NV centers | Nitrogen vacancies

22. November 2022

Due to their high reliability and – relatively – simple implementation, qubits based on nitrogen-vacancy (NV) centres are a promising technological approach for quantum computing. They do not require any cooling and can therefore also be used in mobile applications – a major advantage over other, more complex systems. This enables mobile quantum computers, for example in aircraft and satellites. However, NV centres can do more than just calculate. Because they are sensitive to magnetic fields, they can also be used as extremely sensitive quantum sensors with a wide range of applications.

Diamond crystal with NV spin qubits on a photonic microchip | Image: XeedQ

Significance for Germany

Alongside ion traps, NV centres are one of the quantum technologies most strongly established in German industry. A vibrant ecosystem of many companies and start-ups has emerged centred around their production, categorisation and use. Numerous German research institutions are international leaders in this field. This expertise is an asset for the entire quantum computing ecosystem.

NV centers in the DLR QCI

The first contract focusing on NV centres involves the construction of two demonstrator systems with at least four qubits and a simple user interface. Such a system already exists as a prototype, is mobile and about the size of a small refrigerator – therefore it can quickly be made available for users at DLR. This will allow them to test newly developed quantum algorithms directly using real quantum hardware.

The next big step is the further development of larger systems. By the end of the project, it is expected that two quantum computers will be available with 32 qubits that are scalable and error-correctable and can execute algorithms with high user-friendliness. The development will cover several work packages so that the number of qubits, their quality and the functionality of the control software can be gradually increased.

Additionally to these contracts we contracted two companies to deliver solid-state spin enabling technologies for the production of high quality diamonds and their characterisation.

Mobile NV Centers Quantum Computer | Image: SaxonQ

All NV center projects

Luminescence NV center | Bild: SaxonQ

Technical implementation

Quantum computers based on NV centres use imperfections in diamond crystals to create qubits. This involves replacing a carbon atom in the crystal structure of the diamond with a nitrogen atom. Adjacent to the nitrogen atom, a vacancy – a gap in the crystal – is created, which is occupied by electrons. Through the interaction of the spin of these electrons with the nuclear spins of the surrounding carbon and nitrogen atoms, the spin of the nitrogen-vacancy centre and the spins of the surrounding nuclei can be used as qubits. The entanglement results from the interactions of the spins. By manipulating these spins with microwaves and radio waves, gate operations can be implemented for calculations.

The key technological challenge is the controlled production of multiple NV centres, which must be very close together – less than 20 nanometres is common. This controlled production and placement is the bottleneck for the scalability of quantum computers with NV-centre qubits. That is why one goal of the DLR QCI contract is to further develop their clever two- and three-dimensional arrangement. The extensive experience with NV-centre quantum sensors in Germany is of great help here.

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