Linear-Optical Processing Cannot Increase Photon Efficiency

Linear-optical processing cannot increase photon efficiency.

We answer the question whether linear-optical processing of the states produced by one or multiple imperfect single-photon sources can improve the single-photon fidelity. This processing can include arbitrary interferometers, coherent states, feedforward, and conditioning on results of detections. We show that without introducing multiphoton components, the single-photon fraction in any of the ...

Efficiency limits for linear optical processing of single photons and single-rail qubits

We analyze the problem of increasing the efficiency of single-photon sources or single-rail photonic qubits via linear optical processing and destructive conditional measurements. We allow for the use of coherent states and do not limit to photon-counting measurements. We conjecture that, with the limitation that multiphoton components in the output are not permitted, it is not possible to incr...

Entanglement concentration of individual photon pairs via linear optical logic

Entanglement has played a key role in many quantum information processing, such as quantum computation [1], quantum teleportation [2], quantum dense coding [3], and entanglement-assisted quantum cryptography [4]. To function optimally these applications requires maximally entanglement. However, unwanted coupling to the environment causes the degradation of entanglement and entanglement concentr...

Membrane reactors: A way to increase efficiency

Single and Two-Photon Fluorescence Studies of Linear and Non-Linear Optical Chromophores

The subject matter presented in this thesis concerns the structural and dynamic studies of new fluorescent probe molecules and the application of polarised fluorescence techniques and analysis to molecular motion, order and solvation in a highly ordered environment. Chapter 1 reviews recent group research providing a context to the work in this thesis, whilst Chapters 2 and 3 concern the study ...