Scientists discover a new kind of quantum entanglement
A joint research team of the STAR group of the University of Science and Technology of China (USTC) and Brookhaven National Laboratory and Shandong University, which plays a leading role in the STAR International Collaboration Group [1], has realized the first Fermi-scale single-particle double-slit interference experiment with an unstable particle ρ0 meson as an entity during high-energy heavy-ion collisions, and observed polarization space using the linear polarization feature of the process interferometric phenomena using the linear polarization feature of the process. The study was published in Science Advances on January 4 under the title "Tomography of ultra-relativistic nuclei with polarized photon-gluon collisions" [2].
Associate Professor Wangmei Cha of the School of Physics, Particle Physics and Atomic Nuclei Physics, CSU, was the lead author of this collaborative group article and made outstanding contributions in the experimental analysis. This research was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology, and other organizations.
STAR is a large international collaborative group based on the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, USA, consisting of more than seven hundred researchers from 71 units in 14 countries.
Relativistic Heavy Ion Collider
A new kind of quantum entanglement
Wave-particle duality is one of the cornerstone principles of quantum mechanics and one of the sources of its "counter-common sense" and "counter-intuition". The single-particle double-slit interference thought experiment can explain wave-particle duality in a very direct way. In the past half century, experimentalists have realized this idea experiment with photons, electrons, atoms, molecules and biological macromolecules as interfering entities. So, can the unstable particles commonly found in high-energy nuclear physics experiments also be used as entities to produce double-slit interference phenomena?
STAR's research team has realized a Fermi-scale double-slit interference experiment using an unstable particle ρ0 (with a lifetime of about 1 fermi/light speed), which is the smallest scale double-slit interference experiment so far, as an interfering entity in a very high-energy nuclear collision.
As shown in the figure below, in a gold nucleus-gold nucleus collision, both colliding nuclei can serve as target nuclei ("slits") for ρ0 meson scattering, resulting in interference. The ρ0 meson produced by this process is fully linearly polarized, and its decay products tend to move along the polarization direction, which leads to the second-order cosine modulation of the decay angle showing a periodic variation with the magnitude of the ρ0 meson transverse momentum (as shown in the figure below), which is the first manifestation of the double-slit interference phenomenon in the polarization space.
Schematic diagram of the double-slit interference of the ρ0 meson and the measurement of its decay angle second-order cosine modulation coefficient
Interestingly, the typical distance between the two "slits" in these collisions is about 20 fm, much larger than the distance that can be reached before the decay of the ρ0 mesons, indicating that the wave functions of the ρ0 mesons from the two "slits" have decayed before they meet and overlap, and that the double-slit interference of the ρ 0 meson double-slit interference is actually produced by the concerted cooperation of its decay products (e.g., π+π- pairs).
These decaying π+π-pairs interfere in a "supertemporal" cooperative manner, which is an excellent model for the interpretation of quantum entanglement phenomena.
James Daniel Brandenburg, one of the authors of the paper, explains [3], "This is the first experimental observation of entanglement between different particles." Brookhaven National Laboratory reported under the title "New entanglement lets scientists 'see' inside nuclei," that "if two gold ions pass each other very close together without colliding, photons surrounding one ion can probe the internal structure of the other. "
Reference links:
[1]http://news.ustc.edu.cn/info/1055/81542.htm
[2]https://www.science.org/doi/10.1126/sciadv.abq3903
[3]https://www.bnl.gov/newsroom/news.php?a=120816
