Periodic Reporting for period 1 - INGENIOUS (sINGle microwave photon dEtection for hybrid quaNtum Information prOcessing and quantUm enhanced Sensing)
Período documentado: 2022-12-01 hasta 2025-05-31
The INGENIOUS project was conceived to overcome a long-standing barrier in quantum science—the reliable detection of individual microwave photons. Unlike optical photon detectors, which have revolutionized many fields, the low energy of microwave photons renders conventional detection methods ineffective. By leveraging superconducting quantum circuits and innovative dissipation engineering, our approach transforms a challenging problem into an opportunity for breakthrough. Over the past two years, we have developed a high-performance microwave photon detector that achieves robust, continuous photon counting. Through systematic optimization of the quantum circuit, we dramatically reduced dark count rates and significantly boosted detection efficiency, thereby accelerating measurement speeds by a factor of 100. A central element of our strategy is modularity: the detector is decoupled from the system under study via standard microwave components operating at millikelvin temperatures, allowing independent optimization of both the detection unit and the experimental apparatus.
This breakthrough technology is enabling transformative applications that extend far beyond the detector itself. In magnetic resonance, our technology empowers the detection of the faint microwave fluorescence emitted by individual electron or nuclear spins. This capability heralds a new era in quantum sensing, offering unprecedented insight into the magnetic properties of molecular systems and materials at the nanoscale. By capturing these subtle signals, we can probe the structure and dynamics of individual atoms with remarkable precision, paving the way for advanced quantum computing where high-coherence spin systems are interfaced with superconducting qubits. In such hybrid architectures, individual spins serve as robust quantum memories and processing units, forming the cornerstone of scalable quantum computing platforms with high-fidelity operations and error-corrected quantum state manipulation. Moreover, our detector’s versatility extends to high-energy physics, where its enhanced sensitivity is now being explored for the search for dark matter axions. By resolving extremely weak microwave signals that could indicate axion interactions in strong magnetic fields, our technology holds the promise of significantly reducing search times and expanding the accessible parameter space. Together, these applications underscore the true impact of the INGENIOUS project—a practical, high-performance detector that is not only advancing the frontiers of microwave photon counting but also serving as a critical enabling technology for next-generation quantum information processing, magnetic resonance sensing, and fundamental physics research.
This breakthrough technology is enabling transformative applications that extend far beyond the detector itself. In magnetic resonance, our technology empowers the detection of the faint microwave fluorescence emitted by individual electron or nuclear spins. This capability heralds a new era in quantum sensing, offering unprecedented insight into the magnetic properties of molecular systems and materials at the nanoscale. By capturing these subtle signals, we can probe the structure and dynamics of individual atoms with remarkable precision, paving the way for advanced quantum computing where high-coherence spin systems are interfaced with superconducting qubits. In such hybrid architectures, individual spins serve as robust quantum memories and processing units, forming the cornerstone of scalable quantum computing platforms with high-fidelity operations and error-corrected quantum state manipulation. Moreover, our detector’s versatility extends to high-energy physics, where its enhanced sensitivity is now being explored for the search for dark matter axions. By resolving extremely weak microwave signals that could indicate axion interactions in strong magnetic fields, our technology holds the promise of significantly reducing search times and expanding the accessible parameter space. Together, these applications underscore the true impact of the INGENIOUS project—a practical, high-performance detector that is not only advancing the frontiers of microwave photon counting but also serving as a critical enabling technology for next-generation quantum information processing, magnetic resonance sensing, and fundamental physics research.
The project is organized along three main work packages (WPs), with significant progress in each.
WP1: Ultra-Low Dark Count Microwave Photon Counter
WP1.1: Direct Optimization of Dark Count and Efficiency Performances
We optimized the quantum circuit:
• Qubit relaxation time: ~10 µs → ~100 µs
• Thermal occupancy: ~1% → ~0.05%
• Implemented in situ bandwidth tuning
Outcomes: dark counts ~1000 Hz → ~50 Hz; efficiency ~40% → ~80%; ~100× faster measurements for faint single-photon sources. Publications: Balembois et al., Phys. Rev. Applied 21, 014043 (2025); Pallegoix et al., arXiv:2501.07354.
