Room 117

Creating a Superposition of Unknown Quantum States

Prathik Cherian J

IMSc

The superposition principle is one of the landmarks of quantum
mechanics. The importance of quantum superpositions provokes questions
about the limitations that quantum mechanics itself imposes on the
possibility of their generation. In this work, we systematically study the
problem of the creation of superpositions of unknown quantum states. First,
we prove a no-go theorem that forbids the existence of a universal
probabilistic quantum protocol producing a superposition of two unknown
quantum states. Second, we provide an explicit probabilistic protocol
generating a superposition of two unknown states, each having a fixed
overlap with the known referential pure state.The protocol can be applied
to generate coherent superposition of results of independent runs of subroutines in
a quantum computer. Moreover, in the context of quantum optics it can be used to
efficiently generate highly nonclassical states or non-Gaussian states.

Journal Ref. : Phys. Rev. Lett. 116, 110403 (2016) [ journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.110403 ]