Alexei Kitaev (Russian: Алексей Юрьевич Китаев; born August 26, 1963) is a Russian–American professor of physics at the California Institute of Technology and permanent member of the Kavli Institute for Theoretical Physics. He is best known for introducing the quantum phase estimation algorithm and the concept of the topological quantum computer while working at the Landau Institute for Theoretical Physics. For this work, he was awarded a MacArthur Fellowship in 2008. He is also known for introducing the complexity class QMA and showing that some local Hamiltonian problems are QMA-complete.
Kitaev was educated in Russia, receiving an M.Sc from the Moscow Institute of Physics and Technology (1986), and a Ph.D from the Landau Institute for Theoretical Physics (1989). He served previously as a researcher (1999–2001) at Microsoft Research, a research associate (1989–1998) at the Landau Institute and a professor at Caltech (2002–present).
In 2008 Kitaev was awarded a MacArthur Fellowship. In July 2012, he was an inaugural awardee of the Fundamental Physics Prize, the creation of physicist and internet entrepreneur, Yuri Milner. In 2015, he was jointly awarded the 2015 Dirac Medal by ICTP.