Subir Sachdev is Herchel Smith Professor of physics[1] at Harvard University specializing in condensed matter.

[6] 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.

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[8] which applies to a wide variety of correlated electron materials, including the copper-oxide materials exhibiting high temperature superconductivity.

The strange metallicity and superconductivity are manifestations of an underlying quantum critical state of matter without quasiparticle excitations.

[10] Sachdev proposed[7][12] a solvable model of a strange metal (a variant of which is now called the Sachdev–Ye–Kitaev (SYK),[13] which was shown to saturate such a bound on the time to reach quantum chaos.

And this similarity to quantum matter without quasiparticles is not a co-incidence: Sachdev argued[9] that the SYK model maps holographically to the low energy physics of charged black holes in 4 spacetime dimension.

[21] The SYK model plays a key role in the computation of the density of low energy quantum states of non-supersymmetric charged black holes in 4 spacetime dimensions,[22][23] and provides the underlying Hamiltonian system upon which advances on the Page curve of entanglement entropy of evaporating black holes have been tested.

[24] Sachdev has also developed the theory of critical quantum spin liquids which feature fractionalization and emergent gauge fields, along with absence of quasiparticles.

The existence of such RVB ground states, and of the deconfinement of fractionalized excitations was first established by Read and Sachdev[26] and Wen[27] by the connection to a Z2 gauge theory.

Using this theory, various universal properties of the RVB state were understood, including constraints on the symmetry transformations of the anyon excitations.

The Dirac Medal was awarded to Professor Sachdev in recognition of his many seminal contributions to the theory of strongly interacting condensed matter systems: quantum phase transitions, including the idea of critical deconfinement and the breakdown of the conventional symmetry based Landau–Ginsburg–Wilson paradigm; the prediction of exotic 'spin-liquid' and fractionalized states; and applications to the theory of high-temperature superconductivity in the cuprate materials.