Publications

Group member

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2026

Nature Materials (2026) News & Views

DOI

@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}
}

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
```
@unpublished{zhang_resolving_2026,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.
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
```
@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.
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
```
@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.
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.
Observation of interface piezoelectricity in superconducting devices on silicon

H. Zhou, E. Li, K. Godeneli, Z.-H. Zhang, S. Jahanbani, K. Yu, M. Odeh, S. Aloni, S. Griffin, A. Sipahigil

Nature Communications 17, 377 (2026)

DOI arXiv
```
@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.

2025

Multiplexed color centers in a silicon photonic cavity array

L. Komza, X. Zhang, H. Song, Y.-L. Tang, X. Wei, A. Sipahigil

Optica 12, 1400 (2025)

DOI arXiv
```
@article{komza_multiplexed_2025,
  title = {Multiplexed color centers in a silicon photonic cavity array},
  volume = {12},
  url = {https://opg.optica.org/abstract.cfm?URI=optica-12-9-1400},
  doi = {10.1364/OPTICA.564691},
  journal = {Optica},
  number = {9},
  pages = {1400},
  issn = {2334-2536},
  author = {Komza, Lukasz and Zhang, Xueyue and Song, Hanbin and Tang, Yu-Lung and Wei, Xin and Sipahigil, Alp},
  month = sep,
  year = {2025},
  arxiv = {2501.17339}
}
```
Entanglement distribution is central to the modular scaling of quantum processors and establishing quantum networks. Color centers with telecom-band transitions and long spin coherence times are suitable candidates for long-distance entanglement distribution. However, high-bandwidth memory-enhanced quantum communication is limited by high-yield, scalable creation of efficient spin-photon interfaces. Here, we develop a silicon photonics platform consisting of arrays of bus-coupled cavities. The coupling to a common bus waveguide enables simultaneous access to individually addressable cavity-enhanced T center arrays. We demonstrate frequency-multiplexed operation of two T centers in separate photonic crystal cavities. In addition, we investigate the cavity enhancement of a T center through hybridized modes formed between physically distant cavities. Our results show that bus-coupled arrays of cavity-enhanced color centers could enable efficient on-chip and long-distance entanglement distribution.
Non-Markovian dynamics of a superconducting qubit in a phononic bandgap

M. Odeh, K. Godeneli, E. Li, R. Tangirala, H. Zhou, X. Zhang, Z.-H. Zhang, A. Sipahigil

Nature Physics 21, 406–411 (2025)

DOI arXiv News & Views
```
@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.
Probing negative differential resistance in silicon with a P-I-N diode-integrated T center ensemble

A. M. Day, C. Zhang, C. Jin, H. Song, M. Sutula, A. Sipahigil, M. K. Bhaskar, E. L. Hu

arXiv:2501.11888 (2025)

arXiv
```
@unpublished{day_probing_2025,
  title = {Probing negative differential resistance in silicon with a P-I-N diode-integrated T center ensemble},
  url = {http://arxiv.org/abs/2501.11888},
  doi = {10.48550/arXiv.2501.11888},
  author = {Day, Aaron M. and Zhang, Chaoshen and Jin, Chang and Song, Hanbin and Sutula, Madison and Sipahigil, Alp and Bhaskar, Mihir K. and Hu, Evelyn L.},
  month = jan,
  year = {2025},
  note = {arXiv:2501.11888 [quant-ph]},
  arxiv = {2501.11888}
}
```
The T center in silicon has recently emerged as a promising candidate for scalable quantum technologies, due to its telecommunications band optical transition and microwave addressable ground state spin. The immense promise of the T center is driven by its silicon host material; silicon is by far the most mature, manufacturable semiconductor material for integrated photonic and electronic devices. Here, we present the first study of T-centers in an electrical device. We study an ensemble of T centers coupled to a buried lateral P-I-N diode in silicon, observing the T-center’s optical response to static and dynamic electric fields. We utilize the defect’s optical response as a probe of device nonlinearity, observing a phase transition of the carrier density into a stable oscillatory regime characteristic of negative differential resistance. These findings provide fundamental insight into the physics of the T-center for improved quantum device performance and open a promising new direction for defect-based local quantum sensing in semiconductor devices.
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.

2024

Acceptor-Induced Bulk Dielectric Loss in Superconducting Circuits on Silicon

Z.-H. Zhang*, K. Godeneli*, J. He, M. Odeh, H. Zhou, S. Meesala, A. Sipahigil

Physical Review X 14, 041022 (2024)

DOI arXiv
```
@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
Indistinguishable photons from an artificial atom in silicon photonics

L. Komza*, P. Samutpraphoot*, M. Odeh, Y.-L. Tang, M. Mathew, J. Chang, H. Song, M.-K. Kim, Y. Xiong, G. Hautier, A. Sipahigil

Nature Communications 15, 6920 (2024)

DOI arXiv
```
@article{komza_indistinguishable_2024,
  title = {Indistinguishable photons from an artificial atom in silicon photonics},
  volume = {15},
  url = {https://www.nature.com/articles/s41467-024-51265-1},
  doi = {10.1038/s41467-024-51265-1},
  journal = {Nature Communications},
  number = {1},
  pages = {6920},
  issn = {2041-1723},
  author = {Komza, Lukasz and Samutpraphoot, Polnop and Odeh, Mutasem and Tang, Yu-Lung and Mathew, Milena and Chang, Jiu and Song, Hanbin and Kim, Myung-Ki and Xiong, Yihuang and Hautier, Geoffroy and Sipahigil, Alp},
  month = aug,
  year = {2024},
  arxiv = {2211.09305}
}
```
Abstract Silicon is the ideal material for building electronic and photonic circuits at scale. Integrated photonic quantum technologies in silicon offer a promising path to scaling by leveraging advanced semiconductor manufacturing and integration capabilities. However, the lack of deterministic quantum light sources and strong photon-photon interactions in silicon poses a challenge to scalability. In this work, we demonstrate an indistinguishable photon source in silicon photonics based on an artificial atom. We show that a G center in a silicon waveguide can generate high-purity telecom-band single photons. We perform high-resolution spectroscopy and time-delayed two-photon interference to demonstrate the indistinguishability of single photons emitted from a G center in a silicon waveguide. Our results show that artificial atoms in silicon photonics can source single photons suitable for photonic quantum networks and processors.
A Nanomechanical Atomic Force Qubit

S. Jahanbani, Z.-H. Zhang, B. Hua, K. Godeneli, B. Müllendorff, X. Zhang, H. Zhou, A. Sipahigil

arXiv:2407.15387 (2024)

