Pablo Jarillo-Herrero

An All-van-der-Waals Qubit

  1. Sein Park,
  2. Sameia Zaman,
  3. Junghyun Kim,
  4. Junyoung An,
  5. Daniel Rodan-Legrain,
  6. Hung-Yu Tsao,
  7. Chia-Chin Tsai,
  8. Aranya Goswami,
  9. Réouven Assouly,
  10. William P. Banner,
  11. Gabriel D. Cutter,
  12. Kenji Watanabe,
  13. Takashi Taniguchi,
  14. Terry P. Orlando,
  15. Gil-Ho Lee,
  16. Kyle Serniak,
  17. Max Hays,
  18. Jeffrey A. Grover,
  19. Philip Kim,
  20. Pablo Jarillo-Herrero,
  21. Joel I.J. Wang,
  22. and William D. Oliver
Advances in solid-state physics, materials science, and device engineering have accelerated the development of superconducting qubits. Among emerging platforms, van der Waals (vdW)
materials and their heterostructures are potentially attractive building blocks for quantum devices, yet their realization in qubit architectures remains largely underexplored. Here we report an all-vdW superconducting qubit based on a NbSe2-hBN-NbSe2 junction, in which a thin hBN layer simultaneously provides Josephson coupling and capacitive shunting between two NbSe2 islands, forming a „merged-element“ transmon. Temporal characterization using circuit quantum electrodynamics (cQED) techniques yields an average energy-relaxation time T1,avg=55 μs, Hahn-echo coherence time T2E,avg=21 μs, and Ramsey coherence time T2R,avg=1.9 μs. The relatively low Ramsey time is primarily attributable to an enhanced sensitivity to charge noise consistent with the realized device parameters and not a fundamental limitation. These results show that lumped-element superconducting qubits based on vdW heterostructures can achieve coherence times comparable to those of conventional Al-AlOx-Al qubits, while offering a reduced device footprint and suppressed stray capacitive coupling.
arxiv pdf

Hexagonal Boron Nitride (hBN) as a Low-loss Dielectric for Superconducting Quantum Circuits and Qubits

  1. Joel I.J. Wang,
  2. Megan A. Yamoah,
  3. Qing Li,
  4. Amir Karamlou,
  5. Thao Dinh,
  6. Bharath Kannan,
  7. Jochen Braumüller,
  8. David Kim,
  9. Alexander J. Melville,
  10. Sarah E. Muschinske,
  11. Bethany M. Niedzielski,
  12. Kyle Serniak,
  13. Youngkyu Sung,
  14. Roni Winik,
  15. Jonilyn L. Yoder,
  16. Mollie Schwartz,
  17. Kenji Watanabe,
  18. Takashi Taniguchi,
  19. Terry P. Orlando,
  20. Simon Gustavsson,
  21. Pablo Jarillo-Herrero,
  22. and William D. Oliver
Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. We study the dielectric loss of hexagonal boron nitride
(hBN) thin films in the microwave regime by measuring the quality factor of parallel-plate capacitors (PPCs) made of NbSe2-hBN-NbSe2 heterostructures integrated into superconducting circuits. The extracted microwave loss tangent of hBN is bounded to be at most in the mid-10-6 range in the low temperature, single-photon regime. We integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits with coherence times reaching 25 μs, consistent with the hBN loss tangent inferred from resonator measurements. The hBN PPC reduces the qubit feature size by approximately two-orders of magnitude compared to conventional all-aluminum coplanar transmons. Our results establish hBN as a promising dielectric for building high-coherence quantum circuits with substantially reduced footprint and, with a high energy participation that helps to reduce unwanted qubit cross-talk.
arxiv pdf