  The lecture note consists of four parts. In the first part, we review a 2+1
dimensional lattice model which realizes emergent supersymmetry at a quantum
critical point. The second part is devoted to a phenomenon called
fractionalization where gauge boson and fractionalized particles emerge as low
energy excitations as a result of strong interactions between gauge neutral
particles. In the third part, we discuss about stability and low energy
effective theory of a critical spin liquid state where stringy excitations
emerge in a large N limit. In the last part, we discuss about an attempt to
come up with a prescription to derive holographic theory for general quantum
field theory.