arXiv
```
@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.
Midgap state requirements for optically active quantum defects

Y. Xiong, M. Mathew, S. M. Griffin, A. Sipahigil, G. Hautier

Materials for Quantum Technology 4, 013001 (2024)

DOI arXiv
```
@article{xiong_midgap_2024,
  title = {Midgap state requirements for optically active quantum defects},
  volume = {4},
  url = {https://doi.org/10.1088/2633-4356/ad1d38},
  doi = {10.1088/2633-4356/ad1d38},
  journal = {Materials for Quantum Technology},
  pages = {013001},
  author = {Xiong, Y. and Mathew, M. and Griffin, S. M. and Sipahigil, A. and Hautier, G.},
  month = jan,
  year = {2024},
  arxiv = {2302.10767}
}
```
Optically active quantum defects play an important role in quantum sensing, computing and communication. The electronic structure and the single-particle energy levels of these quantum defects in the semiconducting host have been used to understand their optoelectronic properties. Optical excitations that are central for their initialization and readout are linked to transitions between occupied and unoccupied single-particle states. It is commonly assumed that only quantum defects introducing levels well within the band gap and far from the band edges are of interest for quantum technologies as they mimic an isolated atom embedded in the host. In this perspective, we contradict this common assumption and show that optically active defects with energy levels close to the band edges can display similar properties. We highlight quantum defects that are excited through transitions to or from a band-like level (bound exciton) such as the T center and Se S i + in silicon. We also present how defects such as the silicon split-vacancy in diamond can involve transitions between localized levels that are above the conduction band or below the valence band. Loosening the commonly assumed requirement on the electronic structure of quantum defects offers opportunities in quantum defects design and discovery especially in smaller band gap hosts such as silicon. We discuss the challenges in terms of operating temperature for photoluminescence or radiative lifetime in this regime. We also highlight how these alternative type of defects bring their own needs in terms of theoretical developments and fundamental understanding. This perspective clarifies the electronic structure requirement for quantum defects and will facilitate the identification and design of new color centers for quantum applications especially driven by first principles computations.
Toward high-fidelity quantum information processing and quantum simulation with spin qubits and phonons

I. Arrazola, Y. Minoguchi, M.-A. Lemonde, A. Sipahigil, P. Rabl

Physical Review B 110, 045419 (2024)

DOI arXiv
```
@article{arrazola_toward_2024,
  title = {Toward high-fidelity quantum information processing and quantum simulation with spin qubits and phonons},
  volume = {110},
  url = {https://doi.org/10.1103/PhysRevB.110.045419},
  doi = {10.1103/PhysRevB.110.045419},
  journal = {Physical Review B},
  pages = {045419},
  author = {Arrazola, I. and Minoguchi, Y. and Lemonde, M.-A. and Sipahigil, A. and Rabl, P.},
  year = {2024},
  arxiv = {2402.16960}
}
```
We analyze the implementation of high-fidelity, phonon-mediated gate operations and quantum simulation schemes for spin qubits associated with silicon vacancy centers in diamond. Specifically, we show how the application of continuous dynamical decoupling techniques can substantially boost the coherence of the qubit states while increasing at the same time the variety of effective spin models that can be implemented in this way. Based on realistic models and detailed numerical simulations, we demonstrate that this decoupling technique can suppress gate errors by more than two orders of magnitude and enable gate infidelities below 10⁻⁴ for experimentally relevant noise parameters. Therefore, when generalized to phononic lattices with arrays of implanted defect centers, this approach offers a realistic path toward moderate- and large-scale quantum devices with spins and phonons, at a level of control that is competitive with other leading quantum-technology platforms.
Compressive-Sensing-Enhanced First-Principles Calculation of Photoluminescence Spectra in Color Centers: A Comparison between Theory and Experiment for the G Center in Silicon

J. Zheng, L. Komza, Y. Xiong, N. Sheremetyeva, C. Lin, S. M. Griffin, A. Sipahigil, G. Hautier

arXiv:2402.08067 (2024)

arXiv
```
@unpublished{zheng_compressive-sensing-enhanced_2024,
  title = {Compressive-{Sensing}-{Enhanced} {First}-{Principles} {Calculation} of {Photoluminescence} {Spectra} in {Color} {Centers}: A {Comparison} between {Theory} and {Experiment} for the G {Center} in {Silicon}},
  url = {https://arxiv.org/abs/2402.08067},
  doi = {10.48550/ARXIV.2402.08067},
  author = {Zheng, Jiongzhi and Komza, Lukasz and Xiong, Yihuang and Sheremetyeva, Natalya and Lin, Changpeng and Griffin, Sinéad M. and Sipahigil, Alp and Hautier, Geoffroy},
  year = {2024},
  note = {Version Number: 2},
  arxiv = {2402.08067}
}
```
Photoluminescence (PL) spectra are a versatile tool for exploring the electronic and optical properties of quantum defect systems. In this work, we investigate the PL spectra of the G center in silicon by combining first-principles computations with a machine-learned compressive-sensing technique and experiment. We show that the compressive-sensing technique provides a speed up of approximately 20 times compared with the finite-displacement method with similar numerical accuracy. We compare theory and experiment and show good agreement for the historically proposed configuration B of the G center. In particular, we attribute the experimentally observed E-line of the G center to a local vibration mode mainly involving two substitutional C atoms and one interstitial Si atom. Our theoretical results also well reproduce and explain the experimental E-line energy shifts originating from the carbon isotopic effect. In addition, our results demonstrate that some highly anharmonic modes that are apparent in computed spectra could be absent experimentally because of their short lifetime. Our work not only provides a deeper understanding of the G-center defect but also paves the way to accelerate the calculation of PL spectra for color centers.

2023

High-throughput identification of spin-photon interfaces in silicon

Y. Xiong, C. Bourgois, N. Sheremetyeva, W. Chen, D. Dahliah, H. Song, J. Zheng, S. M. Griffin, A. Sipahigil, G. Hautier

Science Advances 9, eadh8617 (2023)

DOI arXiv
```
@article{xiong_high-throughput_2023,
  title = {High-throughput identification of spin-photon interfaces in silicon},
  volume = {9},
  url = {https://www.science.org/doi/10.1126/sciadv.adh8617},
  doi = {10.1126/sciadv.adh8617},
  journal = {Science Advances},
  number = {40},
  pages = {eadh8617},
  issn = {2375-2548},
  author = {Xiong, Yihuang and Bourgois, Céline and Sheremetyeva, Natalya and Chen, Wei and Dahliah, Diana and Song, Hanbin and Zheng, Jiongzhi and Griffin, Sinéad M. and Sipahigil, Alp and Hautier, Geoffroy},
  month = oct,
  year = {2023},
  arxiv = {2303.01594}
}
```
Color centers in host semiconductors are prime candidates as spin-photon interfaces for quantum applications. Finding an optimal spin-photon interface in silicon would move quantum information technologies toward a mature semiconducting host. However, the space of possible charged defects is vast, making the identification of candidates from experiments alone extremely challenging. Here, we use high-throughput first-principles computational screening to identify spin-photon interfaces among more than 1000 charged defects in silicon. The use of a single-shot hybrid functional approach is critical in enabling the screening of many quantum defects with a reasonable accuracy. We identify three promising spin-photon interfaces as potential bright emitters in the telecom band: T i i + , F e i 0 , and R u i 0 . These candidates are excited through defect-bound excitons, stressing the importance of such defects in silicon for telecom band operations. Our work paves the way to further large-scale computational screening for quantum defects in semiconductors. , First principles screening reveals three quantum defect candidates in silicon for spin-photon interfaces.

