Quantum signals have intriguing properties and a characteristic feature of them is their intrinsic noise. This results in uncertainty relations restricting our ability to measure conjugate variables with absolute precision simultaneously. In the context of amplification, this noise forbids an unknown quantum signal to be amplified perfectly in a deterministic manner. In the first part of this thesis we propose a method to amplify coherent states probabilistically. Our method is based on coherent state comparison and photon subtraction. We found that for an input chosen at random from a binary set of states, under certain circumstances the fidelity can reach 100%. The probability of success is very high (~ 10  40%) and it increases with gain. We tested the experimental performance of our protocol for a gain of g² = 1:8 and verified that the experimental results were in line with the theoretical predictions. For an input state chosen from a binary set the fidelity was > 98% and the success rate of our amplifier was > 26000 ampli ed states per second. In the second part of the thesis we propose a new form of orbital angular momentum and angle states. These states consist of a sum of overlapping Gaussians in the angular position representation. We calculated both the uncertainty product and the entropic uncertainty relation for orbital angular momentum and angle. We found that in both cases our new states have a lower uncertainty than the intelligent states.Bringing all results together, our proposals have implications in quantum communications: as our amplification protocol gives a perfect fidelity while maintaining a high success probability it can find application as a quantum optical repeater, and as our overlapping Gaussian states are welldefined for any value of the angular uncertainty and have lower uncertainty relations than the intelligent states, they could find applications in protocols exploiting the highdimensional basis of orbital angular momentum states.
Date of Award  14 Apr 2015 

Original language  English 

Awarding Institution   University Of Strathclyde


Sponsors  EPSRC (Engineering and Physical Sciences Research Council) 

Supervisor  John Jeffers (Supervisor) & Alison Yao (Supervisor) 
