Magic-Angle Bilayer Graphene Nanocalorimeters: Toward Broadband, Energy-Resolving Single Photon Detection

Abstract

Because of the ultra-low photon energies in the mid-infrared and terahertz frequencies, in these bands photodetectors are notoriously underdeveloped, and broadband single photon detectors (SPDs) are non-existent. Advanced SPDs exploit thermal effects in nanostructured superconductors, and their performance is currently limited to the more energetic near-infrared photons due to their high electronic heat capacity. Here, we demonstrate a superconducting magic-angle twisted bilayer graphene (MAG) device that is capable of detecting single photons of ultra-low energies by utilizing its record-low heat capacity and sharp superconducting transition. We theoretically quantify its calorimetric photoresponse and estimate its detection limits. This device allows the detection of ultrabroad range single photons from the visible to sub-THz with response time around 4 ns and energy resolution better than 1 THz. These attributes position MAG as an exceptional material for long-wavelength single photon sensing, which could revolutionize such disparate fields as quantum information processing and radio astronomy. Introduction:The detection of single photons is a key enabling technology in many research areas including quantum sensing, quantum key distribution, information processing and radio astronomy. Single photon detectors (SPDs) for wavelengths ranging from the visible to near infrared (nIR) have already been developed and even commercialized. State-of-the-art SPD technologies rely on heat-induced breaking of the superconducting state in nano-structured superconductors (SCs). Here, superconducting transition-edge sensors (TES) and superconducting nanowire single photon detectors (SNSPDs) have developed into the SPDs with the highest detection efficiencies, lowest dark count rates and operation wavelengths up to 10 µm (1-8). However, while no theoretical performance limits are evident so far, extending the broadband detection of single photons from the nIR to the far-infrared and the terahertz (THz), has yet to be demonstrated. TESs exploit the steepness of the temperature dependent resistance at the superconducting transition edge, which enables the generation of detectable voltages pulses upon heating electrons by absorbed light quanta (4, 5,9). Because the energy of an absorbed photon is transferred to the whole ensemble of electrons, the performance of TESs is determined by the heat capacity of the calorimetric materials used. This currently limits the SPD operation of TESs to wavelengths below 8µm(10), temperatures below 100mK, and detection times above ~10s(10-13).

Roadmap of Terahertz Imaging 2021

“…The first one relates to the availability and the operational conditions of power detectors with a useful response to single or only a few THz photons. One would expect that superconducting detectors are capable of such performance, but their single-detection capability, for various reasons, is limited to shorter wavelengths [340,341]. Single-photon detection is possible with cryogenically cooled quantum-dot detectors (which use a single-electron transistor as sensor for the polarization of the dot) and with charge-sensitive IR phototransistors (using quantum wells sensed by a 2DEG) [340].…”

“…Single-photon detection is possible with cryogenically cooled quantum-dot detectors (which use a single-electron transistor as sensor for the polarization of the dot) and with charge-sensitive IR phototransistors (using quantum wells sensed by a 2DEG) [340]. New types of detectors, exploiting novel material systems, such as a magic-angle bilayer graphene, are under development [341]. However, the THz frequency range is affected much more severely than the IR or VIS ranges by ambient radiation, and, to have a "THz-dark" environment means to place the experiment with the specimen entirely into an ultracold cryostat, which is not very conducive for experiments on living cells, but at least experiments on dead biological matter are possible under such conditions.…”

2D Material‐Based Photodetectors for Infrared Imaging

“…The photodetector shows the ultrafast response time around 4 ns and energy resolution better than 1 THz. [ 16 ] These two mechanisms show great development potential.…”

2D THz Optoelectronics

“…Hot‐electron bolometers based on magic‐angle bilayer graphene provide spectrally resolved single photon detection in the THz range. [ 65 ]…”