Quantum networks promise to revolutionise computation and sensing, but building them requires linking multiple quantum nodes together, a task hampered by the complexity of individual devices. Prithvi Gundlapalli, Philipp J. Vetter, and Genko Genov, from Ulm University, alongside colleagues including Matthias M. Müller from Forschungszentrum Jülich GmbH, now demonstrate a significant step towards scalable quantum networks by establishing the germanium-vacancy (GeV) center in diamond as a viable platform. The team achieves high-fidelity, single-shot readout of both the GeV center itself and a neighbouring nuclear spin, overcoming challenges posed by the center’s inherent spin properties and enabling indirect control of these nuclear spins. This breakthrough establishes the GeV center as a compelling candidate for building the next generation of robust and interconnected quantum network nodes, paving the way for more powerful and versatile quantum technologies.

Group-IV color centers in diamond offer a pathway to overcome the limitations of single quantum devices by connecting multiple nodes into a scalable architecture. These centers, paired with long-lived nuclear spins, have emerged as promising building blocks for technologies such as blind quantum computing and quantum-enhanced sensing. This work establishes the germanium-vacancy (GeV) center as a viable platform for such network nodes. Researchers utilized correlation spectroscopy to identify individual nuclear spins within a complex spin environment, overcoming previous limitations imposed by the color center’s inherent properties.

Controlling Distant Nuclear Spins via Germanium-Vacancy Centers

This research establishes the germanium-vacancy (GeV) center in diamond as a promising platform for building scalable quantum networks, addressing a key challenge in creating large-scale electro-nuclear registers. Scientists focused on the GeV center and its surrounding nuclear spins, which offer long-lived quantum information storage. The study pioneered a two-dimensional correlation spectroscopy technique to identify and control individual nuclear spins within the complex spin environment surrounding the GeV center, a feat previously hindered by overlapping signals and strong coupling effects. This innovative method allows for selective control of distant, weakly-coupled 13C nuclear spins via the GeV center, enabling conditional gate operations crucial for quantum information processing.

To achieve high-fidelity control and readout, the team engineered an experimental setup utilizing a high-pressure, high-temperature grown diamond crystal with naturally abundant 13C. Experiments were conducted at a base temperature of approximately 80 mK within a dilution refrigerator, and the GeV center was coupled to surrounding 13C spins embedded within a solid immersion lens. An external magnetic field was applied to access and coherently control the electron spin qubit manifold using microwave fields. Optical addressing and readout were performed using a tunable laser, achieving an initial state preparation fidelity of 98%.

A critical achievement of the work was the demonstration of record-high single-shot readout (SSR) fidelity, reaching 95. 80% on the GeV center. This was accomplished through the implementation of composite pulses to mitigate state preparation errors and an anti-correlation check to reject blinking events, significantly improving the reliability of the readout process. Furthermore, scientists achieved a fidelity of 93. 66% in single-shot readout on a nearby 13C nuclear spin using optimized pulses. The team estimates a cyclicity of approximately 104, enabling effective single-shot readout despite the system’s low collection efficiency. These advances position the GeV center as a compelling candidate for next-generation network nodes, paving the way for scalable quantum networks based on group-IV color centers in diamond.

Germanium-Vacancy Centre Shows Nuclear Spin Control

Scientists have established the germanium-vacancy (GeV) center in diamond as a promising platform for building scalable quantum networks. This work overcomes a major challenge in realizing large-scale electro-nuclear registers by demonstrating precise control and readout of both the GeV center itself and neighboring nuclear spins. The team achieved high-fidelity single-shot readout of the GeV center and a neighboring nuclear spin, critical for implementing feed-forward control within the network. Experiments revealed a complex spin environment surrounding the GeV center, identifying individual nuclear spins using correlation spectroscopy.

This method allows for the extraction of resonance frequencies of individual nuclear spins, enabling direct control over them. The team successfully distinguished the hyperfine interactions with two nearby 13C nuclear spins and determined hyperfine coupling values. The team achieved a nuclear spin coherence time of (1. 98 ±0. 15) ms. By implementing a measurement-based initialization protocol, scientists prepared a nuclear spin in a superposition state and performed a Ramsey measurement, observing nuclear spin precession at distinct frequencies depending on the electron spin state. These results position the GeV center as a compelling candidate for next-generation network nodes, enabling advanced quantum information processing.

Germanium-Vacancy Centre Enables High-Fidelity Quantum Control

This research establishes the germanium-vacancy (GeV) center in diamond as a promising platform for building scalable quantum networks. Scientists successfully demonstrated high-fidelity, single-shot readout of both the GeV center itself and a neighboring nuclear spin, achieving fidelities of 95. 80% and 93. 66% respectively. These results represent a significant improvement over previously reported fidelities and are crucial for error detection, correction, and feed-forward operations essential for quantum networks.

A key achievement lies in the ability to identify and control multiple nuclear spins within the complex spin environment of the GeV center, overcoming a limitation inherent in many spin-1/2 systems. Researchers employed correlation spectroscopy to pinpoint these nuclear spins and then utilized a basis-transformed gate to initialize them for measurement, enabling observation of their effective Larmor frequencies. This method paves the way for scaling up spin registers, vital for preserving information during entanglement and implementing robust error correction schemes. The authors acknowledge that the fidelity of certain operations is currently limited by interactions between the electron and nuclear spins. Future work will focus on optimizing control techniques, including the implementation of optimal control methods and combining radio-frequency control with decoupling gates, to further enhance gate fidelities and signal strength. These advancements position the GeV center and its surrounding nuclear spins as a compelling building block for fully operational quantum network nodes.

👉 More information
🗞 High-Fidelity Single-Shot Readout and Selective Nuclear Spin Control for a Spin-1/2 Quantum Register in Diamond
🧠 ArXiv: https://arxiv.org/abs/2510.09164