Sachdev's research describes the consequences of quantum entanglement on the macroscopic properties of natural systems. He has made extensive contributions to the description of the diverse varieties of states of quantum matter, and of their behavior near quantum phase transitions. Many of these contributions have been linked to experiments, especially to the rich phase diagrams of the copper-oxide high temperature superconductors. Sachdev's research has also exposed remarkable connections between the nature of multi-particle quantum entanglement in certain laboratory materials, and the quantum entanglement in black holes, and these connections have led to new insights on the entropy and radiation of black holes.

Sachdev has studied the nature of quantum entanglement in two-dimensional antiferromagnets, introducing several key ideas in a series of papers in 1989-1992. He has developed the theory of quantum criticality, elucidating its implications for experimental observations on materials at non-zero temperature. In this context, he proposed a solvable model of complex quantum entanglement in a metal which does not have any particle-like excitations in Physical Review Letters 70, 3339 (1993): an extension of this is now called the Sachdev-Ye-Kitaev (SYK) model. These works have led to a theory of quantum phase transitions in metals in the presence of impurity-induced disorder, and a universal theory of strange metals in Science 381, 790 (2023); this theory applies to a wide variety of correlated electron materials, including the copper-oxide materials exhibiting high temperature superconductivity. Many puzzling features of the `psuedogap' phase of these materials are also resolved by these theories. A connection between the structure of quantum entanglement in the SYK model and in black holes was first proposed by Sachdev in Physical Review Letters 105, 151602 (2010), and these connections have led to extensive developments in the quantum theory of black holes.

For more information, see Sachdev's selected papers with commentaries.