Graphene heat detectors go quantum

Researchers have created a bolometer, a heat detecting device, that can detect single microwave photons and is compatible with quantum computing. The device, made of a single sheet of graphene, could find a range of applications in quantum technologies, radio astronomy and even in search for dark matter.

A bolometer is a device that detects incoming radiation by absorbing photons and converting them to heat. A measure of device temperature yields the intensity of the radiation. Bolometers capable of detecting single microwave photons would be very useful in creating quantum computers and other technologies that use quantum bits (qubits). However, overcoming the challenges of low energies of microwave photons and high speed required for qubit detection has been elusive.

The graphene device, reported by a team from Finland in the journal Nature, makes use of the small heat capacity of graphene which makes the material heat up much for each photon absorbed. Using graphene also increased the detector speed by 100 times compared to previously used bolometers that the team built from a gold-palladium alloy. With time constants of less than half a microsecond, these graphene bolometers match the timescales required for superconducting qubit detection.

Illustration: Graphene quantum bolometer (Courtesy: Heikka Valja).

Previously, a different team led by Dmitri Efetov made highly-sensitive graphene bolometers that ran at room temperatures. To achieve high sensitivity, the team used a different approach, coupling the graphene to a photonic nanocavity. Room-temperature operation meant that the device could be used to monitor heat escape from buildings, or to bridge the terahertz gap in astronomy. In follow-up research, Efetov and his colleagues constructed a graphene-based bolometer that has the highest sensitivity allowed by thermodynamics. The device is made of graphene integrated in a superconducting Josephson junction and is 100,000 times faster than microwave bolometers made of other materials.

These achievements highlight the applications of graphene in quantum technology, a technology sector that demands new materials to address key issues as it matures towards commercial scale.

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