High-efficiency microwave photodetection by cavity-coupled double quantum dots with single-cavity-photon sensitivity
Subhomoy Haldar, Harald Havir, Waqar Hussain Khan, Drilon Zenelaj, Patrick P. Potts, Sebastian Lehmann, Kimberly A. Dick, Peter Samuelsson, V. F. Maisi
We present a superconducting cavity-coupled double quantum dot (DQD) photodiode that achieves a maximum photon-to-electron conversion efficiency of 25% in the microwave domain. With a higher-quality-factor cavity and improved device design to prevent photon leakages through unwanted pathways, our device measures microwave signals down to the 100-aW power level and achieves sensitivity to probe microwave signals with one photon at a time in the cavity. We analyze the photodiode operation using the Jaynes-Cummings input-output theory, identifying the key improvements of stronger cavity-DQD coupling needed to achieve near-unity photodetection efficiency. The results presented in this work represent a crucial advancement toward near-unity microwave photodetection efficiency with single-cavity-photon sensitivity.
We present a superconducting cavity-coupled double quantum dot (DQD) photodiode that achieves a maximum photon-to-electron conversion efficiency of 25% in the microwave domain. With a higher-quality-factor cavity and improved device design to prevent photon leakages through unwanted pathways, our device measures microwave signals down to the 100-aW power level and achieves sensitivity to probe microwave signals with one photon at a time in the cavity. We analyze the photodiode operation using the Jaynes-Cummings input-output theory, identifying the key improvements of stronger cavity-DQD coupling needed to achieve near-unity photodetection efficiency. The results presented in this work represent a crucial advancement toward near-unity microwave photodetection efficiency with single-cavity-photon sensitivity.
Motivated by recent interest in implementing circuit quantum electrodynamics with semiconducting quantum dots, we consider a double quantum dot (DQD) capacitively coupled to a superconducting resonator that is driven by the microwave field of a superconducting transmission line. We analyze the DQD current response using input-output theory and show that the resonator-coupled DQD is a sensitive microwave single photon detector. Using currently available experimental parameters of DQD-resonator coupling and dissipation, including the effects of 1/f charge noise and phonon noise, we determine the parameter regime for which incident photons are completely absorbed and near-unit $\ensuremath{\gtrsim}98$% efficiency can be achieved. We show that this regime can be reached by using very high quality resonators with quality factor $Q\ensuremath{\simeq}{10}^{5}$.
High-efficiency single-photon detection in the microwave domain is a key enabling technology for various quantum applications. However, the extremely low energy of microwave photons presents a fundamental challenge, preventing direct photon-to-charge conversion as achieved in optical systems using semiconductors. Here, we demonstrate continuous microwave photon detection with an efficiency approaching 70% in the single-photon regime. We use a hybrid system comprising a gate-defined double quantum dot (DQD) charge qubit in a gallium arsenide/aluminum gallium arsenide heterostructure, coupled to a high-impedance Josephson junction array cavity. We systematically optimize the hybrid architecture to maximize the detection efficiency by leveraging strong charge-photon coupling, tunable DQD tunnel rates, and the frequency tunability of both subsystems. The system efficiency is characterized over a frequency range of 3 to 5.2 gigahertz. Our results establish semiconductor-based cavity-quantum electrodynamics architectures as a scalable and versatile platform for efficient microwave photon detection, opening promising avenues for quantum microwave optics and quantum information technologies.
We present a continuous microwave photon counter based on superconducting cavity-coupled semiconductor quantum dots. The device utilizes photon-assisted tunneling in a double quantum dot with tunneling events being probed by a third dot. Our device detects both single and multiple-photon absorption events independently, thanks to the energy tunability of a two-level double-dot absorber. We show that the photon-assisted tunnel rates serve as the measure of the cavity photon state in line with the P(E) theory-a theoretical framework delineating the mediation of the cavity photon field via a two-level absorber. We further describe the single photon detection using the Jaynes-Cummings input-output theory and show that it agrees with the P(E) theory predictions at a low-power regime.
