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arXiv:2403.02049

Ultra-low carrier density superconducting bolometers with single photon sensitivity based on magic-angle twisted bilayer graphene

Giorgio Di Battista, Kin Chung Fong, A. Díez-Carlón, Kenji Watanabe, Takashi Taniguchi, Dmitri K. Efetov

Published Mar 4, 2024• 1 citation
arXivHTMLPDF

Abstract

The superconducting (SC) state of magic-angle twisted bilayer graphene (MATBG) shows exceptional properties, as it consists of an unprecedentedly small electron (hole) ensemble of only ~ 10 power 11 carriers per square centimeter, which is five orders of magnitude lower than in traditional superconductors. This results in an ultra-low electronic heat capacity and kinetic inductance of this truly two-dimensional SC, and provides record-breaking key parameters for a variety of quantum sensing applications, in particular in thermal sensing and single photon detection (SPD), which traditionally exploit thermal effects in nanostructured superconducting thin films. In this work, we systematically study the interaction of the superconducting state of MATBG with individual light quanta. We discover full destruction of the SC state upon absorption of a single infrared photon even in a 16 square micrometer sized device, which showcases its exceptional bolometric sensitivity. Upon voltage biasing close to its critical current, we further show that this non-optimized device can be used as a SPD, whose click-rate is proportional to the number of absorbed photons, following Poissonian statistics. Our work offers insights into the MATBG-photon interaction and shows up pathways to use low-carrier density graphene-based superconductors as a new platform for developing revolutionary new quantum devices and sensors.

