Delft University Team Advances Quantum Computing with High-Fidelity Gates

Researchers from QuTech Delft University of Technology, Kavli Institute of Nanoscience Delft, Department of Quantum and Computer Engineering, Department of Microelectronics Delft University of Technology, and Element Six have made significant advancements in quantum computing. They have designed a complete high-fidelity gate set for a two-qubit system using the electron and nuclear spin of a nitrogen-vacancy center in diamond. The team achieved single-qubit gate fidelities of up to 99.9991% and a two-qubit gate fidelity of 99.935%. This development could lead to larger-scale quantum systems and new opportunities for quantum processing with color-center qubits.

What are the New Developments in Quantum Computing?

Quantum computing is a rapidly evolving field, with researchers constantly pushing the boundaries of what is possible. A team of researchers from QuTech Delft University of Technology, Kavli Institute of Nanoscience Delft, Department of Quantum and Computer Engineering, Department of Microelectronics Delft University of Technology, and Element Six have made significant strides in this area. They have designed and demonstrated a complete high-fidelity gate set for a two-qubit system formed by the electron and nuclear spin of a nitrogenvacancy center in diamond.

The team used gate set tomography (GST) to systematically optimize the gates and achieved single-qubit gate fidelities of up to 99.9991% and a two-qubit gate fidelity of 99.935%. These gates are designed to decouple unwanted interactions and can be extended to other electron-nuclear spin systems. The high fidelities demonstrated provide new opportunities towards larger-scale quantum processing with color-center qubits.

How Does This Advance Quantum Computing?

Quantum computing relies on the principles of quantum mechanics to process information. Qubits, or quantum bits, are the basic units of quantum information. They are significantly more powerful than classical bits because they can exist in multiple states at once, thanks to a property known as superposition. This allows quantum computers to process a vast number of computations simultaneously.

The researchers’ work on high-fidelity quantum gates for spin qubits in diamonds represents a significant step forward in the field. Quantum gates are fundamental to quantum computing, as they allow for the manipulation of qubits. High-fidelity quantum gates are particularly desirable because they reduce the likelihood of errors in quantum computations.

The team’s achievement in realizing high-fidelity universal quantum gates for a two-qubit system is a key advancement toward larger-scale quantum systems. Their work also opens up new opportunities for quantum processing with color-center qubits, which are promising for quantum computation and quantum networks.

What is the Significance of the Nitrogen-Vacancy Center in Diamond?

The nitrogen-vacancy (NV) center in diamonds is a defect in the crystal structure of diamonds where a nitrogen atom replaces a carbon atom and an adjacent lattice site is vacant. This defect forms a stable, controllable, and coherent two-level system that can be manipulated at room temperature, making it an attractive platform for quantum computing.

In this study, the researchers used the NV center in a diamond as a two-qubit system consisting of the NV electron spin and the intrinsic 14N nuclear spin. They demonstrated high-fidelity single-qubit gates for the NV electron spin and reported a high two-qubit electron-nuclear gate fidelity of 99.92%.

How Does Gate Set Tomography (GST) Contribute to This Research?

Gate set tomography (GST) is used to characterize quantum gates. It involves applying a sequence of quantum gates to a quantum system and measuring the resulting state. By comparing the measured states with the expected states, researchers can determine the accuracy of the quantum gates.

In this study, the researchers used GST to systematically optimize the gates for the two-qubit system formed by the NV electron and nitrogen spins. They obtained the process matrix for both single and two-qubit gates in the full two-qubit space and demonstrated high fidelities for all gates in the two-qubit space.

What are the Future Implications of This Research?

The high gate fidelities achieved by the researchers provide a promising starting point toward larger-scale quantum systems based on color-center qubits. Decoupling unwanted interactions and extending this approach to other electron-nuclear spin systems could lead to further advancements in quantum computing.

Moreover, the researchers’ work illustrates how the information of the gate errors can be used to implement error mitigation techniques. They used a SWAP gate to store quantum states in the nitrogen quantum memory for over 100 seconds, demonstrating long-term quantum information storage potential.

In conclusion, this research represents a significant step forward in the field of quantum computing, bringing us closer to the realization of larger-scale quantum systems. The high-fidelity quantum gates developed by the researchers could pave the way for more complex quantum algorithms and more robust quantum networks.