Single T centers in silicon are promising spin-photon interfaces for quantum networking applications. We report electric field control for device-coupled single T centers, demonstrating DC Stark tuning and up to 30% spectral linewidth narrowing.
Single T centers in silicon have emerged as promising optically active spins for quantum networking applications. One of the major obstacles to advancing the system is their broad optical linewidth due to spectral diffusion, which is two orders of magnitude larger than their cavity-enhanced radiative linewidth. We tackle this issue by utilizing above-band optical excitation delivered via a laser scanning microscope to device-coupled single T centers, achieving up to 70% optical linewidth reduction. We attribute the linewidth narrowing effect to the filling of nearby charge traps by photo-generated free carriers. We analyze charge stabilization dynamics by exploiting pulsed above-band excitation and develop a rate equation model to describe the dynamics and to explain the observed linewidth narrowing and center shift. This work provides an effective pathway to control and reduce the optical linewidth for single T centers, clearing one of the major roadblocks to advance the single T center spin platform for quantum information and networking applications.
Electrons bound to shallow donors in ZnSe quantum wells are promising candidates for optically addressable spin qubits and single-photon sources. However, their optical coherence and indistinguishability are often limited by spectral broadening arising from charge fluctuations in the local environment. Here, we report electrical control of single donor qubits in ZnSe quantum wells. The applied field induces a DC Stark shift that tunes the emission energy over a range exceeding 30 times the inhomogeneous linewidth, effectively compensating for emitter-to-emitter variations. Concurrently, the field stabilizes trap occupancy, yielding a twofold reduction in optical linewidth and the suppression of spectral wandering. A statistical model based on trap dynamics qualitatively reproduces these observations and elucidates the mechanism of field-assisted charge noise suppression. Our results identify electrical control as a versatile pathway to significantly improve optical and spin addressability.
Spin-photon interfaces based on silicon quantum emitters offer a scalable platform for quantum computing and networking. However, achieving coherent photon emission remains a primary challenge due to stringent material quality requirements. To overcome this, we utilise high-purity molecular-beam epitaxy (MBE) to epitaxially incorporate single T centres in silicon-on-insulator (SOI) wafers. We demonstrate single T-centre emission coupled to a nanophotonic waveguide and observe significant suppression of homogeneous broadening, yielding optical linewidths as narrow as 30 MHz using natural silicon for crystal growth. These results establish epitaxial T centres as a robust foundation for coherent spin-photon interfaces in silicon quantum photonics.
Single photons enable the distribution of quantum information over large distances and thus play a major role in quantum technologies such as communication and computing. Solid-state emitters are practical and efficient sources of single photons that can be manufactured in large numbers. When combined with a spin, the resulting spin-photon interfaces can store quantum states for extended periods and serve as the basis for quantum networks and repeaters. Among the many host materials explored over the past few decades, silicon stands out for its advanced nanofabrication, the maturity of its integrated photonics and microelectronics, and its high isotopic purity, which leads to exceptionally long spin coherence. These properties position silicon single-photon emitters and spin-photon interfaces among the most promising hardware platforms for implementing quantum networks and distributed quantum information processors. This review summarizes the current state of the art and open challenges towards coherent single-photon sources and scalable spin-photon interfaces based on color centers and erbium dopants in nanophotonic silicon structures.
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.
Quantum networking is a crucial technology towards constructing large-scale distributed quantum systems. The structure of photonic link and distributed network nodes allows high-speed and high-fidelity interconnect, enabling various applications such as distributed quantum computing and sensing, as well as secure quantum communications. Optically interfaced solid-sate spins are promising candidates for building a quantum network due to their active spin-photon interfaces, compatibility, and scalability for device integration. Especially for defect spins in silicon, the platform benefits from mature silicon photonic industry, and can access to the integration techniques developed over the past decades. T center in silicon particularly holds great expectations because of the telecom-O band optical interface, ground state doublet spin manifold, and long-lived nuclear spin coherence. Their telecom spin-photon interface provides a direct link between stationary quantum memory and flying qubits that are compatible with the existing telecommunication fiber network infrastructure. This work focuses on investigating cavity quantum electrodynamics (cQED) for cavity-coupled single T centers, its applications in quantum optical control of T center optical properties, and in realizing single-shot spin state readout. The cavity enhanced light-matter interaction mitigates the caveats of T center, such as long radiative lifetime, low Debye-Waller factor, and lack of polarization selection rule for the optical transitions. In this work, by integrating single T centers with a low-loss, small mode volume silicon photonic cavity, we have achieved the Purcell enhancement for boosting the T center fluorescence rate with a factor of 6.89. We build up the theoretical framework based on the Jaynes-Cummings model and Lindblad master equation to explain experimental observations and reveal cQED parameters. The further study on the electronic spin state readout is carried out as the fast, high-fidelity single-shot readout is critical for quantum information processing. Two methods are proposed based on realistic cQED parameters: resonant fluorescence readout in the low-cooperativity regime and spin-dependent cavity-reflection readout for intermediate- and high-cooperativity regimes. Both approaches demonstrate feasibility of high-fidelity (F > 0.95) readout, particularly the reflection readout allows F > 0.99 within a short readout time of 50 μs. This work demonstrates a promising telecom spin-photon interface with high-fidelity readout based on cavity-coupled single T centers in silicon, which are promising candidates for building future large-scale quantum networks.