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Step towards long-lasting quantum memory: NUST MISIS scientists make photons interact

MOSCOW, Feb. 6 / PRNewswire / - An international team of researchers can for the first time present experimental evidence of effective interaction between microwave photons via superconducting qubits. The study published in npj Quantum Materials (https://www.nature.com/articles/s41535-021-00310-z) could be a step towards long-lived quantum memory and the development of commercial quantum devices.

Scientists believe that single particles of light, or photons, are perfect for sending quantum information. Encoded with quantum data, they could literally transmit information at the speed of light. While photons would make great carriers because of their speed, they don't like to interact with each other, which makes it difficult to achieve quantum entanglement.

A team of scientists from NUST MISIS, the Karlsruhe Institute of Technology, the Russian Quantum Center and the Joffe Institute St. Petersburg has for the first time succeeded in making photons interact effectively with one another using a series of superconducting qubits and a waveguide. In their experiments, the researchers used photons with a frequency of a few GHz and a wavelength of a few centimeters.

"We used superconducting qubits, which are basically artificial atoms, because they have been shown to interact strongly with light. The interaction between natural atoms and natural light is weak because of the small size of natural atoms. Superconducting qubits are man-made, their size can be up to 0.1 mm, which makes it possible to significantly increase their dipole moment and polarity and to develop a strong interaction between light and matter ", explained Prof. Alexey Ustinov, head of the laboratory for superconducting metamaterials at NUST MISIS and group leader at Russian Quantum Center, who co-authored the study.

Superconducting qubits are a leading qubit modality currently being pursued by industry and science for quantum computing applications. However, they need millikelvin temperatures (mK) to function. The most powerful of the current superconducting quantum devices contains fewer than 100 qubits. As qubits are added, the number of operations a quantum computer can perform grows exponentially. However, the maximum number of qubits that can be integrated into a quantum computer is limited by the size of the refrigerators that are used to cool them to operating temperature. With this in mind, recent efforts by scientists have focused on increasing the computing power of a quantum computer by transmitting quantum signals from one refrigerator to another. To construct this transmission, the scientists coupled eight superconducting transmon qubits to a common waveguide - a structure that guides waves such as light waves.

"By using dedicated flux bias lines for each qubit, we gain control over their transition frequencies. It has been deduced and experimentally confirmed that multiple qubits get an infinite-range effective interaction mediated by photons that can be adjusted to the spacing between qubits." , says Alexey Ustinov.

The circuit of this work extends experiments with one and two qubits to a full-blown quantum metamaterial and thus paves the way for large-scale applications in superconducting waveguide quantum electrodynamics.

Link - https://en.misis.ru/university/news/science/2021-04/7320/

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Original content by: The National University of Science and Technology MISiS, transmitted by news aktuell