Speaker
Description
Ultralight \textit{axion-like particles} (ALPs) are among the most theoretically motivated dark matter candidates, yet their detection remains challenging across a wide range of masses. We present a novel \textbf{heterodyne atom interferometry scheme} that dramatically extends the sensitivity of quantum sensors to ALP dark matter, covering up to \textit{six orders of magnitude} in axion mass beyond conventional configurations.
The method exploits the coupling of the ALP field to nuclear spins, $\Delta E \propto g_{aNN}\,\nabla a \cdot \mathbf{s}$, and overcomes the fundamental limitation of standard axion searches at low frequencies: the dominance of $1/f$ noise from seismic and gravity-gradient backgrounds. By applying a rotating magnetic field that induces coherent spin precession at a tunable frequency $\Omega$, the axion-induced signal is upconverted from near-DC to a well-controlled carrier, where synchronous detection suppresses environmental noise by orders of magnitude. This shifts the accessible axion mass window from the sub-Hz regime to frequencies up to $\sim\!100$\,kHz, probing a largely unexplored region of parameter space.
We implement this scheme using \textbf{fermionic $^{87}$Sr} in a Ramsey interferometry configuration, which provides direct sensitivity to internal-state energy shifts and offers superior broadband response compared to Mach--Zehnder geometries. The sensitivity of the scheme scales with interrogation time and atom number, making it complementary to existing haloscope and spin-precession experiments such as CASPEr and ABRACADABRA in the ultralight mass range ($m_a \lesssim 10^{-10}$\,eV).
To distinguish genuine ALP signals from magnetic backgrounds, we propose a \textbf{differential double atom interferometer} configuration combined with \textbf{sidereal modulation} as a direction-sensitive discriminator. This provides a robust veto against local systematic effects and constitutes a key signature of a dark matter origin. Together, these features make atom interferometry a powerful and scalable platform for next-generation ALP searches, with a clear path toward probing axion--nucleon couplings at or below the level predicted for QCD axion models.
