Modern quantum computers and algorithms traditionally rely on one- and two-qubit gates. To implement operations on three qubits, eight two-qubit operations must be performed sequentially, which complicates the algorithms and increases the number of errors. In Russia, for the first time, an operation was performed on three qubits at once with record accuracy.
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About work reported scientists from MISIS University, Russian Quantum Center, Institute of Microelectronics Nanotechnologies of the Russian Academy of Sciences and MIPT. Strictly speaking, we are not talking about the development of a superconducting quantum processor, as the official press release tells us, but about the ability to perform a complex operation on all three qubits at once with record accuracy.
The device is based on three superconducting fluxonium qubits connected through a common control element – transmon. It allows you to influence a certain combination of states of all three qubits, performing the so-called CCZ (Controlled-Controlled-Z) operation. It changes the phase of one of eight possible combinations of qubit states. Similar operations are used in quantum algorithms, as well as in the creation of error correction systems necessary to increase the reliability of calculations, as well as for factorization of large numbers, which potentially threatens cryptocurrency and ciphers.
“We experimentally implemented a three-qubit CCZ gate directly, rather than a cascade of one- and two-qubit operations. At the same time, the control remains as simple as for standard two-qubit gates: one microwave pulse with a duration of 65 ns is enough, which is calibrated using traditional methods – Rabi and Ramsey oscillations, which allow tracking changes in the state of qubits under the influence of a microwave signal,” said Grigory Mazhorin, a researcher at the Laboratory of Superconducting Quantum Technologies of NUST MISIS and the group “Superconducting Qubits and Quantum Circuits” of the RCC.
Image Source: MISIS
With the traditional approach, to achieve comparable accuracy of the final operation, individual two-qubit gates must operate with an accuracy of about 99.94% each, which today is only possible on a limited number of the most modern and complex quantum computers. The Russian development makes it possible to perform the same operation with 99.39% accuracy in one sitting on simpler and less demanding equipment.
“The developed architecture can become the basis for scaling superconducting quantum processors. According to scientists, the created module can be integrated into a two-dimensional circuit, retaining the mechanisms for suppressing unwanted interactions between its elements,” the developers summarize.
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