First universal diamond spin qubit gate
Fujitsu and QuTech in Delft have demonstrated a complete universal quantum gate set for diamond spin qubits for the first time.
The universal spin qubits have an error probability below 0.1%, achieving a fidelity among the highest reported over all quantum hardware technologies.
The collaboration with QuTech, a spin out of the Delft University of Technology in the Netherlands, marks an important step for the diamond spin method towards carrying out quantum error correction and practical quantum computing.
High-purity diamonds create a stable two-qubit system comprising an electron spin and nitrogen nuclear spin within a nitrogen-vacancy centre. The nitrogen vacancy technique is also used by Quantum Brilliance for its diamond foundry service.
These diamond spin qubits still operate at cryogenic temperatures, but 100x higher at around 10 Kelvin.
A key difference from superconducting qubits such as transmons is that the diamond spin qubits can transmit quantum states using photons and so link directly to optical interconnects. This is seen as a promising path towards scalable quantum computers and distributed computing via quantum networks.
The artificial diamond substrate in this case was jointly developed by Element Six and TU Delft with a low concentration of the carbon-13 isotope of 0.01%, reduced from 1%. This helps to reduce the noise of the system that hit the fidelity of the qubits.
The decoupling gates for the qubits were designed to mitigate environmental noise. These are sequences of controlled pulses designed to remove the impact of environmental noise on the qubits and extend their ability to retain quantum information.
The team also used gate set tomography, a high-precision technique to measure the performance of qubits and quantum gates, to optimise quantum gate operations. This provided complete information on gate errors, enabling optimization of all parameters of quantum gate operations, including gate pulse strength.
Going forward, Fujitsu and QuTech are looking to scale up the number of qubits used and develop optical quantum chips and cryoCMOS control circuits for large scale diamond spin quantum computers.
The findings were published in Physical Review Applied
www.fujitsu.com; www.qutech.nl
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