IEM Distinguished Lecturers Seminar: Efficient photon and phonon interfaces for spin qubits in diamond
*** An apéro will be served at the end of the talk ***
This is a Joint Seminar with the EPFL Center for Quantum Science and Engineering (QSE Center)
Abstract
Color centers in diamond provide optically accessible, long-lived spin qubits that are promising building blocks for distributed quantum networks. Realizing scalable quantum nodes, however, requires efficient and controllable interfaces between spins and both photons and phonons. In this talk, I will describe our efforts to engineer the electromagnetic and elastic environments of silicon-vacancy (SiV) centers to realize efficient spin–photon and spin–phonon interfaces.
The SiV center exhibits large strain susceptibility, enabling coherent control of its orbital and spin degrees of freedom via mechanical excitations. Our early work demonstrated strain-based control of SiV coherence [1] and coherent acoustic driving of a single SiV spin [2], establishing the foundations of quantum phononics in diamond. Building on this, we recently demonstrated the acoustic Purcell effect in nanomechanical resonators coupled to color centers [3], as well as the formation of phonon-dressed spin states and engineered spin–phonon interactions in the strong-driving regime [4]. We further engineer the phononic local density of states using diamond phononic crystals with complete bandgaps centered around ~60 GHz [5]. By embedding single SiV centers within these structures, we observe up to an 18-fold suppression of single-phonon-induced orbital relaxation, which may extend spin coherence and enable control of phonon-mediated processes at elevated temperatures. Finally, we use strain to engineer diamond nanomechanical resonators themselves resulting in ultrahigh mechanical coherence (Q ≳ 10⁸), revealing microscopic two-level-system defects and establishing a materials foundation for ultra-low-loss phononic quantum interfaces [6].
Complementarily, nanofabricated photonic cavities coupled to diamond color centers have enabled high-efficiency spin–photon interfaces that form the backbone of quantum networking experiments. Such cavity-enhanced nodes were used to demonstrate memory-enhanced quantum communication over metropolitan-scale distances [7] and deterministic entanglement of nanophotonic quantum memory nodes in a telecommunication network [8]. Fabrication advances have recently allowed realization of high-Q photonic crystal cavities (Q ~ 1.8 × 10⁵ in the visible) [9] and slow-light photonic crystal waveguides [10], both fabricated in thin-film diamond.
Together, these results establish a unified diamond platform in which both photon and phonon interfaces can be engineered with high precision. Such simultaneous control of electromagnetic and elastic degrees of freedom opens new opportunities for multiplexed quantum repeaters, quantum acoustodynamics, and hybrid quantum interconnects based on color centers in diamond.
References
[1] Y. I. Sohn et al., “Controlling the coherence of a diamond spin qubit through its strain environment,” Nature Communications, 9, 2012 (2018).
[2] S. Maity et al., “Coherent Acoustic Control of a Single Silicon Vacancy Spin in Diamond,” Nature Communications, 11, 193 (2020).
[3] G. D. Joe et al., “Observation of the acoustic Purcell effect with a color-center and a nanomechanical resonator,” arXiv:2503.09946 (2025).
[4] E. Cornell et al., “All-mechanical continuous coherence protection of a single SiV spin,” arXiv:2508.13356 (2025).
[5] K. Kuruma et al., “Controlling interactions between high-frequency phonons and single quantum systems using phononic crystals,” Nature Physics, 21, 77 (2024).
[6] G. Huang et al., “Strain-engineered ultracoherent diamond nanomechanics,” arXiv:2507.01217 (2025).
[7] M. Bhaskar, et al, “Experimental demonstration of memory-enhanced quantum communication”, Nature, 580, 60 (2020)
[8] Can M Knaut et al, “Entanglement of Nanophotonic Quantum Memory Nodes in a Telecommunication Network”, Nature, 629, 573 (2024)
[9] S. W. Ding et al., “High-Q cavity interface for color centers in thin film diamond,” Nature Communications, 15, 6358 (2024).
[10] S. W. Ding et al., “Purcell-enhanced emissions from diamond color centers in slow-light photonic crystal waveguides,” Nano Letters, 25, 12125 (2025).
Biography
Marko Lončar is Tiantsai Lin Professor of Electrical Engineering at Harvard's John A Paulson School of Engineering and Applied Sciences (SEAS). Lončar received his Diploma from University of Belgrade (R. Serbia) in 1997, and PhD from Caltech in 2003 (with Axel Scherer), both in Electrical Engineering. After completing his postdoctoral studies at Harvard (with Federico Capasso), he joined Harvard faculty in 2006. Lončar is expert in nanophotonics and nanofabrication, and his group has done pioneering work in the field of quantum and nonlinear nanophotonics. In particular, Lončar is recognized for his work on the development of diamond and thin film lithium niobate nanophotonic platforms. Lončar has co-authored more than 250 manuscripts in top scientific journals and has given more than 300 invited talks and seminars. He has received NSF CAREER Award in 2009, Sloan Fellowship in 2010, Marko Jarić Foundation Award in 2020, and Microoptics Conference Award in 2023. In recognition of his teaching activities, Lončar has been awarded Harvard University Levenson Prize for Excellence in Undergraduate Teaching (2012), and has been named Harvard College Professor in 2017. Lončar is Fellow of Optical Society of America and IEEE, as well as Senior Member of SPIE. He is co-founder of HyperLight Corporation (Cambridge, MA), VC backed startup commercializing lithium-niobate technology developed in his lab.
