Diamond quantum memory with Germanium vacancy exceeds coherence time of 20 ms

Diamond color centers are the focus of an increasing number of research studies due to their potential to develop quantum technologies. Some works have specifically explored the use of negatively charged Group-IV diamond defects, which exhibit an effective spin-photon interface, as nodes of quantum networks.

Researchers at the University of Ulm in Germany recently took advantage of a germanium vacancy (GeV) center in diamond. Quantum memory. The resulting quantum memory, presented in a Physical examination letters Paperwas found to exhibit promising convergence times of over 20 ms.

“The main focus of our research group is the search for diamond color centers for quantum applications,” paper co-author Katrina Senkala told Phys.org. “By far the most famous defect in diamond has been the nitrogen vacancy center, but, recently, other color centers have also become the focus of research. These consist of an element in column IV of the periodic table—Si, Ge, Sn or Pb, and a lattice vacancy (ie, missing the next-neighbor carbon atom).”

Group-IV color centers have been found to exhibit much stronger emission in the zero phonon line than previously functionalized nitrogen vacancy centers. In addition, the inversion symmetry of these centers makes them well suited for integration into nanophotonic devices—an important step toward an efficient scalable quantum network based on solid-state, single-photon sources.

“Our goal is to make a significant contribution to the development of quantum networks that facilitate long-distance quantum communication and distributed quantum computing,” Senkla said. “In the realm of quantum networking, an important aspect is the quantum network node, which demands an efficient spin-photon interface and extended memory times.”

The research group at the University of Ulm has been exploring the potential of group IV defects as candidates for quantum network nodes for some time, recently focusing on the GeV center. These particular defects have an inherent efficiency at the spin-photon interface, characterized by a highly coherent flow of photons.

Such coherent flow of photons is a key factor in enabling efficient quantum communication over long distances. Anyway, sense Quantum systems The use of Group IV diamond defects involves overcoming various challenges.

“These defects face constraints related to phonon-mediated relaxation, coherence, and extended memory times due to affecting memory time,” Senkla explained. “Our recent work is focused on solving this important challenge, advancing the development of robust quantum network nodes. Through our efforts, we hope to overcome these obstacles and contribute to its development. are Quantum Technologies“

The system developed by Senkla and his colleagues uses a GV as a quantum memory element. To overcome the challenges typically associated with development group IV defect-based quantum systems, the researchers used a two-fold strategy.

The first part of this strategy aims to reduce the negative effects of phonons on quantum information. Indeed, group IV defects can easily couple to phonons, which can destroy quantum information.

“To overcome this challenge, we used a Dilution Refrigerator (DR), a state-of-the-art device widely used in advanced quantum computing experiments such as IBM’s quantum computing experiments. can produce temperatures in the range of a few hundred millikelvins,” Senkla said.

“The second part of our approach, on the other hand, deals with spin noise and optimization of information storage. Operating in such a low temperature range makes spin noise the main factor in latency. Memory times To prolong and preserve quantum information, we implemented complex spin refocusing with microwave pulses and with strategically selected time intervals in which computational operations can be performed.”

Another aspect Senkala and his colleagues had to consider when developing their quantum memory was managing the heat load introduced with each control pulse. In fact, reduction refrigerators have a limited cooling capacity, and exceeding this limited capacity can increase the temperature and thus facilitate the production of phonons, which in turn can lead to disorder. .

“Developing an optimized pulse sequence involves using the Ornstein-Ahlenbeck process, a noise modeling technique that captures the dynamics of the system,” Senkla said.

“Ornstein-Ohlenbeck simulations provided important insights into noise dynamics, helping to find configurations that balance spin refocusing, computational lags, and experimental heat load management.”

The researchers tested their proposed quantum memory in both experiments and simulations. In particular, the results they obtained in the simulations were in close agreement with the experimental data.

“Ours is the first successful demonstration of efficient spin control for a germanium vacancy (GeV) at millikelvin temperatures,” Senkla said. “The comprehensive approach we introduced has the potential to advance quantum memory performance in diverse experimental conditions and other group IV defects, with relevance beyond GeV.”

The design underlying the researchers’ proposed quantum memory is relatively simple and can be replicated using other Group IV defects beyond GeVs. This design was eventually found to increase the synchronization times of GEV-based memories by a factor of 45, reaching a record synchronization time of 20 milliseconds.

The remarkable results presented in the paper highlight the potential of GEV defects to develop quantum network-based systems. In the future, this work may encourage greater use of group IV defects for quantum communication applications.

“Our study extends beyond the laboratory, offering valuable insight into practical applications of GeV and other group-IV defects in quantum technologies,” Senkla said.

“Our Ornstein-Uhlenbeck simulations pave the way for better control schemes for GeV and similar defects under different experimental conditions. The potential implications extend to industries such as Amazon Web Services (AWS), which have SiV-like Group IV defects. exploring quantum networks based on

The recent study by Senkla and his colleagues could ultimately contribute to the development of quantum communication systems as well as various industries that could benefit from high-performance quantum technologies. Meanwhile, the researchers plan to continue exploring the potential of GeV diamond defects as quantum network nodes.

“In expanding our exploration of GeV and its potential as a quantum network node, we are actively incorporating GeV into a true quantum network,” Senkla said.

“Our team at Ulm is in the process of building experimental setups to serve as additional nodes in this quantum network, which will be a demonstration site for a quantum network focused on group IV defects in Ulm, Germany. is in line with our vision for

In their upcoming studies, the researchers plan to incorporate GEVs into nanophotonic cavities, while also resolving the surrounding atomic spins. Both of these steps are crucial for the growth of quantum networks.

“The first of these steps increases our photon rate and thus the entanglement rate and subsequently enables the implementation of quantum error correction protocols, achieving fault-tolerant quantum computing,” Senkla added. is an important step towards

“We are on an exciting journey and look forward to furthering our research.”

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