This thesis covers two unrelated topics. The first part of my thesis is about quantum money, a cryptographic protocol in which a mint can generate a quantum state that no one can copy. In public-key quantum money, anyone can verify that a given quantum state came from the mint, and in collision-free quantum money, even the mint cannot generate two valid quantum bills with the same serial number...

Abstract We investigate tomography of 21-cm brightness temperature fluctuations during the Dark Ages as a probe for constraining primordial non-Gaussianity. expand up to cubic order in perturbation theory and improve previous models signal by including effect free electron fraction. Using modified standard methods that include baryonic pressure effects we derive an improved secondary bispectrum...