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arXiv:2307.03614

Cyclically operated Single Microwave Photon Counter with $10^\mathrm{-22}$ $\mathrm{W/\sqrt{Hz}}$ sensitivity

Léo Balembois, J. Travesedo, L. Pallegoix, May, Alexandre, Eric Billaud, Marius Villiers, Estève, Daniel, D. Vion, Patrice Bertet, Emmanuel Flurin

Published Jul 7, 2023• 1 citation
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Abstract

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 $η= 0.43$ and an operational dark count rate $α= 85$ $\mathrm{s^{-1}}$, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is $\mathcal{S} = 10^{-22}$ $\mathrm{W/\sqrt{Hz}}$, one order of magnitude lower than the state of the art. The detector operates continuously over hour timescales with a duty cycle $η_\mathrm{D}=0.84$, and offers frequency tunability of at least 50 MHz around 7 GHz.

DOI
10.48550/arxiv.2307.03614

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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.
Efficient detection of single microwave photons is a key capability for emerging quantum technologies. Yet, it remains far less developed than its optical domain counterpart. Realizing detectors that simultaneously achieve high efficiency, low dark counts, and continuous operation has proved challenging. Existing detectors operate cyclically, forcing a trade-off between efficiency and duty cycle. Here, we demonstrate a continuously operated microwave single-photon detector based on a superconducting artificial molecule. In our scheme, an incoming photon is captured by a bright state of the molecule and then transferred to a long-lived dark state via a driven-dissipative process. Photon ``clicks'' are revealed as quantum jumps in the continuously monitored dark state. We observe a cyclic detection efficiency of 0.730.730.73, and a continuous detection efficiency of 0.470.470.47 over a 5 MHz5\,\mathrm{MHz}5MHz instantaneous bandwidth, with a 1 μs1\,μ\mathrm{s}1μs temporal resolution and a 15 μs15\,μ\mathrm{s}15μs dead time. By overcoming the trade-off between efficiency and duty cycle, this approach establishes continuous microwave photon detection for quantum sensing, quantum thermodynamics, and fundamental physics.
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.
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.
We report on the characteristics of a microwave photon-counter device based on a superconducting transmon qubit. Its design is similar to that described by Balembois [], which achieved a sensitivity of 10 − 22 W / Hz , but with an additional bandwidth-tuning circuit that permits tuning the detection bandwidth over an order of magnitude to optimize the efficiency and noise level of the device. As a result of this feature and improvements in device fabrication, a power sensitivity of 3 × 10 − 23 W / Hz is reached. We confirm the high performance of the device by measuring single-spin microwave fluorescence.
Axions detection requires the ultimate sensitivity down to the single-photon limit. In the microwave region, this corresponds to energies in the yJ range. This extreme sensitivity has to be combined with an extremely low dark-count rate since the probability of axions conversion into microwave photons is supposed to be very low. To face this complicated task, we followed two promising approaches that both rely on the use of superconducting devices based on the Josephson effect. The first one is to use a single Josephson junction (JJ) as a switching detector (i.e., exploiting the superconducting to normal state transition in the presence of microwave photons). We designed a device composed of a coplanar waveguide terminated on a current-biased JJ. We tested its efficiency to pulsed (pulse duration 10 ns) microwave signals since this configuration is closer to an actual axions search experiment. We show how our device is able to reach detection capability of the order of ten photons with the frequency of 8 GHz. The second approach is based on an intrinsically quantum device formed by two resonators coupled only via a superconducting qubit network. This approach relies on quantum nondemolition measurements of the resonator photons. We show that by injecting radiofrequency power into the resonator, the frequency position of the resonant drop in the transmission coefficient (S21) can be modulated up to 4 MHz. We anticipate that, once optimized, both the devices have the potential to reach single-photon sensitivity.