2022

Three-dimensional programming of nanolaser arrays through a single optical microfiber

D. I. Song, A. Yu, P. Samutpraphoot, J. Lee, M. Kim, B. J. Park, A. Sipahigil, M.-K. Kim

Optica 9, 1424 (2022)

DOI
```
@article{song_three-dimensional_2022,
  title = {Three-dimensional programming of nanolaser arrays through a single optical microfiber},
  volume = {9},
  url = {https://opg.optica.org/abstract.cfm?URI=optica-9-12-1424},
  doi = {10.1364/OPTICA.471715},
  journal = {Optica},
  number = {12},
  pages = {1424},
  issn = {2334-2536},
  author = {Song, Da In and Yu, Aran and Samutpraphoot, Polnop and Lee, Jungmin and Kim, Moohyuk and Park, Byoung Jun and Sipahigil, Alp and Kim, Myung-Ki},
  month = dec,
  year = {2022}
}
```
Efficient programming of integrated small optical sources is a key component of photonic technologies. However, as the density of laser arrays increases, the miniaturization and scalability of laser control using an electric drive are pushed to the limit. This study presents an all-optical drive scheme for complete programming of nanolaser arrays through a single waveguide port. Three photonic crystal nanolasers, printed three-dimensionally on the sides of a 2-µm-diameter fiber with an 18 µm laser spacing, were entirely controlled by modal interference, adjusted by the polarization and pulse width of the pump beam through the same fiber. Our approach is applicable to various small optical sources coupled to a single waveguide, and it will lay the foundation for applications in high-density optical integrated circuits, biosensing, and quantum network technologies.
First-principles study of the T center in silicon

D. Dhaliah, Y. Xiong, A. Sipahigil, S. M. Griffin, G. Hautier

Physical Review Materials 6, L053201 (2022)

DOI arXiv
```
@article{dhaliah_first-principles_2022,
  title = {First-principles study of the T center in silicon},
  volume = {6},
  url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.6.L053201},
  doi = {10.1103/PhysRevMaterials.6.L053201},
  journal = {Physical Review Materials},
  number = {5},
  pages = {L053201},
  issn = {2475-9953},
  author = {Dhaliah, Diana and Xiong, Yihuang and Sipahigil, Alp and Griffin, Sinéad M. and Hautier, Geoffroy},
  month = may,
  year = {2022},
  arxiv = {2202.04149}
}
```
The T-center in silicon is a well-known carbon-based color center that has been recently considered for quantum technology applications. Using first principles computations, we show that the excited state is formed by a defect-bound exciton made of a localized defect state occupied by an electron to which a hole is bound. The localized state is of strong carbon p character and reminiscent of the localization of the unpaired electron in the ethyl radical molecule. The radiative lifetime for the defect-bound exciton is calculated to be on the order of μs, much longer than other quantum defects such as the NV center in diamond and in agreement with experiments. The longer lifetime is associated with the small transition dipole moment as a result of the very different nature of the localized and delocalized states forming the defect-bound exciton. Finally, we use first principles calculations to assess the stability of the T-center. We find the T-center to be stable against decomposition into simpler defects when keeping the stoichiometry fixed. However, we identify that the T-center is easily prone to (de)hydrogenation and so requires very precise annealing conditions (temperature and atmosphere) to be efficiently formed.

2021

Collapse and Revival of an Artificial Atom Coupled to a Structured Photonic Reservoir

V. S. Ferreira*, J. Banker*, A. Sipahigil, M. H. Matheny, A. J. Keller, E. Kim, M. Mirhosseini, O. Painter

Physical Review X 11, 041043 (2021)

DOI arXiv
```
@article{ferreira_collapse_2021,
  title = {Collapse and {Revival} of an {Artificial} {Atom} {Coupled} to a {Structured} {Photonic} {Reservoir}},
  volume = {11},
  url = {https://doi.org/10.1103/PhysRevX.11.041043},
  doi = {10.1103/PhysRevX.11.041043},
  journal = {Physical Review X},
  pages = {041043},
  author = {Ferreira, V. S. and Banker, J. and Sipahigil, A. and Matheny, M. H. and Keller, A. J. and Kim, E. and Mirhosseini, M. and Painter, O.},
  month = dec,
  year = {2021},
  arxiv = {2001.03240}
}
```
A structured electromagnetic reservoir can result in novel dynamics of quantum emitters. In particular, the reservoir can be tailored to have a memory of past interactions with emitters, in contrast to memory-less Markovian dynamics of typical open systems. In this Article, we investigate the non-Markovian dynamics of a superconducting qubit strongly coupled to a superconducting slow-light waveguide reservoir. Tuning the qubit into the spectral vicinity of the passband of this waveguide, we find non-exponential energy relaxation as well as substantial changes to the qubit emission rate. Further, upon addition of a reflective boundary to one end of the waveguide, we observe revivals in the qubit population on a timescale 30 times longer than the inverse of the qubit’s emission rate, corresponding to the round-trip travel time of an emitted photon. By tuning of the qubit-waveguide interaction strength, we probe a crossover between Markovian and non-Markovian qubit emission dynamics. These attributes allow for future studies of multi-qubit circuits coupled to structured reservoirs, in addition to constituting the necessary resources for generation of multiphoton highly entangled states.
Quantum Electrodynamics in a Topological Waveguide

E. Kim*, X. Zhang*, V. S. Ferreira, J. Banker, J. K. Iverson, A. Sipahigil, M. Bello, A. González-Tudela, M. Mirhosseini, O. Painter

Physical Review X 11, 011015 (2021)

DOI arXiv Physics Viewpoint
```
@article{kim_quantum_2021,
  title = {Quantum {Electrodynamics} in a {Topological} {Waveguide}},
  volume = {11},
  url = {https://doi.org/10.1103/PhysRevX.11.011015},
  doi = {10.1103/PhysRevX.11.011015},
  journal = {Physical Review X},
  pages = {011015},
  author = {Kim, E. and Zhang, X. and Ferreira, V. S. and Banker, J. and Iverson, J. K. and Sipahigil, A. and Bello, M. and González-Tudela, A. and Mirhosseini, M. and Painter, O.},
  month = jan,
  year = {2021},
  arxiv = {2005.03802}
}
```
While designing the energy-momentum relation of photons is key to many linear, non-linear, and quantum optical phenomena, a new set of light-matter properties may be realized by employing the topology of the photonic bath itself. In this work we investigate the properties of superconducting qubits coupled to a metamaterial waveguide based on a photonic analog of the Su-Schrieffer-Heeger model. We explore topologically-induced properties of qubits coupled to such a waveguide, ranging from the formation of directional qubit-photon bound states to topology-dependent cooperative radiation effects. Addition of qubits to this waveguide system also enables direct quantum control over topological edge states that form in finite waveguide systems, useful for instance in constructing a topologically protected quantum communication channel. More broadly, our work demonstrates the opportunity that topological waveguide-QED systems offer in the synthesis and study of many-body states with exotic long-range quantum correlations.

2020

Superconducting qubit to optical photon transduction

M. Mirhosseini*, A. Sipahigil*, M. Kalaee*, O. Painter

