Periodic Reporting for period 4 - 2D4QT (2D Materials for Quantum Technology)
Periodo di rendicontazione: 2024-03-01 al 2025-08-31
Quantum technologies represent a dynamic frontier of modern science, at the intersection of physics, engineering, and materials science. Beyond the widely known example of quantum computing, a broad spectrum of research areas — including quantum cryptography, quantum sensing, quantum simulation, and quantum metrology — harness quantum phenomena to achieve unprecedented levels of performance. The realization of these technologies depends, however, on the availability of suitable material platforms capable of supporting and manipulating quantum states with high precision.
Among the promising candidates, two-dimensional (2D) materials such as graphene, bilayer graphene, and transition metal dichalcogenides have attracted enormous attention. Their exceptional electronic, optical, and mechanical properties, combined with the ability to stack different 2D layers to form artificial solids — known as van der Waals heterostructures — open up unique possibilities for designing systems with tailored quantum-mechanical properties. These materials offer a versatile platform to explore and exploit new quantum effects, potentially enabling innovative device concepts.
The 2D4QT project set out to experimentally assess the potential of graphene-based van der Waals heterostructures for applications in quantum technologies. The project specifically aimed to implement and test theoretical proposals that utilize the spin and valley degrees of freedom in graphene and bilayer graphene for quantum information processing. By confronting theory with experiment, 2D4QT sought to determine whether these 2D material systems can fulfill their promise as quantum platforms or whether they still conceal unexplored phenomena awaiting discovery.
Among the promising candidates, two-dimensional (2D) materials such as graphene, bilayer graphene, and transition metal dichalcogenides have attracted enormous attention. Their exceptional electronic, optical, and mechanical properties, combined with the ability to stack different 2D layers to form artificial solids — known as van der Waals heterostructures — open up unique possibilities for designing systems with tailored quantum-mechanical properties. These materials offer a versatile platform to explore and exploit new quantum effects, potentially enabling innovative device concepts.
The 2D4QT project set out to experimentally assess the potential of graphene-based van der Waals heterostructures for applications in quantum technologies. The project specifically aimed to implement and test theoretical proposals that utilize the spin and valley degrees of freedom in graphene and bilayer graphene for quantum information processing. By confronting theory with experiment, 2D4QT sought to determine whether these 2D material systems can fulfill their promise as quantum platforms or whether they still conceal unexplored phenomena awaiting discovery.
Consistent part of the work performed within the 2D4QT project has focused on the development and experimental investigation of gate-defined quantum dots in bilayer graphene (BLG). Quantum dots are nanoscale solid-state systems capable of confining and manipulating individual electrons, and represent a fundamental building block for spin-based quantum information.
Within 2D4QT, we successfully established a reliable fabrication process for highly tunable bilayer graphene quantum dot devices, enabling full electrostatic control over both charge occupation and tunnel barriers. This technological advance allowed us to realize and study both electron and hole quantum dots — a distinctive capability of bilayer graphene. Using systematic low-temperature quantum transport measurements, we obtained a comprehensive understanding of the single- and two-particle energy spectra in these systems. Furthermore, we demonstrated high-frequency manipulation of quantum dot states, dispersive charge readout, and spin–valley Pauli blockade, essential ingredients for future quantum information applications.
A key achievement of the project has been the discovery that bilayer graphene enables electron–hole double quantum dots with nearly perfect particle–hole symmetry, which allow for a unique single-particle blockade, promising for qubit readout. Another breakthrough was the demonstration of electrostatic tunability of the spin–orbit gap in bilayer graphene/WSe2 heterostructures. In addition, we achieved the first observation of coherent charge oscillations in BLG double quantum dots, demonstrating phase-coherent charge dynamics in a graphene quantum device for the first time. Although the full realization of qubit operation in bilayer graphene has not yet been achieved, the results of 2D4QT represent decisive milestones on the path toward this goal.
