Niccolo Fiaschi

Former Postdoc · 2024-2025

Next: Arq Quantum Technologies

Group publications 2

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Entanglement of a nuclear spin qubit register in silicon photonics

H. Song, X. Zhang, L. Komza, N. Fiaschi, Y. Xiong, Y. Zhi, S. Dhuey, A. Schwartzberg, T. Schenkel, G. Hautier, Z.-H. Zhang, A. Sipahigil

Nature Nanotechnology 21, 53–57 (2026)

DOI arXiv News & Views
```
@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.
Laser-Induced Spectral Diffusion of T Centers in Silicon Nanophotonic Devices

X. Zhang, N. Fiaschi, L. Komza, H. Song, T. Schenkel, A. Sipahigil

PRX Quantum 6, 030351 (2025)

DOI arXiv
```
@article{zhang_laser-induced_2025,
  title = {Laser-{Induced} {Spectral} {Diffusion} of T {Centers} in {Silicon} {Nanophotonic} {Devices}},
  volume = {6},
  url = {https://doi.org/10.1103/x2cv-2gcw},
  doi = {10.1103/x2cv-2gcw},
  journal = {PRX Quantum},
  pages = {030351},
  author = {Zhang, X. and Fiaschi, N. and Komza, L. and Song, H. and Schenkel, T. and Sipahigil, A.},
  year = {2025},
  arxiv = {2504.08898}
}
```
Color centers in silicon are emerging as spin-photon interfaces operating at telecommunication wavelengths. The nanophotonic device integration of silicon color centers via ion implantation leads to significant optical-linewidth broadening, which makes indistinguishable photon generation challenging. Here, we study the optical spectral diffusion of T centers in a silicon photonic crystal cavity. We investigate the linewidth-broadening timescales and origins by measuring the temporal correlations of the resonance frequency under different conditions. Spectral hole-burning measurements reveal no spectral broadening at short timescales from 102 ns to 725 ns. We probe broadening at longer timescales using a check pulse to herald the T-center frequency and a probe pulse to measure the frequency after a wait time. The optical resonance frequency is stable up to 3 ms in the dark. Laser pulses below the silicon band gap applied during the wait time lead to linewidth broadening. Our observations establish laser-induced processes as the dominant spectral-diffusion mechanism for T centers in devices and inform materials and feedback strategies for indistinguishable photon generation.