Jun 3 2019
Scientists, for the first time, have witnessed a break in a single quantum system. The observation — and how they carried out this observation — has promising implications for physics outside the typical understanding of how quantum particles interact to create matter and enable the world to function as one knows it.
The figure describes the dynamics of two spins as a harmonious couple-dance. Different from a solo-dance of a single spin, the couple-dance would present more unique and charming features, such as parity-time symmetry breaking demonstrated in the work. (Image credit: Guoyan Wang and Lei Chen)
The scientists published their results on May 31st, in the journal Science.
Referred to as Parity-Time (PT) Symmetry, the mathematical term defines the properties of a quantum system — the evolution of time for a quantum particle, as well as if the particle is odd or even. Whether the particle moves backward or forward in time, the state of evenness or oddness stays the same in the balanced system. When the parity varies, the balance of system — the system’s symmetry — breaks.
So as to better comprehend quantum interactions and build next-generation devices, scientists should be able to regulate the symmetry of systems. If they can disrupt the symmetry, they could exploit the spin state of the quantum particles as they network, resulting in organized and predicted results.
"Our work is about that quantum control," said Yang Wu, an author on the paper and a PhD student in the Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics at the University of Science and Technology of China. Wu is also a member of the Chinese Academy of Sciences Key Laboratory of Microscale Magnetic Resonance.
Wu, his PhD supervisor Rong and colleagues used a nitrogen-vacancy center in a diamond as their platform. The nitrogen atom with an additional electron, enclosed by carbon atoms, forms the ideal capsule to further examine the PT symmetry of the electron. The electron is a single-spin system, meaning the scientists can control the whole system merely by altering the evolution of the electron spin state.
Through what Wu and Rong term as a dilation technique, the scientists applied a magnetic field to the axis of the nitrogen-vacancy center, drawing the electron into an excitability state. They then applied vacillating microwave pulses, altering the system’s parity and time direction, causing it to break and decay with time.
"Due to the universality of our dilation method and the high controllability of our platform, this work paves the way to study experimentally some new physical phenomena related to PT symmetry," Wu said.
Corresponding authors Jiangfeng Du and Xing Rong, professors with the Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics at the University of Science and Technology of China, were on the same wavelength.
The information extracted from such dynamics extends and deepens the understanding of quantum physics. The work opens the door to the study of exotic physics with non-classical quantum systems.
Jiangfeng Du, Professor, Hefei National Laboratory for Physical Sciences, Microscale and Department of Modern Physics, University of Science and Technology of China
Du is also an academician of the Chinese Academy of Sciences.
The other authors include Wenquan Liu, Jianpei Geng, Xingrui Song, Xiangyu Ye, Chang-Kui Duan, and Xing Rong. All of the authors are affiliated with the Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics at the University of Science and Technology of China. Liu, Ye, Duan, Rong, and Du are also affiliated with both the University's CAS Key Laboratory of Microscale Magnetic Resonance, and the University's Synergetic Innovation Center of Quantum Information and Quantum Physics.