  Linearity and unitarity are two fundamental tenets of quantum theory. Any
consequence that follows from these must be respected in the quantum world. The
no-cloning theorem and the no-deleting theorem are the consequences of the
linearity and the unitarity. Together with the stronger no-cloning theorem they
provide permanence to quantum information, thus, suggesting that in the quantum
world information can neither be created nor be destroyed. In this sense
quantum information is robust, but at the same time it is also fragile because
any interaction with the environment may lead to loss of information. Recently,
another fundamental theorem was proved, namely, the no-hiding theorem that
addresses precisely the issue of information loss. It says that if any physical
process leads to bleaching of quantum information from the original system,
then it must reside in the rest of the universe with no information being
hidden in the correlation between these two subsystems. This has applications
in quantum teleportation, state randomization, private quantum channels,
thermalization and black hole evaporation. Here, we report experimental test of
the no-hiding theorem with the technique of nuclear magnetic resonance (NMR).
We use the quantum state randomization of a qubit as one example of the
bleaching process and show that the missing information can be fully recovered
up to local unitary transformations in the ancilla qubits. Since NMR offers a
way to test fundamental predictions of quantum theory using coherent control of
quantum mechanical nuclear spin states, our experiment is a step forward in
this direction.
