Graphene Junctions Detect Terahertz Light, Paving the Way for New Sensors

X. Zhou and colleagues at National University of Singapore in collaboration with Moscow Pedagogical State University, Center for Neurophysics and Neuromorphic Technologies and National Institute of Materials Science, report a strong photoresponse in these junctions at terahertz frequencies, an area where current sensor technology is limited. The findings represent a key first step towards graphene-based quantum sensors for this challenging band, achieving a responsivity of 88kV W⁻¹ and a noise-equivalent power of 45 aW Hz⁻¹/² at 1.7 K. The gate-tunable nature of these junctions enables operation up to 0.9 K, potentially allowing single-photon terahertz detection without requiring extremely low millikelvin temperatures

Graphene Josephson junctions demonstrate high-responsivity terahertz detection with tunable

A responsivity of 88kV W⁻¹, exceeding previous superconducting hot-electron bolometers by over an order of magnitude, has been achieved in graphene Josephson junctions at terahertz frequencies. This breakthrough overcomes limitations in microwave and infrared detectors, opening a pathway to sensitive quantum sensing in the THz band, a region where such technology was previously absent. The team recorded a noise-equivalent power of 45 aW Hz⁻¹/² at 1.7 Kelvin, and key gate tunability allows operation up to 0.9 Kelvin, potentially enabling single-photon terahertz detection without extremely low millikelvin temperatures.

Graphene Josephson junctions now provide a flexible platform for broadband cryogenic radiation sensing and suggest their use as quantum sensors at terahertz frequencies. The devices exhibited a pronounced suppression of the critical current, generating a strong photovoltage under current bias; amplitude variations correlated with differing incident power levels, confirming operation across a broad spectrum from millimetre-waves to far-infrared radiation. Analysis of the photovoltage and electron temperature as a function of absorbed power revealed a responsivity of 88kV W -1 and a noise-equivalent power of 45 aW Hz -1/2 at 1.7 K. Furthermore, gate tunability of the junction enables access to a regime where hysteretic current-voltage characteristics persist up to 0.9 K, offering a potential route toward single-photon terahertz detection beyond millikelvin temperatures. Calibration using the device’s electronic properties allowed determination of a dynamic thermal conductance, achieving a noise-equivalent power at temperatures higher than previous reports and without requiring SQUID measurements.

Terahertz radiation detection via critical current suppression in graphene Josephson junctions

A technique centred on suppressing the critical current in graphene Josephson junctions proved pivotal to this work. A Josephson junction functions as a tiny electronic switch responding to electromagnetic radiation, relying on a ‘critical current’, the maximum current it can conduct while remaining superconducting; exceeding this value destroys the superconducting state. Scientists deliberately exposed these junctions to terahertz radiation, a type of electromagnetic wave between microwaves and infrared light often used in security scanners and materials analysis, to induce rapid heating of electrons within the graphene.

Tiny electronic switches, graphene Josephson junctions, were used to detect terahertz radiation, a region of the electromagnetic spectrum currently lacking sensitive quantum sensors. Cooled to 1.7 Kelvin to enable superconductivity, the junctions allowed measurement of the critical current, the maximum current a superconductor can carry. Suppressing this critical current with terahertz radiation generated a photovoltage, which was then measured, yielding a responsivity of 88kV W^-1 and a noise-equivalent power of 45 aW Hz^-1/2; this approach bypasses limitations of existing microwave and infrared detectors.

Graphene Josephson junctions enable ultra-sensitive terahertz detection approaching the

The terahertz band of the electromagnetic spectrum is increasingly the focus of scientists, a region vital for applications like security scanning and materials analysis, yet hampered by a lack of sensitive quantum sensors. This research demonstrates a promising new detector based on graphene, a material with exceptional properties for light detection, although achieving truly single-photon sensitivity, detecting one particle of light, remains elusive. Nevertheless, despite not yet reaching this ultimate goal, this work represents a major advance in terahertz technology.

Current terahertz sensors struggle with sensitivity; this research demonstrates a graphene-based detector achieving a noise level equivalent to just 45 attowatts, a remarkably faint signal. Graphene Josephson junctions, a key component, offer advantages over existing materials due to their unique electronic properties and broad bandwidth, potentially unlocking new applications in security and materials science even at this stage of development. Researchers have created a terahertz detector utilising graphene, achieving a noise level of 45 attowatts.

This new device, employing graphene Josephson junctions, offers a pathway towards more sensitive and efficient terahertz technology and will likely spur advances in security and materials analysis within the decade. Graphene Josephson junctions now demonstrate a measurable response to terahertz radiation, filling a gap in current quantum sensing technology. These junctions, combining graphene’s unique properties with superconductivity, convert incoming light into an electrical signal, allowing for sensitive detection where existing sensors are limited. A responsivity of 88kV W⁻¹ confirms the potential of this approach for ultra-broadband cryogenic radiation sensing. This work therefore shifts the focus to optimising these junctions for operation at higher temperatures and, ultimately, exploring the possibility of detecting individual photons at terahertz frequencies.

Researchers have demonstrated a strong photoresponse in graphene Josephson junctions at terahertz frequencies, establishing a first experimental step towards new quantum sensors. This is important because sensitive terahertz detection is currently lacking, hindering advances in areas like security scanning and materials analysis. The device achieved a noise-equivalent power of 45 aW Hz⁻¹/₂ at 1.7 K, and a responsivity of 88kV W⁻¹, indicating potential for ultra-broadband cryogenic radiation sensing. The authors suggest future work will focus on optimising the junctions for operation at higher temperatures.