This is a Joint Seminar with the EPFL Center for Quantum Science and Engineering (QSE Center)
Abstract
Color centers in diamond provide optically accessible, long-lived spin qubits that are promising building blocks for distributed quantum networks. Realizing scalable quantum nodes, however, requires efficient and controllable interfaces between spins and both photons and phonons. In this talk, I will describe our efforts to engineer the electromagnetic and elastic environments of silicon-vacancy (SiV) centers to realize efficient spin–photon and spin–phonon interfaces.
The SiV center exhibits large strain susceptibility, enabling coherent control of its orbital and spin degrees of freedom via mechanical excitations. Our early work demonstrated strain-based control of SiV coherence [1] and coherent acoustic driving of a single SiV spin [2], establishing the foundations of quantum phononics in diamond. Building on this, we recently demonstrated the acoustic Purcell effect in nanomechanical resonators coupled to color centers [3], as well as the formation of phonon-dressed spin states and engineered spin–phonon interactions in the strong-driving regime [4]. We further engineer the phononic local density of states using diamond phononic crystals with complete bandgaps centered around ~60 GHz [5]. By embedding single SiV centers within these structures, we observe up to an 18-fold suppression of single-phonon-induced orbital relaxation, which may extend spin coherence and enable control of phonon-mediated processes at elevated temperatures. Finally, we use strain to engineer diamond nanomechanical resonators themselves resulting in ultrahigh mechanical coherence (Q ≳ 10⁸), revealing microscopic two-level-system defects and establishing a materials foundation for ultra-low-loss phononic quantum interfaces [6].
Complementarily, nanofabricated photonic cavities coupled to diamond color centers have enabled high-efficiency spin–photon interfaces that form the backbone of quantum networking experiments. Such cavity-enhanced nodes were used to demonstrate memory-enhanced quantum communication over metropolitan-scale distances [7] and deterministic entanglement of nanophotonic quantum memory nodes in a telecommunication network [8]. Fabrication advances have recently allowed realization of high-Q photonic crystal cavities (Q ~ 1.8 × 10⁵ in the visible) [9] and slow-light photonic crystal waveguides [10], both fabricated in thin-film diamond.
Together, these results establish a unified diamond platform in which both photon and phonon interfaces can be engineered with high precision. Such simultaneous control of electromagnetic and elastic degrees of freedom opens new opportunities for multiplexed quantum repeaters, quantum acoustodynamics, and hybrid quantum interconnects based on color centers in diamond.
References
[1] Y. I. Sohn et al., “Controlling the coherence of a diamond spin qubit through its strain environment,” Nature Communications, 9, 2012 (2018).
[2] S. Maity et al., “Coherent Acoustic Control of a Single Silicon Vacancy Spin in Diamond,” Nature Communications, 11, 193 (2020).
[3] G. D. Joe et al., “Observation of the acoustic Purcell effect with a color-center and a nanomechanical resonator,” arXiv:2503.09946 (2025).
[4] E. Cornell et al., “All-mechanical continuous coherence protection of a single SiV spin,” arXiv:2508.13356 (2025).
[5] K. Kuruma et al., “Controlling interactions between high-frequency phonons and single quantum systems using phononic crystals,” Nature Physics, 21, 77 (2024).
[6] G. Huang et al., “Strain-engineered ultracoherent diamond nanomechanics,” arXiv:2507.01217 (2025).
[7] M. Bhaskar, et al, “Experimental demonstration of memory-enhanced quantum communication”, Nature, 580, 60 (2020)
[8] Can M Knaut et al, “Entanglement of Nanophotonic Quantum Memory Nodes in a Telecommunication Network”, Nature, 629, 573 (2024)
[9] S. W. Ding et al., “High-Q cavity interface for color centers in thin film diamond,” Nature Communications, 15, 6358 (2024).
[10] S. W. Ding et al., “Purcell-enhanced emissions from diamond color centers in slow-light photonic crystal waveguides,” Nano Letters, 25, 12125 (2025).
Biography
Marko Lončar is Tiantsai Lin Professor of Electrical Engineering at Harvard's John A Paulson School of Engineering and Applied Sciences (SEAS). Lončar received his Diploma from University of Belgrade (R. Serbia) in 1997, and PhD from Caltech in 2003 (with Axel Scherer), both in Electrical Engineering. After completing his postdoctoral studies at Harvard (with Federico Capasso), he joined Harvard faculty in 2006. Lončar is expert in nanophotonics and nanofabrication, and his group has done pioneering work in the field of quantum and nonlinear nanophotonics. In particular, Lončar is recognized for his work on the development of diamond and thin film lithium niobate nanophotonic platforms. Lončar has co-authored more than 250 manuscripts in top scientific journals and has given more than 300 invited talks and seminars. He has received NSF CAREER Award in 2009, Sloan Fellowship in 2010, Marko Jarić Foundation Award in 2020, and Microoptics Conference Award in 2023. In recognition of his teaching activities, Lončar has been awarded Harvard University Levenson Prize for Excellence in Undergraduate Teaching (2012), and has been named Harvard College Professor in 2017. Lončar is Fellow of Optical Society of America and IEEE, as well as Senior Member of SPIE. He is co-founder of HyperLight Corporation (Cambridge, MA), VC backed startup commercializing lithium-niobate technology developed in his lab.
Practical information
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