DOI
10.48550/arxiv.2403.02049

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The superconducting (SC) state of magic-angle twisted bilayer graphene (MATBG) shows exceptional properties, as it consists of an unprecedentedly small electron (hole) ensemble of only ~ 10 power 11 carriers per square centimeter, which is five orders of magnitude lower than in traditional superconductors. This results in an ultra-low electronic heat capacity and kinetic inductance of this truly two-dimensional SC, and provides record-breaking key parameters for a variety of quantum sensing applications, in particular in thermal sensing and single photon detection (SPD), which traditionally exploit thermal effects in nanostructured superconducting thin films. In this work, we systematically study the interaction of the superconducting state of MATBG with individual light quanta. We discover full destruction of the SC state upon absorption of a single infrared photon even in a 16 square micrometer sized device, which showcases its exceptional bolometric sensitivity. Upon voltage biasing close to its critical current, we further show that this non-optimized device can be used as a SPD, whose click-rate is proportional to the number of absorbed photons, following Poissonian statistics. Our work offers insights into the MATBG-photon interaction and shows up pathways to use low-carrier density graphene-based superconductors as a new platform for developing revolutionary new quantum devices and sensors.
carriers per square centimeter, which is five orders of magnitude lower than traditional superconductors (SCs). This results in an ultralow electronic heat capacity and a large kinetic inductance of this truly two-dimensional SC, providing record-breaking parameters for quantum sensing applications, specifically thermal sensing and single-photon detection. To fully exploit these unique superconducting properties for quantum sensing, here, we demonstrate a proof-of-principle experiment to detect single near-infrared photons by voltage biasing an MATBG device near its superconducting phase transition. We observe complete destruction of the SC state upon absorption of a single infrared photon even in a 16-square micrometer device, showcasing exceptional sensitivity. Our work offers insights into the MATBG-photon interaction and demonstrates pathways to use moiré superconductors as an exciting platform for revolutionary quantum devices and sensors.
Abstract At a magic relative twist angle, magic angle twisted bilayer graphene (MATBG) has an octet of flat bands that can host strong correlation physics when partially filled. A key theoretical discovery in MATBG is the existence of ferromagnetic Slater determinants as exact ground states of the corresponding flat band interacting (FBI) Hamiltonian. The FBI Hamiltonian describes the behavior of electrons that interact with each other in a high-dimensional space, and is constructed from the band structure of the non-interacting Bistritzer–MacDonald model at the chiral limit. A key property of the FBI Hamiltonian for MATBG is that it is frustration-free and can be written as a sum of non-commuting terms. In this work, we provide a complete characterization of the ground state manifold of the FBI Hamiltonian, proving that it is precisely the linear span of such ferromagnetic Slater determinants.
We propose a novel quantum computing architecture that combines the engineered electromagnetic properties of quantum metamaterials with the strongly correlated electron physics of magic-angle systems. By integrating magic-angle twisted bilayer graphene (MATBG) into superconducting metamaterial waveguides, we demonstrate theoretically that the resulting hybrid system exhibits: (1) enhanced qubit coherence through geometric control of electromagnetic modes, (2) tunable qubit-qubit coupling via metamaterial dispersion engineering, and (3) topologically protected quantum states arising from the interplay of moiré band structure and metamaterial boundary conditions. Our framework provides design equations for a scalable quantum computing platform that leverages both the flat-band physics of magic-angle materials and the controllable photon-matter interactions of quantum metamaterials.
Abstract. Recent experiments have shown that magic angle twisted bilayer graphene (MATBG) can exhibit correlated insulator behavior at half-filling. Seminal theoretical results towards understanding this phase in MATBG have shown that Hartree–Fock ground states (with a positive single-particle excitation gap) can be exact many-body ground states of an idealized flat band interacting (FBI) Hamiltonian. We prove that in the absence of spin and valley degrees of freedom, the only Hartree–Fock ground states of the FBI Hamiltonian for MATBG are two ferromagnetic Slater determinants. Incorporating spin and valley degrees of freedom, we provide a complete characterization of the Hartree–Fock ground state manifold, which is generated by a [Formula: see text] hidden symmetry group acting on five elements. We also introduce new tools for ruling out translation symmetry breaking in the Hartree–Fock ground state manifold, which may be of independent interest.
Magic-angle twisted bilayer graphene Josephson junctions (MATBG-JJ) with a gate-tunable valley-polarized weak link exhibit an intrinsic Josephson diode effect originating from broken symmetries associated with valley polarization and band-structure anisotropy. Exploiting this nonreciprocal superconducting platform, we construct quantum Stirling (QSC), Otto (QOC), and Carnot (QCC) thermodynamic cycles, where the valley-polarization potential ΔvΔ_vΔv​ acts as the principal control parameter, in contrast to conventional Josephson thermal machines driven by superconducting phase bias. We systematically compare the performance of MATBG-based Josephson diode thermal machines (MATBG-JDTM) with MATBG-based Josephson junction thermal machines (MATBG-JJTM) and AA-stacked bilayer graphene Josephson junction thermal machines (AABLG-JJTM). Owing to the flat-band-enhanced density of states and electrically tunable nonreciprocal transport in MATBG, both MATBG-JDTM and MATBG-JJTM exhibit significantly enhanced work output and efficiency over a broad operating regime compared to AABLG-JJTM. In particular, the gate-controlled MATBG-JDTM provides a flux-free alternative to conventional phase-driven architectures, mitigating limitations associated with magnetic-flux control and flux-noise effects. Our results establish MATBG Josephson diode platforms as a promising route toward electrically tunable quantum thermal machines and nonreciprocal superconducting caloritronics.
Zero energy eigenstates ψ 0 ( θ ) of the twisted bilayer graphene Hamiltonian at the Dirac point show a high sensitivity to the twist angle θ near the magic angles where the effective Fermi velocity vanishes. We use information theory markers, like fidelity-susceptibility and entanglement entropy of the reduced density matrix to the layer sector, to capture this quantum criticality of zero modes at magic twist angles. • This article contributes to unravel the magic behind the electronic properties and exotic quantum states of twisted bilayer graphene. • The quantum criticality of zero modes at magic twist angles is revealed by fidelity and entanglement measures, as an alternative complement to the usual Fermi velocity, conductivity and band flattening characteristics. • We provide plots of fidelity, entanglement and interlayer hopping probabilities of conduction and valence zero modes as a function of the twist angle, where magic angles are conspicuous.