High-efficiency single-photon detection in the microwave domain is a key enabling technology for various quantum applications. However, the extremely low energy of microwave photons presents a fundamental challenge, preventing direct photon-to-charge conversion as achieved in optical systems using semiconductors. Here, we demonstrate continuous microwave photon detection with an efficiency approaching 70% in the single-photon regime. We use a hybrid system comprising a gate-defined double quantum dot (DQD) charge qubit in a gallium arsenide/aluminum gallium arsenide heterostructure, coupled to a high-impedance Josephson junction array cavity. We systematically optimize the hybrid architecture to maximize the detection efficiency by leveraging strong charge-photon coupling, tunable DQD tunnel rates, and the frequency tunability of both subsystems. The system efficiency is characterized over a frequency range of 3 to 5.2 gigahertz. Our results establish semiconductor-based cavity-quantum electrodynamics architectures as a scalable and versatile platform for efficient microwave photon detection, opening promising avenues for quantum microwave optics and quantum information technologies.
This thesis investigates hybrid circuit quantum electrodynamics (cQED) as a versatile platform that unites superconducting resonators with semiconductor quantum dots. The central motivation is to harness strong light-matter coupling at the single-photon level, which enables coherent photon-qubit interactions and paves the way for quantum technologies in computation, communication, and sensing. The first part of this work combines hybrid cQED with holes in planar Ge/SiGe, a material system that has only recently become accessible for quantum devices. Planar Ge offers unique advantages for this purpose and has attracted considerable attention in the context of quantum computing. In contrast, its potential for hybrid cQED has remained largely unexplored, making the present work one of the first demonstrations of strong light-matter interaction in this platform. Within this framework, we demonstrate strong charge-photon coupling in planar Ge by observing vacuum Rabi splitting between a hole charge qubit based on a double quantum dot (DQD) and a microwave resonator. We employ a frequency-tunable high-impedance resonator to perform qubit spectroscopy, enabling systematic exploration of coupling regimes and confirming device controllability. In addition, we use this setup to carry out excited-state spectroscopy of strongly correlated states in the DQD, revealing the formation of Wigner molecules and illustrating how the hybrid architecture can be harnessed to access many-body physics. While these experiments in Ge demonstrate how strong coupling can be harnessed to explore qubit physics and correlated states, they also exemplify the wider potential of hybrid cQED. A particularly pressing application is in quantum optics, where efficient single-photon detectors are still lacking in the microwave regime. Such detectors are essential for enabling experiments in quantum communication and microwave quantum optics. In the second part of this thesis, we address this challenge by realizing a photodetector based on a GaAs DQD coupled to a superconducting resonator. The detector operates via photon-to-charge conversion and achieves efficiencies approaching unity. Strong coupling plays a central role by ensuring that incoming photons are absorbed before being lost to the environment, which is key to the high performance of the detector. We further exploit the frequency tunability of the resonator to investigate device performance and identify the parameters that optimize detection efficiency. The broader impact of this work lies in advancing quantum technologies that rely on coherent microwave photons. Applications include spin qubit readout, long-distance photon-mediated coupling, quantum communication, and microwave quantum optics. Looking forward, planar Ge is identified as a highly competitive platform for hybrid cQED. Future directions include the development of single-photon sources, quantum- limited detectors, and analog quantum simulators based on engineered resonator-qubit arrays.
Coupling double-quantum-dot circuits to microwave cavities provides a powerful means to control, couple, and manipulate qubits based on the charge or spin of individual electrons. Here, we revisit this standard configuration by adding superconductivity to the circuit. We combine theory and experiment to study a superconductor--double-quantum-dot circuit coupled to microwave cavity photons. First, we use the cavity as a spectroscopic probe. This allows us to determine the low-energy spectrum of the device and to reveal directly Cooper-pair-assisted tunneling between the two dots. Second, we observe a vacuum Rabi splitting which is a signature of strong charge photon coupling and a premiere with carbon-nanotube-based quantum-dot circuits. We show that our circuit design intrinsically combines a set of key features to achieve the strong coupling regime to the cavity. A low charging energy reduces the device sensitivity to charge noise, while sufficient coupling is provided by the shaping of the spectrum of the double quantum dot by the superconducting reservoir. Our findings could be adapted to many other circuit designs and shed light on the coupling of superconducting nanoscale devices to microwave fields.