Quantum Entanglement in Nature: From Superconductors to Black Holes

In this inaugural P. Rajagopalan Memorial Lecture at ICTS, Subir Sachdev presents a comprehensive overview of quantum entanglement and its role in understanding high-temperature superconductors and black holes. He begins by introducing the historical context of superconductivity, from the discovery of mercury’s zero resistance to the 1986 breakthrough with cuprate materials like YBCO, which superconduct at liquid nitrogen temperatures. Sachdev explains that the standard Sommerfeld theory of metals fails for these materials, necessitating a deeper understanding of many-body quantum physics. He introduces the superposition principle as the core of quantum mechanics and discusses the Einstein-Podolsky-Rosen paradox, illustrating how entanglement challenges classical intuitions. The talk then progresses to the concept of quantum entanglement in many-particle systems, leading to the Sachdev-Ye-Kitaev (SYK) model, a simplified theoretical framework that captures the essential physics of strongly correlated systems. Sachdev highlights how the SYK model provides insights into the strange properties of high-temperature superconductors and also connects to the quantum theory of black holes, particularly the holographic principle and the nature of Hawking radiation. He emphasizes the interdisciplinary impact of these ideas, bridging condensed matter physics, quantum information, and gravitational physics. The lecture concludes with a discussion of open questions and the potential for future discoveries in quantum materials and fundamental physics.