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.
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.
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.
Cyclically operated Single Microwave Photon Counter with 10−22W/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=0.43 and an operational dark count rate α=85s−1, mainly due to the out-of-equilibrium microwave photons in the input line. The corresponding power sensitivity is S=10−22W/Hz, one order of magnitude lower than the state of the art. The detector operates continuously over hour timescales with a duty cycle ηD=0.84, and offers frequency tunability of at least 50 MHz around 7 GHz.
Superconducting circuits have recently become a major contender for the implementation of quantum computers owing to their compatibility with existing microchip fabrication technologies. Their utility stems largely from their ability to be coupled with resonant cavities for the purposes of trapping and relaying microwave radiation. Because of this feature, scientists are able to transmit quantum information from a variety of qubits. Though quantum-limited amplifiers exist, unfortunately there currently exists no microwave photon counter capable of single shot quantum detection. Hence, we use superconducting circuits with Josephson junctions to design a microwave photon detector based on a modified phase qubit that exhibits a bandwidth of 4GHz, and a detection fidelity of 98%. We use metastable barrier transition (driven by incident photons) to create an avalanche effect analogous to current photo-diodes. Linear coupling of the junction flux with the radiation permits photodetection from an arbitrary quantum source in the GHz range. We show the device to be robust to changes in drive frequency, temporal photon width, and resonator quality factor, and we optimize our device with respect to these parameters. We show the device to be stable over the necessary time scales, and yet sensitive enough to accurately measure photons on demand.
Various types of single-photon counters operating in infrared, ultraviolet, and optical wavelength ranges are successfully used to study electromagnetic fields, analyze radiation sources, and solve problems in quantum informatics. However, their operating principles become ineffective at millimeter band, S-band, and ultra-high frequency bands of wavelengths due to the decrease in quantum energy by 4–5 orders of magnitude. Josephson circuits with discrete Hamiltonians and qubits are a good foundation for the construction of single-photon counters at these frequencies. This paper presents a frequency-tuned microwave photon counter based on a single-junction superconducting quantum interferometer and flux qutrit. The control pulse converts the interferometer into a two-level system for resonance absorption of photons. Decay of the photon-induced excited state changes the magnetic flux in the interferometer, which is measured by a SQUID magnetometer. Schemes for recording the magnetic flux using a DC SQUID or ideal parametric detector, based on a qutrit with high-frequency excitation, are discussed. It is shown that the counter consisting of an interferometer with a Josephson junction and a parametric detector demonstrates high performance and is capable of detecting single photons in a microwave band.
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.
Abstract We present a detailed study of a microwave single-photon source utilizing a transmon qubit asymmetrically coupled to two transmission lines: a weakly coupled drive line and a strongly coupled emission line. Our design allows for the generation of single photons in the microwave regime, which are essential for quantum communication, computing, and sensing applications. In addition to single-photon generation, the same design functions as a power sensor and enables precise measurement of the system’s attenuation. This dual functionality allows us to calibrate the noise of our amplification chain. This enables a self-calibrated architecture in which the same device acts simultaneously as the photon source and as a reference standard, eliminating the need for external tones or calibrated inputs. With this calibration we reconstruct the density matrix of the emitted photon state, for which we achieve a fidelity of 61.4% and measure a second-order correlation function of g ( 2 ) ( 0 ) = 0.06 − 0.06 + 0.45 , indicating quantum nature and single-photon characteristics. These results confirm generation of single photons and demonstrate the potential of transmon qubits in advancing quantum technologies in the microwave domain.