Chinese Physicists Realize Quantum Simulation
of the Unruh Effect
SCIENCE CHINA-PHYSICS, MECHANICS & ASTRONOMY, CHINA
Quantum mechanics and relativity theory are two pillars of modern physics. With their amalgamation, many novel phenomena have been identified. For example, the Unruh effect  is one of the most significant outcomes of quantum field theory. This effect serves as an important tool to investigate phenomena such as the thermal emission of particles from black holes and cosmological horizons . It has been 40 years since the discovery of the Unruh effect. However, this effect is too weak to be observed with current techniques. There have been many attempts to search for observational evidence of the Unruh effect and, in general, experimental observation is still a great challenge. To address this issue, quantum simulators [3, 4] may provide a promising approach. Quantum simulation is widely applied in simulating the quantum systems that cannot be efficiently simulated by classical computers, or are not directly tractable by current techniques in the laboratory.
Researchers, led by Prof. Jiangfeng Du from the University of Science and Technology of China, reported an experimental simulation of the Unruh effect with an NMR quantum simulator . The experiments were performed on a Bruker Avance III 400 MHz spectrometer. The researchers used a sample of 13C, 1H and 19F nuclear spins in chloroform as the NMR quantum simulator, as shown in Figure 1(a). The simulated Unruh effect on the quantum states can be realized by the pulse sequence acting on the sample, as depicted in Figure 1(b). Using the quantum simulator, they experimentally demonstrated the behavior of Unruh temperature with acceleration, which agrees nicely with the theoretical prediction, as shown in Figure 2. Furthermore, they investigated the quantum correlations quantified by quantum discord between two fermionic modes as seen by two relatively accelerated observers. It is shown for the first time that quantum correlations can be created by the Unruh effect from classically correlated states. This work was recently published in the journal Science China-Physics, Mechanics & Astronomy.
Fig. 1: (a) The NMR quantum simulator consists of 13C, 1H and 19F nuclear spins in chloroform. (b) The experimental pulse sequence for simulating the Unruh effect.
Fig. 2: Experimental results (blue triangles) of simulating the Unruh temperature with the acceleration parameter. The blue line is the theoretical prediction.
It is interesting that the Unruh effect was on Feynman's blackboard as one of the issues to learn at the time of his death in 1988, while it was also Feynman who conceived of the idea of quantum simulation in 1982. This quantum simulation of the Unruh effect will provide a promising window to explore the quantum physics of accelerated systems, which widely appear in black hole physics, cosmology and particle physics.
This research was funded by the National Key Basic Research Program of China (Grant Nos. 2013CB921800 and 2014CB848700) and the National Natural Science Foundation of China (Grant Nos. 11227901, 91021005, 11375167, 11374308, 11104262 and 11275183).
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 F. Jin, H. Chen, X. Rong, H. Zhou, M. Shi, Q. Zhang, C. Ju, Y. Cai, S. Luo, X. Peng, and J. Du, Experimental simulation of the Unruh effect on an NMR quantum simulator, Science China-Physics, Mechanics & Astronomy, 2016, Vol. 59, Issue (3): 630302, DOI: 10.1007/s11433-016-5779-7. http://phys.scichina.com:8083/sciGe/EN/Y2016/V59/I3/630302
Yuanyuan Guo received her PhD in theoretical physics from the Institute of Theoretical Physics, Chinese Academy of Sciences. Since 2011, she has been an editor of Science China-Physics, Mechanics & Astronomy, a monthly peer-reviewed research journal focusing on high quality and innovative research results, in the fields of physics, mechanics and astronomy.