AQP Seminar: Bolometry with graphene Josephson junction

Aalto Quantum Physics Seminar (Nanotalo). Speaker:  Roope Kokkoniemi (QCD, Aalto)

A bolometer detects electromagnetic radiation by absorbing it and measuring the resulting temperature increase in the absorbing element. Graphene is a promising candidate for the absorber material due to its true 2D nature, allowing the fabrication of an absorber with extremely small volume. Thus, even a single microwave photon incident on the small graphene absorber can increase its temperature substantially. Properties of graphene can also be modified with an electric field which in turn allows tuning the properties of the bolometer in situ. Furthermore, a Josephson junction is an attractive choice for the temperature sensor since its critical current has roughly exponential dependence on the temperature. For these reasons, we have experimentally studied a graphene-Josephson-junction-based bolometer. Our preliminary results suggest noise equivalent power of 50 zW/rtHz. Together with a thermal time constant of 0.5 µs this implies energy resolution below h×50 GHz, bringing detection of single microwave photon with thermal detectors a step closer to reality.

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