Stanford Engineering
Nanoscale and Quantum Photonics Lab

Semiconductor Quantum Systems (Diamond, Silicon Carbide, and Gallium Arsenide): Cavity QED Quantum Simulator, Quantum Networks, Quantum Sensors

Diamond Quantum Optics

 

Tin-vacancy color centers in a 1D photonic crystal cavity [5]

Nanophotonics

Diamond is a wide bandgap, high refractive index material that can host optically active defects with quantum properties (called “color centers”), making it an excellent platform for nanophotonics-enabled quantum technologies. In the Vučković group, we design and fabricate nanophotonic cavities to study the interaction of confined light with the color centers embedded within. Enhancing these light-matter interactions at high quality factors and small mode volumes opens the door to implementing entanglement schemes necessary for quantum networks and quantum computing.

Our group’s research directions in diamond nanophotonics include design and fabrication of photonic crystal cavities and whispering gallery mode disk resonators [4, 5], incorporation and enhancement of spin qubits in photonic structures [3, 5], and heterogeneous integration of diamond with nonlinear or otherwise advantageous materials [1].

Silicon-vacancy color centers in a diamond nanobeam integrated with thin film lithium niobate [1]

Tin-Vacancy Centers

Diamond is a host material for many different color centers– optically active atomic defects which can have interesting quantum properties. The tin-vacancy center (SnV-) in diamond is a promising qubit for quantum information technologies and in particular for quantum networks. This is because the tin-vacancy center has both favorable optical properties including high Debye-Waller factor, high quantum efficiency, and relatively stable optical lines enabled by inversion symmetry. The SnV- also has favorable spin properties including long spin coherence times at temperatures above 1 Kelvin.

In the Vučković group we are interested in studying both the basic properties of this qubit and its application as a spin-photon interface for quantum networks. Advances in the group include progress on understanding the Hamiltonian of the qubit [6,7], integrating tin-vacancy centers into nanophotonic devices [3,5], and exploring the color center’s properties as a spin qubit including coherent microwave spin control [7] and single-shot spin readout [8].

In the future, we are interested in experiments which advance integration of the tin-vacancy center with nanophotonic structures, improve upon its properties as a spin qubit, and combine these efforts to advance the tin-vacancy qubit as a building block for quantum networks. For example, we are interested in coherent nuclear spin control of isotopically selected tin-vacancy centers, using cavity quantum electrodynamics to enhance optical spin readout, and heterogeneous integration of tin-vacancy qubits in diamond with nonlinear optical materials.

The tin-vacancy center in diamond as a spin qubit. (a) Rabi oscillations driving with a microwave control field and (b) Ramsey experiment to measure spin coherence . (c) Single-shot readout of its spin.

References:

[1] Riedel D, Lee H, Herrmann JF, Grzesik J, Ansari V, Borit J-M, et al. Efficient Photonic Integration of Diamond Color Centers and Thin-Film Lithium Niobate. arXiv [physics.optics]. 2023. Available: http://arxiv.org/abs/2306.15207
[2] Rugar AE, Lu H, Dory C, Sun S, McQuade PJ, Shen Z-X, et al. Generation of Tin-Vacancy Centers in Diamond via Shallow Ion Implantation and Subsequent Diamond Overgrowth. Nano Lett. 2020;20: 1614–1619.
[3] Rugar AE, Dory C, Aghaeimeibodi S, Lu H, Sun S, Mishra SD, et al. Narrow-Linewidth Tin-Vacancy Centers in a Diamond Waveguide. ACS Photonics. 2020;7: 2356–2361.
[4] Dory C, Vercruysse D, Yang KY, Sapra NV, Rugar AE, Sun S, et al. Inverse-designed diamond photonics. Nat Commun. 2019;10: 3309.
[5] Rugar AE, Aghaeimeibodi S, Riedel D, Dory C, Lu H, McQuade PJ, et al. Quantum Photonic Interface for Tin-Vacancy Centers in Diamond. Phys Rev X. 2021;11: 031021.
[6] Rugar AE, Dory C, Sun S, Vučković J. Characterization of optical and spin properties of single tin-vacancy centers in diamond nanopillars. Phys Rev B: Condens Matter Mater Phys. 2019. Available: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.99.205417
[7] Rosenthal EI, Anderson CP, Kleidermacher HC, Stein AJ, Lee H, Grzesik J, et al. Microwave Spin Control of a Tin-Vacancy Qubit in Diamond. Phys Rev X. 2023;13: 031022.
[8] Rosenthal EI, Biswas S, Scuri G, Lee H, Stein AJ, Kleidermacher HC, et al. Single-Shot Readout and Weak Measurement of a Tin-Vacancy Qubit in Diamond. arXiv [quant-ph]. 2024. Available: http://arxiv.org/abs/2403.13110

Silicon Carbide Photonics

Our research group focuses on harnessing the unique properties of 4H-Silicon Carbide (4H-SiC) for advancing on-chip quantum photonics. With its variety of promising color centers and strong second- and third-order optical nonlinearities, 4H-SiC stands out as an ideal material for integrated quantum technologies. We have pioneered a fabrication process for thin films of 4H-SiC-on-Insulator (SiCOI) that is fully compatible with industry-standard CMOS nanofabrication techniques. This allows us to explore the efficient integration of optically addressable qubits within SiC into photonic circuits and to investigate monolithic quantum frequency conversion to the telecommunications band.

 

Figure 1. (a) Silicon vacancy color centers in 4H-SiCOI. (b) SiCOI photonics scanning electron microscope image. (c) Experimentally measured high quality factors demonstrate the potential of SiC for low-loss photonics applications.

 

We have demonstrated Stark tuning properties of the silicon vacancy (VSi) in silicon carbide, a color center that holds promise for optical quantum information processing technologies. Our studies have shown that the VSi exhibits exceptional spectral stability and tunability, enabling us to explore fast modulation regimes, observe two-photon correlations, and demonstrate advanced spectral engineering. These findings underscore the potential of frequency modulation as a powerful tool for generating new light states with unparalleled control over the spectral and temporal properties of single photons.

Figure 2. (a) Spin-level structure of silicon vacancy in SiC and linear Stark tuning. (b) Floquet states obtained in spectral emission with a harmonic drive.

One of the critical challenges in color center quantum technologies is integrating optically coherent emitters into scalable thin-film photonics—a crucial step for large-scale photonics integration within commercial foundry processes. We have successfully integrated near-transform-limited VSi defects into micro-disk resonators fabricated on a CMOS-compatible 4H-SiCOI platform. Our demonstrations include achieving a single-emitter cooperativity of up to 0.8 and observing optical superradiance from pairs of color centers coupled to the same cavity mode. Additionally, we investigate the impact of multimode interference on photon scattering dynamics in this multi-emitter cavity quantum electrodynamics system.

Figure 3. (a), (b) Second-order correlation between single port and two ports of a waveguide cavity coupled system with two-emitters, showing bunching and antibunching, respectively. (c) The level structure representing the pair of two-level-system emitters decaying into degenerate clockwise (red arrows) and counterclockwise (blue arrows) optical modes. (d) Theoretically predicted phase- dependent cross-correlation between clockwise and counterclockwise modes for a pair of ideal two-level emitters. 

These advancements are pivotal for the development of quantum networks in silicon carbide, bridging the gap between classical and quantum photonics by uniting optically coherent spin defects with wafer-scalable, cutting-edge photonic technologies.

Relevant Publications