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arXiv:2502.14804

Noise Mitigation in Single Microwave Photon Counting by Cascaded Quantum Measurements

May, Alexandre S., Leo Sutevski, Jeanne Solard, Cardoso, Gil, Léon Carde, L. Pallegoix, Raphaël Lescanne, D. Vion, Patrice Bertet, Emmanuel Flurin

Published Feb 20, 2025• 0 citations
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Abstract

While single-photon counting is routinely achieved in the optical domain, operational single microwave photon detectors (SMPDs) have only recently been demonstrated. SMPDs are critical for sensing weak signals from incoherent emitters, with applications ranging from the detection of individual electron spins and dark-matter candidates to advancements in hybrid quantum devices and superconducting quantum computing. These detectors offer a substantial advantage over quantum-limited amplification schemes by bypassing the standard quantum limit for power detection, therefore further reductions in their intrinsic noise are essential for advancing quantum sensing at microwave frequencies. Several SMPD designs utilize the state of a superconducting qubit to encode the detection of an itinerant photon, and rely on a non-destructive photon-qubit interaction. Here, we leverage this Quantum-Non-Demolition feature by repeatedly measuring the impinging photon with cascaded Four-Wave-Mixing processes and encoding the detection on several qubits. This cascaded detector mitigates the intrinsic local noise of individual qubits, achieving a two-order-of-magnitude reduction in intrinsic detector noise at the cost of halving the efficiency. We report an intrinsic sensitivity of $8(1)\times10^{-24}\text{W}/\sqrt{\text{Hz}}$, with an operational sensitivity of $5.9(6)\times 10^{-23}\text{W}/\sqrt{\text{Hz}}$ limited by thermal photons in the input line.