Nature 588, 599–603 (2020)

DOI arXiv Talk
```
@article{mirhosseini_superconducting_2020,
  title = {Superconducting qubit to optical photon transduction},
  volume = {588},
  url = {https://www.nature.com/articles/s41586-020-3038-6},
  doi = {10.1038/s41586-020-3038-6},
  journal = {Nature},
  number = {7839},
  pages = {599--603},
  issn = {0028-0836, 1476-4687},
  author = {Mirhosseini, Mohammad and Sipahigil, Alp and Kalaee, Mahmoud and Painter, Oskar},
  month = dec,
  year = {2020},
  arxiv = {2004.04838}
}
```
Bidirectional conversion of electrical and optical signals lies at the foundation of the global internet. Such converters are employed at repeater stations to extend the reach of long-haul fiber optic communication systems and within data centers to exchange high-speed optical signals between computers. Likewise, coherent microwave-to-optical conversion of single photons would enable the exchange of quantum states between remotely connected superconducting quantum processors, a promising quantum computing hardware platform. Despite the prospects of quantum networking, maintaining the fragile quantum state in such a conversion process with superconducting qubits has remained elusive. Here we demonstrate the conversion of a microwave-frequency excitation of a superconducting transmon qubit into an optical photon. We achieve this using an intermediary nanomechanical resonator which converts the electrical excitation of the qubit into a single phonon by means of a piezoelectric interaction, and subsequently converts the phonon to an optical photon via radiation pressure. We demonstrate optical photon generation from the qubit with a signal-to-noise greater than unity by recording quantum Rabi oscillations of the qubit through single-photon detection of the emitted light over an optical fiber. With proposed improvements in the device and external measurement set-up, such quantum transducers may lead to practical devices capable of realizing new hybrid quantum networks, and ultimately, distributed quantum computers.
Nano-acoustic resonator with ultralong phonon lifetime

G. S. MacCabe*, H. Ren*, J. Luo, J. D. Cohen, H. Zhou, A. Sipahigil, M. Mirhosseini, O. Painter

Science 370, 840–843 (2020)

DOI arXiv
```
@article{maccabe_phononic_2020,
  title = {Nano-acoustic resonator with ultralong phonon lifetime},
  volume = {370},
  url = {https://doi.org/10.1126/science.abc7312},
  doi = {10.1126/science.abc7312},
  journal = {Science},
  number = {6518},
  pages = {840--843},
  author = {MacCabe, G. S. and Ren, H. and Luo, J. and Cohen, J. D. and Zhou, H. and Sipahigil, A. and Mirhosseini, M. and Painter, O.},
  month = nov,
  year = {2020},
  arxiv = {1901.04129}
}
```
The ideal platform for quantum-computing and quantum-sensing applications is likely to be a hybrid system that combines the best features of different components. Superconducting circuits are relatively advanced, and finding components that can control and manipulate the microwaves will be essential. MacCabe et al. explored the use of high-quality microresonators in which the acoustic environment could be engineered such that the phonon lifetime could be extended to more than 1 second. Operating at microwave frequencies of 5 gigahertz, these quantum acoustic-dynamic devices could be coupled with superconducting circuits. Science , this issue p. 840

2019

Microwave-to-optical conversion via four-wave mixing in a cold ytterbium ensemble

J. P. Covey, A. Sipahigil, M. Saffman

Physical Review A 100, 012307 (2019)

DOI arXiv
```
@article{covey_microwave-to-optical_2019,
  title = {Microwave-to-optical conversion via four-wave mixing in a cold ytterbium ensemble},
  volume = {100},
  url = {https://doi.org/10.1103/PhysRevA.100.012307},
  doi = {10.1103/PhysRevA.100.012307},
  journal = {Physical Review A},
  pages = {012307},
  author = {Covey, J. P. and Sipahigil, A. and Saffman, M.},
  month = jul,
  year = {2019},
  arxiv = {1904.08999}
}
```
Interfacing superconducting qubits with optical photons requires noise-free microwave-to-optical transducers, a technology currently not realized at the single-photon level. We propose to use four-wave-mixing in an ensemble of cold ytterbium (Yb) atoms prepared in the metastable ’clock’ state. The parametric process uses two high-lying Rydberg states for bidirectional conversion between a 10 GHz microwave photon and an optical photon in the telecommunication E-band. To avoid noise photons due to spontaneous emission, we consider continuous operation far detuned from the intermediate states. We use an input-output formalism to predict conversion efficiencies of ≈50% with bandwidths of ≈100 kHz.
Cavity quantum electrodynamics with atom-like mirrors

M. Mirhosseini*, E. Kim*, X. Zhang, A. Sipahigil, P. B. Dieterle, A. J. Keller, A. Asenjo-Garcia, D. E. Chang, O. Painter

Nature 569, 692–697 (2019)

DOI arXiv
```
@article{mirhosseini_cavity_2019,
  title = {Cavity quantum electrodynamics with atom-like mirrors},
  volume = {569},
  url = {https://doi.org/10.1038/s41586-019-1196-1},
  doi = {10.1038/s41586-019-1196-1},
  journal = {Nature},
  pages = {692--697},
  author = {Mirhosseini, M. and Kim, E. and Zhang, X. and Sipahigil, A. and Dieterle, P. B. and Keller, A. J. and Asenjo-Garcia, A. and Chang, D. E. and Painter, O.},
  month = may,
  year = {2019},
  arxiv = {1809.09752}
}
```
Waveguide quantum electrodynamics studies photon-mediated interactions of quantum emitters in a one-dimensional radiation channel. Although signatures of such interactions have been observed previously in a variety of physical systems, observation of coherent cooperative dynamics has been obscured by radiative decay of atoms into the waveguide. Employing transmon qubits as artificial atoms coupled to a microwave coplanar waveguide, here we observe dynamical oscillations in an open system where a designated probe qubit interacts with an entangled dark state of an array of qubits which effectively traps radiation as an atomic cavity. The qubit-cavity system is shown to achieve a large cooperativity of C=172 due to collective enhancement of photon-mediated interactions, entering the strong coupling regime. The quantum coherence of the dark state cavity is also explored through its nonlinear response at the single-excitation level. With realistic refinements, this system is suitable for studying the many-body dynamics of large (N>10) quantum spin chains, synthesizing highly non-classical radiation fields on demand, and implementing universal quantum logic operations with high fidelity on information encoded within decoherence-free subspaces.
Telecom-band quantum optics with ytterbium atoms and silicon nanophotonics

J. P. Covey, A. Sipahigil, S. Szoke, N. Sinclair, M. Endres, O. Painter

Physical Review Applied 11, 034044 (2019)

DOI arXiv
```
@article{covey_telecom-band_2019,
  title = {Telecom-band quantum optics with ytterbium atoms and silicon nanophotonics},
  volume = {11},
  url = {https://doi.org/10.1103/PhysRevApplied.11.034044},
  doi = {10.1103/PhysRevApplied.11.034044},
  journal = {Physical Review Applied},
  pages = {034044},
  author = {Covey, J. P. and Sipahigil, A. and Szoke, S. and Sinclair, N. and Endres, M. and Painter, O.},
  month = mar,
  year = {2019},
  arxiv = {1810.12821}
}
```
