(PhysicsWorld) Researchers at the Center for Quantum Information at Tsinghua University in Beijing, have developed an efficient way to characterize the effective many-body Hamiltonian of the solid-state spin system associated with a nitrogen-vacancy (NV) centre in diamond. The technique will be important for making and controlling high-fidelity quantum gates in this multi-spin quantum register.
In their work, the researchers characterized the effective many-body coupling Hamiltonian of an NV centre containing one electron spin and ten weakly coupled 13C nuclear spins. They then used the learnt Hamiltonian parameters to optimize the dynamical decoupling sequence and so minimize the effect from the unwanted crosstalk coupling. This adaptive scheme was first put forward by researchers at Delft University in the Netherlands.
The researchers validated their technique by designing a universal quantum gate set that includes three single-qubit gates for each of the 11 qubits and the entangling two-qubit gate between the electron spin and each of the 10 nuclear spins. “In principle, we can realize any unitary operation on this 11-qubit register by combining the above gate set,” said Panyu Hou, leader of the study.
“This learning technique could be a useful tool to characterize many-body Hamiltonians with a constantly-on interaction,” he adds. “The 11-qubit quantum register that we made might also be used as a proof-of-principle test of some quantum algorithms.”

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