A New Spin On Quantum Measurements

Researchers have developed a method for quantifying the collective spin motions in a magnet using an elementary quantum-computing device.

AsianScientist (Nov. 28, 2017) – A research group at the University of Tokyo had observed magnons—the smallest units of energy in a magnet—as discrete units using a superconducting quantum bit. They published their findings in Physical Review Letters.

Magnons have the potential to enable new types of wave-based computing technologies that are free from existing limitations such as dissipation of energy. Previously, a method for quantifying the collective spin motions of magnons in a magnet (ferromagnetic material) at the single-quantum level did not exist.

In this study, a research group led by Professor Yasunobu Nakamura and Assistant Professor Yutaka Tabuchi at the Research Center for Advanced Science and Technology of the University of Tokyo, Japan, used a superconducting quantum bit—the minimum unit of quantum information based on a superconducting circuit—as a highly sensitive detector to measure the number distribution of magnons excited in a ferromagnetic single-crystalline sphere.

They also measured the quantum-mechanical distribution of microwave photons in a transmission line. Their results suggest that superconducting qubit devices are suitable as detectors for quantum-mechanical behaviors of matter, through the hybridization of quantum technologies combining superconducting qubits with magnons in a quantum-mechanical state.

The hybrid quantum systems created by merging superconducting quantum bits and other physical systems are likely to find applications in the development of new sensor technologies and lead to the adoption of advanced quantum information technologies, including quantum computers, quantum communications and quantum cryptography, in the future.

“The technique we established opens up the plausibility of a new quantum-sensing application of hybrid quantum systems using a quantum bit based on a superconducting circuit,” said Nakamura.

“We also measured the number distribution of propagating microwave photons with a similar technique,” Tabuchi added. “We hope to accelerate our efforts in the research and development of quantum computing technology as well as further develop hybrid quantum technology combining various physical systems and superconducting quantum-bit devices.”

The article can be found at: Kono et al. (2017) Nonclassical Photon Number Distribution in a Superconducting Cavity under a Squeezed Drive.


Source: University of Tokyo; Photo: Yasunobu Nakamura.
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