Wavelengths in the telecommunication window ( 1.25-1.65 microns) are ideal for quantum communication due to low transmission loss in fiber networks. To realize quantum networks operating at these wavelengths, long-lived quantum memories that couple to telecom-band photons with high efficiency need to be developed. We propose coupling neutral ytterbium atoms, which have a strong telecom-wavelength transition, to a silicon photonic crystal cavity. Specifically, we consider the 3P0-3D1 transition in neutral 171Yb to interface its long-lived nuclear spin in the metastable 3P0 ’clock’ state with a telecom-band photon at 1.4 microns. We show that Yb atoms can be trapped using a short wavelength ( 470 nm) tweezer at a distance of 350 nm from the silicon photonic crystal cavity. At this distance, due to the slowly decaying evanescent cavity field at a longer wavelength, we obtain a single-photon Rabi frequency of g/(2pi) 100 MHz and a cooperativity of C 47 while maintaining a high photon collection efficiency into a single mode fiber. The combination of high system efficiency, telecom-band operation, and long coherence times makes this platform well suited for quantum optics on a silicon chip and long-distance quantum communication.

2018

Photon-mediated interactions between quantum emitters in a diamond nanocavity

R. E. Evans*, M. K. Bhaskar*, D. D. Sukachev*, C. T. Nguyen, A. Sipahigil, M. J. Burek, B. Machielse, G. H. Zhang, A. S. Zibrov, E. Bielejec, H. Park, M. Loncar, M. D. Lukin

Science 362, 662–665 (2018)

DOI arXiv
```
@article{evans_photon-mediated_2018,
  title = {Photon-mediated interactions between quantum emitters in a diamond nanocavity},
  volume = {362},
  url = {https://doi.org/10.1126/science.aau4691},
  doi = {10.1126/science.aau4691},
  journal = {Science},
  number = {6415},
  pages = {662--665},
  author = {Evans, R. E. and Bhaskar, M. K. and Sukachev, D. D. and Nguyen, C. T. and Sipahigil, A. and Burek, M. J. and Machielse, B. and Zhang, G. H. and Zibrov, A. S. and Bielejec, E. and Park, H. and Loncar, M. and Lukin, M. D.},
  month = nov,
  year = {2018},
  arxiv = {1807.04265}
}
```
The development of scalable quantum systems will require the ability to control the interactions between the individual quantum building blocks of the system. Evans et al. used a pair of silicon vacancy centers embedded in a diamond nanocavity to show that interactions between the quantum emitters can be mediated optically (see the Perspective by Lodahl). Such optical control provides a speed advantage as well as the potential to develop an integrated platform for future quantum communication and quantum networking. Science , this issue p. 662 ; see also p. 646
Superconducting metamaterials for waveguide quantum electrodynamics

M. Mirhosseini, E. Kim, V. S. Ferreira, M. Kalaee, A. Sipahigil, A. J. Keller, O. Painter

Nature Communications 9, 3706 (2018)

DOI arXiv
```
@article{mirhosseini_superconducting_2018,
  title = {Superconducting metamaterials for waveguide quantum electrodynamics},
  volume = {9},
  url = {https://doi.org/10.1038/s41467-018-06142-z},
  doi = {10.1038/s41467-018-06142-z},
  journal = {Nature Communications},
  pages = {3706},
  author = {Mirhosseini, M. and Kim, E. and Ferreira, V. S. and Kalaee, M. and Sipahigil, A. and Keller, A. J. and Painter, O.},
  month = sep,
  year = {2018},
  arxiv = {1802.01708}
}
```
Embedding tunable quantum emitters in a photonic bandgap structure enables control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite-range emitter–emitter interactions via bound photonic states. Here, we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant ( λ /60). The metamaterial is formed by periodically loading a transmission line with compact, low-loss, low-disorder lumped-element microwave resonators. Tuning the qubit frequency in the vicinity of a band-edge with a group index of n g = 450, we observe an anomalous Lamb shift of −28 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to short-lived radiatively damped and long-lived metastable qubit states.
Strain engineering of the silicon-vacancy center in diamond

S. Meesala*, Y. Sohn*, B. Pingault, L. Shao, H. A. Atikian, J. Holzgrafe, M. Gündoğan, C. Stavrakas, A. Sipahigil, C. Chia, R. Evans, M. J. Burek, M. Zhang, L. Wu, J. L. Pacheco, J. Abraham, E. Bielejec, M. D. Lukin, M. Atatüre, M. Loncar

Physical Review B 97, 205444 (2018)

DOI arXiv
```
@article{meesala_strain_2018,
  title = {Strain engineering of the silicon-vacancy center in diamond},
  volume = {97},
  url = {https://doi.org/10.1103/PhysRevB.97.205444},
  doi = {10.1103/PhysRevB.97.205444},
  journal = {Physical Review B},
  pages = {205444},
  author = {Meesala, S. and Sohn, Y. and Pingault, B. and Shao, L. and Atikian, H. A. and Holzgrafe, J. and Gündoğan, M. and Stavrakas, C. and Sipahigil, A. and Chia, C. and Evans, R. and Burek, M. J. and Zhang, M. and Wu, L. and Pacheco, J. L. and Abraham, J. and Bielejec, E. and Lukin, M. D. and Atatüre, M. and Loncar, M.},
  month = may,
  year = {2018},
  arxiv = {1801.09833}
}
```
We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multi-qubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain suseptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.
Phonon Networks with Silicon-Vacancy Centers in Diamond Waveguides

M.-A. Lemonde, S. Meesala, A. Sipahigil, M. J. A. Schuetz, M. D. Lukin, M. Loncar, P. Rabl

Physical Review Letters 120, 213603 (2018)

DOI arXiv
```
@article{lemonde_phonon_2018,
  title = {Phonon {Networks} with {Silicon}-{Vacancy} {Centers} in {Diamond} {Waveguides}},
  volume = {120},
  url = {https://doi.org/10.1103/PhysRevLett.120.213603},
  doi = {10.1103/PhysRevLett.120.213603},
  journal = {Physical Review Letters},
  pages = {213603},
  author = {Lemonde, M.-A. and Meesala, S. and Sipahigil, A. and Schuetz, M. J. A. and Lukin, M. D. and Loncar, M. and Rabl, P.},
  month = may,
  year = {2018},
  arxiv = {1801.01904}
}
```
We propose and analyze a novel realization of a solid-state quantum network, where separated silicon-vacancy centers are coupled via the phonon modes of a quasi-1D diamond waveguide. In our approach, quantum states encoded in long-lived electronic spin states can be converted into propagating phonon wavepackets and be reabsorbed efficiently by a distant defect center. Our analysis shows that under realistic conditions, this approach enables the implementation of high-fidelity, scalable quantum communication protocols within chip-scale spin-qubit networks. Apart from quantum information processing, this setup constitutes a novel waveguide QED platform, where strong-coupling effects between solid-state defects and individual propagating phonons can be explored at the quantum level.
Controlling the coherence of a diamond spin qubit through its strain environment

Y. I. Sohn*, S. Meesala*, B. Pingault*, H. A. Atikian, J. Holzgrafe, M. Gündoğan, C. Stavrakas, M. J. Stanley, A. Sipahigil, J. Choi, M. Zhang, J. L. Pacheco, J. Abraham, E. Bielejec, M. D. Lukin, M. Atatüre, M. Loncar

Nature Communications 9, 2012 (2018)

DOI arXiv
```
@article{sohn_controlling_2018,
  title = {Controlling the coherence of a diamond spin qubit through its strain environment},
  volume = {9},
  url = {https://doi.org/10.1038/s41467-018-04340-3},
  doi = {10.1038/s41467-018-04340-3},
  journal = {Nature Communications},
  pages = {2012},
  author = {Sohn, Y. I. and Meesala, S. and Pingault, B. and Atikian, H. A. and Holzgrafe, J. and Gündoğan, M. and Stavrakas, C. and Stanley, M. J. and Sipahigil, A. and Choi, J. and Zhang, M. and Pacheco, J. L. and Abraham, J. and Bielejec, E. and Lukin, M. D. and Atatüre, M. and Loncar, M.},
  month = may,
  year = {2018},
  arxiv = {1706.03881}
}
```
The uncontrolled interaction of a quantum system with its environment is detrimental for quantum coherence. For quantum bits in the solid state, decoherence from thermal vibrations of the surrounding lattice can typically only be suppressed by lowering the temperature of operation. Here, we use a nano-electro-mechanical system to mitigate the effect of thermal phonons on a spin qubit – the silicon-vacancy colour centre in diamond – without changing the system temperature. By controlling the strain environment of the colour centre, we tune its electronic levels to probe, control, and eventually suppress the interaction of its spin with the thermal bath. Strain control provides both large tunability of the optical transitions and significantly improved spin coherence. Finally, our findings indicate the possibility to achieve strong coupling between the silicon-vacancy spin and single phonons, which can lead to the realisation of phonon-mediated quantum gates and nonlinear quantum phononics.