WP1.2: Dissipation Engineering for Quantum Error Mitigation of Dark Counts
We encoded detection redundantly across multiple qubits, making it robust to single-qubit failures. Result: ~100× dark-count reduction to ~0.1 Hz, enabling next-generation quantum sensing. Publication: May et al., arXiv:2502.14804.
WP2: Hybrid Quantum Information Processing
WP2.1: Single Spin Detection by Microwave Fluorescence
Using high-Q, small-mode-volume niobium resonators and improved detectors, we achieved single-spin detection of Er electron spins via microwave fluorescence. Publication: Wang et al., Nature 619 (7969), 276–281 (2023).
WP2.2: Quantum Information with Single Electron Spins and Nuclear Spin Clusters
We detected individual 183W nuclear spins via magnetic-dipole coupling to single Er spins (Travesedo, Sci. Adv. 11(10)). We introduced a Raman scheme for nuclear-spin control with multi-second coherence and demonstrated entanglement between two nuclear spins lasting over one second without refocusing pulses (O’Sullivan, arXiv:2410.10432).
WP2.3 & WP2.4: Hybrid Quantum Information – Heralding Spin/Circuit Entanglement
Not yet started; fully aligned with the proposed timeline.
WP3: Quantum-Enhanced Sensing Based on Microwave Fluorescence Detection
WP3.1: ESR Spectroscopy of Biomolecules
We initiated experiments with a new generation of frequency-tunable Bragg-mirror CPW resonators on silicon with RF access. Work runs in the ERC-funded dilution refrigerator (vector magnet, bottom-loading, integrated microwave photon counters), allowing overnight ESR-antenna swaps while cold. As a first step, we use ~500 nm rare-earth-doped oxide nanocrystals from collaborators to validate detection with the new resonators; crystals are positioned by SEM nanomanipulation. The project is ongoing with promising signals.
WP3.2: Dark Matter Search – Axion Fluorescence
We showed our WP1 photon counters can enhance axion haloscope searches by ~20× beyond the standard quantum limit under realistic conditions (>2 T fields, >1 MHz tunability). The result is in press at PRX (arXiv:2403.02321) and multiple collaborations have expressed strong interest.
Summary
By the end of year two, over 80% of objectives have been achieved, with seven high-impact senior-author publications submitted or published. The initial planning and mitigation strategies have proven effective, and no major roadblocks have been encountered.
WP1: Ultra-Low Dark Count Microwave Photon Counter
WP1.1: Direct Optimization of Dark Count and Efficiency Performances
We optimized the quantum circuit:
• Qubit relaxation time: ~10 µs → ~100 µs
• Thermal occupancy: ~1% → ~0.05%
• Implemented in situ bandwidth tuning
Outcomes: dark counts ~1000 Hz → ~50 Hz; efficiency ~40% → ~80%; ~100× faster measurements for faint single-photon sources. Publications: Balembois et al., Phys. Rev. Applied 21, 014043 (2025); Pallegoix et al., arXiv:2501.07354.
WP1.2: Dissipation Engineering for Quantum Error Mitigation of Dark Counts
We encoded detection redundantly across multiple qubits, making it robust to single-qubit failures. Result: ~100× dark-count reduction to ~0.1 Hz, enabling next-generation quantum sensing. Publication: May et al., arXiv:2502.14804.
WP2: Hybrid Quantum Information Processing
WP2.1: Single Spin Detection by Microwave Fluorescence
Using high-Q, small-mode-volume niobium resonators and improved detectors, we achieved single-spin detection of Er electron spins via microwave fluorescence. Publication: Wang et al., Nature 619 (7969), 276–281 (2023).
