Quantum entanglement, a phenomenon once confined to the microscopic realm, has now been detected within a macroscopic object, a centimeter-sized strange metal. This groundbreaking discovery challenges our understanding of quantum behavior and opens up new avenues for exploration in condensed matter physics. The research, published in Nature Physics, reveals that a heavy-fermion compound, Ce3Pd20Si6, exhibits extensive quantum entanglement, a concept typically associated with individual atoms or photons rather than bulk matter.
The study, conducted by researchers at TU Wien and the Institut Laue-Langevin, utilized inelastic neutron scattering to probe the crystal's response under extreme conditions. By focusing on a quantum critical point near a magnetic field of 1.73 tesla, they observed a unique behavior linked to the breakdown of Kondo screening. This transition marks the entry of the material into the strange-metal regime, characterized by linear electrical resistance with temperature at low temperatures.
The key to this discovery lies in the use of quantum Fisher information (QFI), a concept from quantum information theory. QFI quantifies the sensitivity of a quantum system to disturbances. The researchers found that as the system cooled, the QFI density increased sharply, indicating a rise in entanglement. This entanglement depth, calculated from the QFI, revealed at least 9-partite entanglement, suggesting that groups of at least nine quantum-entangled entities act collectively.
This finding has significant implications for our understanding of strange metallicity. Heavy-fermion compounds have long been studied for their peculiar behavior, and Ce3Pd20Si6 is known to exhibit a field-induced strange-metal quantum critical point. The new research adds entanglement to this picture, suggesting that strong entanglement is directly linked to the unusual behavior of strange metals.
Furthermore, the study's agreement with auxiliary-field quantum Monte Carlo simulations in a different model system strengthens the case for enhanced multipartite entanglement in the strange-metal state. This agreement, despite the differences between the model and the material, highlights the potential for neutron scattering to probe QFI in other systems.
The practical implications of this research are far-reaching. It provides a direct method to quantify entanglement in macroscopic quantum materials, offering researchers a new tool to test ideas about strange metals and Kondo destruction. In the long term, this could lead to the exploration of strange metals as high-precision measurement platforms for quantum technology, particularly in quantum metrology.
This discovery challenges our traditional view of quantum behavior and opens up exciting possibilities for future research. As we continue to explore the quantum realm, we may uncover more surprises and gain a deeper understanding of the intricate dance between quantum entities and the macroscopic world.
