Curator's Take
This article shows that a simple array of unentangled Ramsey interferometers can achieve the same √N sensitivity boost traditionally reserved for highly entangled sensors, opening a realistic path to million‑qubit dark‑matter detectors using existing trapped‑ion technology. By exploiting coherent collective qubit responses within a single de Broglie wavelength, the scheme promises to probe couplings beyond current laboratory and astrophysical limits without the overhead of fragile entanglement generation. The approach also extends naturally to other quantum‑sensing platforms and even high‑frequency gravitational‑wave searches, making it a versatile addition to the emerging toolbox of quantum‑enhanced fundamental physics experiments.
— Mark Eatherly
Summary
We propose an array of the Ramsey-type interferometers using $N$ superposition states, $(|0\rangle+ |1\rangle)^{\otimes N}$, as a sensor to detect wave-like dark matter. After the exposure to the dark matter wave, which induces the coherent qubit transitions, the signal is the imbalance between the probabilities of detecting 0 and 1. The signal-to-noise ratio in this scheme is proportional to $\sqrt{N} α$, where $α$ is the coupling of dark matter to the qubits, and thus the sensitivity to the coupling scales as $δα\sim 1 / \sqrt{N}$. For comparison, in the detection scheme based on the Rabi-type transition, $|0\rangle \to |1\rangle$, this scaling is achieved only when highly entangled $N$ qubits are used. Since the Ramsey-type measurement does not require entangled states, one can consider much larger $N$ by simply placing a large number of qubits within the de Broglie wavelength of the dark matter. We demonstrate that, using trapped-ion qubits in a linear Paul trap as the sensor, the projected sensitivity to the coupling matches or surpasses existing laboratory, astrophysical, and cosmological bounds for $N \gtrsim 10^6$. We also evaluate its sensitivity to high-frequency gravitational waves. Our general framework should, in principle, be useful for other quantum sensing platforms.