Group publications 7
-
MRS Bulletin 51, 615–629 (2026)
@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.
-
arXiv:2605.15554 (2026)
@unpublished{zhou_interface_2026, title = {Interface {Piezoelectric} {Loss} in {Superconducting} {Qubits}}, url = {http://arxiv.org/abs/2605.15554}, doi =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.
-
Nature Nanotechnology 21, 53–57 (2026)
@article{song_entanglement_2026, title = {Entanglement of a nuclear spin qubit register in silicon photonics}, volume = {21}, url = {https://doi.org/10.1038/s41565-025-02066-0}, doi = {10.1038/s41565-025-02066-0}, journal = {Nature Nanotechnology}, pages = {53--57}, author = {Song, H. and Zhang, X. and Komza, L. and Fiaschi, N. and Xiong, Y. and Zhi, Y. and Dhuey, S. and Schwartzberg, A. and Schenkel, T. and Hautier, G. and Zhang, Z.-H. and Sipahigil, A.}, month = jan, year = {2026}, arxiv = {2504.15467} }Color centers provide an optical interface to quantum registers based on electron and nuclear spin qubits in solids. The T center in silicon is an emerging spin-photon interface that combines telecom O-band optical transitions and an electron spin in a scalable photonics platform. In this work, we demonstrate the initialization, coherent control, and state readout of a three-qubit register based on the electron spin of a T center coupled to a hydrogen and a silicon nuclear spin. The spin register exhibits spin echo coherence times of 0.41(2) ms for the electron spin, 112(12) ms for the hydrogen nuclear spin, and 67(7) ms for the silicon nuclear spin. We use nuclear-nuclear two-qubit gates to generate entanglement between the two nuclear spins with a fidelity of F=0.77(3) and a coherence time of T*₂=2.60(8) ms. Our results show that a T center in silicon photonics can realize a multi-qubit register with an optical interface for quantum communication.
-
Nature Communications 17, 377 (2026)
@article{zhou_observation_2026, title = {Observation of interface piezoelectricity in superconducting devices on silicon}, volume = {17}, url = {https://doi.org/10.1038/s41467-025-67066-z}, doi = {10.1038/s41467-025-67066-z}, journal = {Nature Communications}, pages = {377}, author = {Zhou, H. and Li, E. and Godeneli, K. and Zhang, Z.-H. and Jahanbani, S. and Yu, K. and Odeh, M. and Aloni, S. and Griffin, S. and Sipahigil, A.}, year = {2026}, arxiv = {2409.10626} }The development of superconducting quantum processors relies on understanding and mitigating decoherence in superconducting qubits. Piezoelectric coupling contributes to decoherence by mediating energy exchange between microwave photons and acoustic phonons. Although bulk centrosymmetric materials like silicon and sapphire are non-piezoelectric and commonly used as qubit substrates, the lack of centrosymmetry at interfaces may induce piezoelectric losses. This effect was predicted decades ago but never experimentally observed in superconducting devices. Here, we report interface piezoelectricity at aluminum-silicon junctions and demonstrate it as a significant loss channel in superconducting devices. Using aluminum interdigital transducers on silicon, we observe piezoelectric transduction from room to millikelvin temperatures, with an effective electromechanical coupling factor K 2 ≈ (3 ± 0.4) × 10 −5 %, comparable to weakly piezoelectric substrates. Modeling shows this mechanism limits qubit quality factors to Q 10 4 − 10 8 , depending on surface participation and mode matching. These findings reveal interface piezoelectricity as a major dissipation channel and highlight the need for heterostructure and phononic engineering in next-generation superconducting qubits.
