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arXiv:2503.18315 · Physical Review Letters

Scalable Architecture for Dark Photon Searches: Superconducting-Qubit Proof of Principle

Runqi Kang, Q. P. Hu, Xiao Cai, Wenlong Yu, Jingwei Zhou, Xing Rong, Du Jiang-Feng

Published Oct 7, 2025• 3 citations
arXivHTMLPDF

Abstract

The dark photon is a well-motivated dark matter candidate that appears in many extensions of the standard model. A fundamental mass-range-sensitivity dilemma is always haunting the dark photon search experiments: resonant haloscopes have excellent sensitivity but are narrowband, while nonresonant haloscopes are broadband but not as sensitive as the resonant ones. A scalable architecture integrating numerous resonant haloscopes would be a desirable solution to this dilemma. However, even the concept of a scalable search remains rarely explored due to the size limitation of conventional haloscopes imposed by the dark photon wavelength. Here, we propose and demonstrate a novel architecture using superconducting qubits as subwavelength haloscope units. By virtue of the scalability of superconducting qubits, it is possible to integrate multiple qubits with different frequencies on a chip-scale device. Furthermore, the frequencies of the qubits can be tuned to extend the search mass range. Thus, our scalable architectures allow for sweepable high-sensitivity dark photon searches at multiple frequencies simultaneously. As a proof-of-principle experiment, we designed and fabricated a three-qubit chip and successfully demonstrated a scalable dark-photon search. Our Letter established constraints on dark photons in the mass range of 15.632-15.638, 15.838-15.845, and 16.463-16.468 μeV, simultaneously, and the constraints are much more stringent than the cosmology constraints. In the future, our Letter can be scaled up to boost the scrutiny of new physics.

DOI
10.1103/9p1t-vc9j

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The dark photon is a well-motivated dark matter candidate that appears in many extensions of the standard model. A fundamental mass-range-sensitivity dilemma is always haunting the dark photon search experiments: resonant haloscopes have excellent sensitivity but are narrowband, while nonresonant haloscopes are broadband but not as sensitive as the resonant ones. A scalable architecture integrating numerous resonant haloscopes would be a desirable solution to this dilemma. However, even the concept of a scalable search remains rarely explored due to the size limitation of conventional haloscopes imposed by the dark photon wavelength. Here, we propose and demonstrate a novel architecture using superconducting qubits as subwavelength haloscope units. By virtue of the scalability of superconducting qubits, it is possible to integrate multiple qubits with different frequencies on a chip-scale device. Furthermore, the frequencies of the qubits can be tuned to extend the search mass range. Thus, our scalable architectures allow for sweepable high-sensitivity dark photon searches at multiple frequencies simultaneously. As a proof-of-principle experiment, we designed and fabricated a three-qubit chip and successfully demonstrated a scalable dark-photon search. Our Letter established constraints on dark photons in the mass range of 15.632-15.638, 15.838-15.845, and 16.463-16.468 μeV, simultaneously, and the constraints are much more stringent than the cosmology constraints. In the future, our Letter can be scaled up to boost the scrutiny of new physics.
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We propose a novel dark matter detection method utilizing the excitation of superconducting transmon qubits. Assuming the hidden photon dark matter of a mass of O(10) μeV, the classical wave-matter oscillation induces an effective ac electric field via the small kinetic mixing with the ordinary photon. This serves as a coherent drive field for a qubit when it is resonant, evolving it from the ground state towards the first-excited state. We evaluate the rate of such evolution and observable excitations in the measurements, as well as the search sensitivity to the hidden photon dark matter. For a selected mass, one can reach ε∼10^{-13}-10^{-12} (where ε is the kinetic mixing parameter of the hidden photon) with a few tens of seconds using a single standard transmon qubit. A simple extension to the frequency-tunable SQUID-based transmon enables the mass scan to cover the range of 4-40 μeV (1-10 GHz) within a reasonable length of run time. The scheme has great potential to extend the sensitivity towards various directions including being incorporated into the cavity-based haloscope experiments or the currently available multibit noisy intermediate-scale quantum (NISQ) computer machines.
Dark matter is an enduring mystery in our quest to understand the fundamental constituents of our universe. Low mass bosons, such the axion or hidden photon, are compelling dark matter candidates. We leverage their potential interactions with electromagnetic fields, whereby the dark matter (of unknown mass) on rare occasion converts into a single photon, to devise a method of detecting these candidates. Current dark matter searches operating at microwave frequencies use a resonant cavity to coherently accumulate the field sourced by the dark matter and a near standard quantum limited (SQL) linear amplifier to read out the cavity signal. To further increase sensitivity to the dark matter signal and enable future searches, sub-SQL detection techniques are required. In this thesis, I report the development of a novel microwave photon counting technique and a new exclusion limit on hidden photon dark matter. We operate a superconducting qubit to make repeated quantum non-demolition measurements of cavity photons and apply a hidden Markov model analysis to reduce the noise to 15.7 dB below the quantum limit, with overall detector performance limited by a residual background of real photons. With the present device, we perform a hidden photon search and constrain the kinetic mixing angle to less than 1.68 X 10^{-15} in a band around 6.011 GHz (24.86 micro-eV) with an integration time of 8.33 s. This demonstrated noise reduction technique enables future dark matter searches to be sped up by a factor of 1300. By coupling a qubit to an arbitrary quantum sensor, more general sub-SQL metrology is possible with the techniques presented in this work.
We report an axion dark matter search with a haloscope equipped with a microwave photon counter. The haloscope is a tunable high quality factor three-dimensional microwave cavity placed in a magnetic field. The photon counter, operated cyclically, maps an incoming microwave photon onto the state of a superconducting transmon qubit. The measurement protocol continuously monitors the power emitted by the haloscope cavity as well as the dark count background and enables tuning of the cavity frequency to probe different axion masses. With this apparatus, we enhance by a factor of 20 the search speed that can be reached with quantum-limited linear amplifiers and set a new standard for probing the existence of axions with resonant detectors above 5 GHz.
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Ultralight bosonic dark matter with masses in the meV range, corresponding to terahertz (THz) Compton frequencies, remains largely unexplored due to the difficulty of achieving both efficient signal conversion and single-photon-sensitive detection at THz frequencies. We propose a hybrid detection architecture that integrates a dielectric haloscope, Rydberg-atom transducer, and superconducting nanowire single-photon detection within a unified cryogenic platform operating at ≲1 K\lesssim 1\,\text{K}≲1K. The dielectric haloscope converts dark matter into THz photons via phase-matched resonant enhancement, achieving form factors C∼0.4C \sim 0.4C∼0.4 and loaded quality factors QL∼104Q_L \sim 10^4QL​∼104. A cold 87^{87}87Rb ensemble then coherently up-converts the THz signal to the optical domain through six-wave mixing among Rydberg states. The intrinsic directionality and narrow bandwidth (Δνatomic∼1 MHzΔν_{\mathrm{atomic}} \sim 1\,\text{MHz}Δνatomic​∼1MHz) of this process provide extra suppression of isotropic thermal backgrounds. With 10 days of integration at 0.3 K0.3\,\text{K}0.3K, we project sensitivity to the axion-photon coupling gaγγ∼10−13 GeV−1g_{aγγ} \sim 10^{-13}\,\mathrm{GeV}^{-1}gaγγ​∼10−13GeV−1 at ma∼0.4 meVm_a \sim 0.4\,\text{meV}ma​∼0.4meV, reaching the QCD axion band and opening the THz window for searches of both axion and dark photon dark matter.