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Sapphire substrate qubit-based detector for light dark matter search

K. Anyang

Published Nov 20, 2023• 0 citations
Publisher

Abstract

Harnessing sub-eV energy excitations from light dark matter interaction with a target material is one of the challenges in exploring promising novel materials for dark matter searches. In polar materials like sapphire, dark matter interaction can excite sub-eV optical phonon modes. Furthermore, the anisotropy of sapphire crystal could provide a signature of daily modulation of the dark matter scattering rate, making it a promising target material. We plan to utilize superconducting qubits on a sapphire substrate to take advantage of the excitation of phonons, which scatter and further down-convert to lower-energy phonons. A good fraction of these phonons are expected to reach the qubit superconductor on the substrate and break Cooper pairs. Such a process can cause qubit decoherence, which can be measured using standard qubit readout protocol. In this talk, we describe our ongoing attempt to build such a prototype detector.

DOI
10.2172/2217168

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Harnessing sub-eV energy excitations from light dark matter interaction with a target material is one of the challenges in exploring promising novel materials for dark matter searches. In polar materials like sapphire, dark matter interaction can excite sub-eV optical phonon modes. Furthermore, the anisotropy of sapphire crystal could provide a signature of daily modulation of the dark matter scattering rate, making it a promising target material. We plan to utilize superconducting qubits on a sapphire substrate to take advantage of the excitation of phonons, which scatter and further down-convert to lower-energy phonons. A good fraction of these phonons are expected to reach the qubit superconductor on the substrate and break Cooper pairs. Such a process can cause qubit decoherence, which can be measured using standard qubit readout protocol. In this talk, we describe our ongoing attempt to build such a prototype detector.
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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.
In recent years, the lack of a conclusive detection of weakly interacting massive particle dark matter at the 10  GeV/c210\text{ }\text{ }\mathrm{GeV}/{\mathrm{c}}^{2}10  GeV/c2 mass scale and above has encouraged development of low-threshold detector technology aimed at probing lighter dark matter candidates. Detectors based on Cooper-pair-breaking sensors have emerged as a promising avenue for this detection due to the low (meV-scale) energy required for breaking a Cooper pair in most superconductors. Among them, devices based on superconducting qubits are interesting candidates for sensing due to their observed sensitivity to broken Cooper pairs. We have developed an end-to-end g4cmp-based simulation framework and have used it to evaluate performance metrics of qubit-based devices operating in a gate-based ``energy relaxation'' readout scheme, akin to those used in recent studies of qubit sensitivity to ionizing radiation. We find that for this readout scheme, the qubit acts as a phonon sensor with an energy threshold ranging down to $\ensuremath{\simeq}0.4\text{ }\text{ }\mathrm{eV}$ for near-term performance parameters.
Currently, there is a critical need for localized, position-dependent calibration of quantum device response to characterize the fundamental sensing mechanism of many superconducting detectors. For example, qubit decoherence has been found to be associated with the generation of electron-hole pairs and phonons through the scattering of radiation in the qubit substrate. Novel particle physics applications seek to use these events as indicators of energy deposition, allowing quantum devices to serve as particle detectors. The low energy threshold of these proposed detectors makes them particularly well-suited for a next-generation dark matter search. We have developed a cryogenic optical beam steering system that delivers monochromatic photons in the range of 250nm - 20um across the surface of any cryogenic quantum device. In this talk, I will present the design overview and specifications of this calibration unit, along with current status and plans of the testing program.
The next generation of rare-event searches, such as those aimed at determining the nature of particle dark matter or measuring fundamental neutrino properties, will benefit from particle detectors with thresholds at the meV scale, 100 – 1000 × lower than currently available. Quantum parity detectors (QPDs) are a class of proposed quantum devices, extending recent work on superconducting qubit sensors, that exploit the fingerprints of single quasiparticle tunneling across a coherent weak link as their detection concept. As envisioned, phonons generated by particle interactions within a crystalline substrate cause an eventual quasiparticle cascade within a surface-patterned superconducting qubit element. This process alters the fundamental charge parity of the device in a binary manner, which can be used to deduce the initial properties of the energy deposition. This work lays out multiple resonator-coupled readout schemes depending on qubit architecture, provides an analytic formulation for reconstructing sensor energies, and details strategies for multiplexing large arrays of sensors. We further compute the sensitivity of QPDs and detail an R&D pathway to demonstrating sub-eV energy deposit thresholds.