All-optical nanoscale thermometry with silicon-vacancy centers in diamond

C. T. Nguyen, R. E. Evans, A. Sipahigil, M. K. Bhaskar, D. D. Sukachev, V. N. Agafonov, V. A. Davydov, L. F. Kulikova, F. Jelezko, M. D. Lukin

Applied Physics Letters 112, 203102 (2018)

DOI arXiv
```
@article{nguyen_all-optical_2018,
  title = {All-optical nanoscale thermometry with silicon-vacancy centers in diamond},
  volume = {112},
  url = {https://doi.org/10.1063/1.5029904},
  doi = {10.1063/1.5029904},
  journal = {Applied Physics Letters},
  pages = {203102},
  author = {Nguyen, C. T. and Evans, R. E. and Sipahigil, A. and Bhaskar, M. K. and Sukachev, D. D. and Agafonov, V. N. and Davydov, V. A. and Kulikova, L. F. and Jelezko, F. and Lukin, M. D.},
  month = may,
  year = {2018},
  arxiv = {1708.05419}
}
```
We demonstrate an all-optical thermometer based on an ensemble of silicon-vacancy centers (SiVs) in diamond by utilizing the sensitivity of the zero-phonon line wavelength to temperature, Δλ/ΔT=0.0124(2) nm K–1 [6.8(1) GHz K–1]. Using SiVs in bulk diamond, we achieve 70 mK precision at room temperature with a temperature uncertainty σT=360 mK/Hz. Finally, we use SiVs in 200 nm nanodiamonds as local temperature probes with 521 mK/Hz uncertainty and achieve sub-Kelvin precision. These properties deviate by less than 1% between nanodiamonds, enabling calibration-free thermometry for sensing and control of complex nanoscale systems.

2017

Silicon-Vacancy Spin Qubit in Diamond: A Quantum Memory Exceeding 10 ms with Single-Shot State Readout

D. D. Sukachev*, A. Sipahigil*, C. T. Nguyen*, M. K. Bhaskar, R. E. Evans, F. Jelezko, M. D. Lukin

Physical Review Letters 119, 223602 (2017)

DOI arXiv
```
@article{sukachev_silicon-vacancy_2017,
  title = {Silicon-{Vacancy} {Spin} {Qubit} in {Diamond}: A {Quantum} {Memory} {Exceeding} 10 ms with {Single}-{Shot} {State} {Readout}},
  volume = {119},
  url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.223602},
  doi = {10.1103/PhysRevLett.119.223602},
  journal = {Physical Review Letters},
  number = {22},
  pages = {223602},
  issn = {0031-9007, 1079-7114},
  author = {Sukachev, D. D. and Sipahigil, A. and Nguyen, C. T. and Bhaskar, M. K. and Evans, R. E. and Jelezko, F. and Lukin, M. D.},
  month = nov,
  year = {2017},
  arxiv = {1708.08852}
}
```
The negatively-charged silicon-vacancy (SiV⁻) color center in diamond has recently emerged as a promising system for quantum photonics. Its symmetry-protected optical transitions enable creation of indistinguishable emitter arrays and deterministic coupling to nanophotonic devices. Despite this, the longest coherence time associated with its electronic spin achieved to date ( 250 ns) has been limited by coupling to acoustic phonons. We demonstrate coherent control and suppression of phonon-induced dephasing of the SiV⁻ electronic spin coherence by five orders of magnitude by operating at temperatures below 500 mK. By aligning the magnetic field along the SiV⁻ symmetry axis, we demonstrate spin-conserving optical transitions and single-shot readout of the SiV⁻ spin with 89% fidelity. Coherent control of the SiV⁻ spin with microwave fields is used to demonstrate a spin coherence time T₂ of 13 ms and a spin relaxation time T₁ exceeding 1 s at 100 mK. These results establish the SiV⁻ as a promising solid-state candidate for the realization of scalable quantum networks.
Optical and microwave control of germanium-vacancy center spins in diamond

P. Siyushev*, M. H. Metsch*, A. Ijaz, J. Binder, M. K. Bhaskar, D. D. Sukachev, A. Sipahigil, R. E. Evans, C. T. Nguyen, M. D. Lukin, P. R. Hemmer, Y. N. Palyanov, I. N. Kupriyanov, Y. M. Borzdov, L. J. Rogers, F. Jelezko

Physical Review B 96, 081201(R) (2017)

DOI arXiv
```
@article{siyushev_optical_2017,
  title = {Optical and microwave control of germanium-vacancy center spins in diamond},
  volume = {96},
  url = {https://doi.org/10.1103/PhysRevB.96.081201},
  doi = {10.1103/PhysRevB.96.081201},
  journal = {Physical Review B},
  pages = {081201(R)},
  author = {Siyushev, P. and Metsch, M. H. and Ijaz, A. and Binder, J. and Bhaskar, M. K. and Sukachev, D. D. and Sipahigil, A. and Evans, R. E. and Nguyen, C. T. and Lukin, M. D. and Hemmer, P. R. and Palyanov, Y. N. and Kupriyanov, I. N. and Borzdov, Y. M. and Rogers, L. J. and Jelezko, F.},
  month = aug,
  year = {2017},
  arxiv = {1612.02947}
}
```
A solid-state system combining a stable spin degree of freedom with an efficient optical interface is highly desirable as an element for integrated quantum optical and quantum information systems. We demonstrate a bright color center in diamond with excellent optical properties and controllable electronic spin states. Specifically, we carry out detailed optical spectroscopy of a Germanium Vacancy (GeV) color center demonstrating optical spectral stability. Using an external magnetic field to lift the electronic spin degeneracy, we explore the spin degree of freedom as a controllable qubit. Spin polarization is achieved using optical pumping, and a spin relaxation time in excess of 20 μs is demonstrated. Optically detected magnetic resonance (ODMR) is observed in the presence of a resonant microwave field. ODMR is used as a probe to measure the Autler-Townes effect in a microwave-optical double resonance experiment. Superposition spin states were prepared using coherent population trapping, and a pure dephasing time of about 19 ns was observed. Prospects for realizing coherent quantum registers based on optically controlled GeV centers are discussed.
A fiber-coupled diamond quantum nanophotonic interface

M. J. Burek, C. Meuwly, R. E. Evans, M. K. Bhaskar, A. Sipahigil, S. Meesala, D. D. Sukachev, C. T. Nguyen, E. Bielejec, M. D. Lukin, M. Loncar

Physical Review Applied 8, 024026 (2017)

DOI arXiv
```
@article{burek_fiber-coupled_2017,
  title = {A fiber-coupled diamond quantum nanophotonic interface},
  volume = {8},
  url = {https://doi.org/10.1103/PhysRevApplied.8.024026},
  doi = {10.1103/PhysRevApplied.8.024026},
  journal = {Physical Review Applied},
  pages = {024026},
  author = {Burek, M. J. and Meuwly, C. and Evans, R. E. and Bhaskar, M. K. and Sipahigil, A. and Meesala, S. and Sukachev, D. D. and Nguyen, C. T. and Bielejec, E. and Lukin, M. D. and Loncar, M.},
  month = aug,
  year = {2017},
  arxiv = {1612.05285}
}
```
Color centers in diamond provide a promising platform for quantum optics in the solid state, with coherent optical transitions and long-lived electron and nuclear spins. Building upon recent demonstrations of nanophotonic waveguides and optical cavities in single-crystal diamond, we now demonstrate on-chip diamond nanophotonics with a high efficiency fiber-optical interface, achieving > 90% power coupling at visible wavelengths. We use this approach to demonstrate a bright source of narrowband single photons, based on a silicon-vacancy color center embedded within a waveguide-coupled diamond photonic crystal cavity. Our fiber-coupled diamond quantum nanophotonic interface results in a high flux of coherent single photons into a single mode fiber, enabling new possibilities for realizing quantum networks that interface multiple emitters, both on-chip and separated by long distances.
Quantum Nonlinear Optics with a Germanium-Vacancy Color Center in a Nanoscale Diamond Waveguide

M. K. Bhaskar, D. D. Sukachev, A. Sipahigil, R. E. Evans, M. J. Burek, C. T. Nguyen, L. J. Rogers, P. Siyushev, M. H. Metsch, H. Park, F. Jelezko, M. Loncar, M. D. Lukin

Physical Review Letters 118, 223603 (2017)

DOI arXiv
```
@article{bhaskar_quantum_2017,
