Karthik Ramanathan, an assistant professor of physics within Arts & Sciences at WashU, has embarked on a mission to unravel one of the Universe's great mysteries: dark matter. As an experimental astrophysicist, his research bridges the realms of particle physics and astrophysics.

His lab, currently under construction in Crow Hall, will be equipped with state-of-the-art instruments, including a dilution refrigerator essential for his cutting-edge experiments. Dark matter, which emits neither light nor energy, remains elusive despite its profound impact on the structure and dynamics of galaxies. Strong cosmological and astrophysical evidence indicates that this missing matter makes up roughly a quarter of the total mass-energy of the universe.

The mass range of potential dark matter particles spans an enormous range, from 10^-22 to 10¹⁸ electron volts (eV), encompassing everything from hypothetical ultralight axions to possibly even massive solar-mass black holes. Different experiments must be tailored to target specific segments of this vast range. For instance, searches for ultralight dark matter focus on the hypothetical particles called axions, with masses ranging from 10^-22 to a few hundred milli-eV. These experiments use strong magnetic fields and low temperatures, as seen in James Buckley's axion experiments. In contrast, high-energy searches in the GeV scale investigate weakly interacting massive particles (WIMPs), using techniques similar to identifying "billiard balls." These experiments often place detectors deep underground, like in the XENON Dark Matter Project, to shield them from cosmic rays. Other searches explore sterile neutrinos, hypothetical particles that do not interact via the standard weak nuclear force, in the eV-keV range by examining radioactive decays.

Ramanathan concentrates on the less-explored mid-range mass spectrum, targeting particles weighing approximately 10^-4 to 1 MeV. This mass range holds considerable theoretical interest and potential for groundbreaking discoveries that could redefine our understanding of dark matter. To tackle this challenge, Ramanathan plans to develop highly sensitive instruments incorporating phonon-mediated sensors capable of detecting the minute vibrations, or phonons, resulting from interactions between dark matter particles and materials such as silicon.

Additionally, Ramanathan is exploring the integration of quantum computing into dark matter detection. Quantum computing uses qubits, which are highly sensitive to changes in their environment. Ramanathan aims to use this sensitivity to detect dark matter. He envisions constructing a dark matter detector that can identify changes caused by phonon vibrations. By studying Cooper pairs, pairs of electrons that move without resistance at very low temperatures, he aims to observe how phonons might break these pairs apart. Ramanathan will use Josephson junctions, quantum mechanical devices that can measure extremely small changes in electrical current, to capture these events. This method could greatly improve the precision of dark matter detection.

Ramanathan's innovative work is bolstered by his affiliations with several prominent research centers at WashU, including his fellowship with the McDonnell Center for Space Sciences (MCSS), as well as his involvement with the Institute for Materials Science and Engineering (IMSE), and the Center for Quantum Leaps (CQL). These affiliations provide a collaborative environment that fosters cutting-edge research and interdisciplinary innovation.

His journey into this field is as fascinating as his scientific endeavors. Born in Nigeria, he moved to Canada at the age of eight, where he later earned a bachelor's degree in Engineering Physics from the University of Toronto. His career briefly pivoted to finance, where he earned a master's degree from the London School of Economics and worked as a quantitative analyst. However, the allure of academia drew him back to physics, leading him to pursue a PhD in physics at the University of Chicago, where he researched dark matter using silicon. He then conducted postdoctoral work at Caltech and the Jet Propulsion Laboratory (JPL) before joining WashU.

Ramanathan and his wife have settled in St. Louis, finding it an ideal place to raise their child. They have already explored local attractions such as the City Museum, the Magic House, and the offerings of Forest Park. His wife, an emergency room physician, holds a position at Barnes-Jewish Hospital (BJC), and Ramanathan has appreciated WashU's highly supportive community.

Karthik Ramanathan’s journey and pioneering work on dark matter continue to push the boundaries of our understanding of the universe. His innovative approaches, combining quantum technologies with novel detection methods, have significant promise for unlocking the secrets of dark matter and advancing the field in meaningful ways.