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arXiv:2603.03157

Achieving speedup in Dark Matter search experiments with a transmon-based NISQ algorithm

Roberto Moretti, Pietro Campana, Rodolfo Carobene, Alessandro Cattaneo, Marco Gobbo, Danilo Labranca, Matteo Borghesi, Marco Faverzani, Elena Ferri, Sara Gamba, Angelo Nucciotti, Andrea Giachero

quant-phSubmitted Mar 3, 2026• Announced Mar 4, 2026• 0 citations
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Abstract

Coherent detection of ultralight bosonic dark matter can be achieved by monitoring slow Rabi oscillations in superconducting qubits. We introduce an ancilla-assisted, gate-based protocol that enhances sensitivity to the hidden photon kinetic mixing parameter $ε$ using a single two-qubit gate, bypassing the need to maintain long-lived multi-qubit entangled states and remaining compatible with the limitations of modern quantum hardware. We characterized the increase in sensitivity accounting for decoherence, thermal occupation, errors in readout and reset, indicating up to a ten-fold reduction in the required integration time to reach the same exclusion limit on $ε$ achievable via Rabi-sampling experiments. Under plausible hardware assumptions and three years of data taking, the projected $95\%$ C.L. exclusion limit on the hidden photon mixing parameter reaches $ε\approx 1\times 10^{-14}$ across $2.5$-$6.0$ GHz ($10$-$25$ \textmu eV).

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Coherent detection of ultralight bosonic dark matter can be achieved by monitoring slow Rabi oscillations in superconducting qubits. We introduce an ancilla-assisted, gate-based protocol that enhances sensitivity to the hidden photon kinetic mixing parameter εεε using a single two-qubit gate, bypassing the need to maintain long-lived multi-qubit entangled states and remaining compatible with the limitations of modern quantum hardware. We characterized the increase in sensitivity accounting for decoherence, thermal occupation, errors in readout and reset, indicating up to a ten-fold reduction in the required integration time to reach the same exclusion limit on εεε achievable via Rabi-sampling experiments. Under plausible hardware assumptions and three years of data taking, the projected 95%95\%95% C.L. exclusion limit on the hidden photon mixing parameter reaches ε≈1×10−14ε\approx 1\times 10^{-14}ε≈1×10−14 across 2.52.52.5-6.06.06.0 GHz (101010-252525 \textmu eV).
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.
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) μeVO(10)\ μ{\rm eV}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∼10−12−10−14ε\sim 10^{-12}-10^{-14}ε∼10−12−10−14 (where εεε is the kinetic mixing parameter of the hidden photon) with a single standard transmon qubit. A simple extension to the frequency-tunable SQUID-based transmon enables the mass scan to cover the whole 4−40 μeV4-40\ μ{\rm eV}4−40 μeV (1−101-101−10 GHz) range within a reasonable length of run time. The sensitivity scalability along the number of the qubits also makes it a promising platform in accord to the rapid evolution of the superconducting quantum computer technology.
Detection mechanisms for low mass bosonic dark matter candidates, such as the axion or hidden photon, leverage potential interactions with electromagnetic fields, whereby the dark matter (of unknown mass) on rare occasion converts into a single photon. 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, sub-SQL detection techniques are required. Here we 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 nondemolition 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 ε≤1.68×10^{-15} in a band around 6.011 GHz (24.86 μeV) 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 1,300. By coupling a qubit to an arbitrary quantum sensor, more general sub-SQL metrology is possible with the techniques presented in this Letter.
We report on an improved microwave detection protocol for dark matter candidates such as the axion and the dark photon. We employ a superconducting transmon qubit dispersively coupled to a double-cavity system, enabling quantum non-demolition measurements of the photon occupation in a relatively short-lived storage cavity. To reduce the experimental cycle time and enhance sensitivity for axion and dark-photon searches, we operate this detector in a regime of increased qubit-cavity coupling, resulting in Stark shifts of 4.6 MHz. In this regime, conventional control pulses suffer from strong frequency-detuning sensitivity and photon-number-dependent errors. We address this limitation by implementing frequency-detuning-robust π/2π/2π/2 pulses (obtained by machine-learning optimization) that preserve high-fidelity qubit control over a bandwidth of approximately 20 MHz. We experimentally validate this protocol and demonstrate single-photon detection performance comparable to previous implementations, despite significantly reduced qubit coherence times and storage-cavity lifetimes. Using parity-based measurement sequences combined with a Hidden Markov Model (HMM) analysis, we achieve background rates on the order of O(20)\mathcal{O}(20)O(20) Hz. In the absence of a magnetic field, we derive exclusion limits on the dark photon model for dark matter, reaching a sensitivity to the kinetic mixing angle of ε95%∼1×10−14ε_{95\%} \sim 1\times10^{-14}ε95%​∼1×10−14 at 5.051 GHz. These results establish machine-learning robust control as a key enabler for faster, more scalable microwave quantum sensors for dark-matter searches.
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.
Quantum error correction using erasure qubits offers higher fault-tolerant thresholds and improved scaling by converting dominant physical errors into detectable erasures. In superconducting circuits, erasure qubits can be constructed using the dual-rail approach, which, however, requires additional qubit-count overhead and tailored coupling elements. Here, we demonstrate a hardware-efficient scheme that operates transmon qutrits as erasure qubits, which is compatible with standard superconducting circuit-QED hardware. The logical states ∣0L⟩\ket{0_\text{L}}∣0L​⟩ and ∣1L⟩\ket{1_\text{L}}∣1L​⟩ are represented by the ground and second excited states, while the dominant relaxation errors can be detected via an ancilla qubit using a microwave-activated two-qutrit SWAP gate. We demonstrate a logical qubit T1T_1T1​ lifetime exceeding 500 μs500\,μ\mathrm{s}500μs, post-selected with repeated mid-circuit erasure detection, which is ten times longer than the T1T_1T1​ time of the transmon physical qubit. Coherence times beyond 300 μs300\,μ\mathrm{s}300μs are achieved using dynamical decoupling. Single-qubit gate operations reach average Clifford gate infidelity on the order of 10−410^{-4}10−4. We further demonstrate dual-purposing an ancilla qubit for both erasure detection and parity checking, showing heralded generation of Bell states between erasure qubits. These results suggest that mainstream architectures of transmon qubit arrays may already be capable of implementing erasure-based QEC strategies for hardware-efficient fault-tolerant quantum computing.