DOI
10.48550/arxiv.2502.14804

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While single-photon counting is routinely achieved in the optical domain, operational single microwave photon detectors (SMPDs) have only recently been demonstrated. SMPDs are critical for sensing weak signals from incoherent emitters, with applications ranging from the detection of individual electron spins and dark-matter candidates to advancements in hybrid quantum devices and superconducting quantum computing. These detectors offer a substantial advantage over quantum-limited amplification schemes by bypassing the standard quantum limit for power detection, therefore further reductions in their intrinsic noise are essential for advancing quantum sensing at microwave frequencies. Several SMPD designs utilize the state of a superconducting qubit to encode the detection of an itinerant photon, and rely on a non-destructive photon-qubit interaction. Here, we leverage this Quantum-Non-Demolition feature by repeatedly measuring the impinging photon with cascaded Four-Wave-Mixing processes and encoding the detection on several qubits. This cascaded detector mitigates the intrinsic local noise of individual qubits, achieving a two-order-of-magnitude reduction in intrinsic detector noise at the cost of halving the efficiency. We report an intrinsic sensitivity of 8(1)×10−24W/Hz8(1)\times10^{-24}\text{W}/\sqrt{\text{Hz}}8(1)×10−24W/Hz​, with an operational sensitivity of 5.9(6)×10−23W/Hz5.9(6)\times 10^{-23}\text{W}/\sqrt{\text{Hz}}5.9(6)×10−23W/Hz​ limited by thermal photons in the input line.
Cyclically operated Single Microwave Photon Counter with 10−2210^\mathrm{-22}10−22 W/Hz\mathrm{W/\sqrt{Hz}}W/Hz​ sensitivity
Single photon detection played an important role in the development of quantum optics. Its implementation in the microwave domain is challenging because the photon energy is 5 orders of magnitude smaller. In recent years, significant progress has been made in developing single microwave photon detectors (SMPDs) based on superconducting quantum bits or bolometers. In this paper we present a practical SMPD based on the irreversible transfer of an incoming photon to the excited state of a transmon qubit by a four-wave mixing process. This device achieves a detection efficiency η=0.43η= 0.43η=0.43 and an operational dark count rate α=85α= 85α=85 s−1\mathrm{s^{-1}}s−1, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is S=10−22\mathcal{S} = 10^{-22}S=10−22 W/Hz\mathrm{W/\sqrt{Hz}}W/Hz​, one order of magnitude lower than the state of the art. The detector operates continuously over hour timescales with a duty cycle ηD=0.84η_\mathrm{D}=0.84ηD​=0.84, and offers frequency tunability of at least 50 MHz around 7 GHz.
Single-photon detection played an important role in the development of quantum optics. Its implementation in the microwave domain is challenging because the photon energy is five orders of magnitude smaller. In recent years, significant progress has been made in developing single microwave photon detectors (SMPDs) based on superconducting quantum bits or bolometers. In this paper we present a practical SMPD based on the irreversible transfer of an incoming photon to the excited state of a transmon qubit by a four-wave mixing process. This device achieves a detection efficiency $\ensuremath{\eta}=0.43$ and an operational dark count rate $\ensuremath{\alpha}=85\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is $\mathcal{S}={10}^{\ensuremath{-}22}\phantom{\rule{0.2em}{0ex}}\mathrm{W}/\sqrt{\mathrm{Hz}}$, one order of magnitude lower than the state of the art. The detector operates continuously over hour time-scales with a duty cycle ${\ensuremath{\eta}}_{D}=0.84$, and offers frequency tunability of at least 50 MHz around 7 GHz.
Single-photon detectors are an essential part of the toolbox of modern quantum optics for implementing quantum technologies and enabling tests of fundamental physics. The low energy of microwave photons, the natural signal path for superconducting quantum devices, makes their detection much harder than for visible light. Despite impressive progress in recent years and the proposal and realization of a number of different detector architectures, the reliable detection of a single itinerant microwave photon remains an open topic. Here, we investigate and simulate a detailed protocol for single-photon multiplication and subsequent amplification and detection. At its heart lies a Josephson-photonics device which uses inelastic Cooper-pair tunneling driven by a dc bias in combination with the energy of an incoming photon to create multiple photons, thus compensating for the low-energy problem. Our analysis provides clear design guidelines for utilizing such devices, which have previously been operated in an amplifier mode with a continuous wave input, for counting photons. Combining a formalism recently developed by Mølmer to describe the full quantum state of in- and outgoing photon pulses with stochastic Schrödinger equations, we can describe the full multiplication and detection protocol and calculate performance parameters, such as detection probabilities and dark count rates. With optimized parameters, a high population of a single output mode can be achieved that can then be easily distinguished from vacuum noise in heterodyne measurements of quadratures with a conventional linear amplifier. Realistic devices with two multiplication stages with multiplication of 161616 reach for an impinging Gaussian pulse of length TTT a detection probability of 84.5%84.5\%84.5% with a dark count rate of 10−3/T10^{-3}/T10−3/T, and promise to outperform competing schemes.
Quantum sensing is a rapidly expanding research field that finds one of its applications in fundamental physics, as the detection of light Dark Matter. Qubit-based superconducting devices have already been successfully applied in detecting few-GHz single photons via Quantum Non-Demolition measurements. The optimization and new design schemes of circuits embedding qubits will yield notable enhancements in sensitivity and suppression of dark count rates in experiments involving high-precision microwave photon detection, particularly in the search for Axions and Dark Photons. The Qub-It collaboration is developing a novel microwave photon detection scheme based on two qubits coupled to the same resonator, both in 2D and 3D formats.
The detection of single microwave photons is becoming a cornerstone of fundamental experiments in circuit quantum electrodynamics and quantum sensing. Experiments in cavity quantum electrodynamics, photon-mediated entanglement, dark-matter axion searches and quantum thermodynamics increasingly rely on single-photon sensitivity. Current technologies exploit superconducting devices, including Josephson parametric detectors, and transmon-based non-demolition counters for dark-matter haloscopes. Hybrid double quantum dot-Josephson systems reach interesting levels of efficiency, while current-biased Josephson junctions show potential for near-quantumlimited resolution. Despite impressive progress, challenges remain in reducing dark counts, improving reset speed, and scaling for multiplexed arrays. Continued advances in superconducting materials, qubit coherence, and hybrid semiconductor-superconductor designs promise to extend detection efficiency and bandwidth. These developments are poised to enable the next generation of quantum-enabled experiments, from foundational tests in quantum optics to searches for new physics.
We present a novel scheme to detect itinerant microwave radiation at the single photon level. Using existing Josephson-photonics devices, where two microwave cavities are coupled by a dc-voltage biased superconducting junction, we theoretically show how to implement a stroboscopically repeated, near-projective measurement of a photon impinging on one of the cavities. Optimizing rate, duration, and strength of the measurement by flux control of the junction and developing a threshold protocol to detect the photon from a homodyne measurement of the radiation output of the other cavity, we achieve highly efficient detection with low dark counts. By cascading the detector with a preamplifier, where a similar two-cavity Josephson-photonics device acts as a photon multiplier, we can further improve the device to reach a detection efficiency of 88.5%88.5 \%88.5% with a dark count rate of ∼10−4γa\sim10^{-4} γ_a∼10−4γa​, set by the resonance width γaγ_aγa​ of the absorbing cavity. These results for a multiplication factor of two suggest that near-unity efficiencies may be reached for higher multiplication factors.