quinn solution to the strong-CP problem. The IBS Center for Axion and Precision Physics Research (CAPP) in Korea will search for the dark matter axion using a method called ``haloscope'', converting axions into microwave photons in a resonant cavity permeated by a strong magnetic field. The initial stage of building CAPP's flagship axion experiment, CULTASK (CAPP's Ultra Low Temperature Axion Search in Korea), is complete with powerful dilution refrigerators, superconducting magnets, frequency tuning systems, RF receiver electronics and ready to take high quality physics data. CAPP is also conducting extensive R{\&}D studies to improve the sensitivity of the experiment, which include the research on more powerful superconducting magnets, high-Q factor cavities and the effort to utilize quantum amplifiers in the RF receiver chain. I will present the status of CULTASK and our future plans to improve through the progress of R{\&}D projects.   

The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) : experimental scheme

The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is an experiment to search for transient events of axion domain walls based on a novel scheme: synchronous measurements of high precision optical magnetometer signals from multiple stations around the Earth. This experiment now consists of more than 10 magnetometer stations located geographically well apart from each other. The GNOME is particularly sensitive to terrestrial events of topological defects such as axion domain walls and interactions of atomic spins with exotic fields of astrophysical origin. We present the experimental scheme and results of the first network run for testing feasibility.   

Characterization of the optical magnetometer at CAPP GNOME station

The optical magnetometer is one of the most sensitive ways to measure low magnetic field and to be used in a wide range of application including fundamental physics. The high sensitive optical magnetometers can also be employed to search for anomalous interaction between atomic spins and exotic fields such as axion domain walls. The Global Network of Optical Magnetometers to search for Exotic physics (GNOME) is an experiment looking for signals from transient events from such spin interaction based on synchronized multiple magnetometer stations located geographically separated on the Earth. One of stations at the Center for Axion and Precision Physics Research (CAPP) is located in Daejeon, South Korea. We present the setup and optimization of the magnetometer at CAPP.