Quantum Devices Group

1. Taking the heat off tantalum

   T. G. Ahn, A. Sipahigil

   Nature Materials (2026) News & Views

   DOI BibTeX

   @article{ahn_taking_2026,
     title = {Taking the heat off tantalum},
     url = {https://www.nature.com/articles/s41563-026-02766-5},
     doi = {10.1038/s41563-026-02766-5},
     journal = {Nature Materials},
     issn = {1476-1122, 1476-4660},
     author = {Ahn, Tae Gyu and Sipahigil, Alp},
     month = oct,
     year = {2026}
   }
   

2. Resolving and resetting the charge environment of single T-centers in silicon p-i-n waveguides

   C. Zhang, H. Song, L. Komza, A. M. Day, E. Garcia, D. Witt, M. K. Bhaskar, A. Sipahigil, E. L. Hu

   arXiv:2608.15993 (2026)

   arXiv BibTeX Abstract

   @unpublished{zhang_resolving_2026,
     title = {Resolving and resetting the charge environment of single T-centers in silicon p-i-n waveguides},
     url = {https://arxiv.org/abs/2608.15993},
     doi = {10.48550/ARXIV.2608.15993},
     author = {Zhang, Chaoshen and Song, Hanbin and Komza, Lukasz and Day, Aaron M. and Garcia, Enrique and Witt, Donald and Bhaskar, Mihir K. and Sipahigil, Alp and Hu, Evelyn L.},
     month = aug,
     year = {2026},
     note = {Version Number: 1},
     arxiv = {2608.15993}
   }
   

   The silicon T-center is a telecom-band spin-photon interface in a manufacturable photonics platform. In nanophotonic devices, however, its optical linewidth is broadened by a fluctuating charge environment, limiting photon indistinguishability for quantum networking. Here, we address this challenge through characterization and suppression of the local charge-noise of single T-centers in lateral p-i-n waveguides, demonstrating an unheralded method of T-center optical linewidth narrowing. Above-band illumination resets the charge environment, neutralizing the local field and suppressing spectral diffusion. Across 46 emitters this reset narrows the median linewidth 3.5-fold to 0.57(11) GHz, and an optimized emitter reaches 128(22) MHz, the narrowest unheralded linewidth reported for an integrated T-center. The narrowed transition supports coherent optical Rabi oscillations with a coherence time of 20(2) ns. Finally, we perform Stark-shift tuning using the p-i-n junction, and read out the local electric field and the charge-noise width at 15 mK. An analytical model of proximal surfaces, bulk, and junction field effects provides good agreement with our findings. Our multi-pronged characterization of the nanophotonic-integrated T-center charge environment enables future device optimization toward scalable quantum interconnects.

3. Point defects in semiconductors: Friends and foes for quantum technologies

   Y. Zhu, Z.-H. Zhang, W. Chen, M. A. Sakib, A. Weber-Bargioni, S. Griffin, A. Raja, A. Sipahigil, G. Hautier

   MRS Bulletin 51, 615–629 (2026)

   DOI BibTeX Abstract

   @article{zhu_point_2026,
     title = {Point defects in semiconductors: {Friends} and foes for quantum technologies},
     volume = {51},
     url = {https://link.springer.com/10.1557/s43577-026-01095-x},
     doi = {10.1557/s43577-026-01095-x},
     journal = {MRS Bulletin},
     number = {5},
     pages = {615--629},
     issn = {0883-7694, 1938-1425},
     author = {Zhu, Yizhi and Zhang, Zi-Huai and Chen, Weiru and Sakib, Mashnoon Alam and Weber-Bargioni, Alexander and Griffin, Sinéad and Raja, Archana and Sipahigil, Alp and Hautier, Geoffroy},
     month = may,
     year = {2026}
   }
   

   Point defects in semiconductors are both a curse and a blessing in microelectronics: they enable the control of electrical conductivity through doping, yet can also act as trapping and recombination centers that degrade device performance. In quantum information science, defects play a similarly dual role. They can be harnessed as spin–photon interfaces enabling the coupling of electronic and nuclear spins to light and the creation of distributed entanglement for quantum networks or used as atomistic scale sensors for quantum sensing. At the same time, defects are a major source of decoherence for superconducting qubits, one of the leading quantum computing platforms. This article discusses how a deeper materials-level understanding of defects can guide the design of improved quantum devices for communication, sensing, and computation.

4. Interface Piezoelectric Loss in Superconducting Qubits

   H. Zhou*, K. Yu*, Y. Balaji, S. Shirol, L. Sementilli, Z.-H. Zhang, A. Schwartzberg, A. Sipahigil

   arXiv:2605.15554 (2026)

   arXiv BibTeX Abstract

   @unpublished{zhou_interface_2026,
     title = {Interface {Piezoelectric} {Loss} in {Superconducting} {Qubits}},
     url = {http://arxiv.org/abs/2605.15554},
     doi = {10.48550/arXiv.2605.15554},
     author = {Zhou, Haoxin and Yu, Kangdi and Balaji, Yashwanth and Shirol, Sanjit and Sementilli, Leo and Zhang, Zi-Huai and Schwartzberg, Adam and Sipahigil, Alp},
     month = may,
     year = {2026},
     note = {arXiv:2605.15554 [quant-ph]},
     arxiv = {2605.15554}
   }
   

   Dissipation remains a central obstacle to improving superconducting quantum circuits, yet the microscopic origins of loss in widely used materials platforms are not fully understood. Here, we report the observation of interface piezoelectricity-induced dissipation in superconducting qubits fabricated on high-resistivity silicon. Our devices use a transmon qubit with a shunt capacitor that simultaneously serves as an interdigital transducer embedded in a surface acoustic wave resonator. By tuning the qubit transition into resonance with discrete mechanical modes, we observe up to a factor-of-two reduction in qubit lifetime, consistent with energy exchange between the qubit and mechanical modes mediated by piezoelectric coupling at the aluminum-silicon interface. Our findings provide direct evidence for interface piezoelectricity as a distinct loss channel in superconducting qubits. Combined with multiphysics simulations, these findings suggest that interface piezoelectric loss can dominate over loss from two-level systems at sufficiently high frequencies.

* Equal contribution