  title = {Quantum {Nonlinear} {Optics} with a {Germanium}-{Vacancy} {Color} {Center} in a {Nanoscale} {Diamond} {Waveguide}},
  volume = {118},
  url = {https://doi.org/10.1103/PhysRevLett.118.223603},
  doi = {10.1103/PhysRevLett.118.223603},
  journal = {Physical Review Letters},
  pages = {223603},
  author = {Bhaskar, M. K. and Sukachev, D. D. and Sipahigil, A. and Evans, R. E. and Burek, M. J. and Nguyen, C. T. and Rogers, L. J. and Siyushev, P. and Metsch, M. H. and Park, H. and Jelezko, F. and Loncar, M. and Lukin, M. D.},
  month = may,
  year = {2017},
  arxiv = {1612.03036}
}
```
We demonstrate a quantum nanophotonics platform based on germanium-vacancy (GeV) color centers in fiber-coupled diamond nanophotonic waveguides. We show that GeV optical transitions have a high quantum efficiency and are nearly lifetime-broadened in such nanophotonic structures. These properties yield an efficient interface between waveguide photons and a single GeV without the use of a cavity or slow-light waveguide. As a result, a single GeV center reduces waveguide transmission by 18 ± 1% on resonance in a single pass. We use a nanophotonic interferometer to perform homodyne detection of GeV resonance fluorescence. By probing the photon statistics of the output field, we demonstrate that the GeV-waveguide system is nonlinear at the single-photon level.
Scalable Focused Ion Beam Creation of Nearly Lifetime-Limited Single Quantum Emitters in Diamond Nanostructures

T. Schröder*, M. E. Trusheim*, M. Walsh*, L. Li, J. Zheng, M. Schukraft, J. L. Pacheco, R. M. Camacho, E. S. Bielejec, A. Sipahigil, R. E. Evans, D. D. Sukachev, C. T. Nguyen, M. D. Lukin, D. Englund

Nature Communications 8, 15376 (2017)

DOI arXiv
```
@article{schroder_scalable_2017,
  title = {Scalable {Focused} {Ion} {Beam} {Creation} of {Nearly} {Lifetime}-{Limited} {Single} {Quantum} {Emitters} in {Diamond} {Nanostructures}},
  volume = {8},
  url = {https://doi.org/10.1038/ncomms15376},
  doi = {10.1038/ncomms15376},
  journal = {Nature Communications},
  pages = {15376},
  author = {Schröder, T. and Trusheim, M. E. and Walsh, M. and Li, L. and Zheng, J. and Schukraft, M. and Pacheco, J. L. and Camacho, R. M. and Bielejec, E. S. and Sipahigil, A. and Evans, R. E. and Sukachev, D. D. and Nguyen, C. T. and Lukin, M. D. and Englund, D.},
  month = may,
  year = {2017},
  arxiv = {1610.09492}
}
```
The controlled creation of defect centre—nanocavity systems is one of the outstanding challenges for efficiently interfacing spin quantum memories with photons for photon-based entanglement operations in a quantum network. Here we demonstrate direct, maskless creation of atom-like single silicon vacancy (SiV) centres in diamond nanostructures via focused ion beam implantation with ∼32 nm lateral precision and <50 nm positioning accuracy relative to a nanocavity. We determine the Si+ ion to SiV centre conversion yield to be ∼2.5% and observe a 10-fold conversion yield increase by additional electron irradiation. Low-temperature spectroscopy reveals inhomogeneously broadened ensemble emission linewidths of ∼51 GHz and close to lifetime-limited single-emitter transition linewidths down to 126±13 MHz corresponding to ∼1.4 times the natural linewidth. This method for the targeted generation of nearly transform-limited quantum emitters should facilitate the development of scalable solid-state quantum information processors.

2016

An integrated diamond nanophotonics platform for quantum optical networks

A. Sipahigil*, R. E. Evans*, D. D. Sukachev*, M. J. Burek, J. Borregaard, M. K. Bhaskar, C. T. Nguyen, J. L. Pacheco, H. A. Atikian, C. Meuwly, R. M. Camacho, F. Jelezko, E. Bielejec, H. Park, M. Loncar, M. D. Lukin

Science 354, 847–850 (2016)

DOI arXiv
```
@article{sipahigil_integrated_2016,
  title = {An integrated diamond nanophotonics platform for quantum optical networks},
  volume = {354},
  url = {https://doi.org/10.1126/science.aah6875},
  doi = {10.1126/science.aah6875},
  journal = {Science},
  number = {6314},
  pages = {847--850},
  author = {Sipahigil, A. and Evans, R. E. and Sukachev, D. D. and Burek, M. J. and Borregaard, J. and Bhaskar, M. K. and Nguyen, C. T. and Pacheco, J. L. and Atikian, H. A. and Meuwly, C. and Camacho, R. M. and Jelezko, F. and Bielejec, E. and Park, H. and Loncar, M. and Lukin, M. D.},
  month = nov,
  year = {2016},
  arxiv = {1608.05147}
}
```
Technologies that exploit the rules of quantum mechanics offer a potential advantage over classical devices in terms of sensitivity. Sipahigil et al. combined the quantum optical features of silicon-vacancy color centers with diamond-based photonic cavities to form a platform for integrated quantum nanophotonics (see the Perspective by Hanson). They could thus generate single photons from the color centers, optically switch light in the cavity by addressing the state of the color center, and quantum-mechanically entangle two color centers positioned in the cavity. The work presents a viable route to develop an integrated platform for quantum networks. Science , this issue p. 847 ; see also p. 835
Narrow-Linewidth Homogeneous Optical Emitters in Diamond Nanostructures via Silicon Ion Implantation

R. E. Evans*, A. Sipahigil*, D. D. Sukachev, A. S. Zibrov, M. D. Lukin

Physical Review Applied 5, 044010 (2016)

DOI arXiv
```
@article{evans_narrow-linewidth_2016,
  title = {Narrow-{Linewidth} {Homogeneous} {Optical} {Emitters} in {Diamond} {Nanostructures} via {Silicon} {Ion} {Implantation}},
  volume = {5},
  url = {https://doi.org/10.1103/PhysRevApplied.5.044010},
  doi = {10.1103/PhysRevApplied.5.044010},
  journal = {Physical Review Applied},
  pages = {044010},
  author = {Evans, R. E. and Sipahigil, A. and Sukachev, D. D. and Zibrov, A. S. and Lukin, M. D.},
  month = apr,
  year = {2016},
  arxiv = {1512.03820}
}
```
The negatively-charged silicon-vacancy (SiV⁻) center in diamond is a bright source of indistinguishable single photons and a useful resource in quantum information protocols. Until now, SiV⁻ centers with narrow optical linewidths and small inhomogeneous distributions of SiV⁻ transition frequencies have only been reported in samples doped with silicon during diamond growth. We present a technique for producing implanted SiV⁻ centers with nearly lifetime-limited optical linewidths and a small inhomogeneous distribution. These properties persist after nanofabrication, paving the way for incorporation of high-quality SiV⁻ centers into nanophotonic devices.

2015

Electron-phonon processes of the silicon-vacancy centre in diamond

K. D. Jahnke*, A. Sipahigil*, J. M. Binder, M. W. Doherty, M. Metsch, L. J. Rogers, N. B. Manson, M. D. Lukin, F. Jelezko

New Journal of Physics 17, 043011 (2015)

DOI arXiv
```
@article{jahnke_electron-phonon_2015,
  title = {Electron-phonon processes of the silicon-vacancy centre in diamond},
  volume = {17},
  url = {https://doi.org/10.1088/1367-2630/17/4/043011},
  doi = {10.1088/1367-2630/17/4/043011},
  journal = {New Journal of Physics},
  pages = {043011},
  author = {Jahnke, K. D. and Sipahigil, A. and Binder, J. M. and Doherty, M. W. and Metsch, M. and Rogers, L. J. and Manson, N. B. and Lukin, M. D. and Jelezko, F.},
  month = apr,
  year = {2015},
  arxiv = {1411.2871}
}
```
We investigate phonon induced electronic dynamics in the ground and excited states of the negatively charged silicon-vacancy (SiV⁻) centre in diamond. Optical transition line widths, transition wavelength and excited state lifetimes are measured for the temperature range 4-350 K. The ground state orbital relaxation rates are measured using time-resolved fluorescence techniques. A microscopic model of the thermal broadening in the excited and ground states of the SiV⁻ centre is developed. A vibronic process involving single-phonon transitions is found to determine orbital relaxation rates for both the ground and the excited states at cryogenic temperatures. We discuss the implications of our findings for coherence of qubit states in the ground states and propose methods to extend coherence times of SiV⁻ qubits.