-
Nature Physics 21, 406–411 (2025)
@article{odeh_non-markovian_2025, title = {Non-{Markovian} dynamics of a superconducting qubit in a phononic bandgap}, volume = {21}, url = {https://www.nature.com/articles/s41567-024-02740-5}, doi = {10.1038/s41567-024-02740-5}, journal = {Nature Physics}, number = {3}, pages = {406--411}, issn = {1745-2473, 1745-2481}, author = {Odeh, Mutasem and Godeneli, Kadircan and Li, Eric and Tangirala, Rohin and Zhou, Haoxin and Zhang, Xueyue and Zhang, Zi-Huai and Sipahigil, Alp}, month = mar, year = {2025}, arxiv = {2312.01031} }The overhead to construct a logical qubit from physical qubits rapidly increases with the decoherence rate. Current superconducting qubits reduce dissipation due to two-level systems (TLSs) by using large device footprints. However, this approach provides partial protection, and results in a trade-off between qubit footprint and dissipation. This work introduces a new platform using phononics to engineer superconducting qubit-TLS interactions. We realize a superconducting qubit on a phononic bandgap metamaterial that suppresses TLS-mediated phonon emission. We use the qubit to probe its thermalization dynamics with the phonon-engineered TLS bath. Inside the phononic bandgap, we observe the emergence of non-Markovian qubit dynamics due to the Purcell-engineered TLS lifetime of 34 μs. We discuss the implications of these observations for extending qubit relaxation times through simultaneous phonon protection and miniaturization.
-
Physical Review X 14, 041022 (2024)
@article{zhang_acceptor-induced_2024, title = {Acceptor-{Induced} {Bulk} {Dielectric} {Loss} in {Superconducting} {Circuits} on {Silicon}}, volume = {14}, url = {https://link.aps.org/doi/10.1103/PhysRevX.14.041022}, doi = {10.1103/PhysRevX.14.041022}, journal = {Physical Review X}, number = {4}, pages = {041022}, issn = {2160-3308}, author = {Zhang, Zi-Huai and Godeneli, Kadircan and He, Justin and Odeh, Mutasem and Zhou, Haoxin and Meesala, Srujan and Sipahigil, Alp}, month = oct, year = {2024}, arxiv = {2402.17155} }The performance of superconducting quantum circuits is primarily limited by dielectric loss due to interactions with two-level systems (TLSs). State-of-the-art circuits with engineered material interfaces are approaching a limit where dielectric loss from bulk substrates plays an important role. However, a microscopic understanding of dielectric loss in crystalline substrates is still lacking. In this work, we show that boron acceptors in silicon constitute a TLS bath that leads to an energy dissipation channel for superconducting circuits. We discuss how the electronic structure of boron acceptors leads to an effective TLS response in silicon. We sweep the boron concentration in silicon and demonstrate the bulk dielectric loss limit from boron acceptors. We show that boron-induced dielectric loss can be reduced in a magnetic field due to the spin-orbit structure of boron. This work provides the first detailed microscopic description of a TLS bath for superconducting circuits and demonstrates the need for ultrahigh-purity substrates for next-generation superconducting quantum processors. Published by the American Physical Society 2024
-
arXiv:2407.15387 (2024)
@unpublished{jahanbani_nanomechanical_2024, title = {A {Nanomechanical} {Atomic} {Force} {Qubit}}, url = {http://arxiv.org/abs/2407.15387}, doi = {10.48550/arXiv.2407.15387}, author = {Jahanbani, Shahin and Zhang, Zi-Huai and Hua, Binhan and Godeneli, Kadircan and Müllendorff, Boris and Zhang, Xueyue and Zhou, Haoxin and Sipahigil, Alp}, month = jul, year = {2024}, note = {arXiv:2407.15387 [quant-ph]}, arxiv = {2407.15387} }Silicon nanomechanical resonators display ultra-long lifetimes at cryogenic temperatures and microwave frequencies. Achieving quantum control of single-phonons in these devices has so far relied on nonlinearities enabled by coupling to ancillary qubits. In this work, we propose using atomic forces to realize a silicon nanomechanical qubit without coupling to an ancillary qubit. The proposed qubit operates at 60 MHz with a single-phonon level anharmonicity of 5 MHz. We present a circuit quantum acoustodynamics architecture where electromechanical resonators enable dispersive state readout and multi-qubit operations. The combination of strong anharmonicity, ultrahigh mechanical quality factors, and small footprints achievable in this platform could enable quantum-nonlinear phononics for quantum information processing and transduction.
* Equal contribution