EPFL microwave photon detector reaches 70% efficiency
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- Pasquale Scarlino and EPFL scientists published a single microwave photon detector in Science Advances, combining a double quantum dot with a superconducting microwave cavity on a GaAs/AlGaAs chip.
- The superconducting cavity, built from an array of Josephson junctions, stores microwave photons at 3–5.2 GHz with high electrical impedance that enables strong interaction with electrons in the quantum dots.
- Detection efficiency ranged from 55% to 67.7% depending on tuning, with the best setting approaching 70% — comparable to state-of-the-art microwave photon detectors, per the researchers.
- The device operates continuously, self-resetting within nanoseconds as electrons move in and out of the quantum dots, contrasting with methods that fail at microwave frequencies because individual photons lack the energy to release charge.
- Researchers note the semiconductor quantum dot design could in principle sit on the same chip as spin qubits, helping connect microwave photonics with semiconductor-based quantum computing.
- When a photon enters the cavity and matches the energy splitting of the double quantum dot, the electron absorbs it, tunnels to a nearby reservoir, and generates a small direct current — the measurable signal.
Why it matters: Microwave photons carry roughly 100,000 times less energy than visible-light photons, which is why single-microwave-photon detection has long required entirely different strategies. Hitting ~70% efficiency with a semiconductor-based, self-resetting device puts the field closer to practical quantum microwave optics and quantum sensing, and the stated design path toward same-chip integration with spin qubits is a concrete route to scalable quantum information platforms.