Phonon-Induced Population Dynamics and Intersystem Crossing in Nitrogen-Vacancy Centers

M. L. Goldman, A. Sipahigil, M. W. Doherty, N. Y. Yao, S. D. Bennett, M. Markham, D. J. Twitchen, N. B. Manson, A. Kubanek, M. D. Lukin

Physical Review Letters 114, 145502 (2015)

DOI arXiv
```
@article{goldman_phonon-induced_2015,
  title = {Phonon-{Induced} {Population} {Dynamics} and {Intersystem} {Crossing} in {Nitrogen}-{Vacancy} {Centers}},
  volume = {114},
  url = {https://doi.org/10.1103/PhysRevLett.114.145502},
  doi = {10.1103/PhysRevLett.114.145502},
  journal = {Physical Review Letters},
  pages = {145502},
  author = {Goldman, M. L. and Sipahigil, A. and Doherty, M. W. and Yao, N. Y. and Bennett, S. D. and Markham, M. and Twitchen, D. J. and Manson, N. B. and Kubanek, A. and Lukin, M. D.},
  month = apr,
  year = {2015},
  arxiv = {1406.4065}
}
```
We report direct measurement of population dynamics in the excited state manifold of a nitrogen-vacancy (NV) center in diamond. We quantify the phonon-induced mixing rate and demonstrate that it can be completely suppressed at low temperatures. Further, we measure the intersystem crossing (ISC) rate for different excited states and develop a theoretical model that unifies the phonon-induced mixing and ISC mechanisms. We find that our model is in excellent agreement with experiment and that it can be used to predict unknown elements of the NV center’s electronic structure. We discuss the model’s implications for enhancing the NV center’s performance as a room-temperature sensor.
State-selective intersystem crossing in nitrogen-vacancy centers

M. L. Goldman, M. W. Doherty, A. Sipahigil, N. Y. Yao, S. D. Bennett, N. B. Manson, A. Kubanek, M. D. Lukin

Physical Review B 91, 165201 (2015)

DOI arXiv
```
@article{goldman_state-selective_2015,
  title = {State-selective intersystem crossing in nitrogen-vacancy centers},
  volume = {91},
  url = {https://doi.org/10.1103/PhysRevB.91.165201},
  doi = {10.1103/PhysRevB.91.165201},
  journal = {Physical Review B},
  pages = {165201},
  author = {Goldman, M. L. and Doherty, M. W. and Sipahigil, A. and Yao, N. Y. and Bennett, S. D. and Manson, N. B. and Kubanek, A. and Lukin, M. D.},
  month = apr,
  year = {2015},
  arxiv = {1412.4865}
}
```
The intersystem crossing (ISC) is an important process in many solid-state atomlike impurities. For example, it allows the electronic spin state of the nitrogen-vacancy (NV) center in diamond to be initialized and read out using optical fields at ambient temperatures. This capability has enabled a wide array of applications in metrology and quantum information science. Here, we develop a microscopic model of the state-selective ISC from the optical excited state manifold of the NV center. By correlating the electron-phonon interactions that mediate the ISC with those that induce population dynamics within the NV center’s excited state manifold and those that produce the phonon sidebands of its optical transitions, we quantitatively demonstrate that our model is consistent with recent ISC measurements. Furthermore, our model constrains the unknown energy spacings between the center’s spin-singlet and spin-triplet levels. Finally, we discuss prospects to engineer the ISC in order to improve the spin initialization and readout fidelities of NV centers.

2014

All-Optical Initialization, Readout, and Coherent Preparation of Single Silicon-Vacancy Spins in Diamond

L. J. Rogers, K. D. Jahnke, M. H. Metsch, A. Sipahigil, J. M. Binder, T. Teraji, H. Sumiya, J. Isoya, M. D. Lukin, P. Hemmer, F. Jelezko

Physical Review Letters 113, 263602 (2014)

DOI arXiv
```
@article{rogers_all-optical_2014,
  title = {All-{Optical} {Initialization}, {Readout}, and {Coherent} {Preparation} of {Single} {Silicon}-{Vacancy} {Spins} in {Diamond}},
  volume = {113},
  url = {https://doi.org/10.1103/PhysRevLett.113.263602},
  doi = {10.1103/PhysRevLett.113.263602},
  journal = {Physical Review Letters},
  pages = {263602},
  author = {Rogers, L. J. and Jahnke, K. D. and Metsch, M. H. and Sipahigil, A. and Binder, J. M. and Teraji, T. and Sumiya, H. and Isoya, J. and Lukin, M. D. and Hemmer, P. and Jelezko, F.},
  month = dec,
  year = {2014},
  arxiv = {1410.1355}
}
```
The silicon-vacancy (SiV⁻) color center in diamond has attracted attention due to its unique optical properties. It exhibits spectral stability and indistinguishability that facilitate efficient generation of photons capable of demonstrating quantum interference. Here we show high fidelity optical initialization and readout of electronic spin in a single SiV⁻ center with a spin relaxation time of T₁=2.4±0.2 ms. Coherent population trapping (CPT) is used to demonstrate coherent preparation of dark superposition states with a spin coherence time of T₂*=35±3 ns. This is fundamentally limited by orbital relaxation, and an understanding of this process opens the way to extend coherences by engineering interactions with phonons. These results establish the SiV⁻ center as a solid-state spin-photon interface.
Indistinguishable Photons from Separated Silicon-Vacancy Centers in Diamond

A. Sipahigil*, K. D. Jahnke*, L. J. Rogers, T. Teraji, J. Isoya, A. S. Zibrov, F. Jelezko, M. D. Lukin

Physical Review Letters 113, 113602 (2014)

DOI arXiv
```
@article{sipahigil_indistinguishable_2014,
  title = {Indistinguishable {Photons} from {Separated} {Silicon}-{Vacancy} {Centers} in {Diamond}},
  volume = {113},
  url = {https://doi.org/10.1103/PhysRevLett.113.113602},
  doi = {10.1103/PhysRevLett.113.113602},
  journal = {Physical Review Letters},
  pages = {113602},
  author = {Sipahigil, A. and Jahnke, K. D. and Rogers, L. J. and Teraji, T. and Isoya, J. and Zibrov, A. S. and Jelezko, F. and Lukin, M. D.},
  month = sep,
  year = {2014},
  arxiv = {1406.4268}
}
```
We demonstrate that silicon-vacancy (SiV) centers in diamond can be used to efficiently generate coherent optical photons with excellent spectral properties. We show that these features are due to the inversion symmetry associated with SiV centers, and demonstrate generation of indistinguishable single photons from separate emitters in a Hong-Ou-Mandel (HOM) interference experiment.Prospects for realizing efficient quantum network nodes using SiV centers are discussed.

2012

Quantum Interference of Single Photons from Remote Nitrogen-Vacancy Centers in Diamond

A. Sipahigil, M. L. Goldman, E. Togan, Y. Chu, M. Markham, D. J. Twitchen, A. S. Zibrov, A. Kubanek, M. D. Lukin

Physical Review Letters 108, 143601 (2012)

DOI arXiv
```
@article{sipahigil_quantum_2012,
  title = {Quantum {Interference} of {Single} {Photons} from {Remote} {Nitrogen}-{Vacancy} {Centers} in {Diamond}},
  volume = {108},
  url = {https://doi.org/10.1103/PhysRevLett.108.143601},
  doi = {10.1103/PhysRevLett.108.143601},
  journal = {Physical Review Letters},
  pages = {143601},
  author = {Sipahigil, A. and Goldman, M. L. and Togan, E. and Chu, Y. and Markham, M. and Twitchen, D. J. and Zibrov, A. S. and Kubanek, A. and Lukin, M. D.},
  month = apr,
  year = {2012},
  arxiv = {1112.3975}
}
```
We demonstrate quantum interference between indistinguishable photons emitted by two nitrogen-vacancy (NV) centers in distinct diamond samples separated by two meters. Macroscopic solid immersion lenses are used to enhance photon collection efficiency. Quantum interference is verified by measuring a value of the second-order cross-correlation function g⁽²⁾(0) = 0.35 ± 0.04<0.5. In addition, optical transition frequencies of two separated NV centers are tuned into resonance with each other by applying external electric fields. Extension of the present approach to generate entanglement of remote solid-state qubits is discussed.

* Equal contribution