WP2.2: Quantum Information with Single Electron Spins and Nuclear Spin Clusters
We detected individual 183W nuclear spins via magnetic-dipole coupling to single Er spins (Travesedo, Sci. Adv. 11(10)). We introduced a Raman scheme for nuclear-spin control with multi-second coherence and demonstrated entanglement between two nuclear spins lasting over one second without refocusing pulses (O’Sullivan, arXiv:2410.10432).
WP2.3 & WP2.4: Hybrid Quantum Information – Heralding Spin/Circuit Entanglement
Not yet started; fully aligned with the proposed timeline.
WP3: Quantum-Enhanced Sensing Based on Microwave Fluorescence Detection
WP3.1: ESR Spectroscopy of Biomolecules
We initiated experiments with a new generation of frequency-tunable Bragg-mirror CPW resonators on silicon with RF access. Work runs in the ERC-funded dilution refrigerator (vector magnet, bottom-loading, integrated microwave photon counters), allowing overnight ESR-antenna swaps while cold. As a first step, we use ~500 nm rare-earth-doped oxide nanocrystals from collaborators to validate detection with the new resonators; crystals are positioned by SEM nanomanipulation. The project is ongoing with promising signals.
WP3.2: Dark Matter Search – Axion Fluorescence
We showed our WP1 photon counters can enhance axion haloscope searches by ~20× beyond the standard quantum limit under realistic conditions (>2 T fields, >1 MHz tunability). The result is in press at PRX (arXiv:2403.02321) and multiple collaborations have expressed strong interest.
Summary
By the end of year two, over 80% of objectives have been achieved, with seven high-impact senior-author publications submitted or published. The initial planning and mitigation strategies have proven effective, and no major roadblocks have been encountered.
This project develops an advanced microwave photon detection platform with ultra-low dark counts and high sensitivity, enabling robust single-photon detection at microwave frequencies for quantum science and fundamental physics. Using superconducting qubits and engineered circuits, the team delivers reliable, low-noise readout essential to many applications.
A key milestone is single-spin detection via fluorescence, departing from conventional inductive methods and markedly boosting sensitivity to individual solid-state spins. The same technology enables observation and control of nuclear spins with exceptionally long coherence, advancing prospects for quantum memories and durable qubits.
The detector also accelerates rare-event searches in fundamental physics. Integrated into specialized cryogenic setups, it enhances sensitivity for hypothetical particles such as axions, cutting the time required to scan large parameter spaces in high-energy experiments.
Modularity is central: the photon counter can be decoupled from the target system and linked by standard millikelvin microwave components, letting each subsystem—spin ensembles or dark-matter instruments—be optimized independently. A multi-qubit detection scheme further employs quantum error mitigation to suppress dark counts beyond prior benchmarks.
Next steps include refining fabrication, expanding quantum control protocols, and opening new directions in sensing and metrology. With modular architecture, robust design, and exceptional sensitivity, this platform is poised to underpin next-generation quantum experiments and high-performance commercial sensors.
A key milestone is single-spin detection via fluorescence, departing from conventional inductive methods and markedly boosting sensitivity to individual solid-state spins. The same technology enables observation and control of nuclear spins with exceptionally long coherence, advancing prospects for quantum memories and durable qubits.
The detector also accelerates rare-event searches in fundamental physics. Integrated into specialized cryogenic setups, it enhances sensitivity for hypothetical particles such as axions, cutting the time required to scan large parameter spaces in high-energy experiments.
Modularity is central: the photon counter can be decoupled from the target system and linked by standard millikelvin microwave components, letting each subsystem—spin ensembles or dark-matter instruments—be optimized independently. A multi-qubit detection scheme further employs quantum error mitigation to suppress dark counts beyond prior benchmarks.
Next steps include refining fabrication, expanding quantum control protocols, and opening new directions in sensing and metrology. With modular architecture, robust design, and exceptional sensitivity, this platform is poised to underpin next-generation quantum experiments and high-performance commercial sensors.