High-efficiency microwave photodetection by cavity coupled double dots with single cavity-photon sensitivity

TL;DR

This paper demonstrates a superconducting cavity-coupled semiconductor double quantum dot photodiode that reaches a 25% photon-to-electron conversion efficiency in the microwave domain with single-cavity-photon sensitivity at input powers as low as 100 aW. By upgrading the resonator to Nb, adding on-chip filtering to suppress photon leakage, and adopting a one-port over-coupled geometry, the device achieves a high internal quality factor and measurable cavity-photon dissipation via the DQD, consistent with Jaynes–Cummings input–output theory. The work identifies strong cavity–DQD coupling and high-impedance cavity designs as key routes toward near-unity detection efficiency, supported by theoretical analyses that map the parameter space for optimal η_PD. These results advance microwave quantum optics and provide a practical platform for studying photon statistics, quantum tomography, and metrology in superconducting–semiconductor hybrid systems.

Abstract

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 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 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 for studies of photon statistics in the microwave range and applications related to quantum information processing.

Figures (4)

• Figure 1: (a) Schematic illustration of the hybrid device, comprising a semiconductor nanowire double quantum dot coupled to a coplanar waveguide cavity. The photocurrent of the device is measured by utilizing the cavity voltage node at the mid-point of the cavity. (b) Optical microscope image of the chip showing the one-port cavity and indicating the input port, ground plane on the DC lines, and location of the DQD. (c) Input coupler of the cavity. (d) Schematic cross-sectional view showing the layered structure of the ground plane capacitor on the DC lines and (e) an inductive filter integrated into a DC line.
• Figure 2: (a) Charge stability diagram of the DQD showing finite bias triangles (FBTs) at charge triple points with $V_b$ = 1 mV and without an RF drive. (b) Measured RF reflectance $R$ with $\omega=\omega_r$ as a function of plunger gate voltages $V_\text{L}$ and $V_\text{R}$ with $V_b$ = 0 and $P_\text{in}$ = 1 fW. Two distinct lines appear due to the DQD absorption at $\pm\delta_r$. (c) The measured RF spectra across the interdot charge transfer line and (d) theoretically fitted RF spectra using the Jaynes-Cummings model. The dashed lines in panel (c) show the lowest two transition energies of the Jaynes-Cummings Hamiltonian, Eq. (\ref{['Eq:dispersive']}). (e) Photocurrent measurement across the plunger gate space with $P_\text{in} = 0.3$ fW and drive frequency 6.716 GHz. (f) Measured reflectance as a function of drive frequency with the DQD tuned to photodetection points at $\pm\delta_r$ at the charge triple points with finite photocurrent and the Coulomb blockade regime $\delta\gg\delta_r$ when $I_\text{SD}$ = 0, showing insights into cavity photon dissipation due to DQD absorption.
• Figure 3: (a) Photocurrent recorded at $\pm\delta_r$ and (b) corresponding photodetection efficiency as a function of input microwave power, $P_\text{in}$. The electron tunneling rate $I_\text{SD}/e$ contributing to the measured signal is also shown on the right-hand side of panel a. The device achieves a maximum photoconversion efficiency of 25%. The solid (dashed-dotted) lines show the theoretically fitted results in the low (high) power regime.
• Figure 4: (a-b) Schematic diagrams showing the tunneling in and out rates for the two operation points, highlighting the asymmetry in device operation. Theoretical predictions of quantum efficiency at the low-power limit of Eq. \ref{['eq:lowpower']} under varying tunnel couplings $\Gamma_\text{L}$ and $\Gamma_\text{R}$, showing the potential for optimizing photo-conversion efficiency at (c) $+\delta_r$ and (d) $-\delta_r$. (e-f) Show the corresponding cavity photon dissipation due to DQD absorption. The star marks in figures (c-f) show the operation point of the present experiment. The white dashed lines in panels (c) and (d) show the efficiency of a symmetrically tunnel-coupled DQD photodiode.