Beyond the core scientific results, a significant part of the project was devoted to advancing the technology of complex van der Waals heterostructures. What was once a delicate, craftsmanship-based process has now matured into a more reproducible technology, enabling systematic device optimization.
Within 2D4QT, we successfully established a reliable fabrication process for highly tunable bilayer graphene quantum dot devices, enabling full electrostatic control over both charge occupation and tunnel barriers. This technological advance allowed us to realize and study both electron and hole quantum dots — a distinctive capability of bilayer graphene. Using systematic low-temperature quantum transport measurements, we obtained a comprehensive understanding of the single- and two-particle energy spectra in these systems. Furthermore, we demonstrated high-frequency manipulation of quantum dot states, dispersive charge readout, and spin–valley Pauli blockade, essential ingredients for future quantum information applications.
A key achievement of the project has been the discovery that bilayer graphene enables electron–hole double quantum dots with nearly perfect particle–hole symmetry, which allow for a unique single-particle blockade, promising for qubit readout. Another breakthrough was the demonstration of electrostatic tunability of the spin–orbit gap in bilayer graphene/WSe2 heterostructures. In addition, we achieved the first observation of coherent charge oscillations in BLG double quantum dots, demonstrating phase-coherent charge dynamics in a graphene quantum device for the first time. Although the full realization of qubit operation in bilayer graphene has not yet been achieved, the results of 2D4QT represent decisive milestones on the path toward this goal.
Beyond the core scientific results, a significant part of the project was devoted to advancing the technology of complex van der Waals heterostructures. What was once a delicate, craftsmanship-based process has now matured into a more reproducible technology, enabling systematic device optimization.
The 2D4QT project has helped establish a new research field focused on gate-defined quantum devices based on bilayer graphene. Together with parallel (and competing) efforts at ETH Zürich, the project’s pioneering work has positioned Europe among the leaders in this emerging area, which is now attracting new research groups worldwide.
The results so far confirm that bilayer graphene is a highly promising material for spin qubits and quantum information applications. Although this platform is still less technologically mature than other semiconductor, it might offer long-term advantages — such as reduced disorder effects and the potential for efficient spin–photon coupling, a key step toward scalable quantum computing and communication.
The project also indicated that van der Waals heterostructures based on bilayer graphene can serve not only as hosts for spin and valley qubits with long relaxation times, but also as a platform for developing low-power cryogenic electronics, an essential component of future quantum computers.
From a broader perspective, the major outcome of the project is the technological leap in the fabrication of electrostatically defined nanostructures in high-quality van der Waals heterostructures. This advancement has transformed the assembly of complex bilayer graphene-based devices from an artisanal process into a reproducible technology, paving the way for systematic device optimization.
The methodologies and fabrication techniques developed in 2D4QT will benefit not only quantum technologies, but also a wide range of emerging applications in terahertz electronics, energy harvesting and storage, telecommunications, and ultra-broadband detection, strengthening Europe’s position in the global race for next-generation quantum and electronic materials.
The results so far confirm that bilayer graphene is a highly promising material for spin qubits and quantum information applications. Although this platform is still less technologically mature than other semiconductor, it might offer long-term advantages — such as reduced disorder effects and the potential for efficient spin–photon coupling, a key step toward scalable quantum computing and communication.
The project also indicated that van der Waals heterostructures based on bilayer graphene can serve not only as hosts for spin and valley qubits with long relaxation times, but also as a platform for developing low-power cryogenic electronics, an essential component of future quantum computers.
From a broader perspective, the major outcome of the project is the technological leap in the fabrication of electrostatically defined nanostructures in high-quality van der Waals heterostructures. This advancement has transformed the assembly of complex bilayer graphene-based devices from an artisanal process into a reproducible technology, paving the way for systematic device optimization.
The methodologies and fabrication techniques developed in 2D4QT will benefit not only quantum technologies, but also a wide range of emerging applications in terahertz electronics, energy harvesting and storage, telecommunications, and ultra-broadband detection, strengthening Europe’s position in the global race for next-generation quantum and electronic materials.