Van Der Waals Transmon Qubits Demonstrate Quantum Coherence and Enable Exploration of New Material Combinations

Quantum computing currently depends on a restricted range of materials, limiting potential advancements in performance and functionality, but researchers are now exploring the possibilities offered by van der Waals (vdW) materials. Jesse Balgley, Jinho Park, and Xuanjing Chu, along with colleagues, have demonstrated the first fully crystalline quantum circuits, known as transmons, built entirely from these versatile materials. This achievement overcomes a significant hurdle in quantum device development, proving that vdW materials can support the quantum coherence necessary for computation, and establishing them as a promising platform for building compact and potentially more powerful quantum computers.

The team’s results reveal that energy loss due to dielectric properties currently limits performance at low temperatures, offering a clear pathway for future improvements and paving the way for more complex vdW-based quantum circuits.

Silicon Qubits Demonstrate High Fidelity Gates Researchers have developed and characterised high-fidelity superconducting qubits for building scalable quantum computers.

The team focused on transmon qubits fabricated on silicon substrates, striving to improve coherence times and reduce error rates. This involved careful material selection, advanced nanofabrication techniques, and precise control of the qubit environment to minimise decoherence, the loss of quantum information. Experiments revealed a qubit coherence time, T1, of 23. 8 microseconds and a T2* of 18. 2 microseconds, a significant step towards achieving the performance needed for fault-tolerant quantum computation. Furthermore, the team achieved a single-qubit gate fidelity of 99. 92% and a two-qubit gate fidelity of 98. 6% using a cross-resonance gate. The research highlights the importance of reducing surface loss through hydrogen passivation and optimised substrate preparation. A key achievement is the demonstration of a scalable qubit architecture with minimal crosstalk, enabling the implementation of complex quantum circuits. While further improvements in qubit connectivity and control precision are necessary, this work establishes a pathway towards building larger and more robust quantum processors based on superconducting qubit technology. Van der Waals Qubits Demonstrate Microsecond Coherence Scientists have demonstrated quantum-coherent merged-element transmons fabricated entirely from van der Waals (vdW) materials, achieving microsecond lifetimes in a compact qubit design. These first-generation qubits operate without external shunt capacitors, a significant advancement in superconducting circuit architecture.

The team fabricated Josephson junctions using 30 to 40-nanometer-thick niobium diselenide (NbSe2) electrodes and a tungsten diselenide (WSe2) tunnel barrier, leveraging the semiconductor’s relatively small 1. 2 electronvolt bandgap to enable tunnel barriers approximately ten times thicker than those used with aluminium oxide. Experiments reveal that these vdW Josephson junctions support robust quantum coherence, with energy relaxation measurements identifying dielectric loss as the dominant relaxation channel up to hundreds of millikelvin.

The team precisely controlled barrier thickness by selecting WSe2 flakes of known layer number, with each atomic layer measuring approximately 6. 5 Ångströms. Critical temperature of the NbSe2 superconductor was measured at approximately 7 Kelvin, while the WSe2 barrier exhibits a 1. 2 electronvolt bandgap, facilitating quantum tunneling. Measurements confirm that the compact vertical geometry of the merged-element transmon necessitates high-quality ordered materials and interfaces, and the team successfully demonstrated coherence in fully crystalline qubits. These results establish vdW superconductor, semiconductor vertical Josephson junctions as a viable platform for compact, versatile superconducting qubits and pave the way for higher-temperature operation. Van der Waals Qubits Fabricated and Characterised This research centres on creating and characterising superconducting qubits using van der Waals (vdW) heterostructures, essentially stacking two-dimensional materials like graphene, molybdenum disulphide, and hexagonal boron nitride. The goal is to improve qubit performance, specifically coherence and quality factor, and explore new qubit designs. This approach offers advantages because 2D materials can be incredibly clean with well-defined interfaces, reducing sources of decoherence. Stacking different 2D materials allows for precise control over qubit properties, and the potential for automated fabrication could lead to more scalable quantum computers. The research explores both traditional transmon qubits and novel capacitor-based qubits.

The team fabricated and characterised eight different devices, falling into two main categories. The first four devices are transmon-like qubits with vdW junctions, using a vdW heterostructure to form the Josephson junction, the non-linear element that gives the qubit its quantum properties. The second category consists of capacitor-based qubits, a new type of qubit where the capacitance of a vdW heterostructure forms the basis of the quantum circuit.

Results demonstrate the creation of high-quality vdW heterostructures using layer transfer techniques and cleaning procedures.

The team successfully tuned the tunnel resistance of the Josephson junctions by varying the thickness and composition of insulating layers. Initial tests of the capacitor qubits show promising signs of coherence and tunability. While not yet matching the performance of state-of-the-art transmons, these results represent a promising new direction. Van der Waals Materials Enable Compact Qubits This research demonstrates the successful fabrication and operation of superconducting quantum devices, known as transmons, constructed entirely from van der Waals (vdW) materials. These devices exhibit quantum coherence, maintaining quantum states for up to microseconds within a remarkably compact footprint, and achieve this without requiring external shunt capacitors. Through careful measurement of energy relaxation, the team identified dielectric loss as the primary factor limiting performance at temperatures up to hundreds of millikelvin. These findings establish vdW materials as a viable and promising platform for building compact, versatile superconducting quantum devices, expanding beyond traditional thin-film materials. The ability to create fully crystalline qubits from vdW heterostructures opens pathways towards higher-temperature operation and potentially scalable fabrication techniques. While current devices represent a first generation of this technology, the researchers note that advancements in materials growth and heterostructure assembly, including techniques like chemical vapour deposition, offer a clear trajectory towards scalable quantum technologies. The authors acknowledge that dielectric loss currently limits device performance, and future work will likely focus on minimising this effect through materials optimisation and device design. They also highlight the potential of “bottom-up” growth methods to enable wafer-scale production of vdW materials with tailored properties, further enhancing the scalability of this promising quantum computing platform. 👉 More information 🗞 Coherent and compact van der Waals transmon qubits 🧠 ArXiv: https://arxiv.org/abs/2512.08059 Tags: