Photonic Entanglement For Applications In Quantum Information Processing

Quantum mechanics is the cornerstone of physical theories and experiments deal-ing with fundamental issues of nature.In particular quantum entanglement is an essen-tial resource for a variety of researches as a direct consequence of nonlocal correlations of entangled systems that are at odds with our common-sense notions of realism and locality.Up to date,quantum entanglement has already been applied to numerous quantum information processing protocols such as quantum teleportation,superdense coding,quantum cryptography,quantum metrology as well as quantum computation.These quantum schemes promise enhancements and significant gains in performance beyond the possibilities of classical physics,and a large-scale commercial implemen-tation of these entanglement-based protocols is requisite in the foreseeable future.In order to achieve their practical implementations,a large number of challenges have to be addressed,including generation,manipulation and measurement of quantum entan-glement.There are a variety of ways for achieving quantum entanglement,wherein entan-gled photon pair is a typical resource since harnessing photonic entanglement is com-paratively easy to be implemented result from well-developed technologies for optical devices.This thesis is intended to provide available schemes to fully harness photon-ic entanglement,and create the opportunity for a completely new class of practical applications in a quantum framework.To this end,the main results of this thesis are:·By superimposing four entangled pair creation possibilities on a polarization beam splitter,time-reversed Hong-Ou-Mandel interference is utilized to determinis-tically route indistinguishable photons into distinct spatial modes without the usual requirement of wavelength distinguishability.Our ultra-bright polarization entangle-ment source yields high-fidelity polarization entanglement and high pair generation rates without any requirement for active interferometric stabilization,which makes it an ideal candidate for a variety of applications,in particular those requiring indistin-guishable photons.·By extending time-reversed Hong-Ou-Mandel interference to the generation of polarization-frequency hyperentanglement,hyperentangled photons are separated in t-wo distinct spatial modes without any requirements for spectral selective filtering.By measuring polarization and frequency entanglement in subspace independently,the es-timated density matrices are characterized with high fidelity in both subspaces,which also implies high quality of hyperentanglement state.The certification of high dimen-sional entanglement on our generated state allows for quantum cryptographic applica-tions.The results are promising that our hyperentanglement source is a good candidate for using in more complex quantum information processing protocols.·Hong-Ou-Mandel effect can be used to precisely measure time delays with wide consensus being that the coherence time imposes the ultimate limit to the precision of such devices.As a consequence,ultra-broad-band photon sources have long been hailed as a vital prerequisite in a wide range of quantum-enabled sensing schemes.An alternative route towards ultra-precise Hong-Ou-Mandel interferometry that ex-ploits discrete frequency entanglement and detection of a coincidence detection on a bi-photon beat note is presented.The sensitivity limits imposed by the Cramer-Rao bound as a function of frequency detuning on the entangled state is also explored.A proof-of-concept experiment in a fiber-based temperature sensor is presented,and the results demonstrate that the frequency entangled states may provide a more practical way of increasing the timing resolution of Hong-Ou-Mandel based sensors.·An essential element in quantum communication,in order to implement fully connected quantum network,is quantum router that fulfilling the task of routing single photons into different output ports.An available scheme to implement quantum router based on interaction-free measurement and quantum dots is presented.This scheme is an interferometric method capable of routing single photons carrying spin or orbital angular momentum,or simultaneous carrying them both.Additionally,it can be ex-tended to cascaded multi-level structure to construct a one-to-many quantum router.The success probability and implementation issues are discussed as well to show that this scheme is viable.·Counterfactual quantum information processing can accomplish the tasks of quantum communication and entanglement distribution without any practical parti-cles travelling through optical channels,thus resulting in absolute security.By using interaction-free measurement and a novel "chained" quantum zeno effect to boost the counterfactual interference probability to unity,a scheme for counterfactual quantum communication network,two schemes for tripartite counterfactual entanglement dis-tribution and one available scheme for multi-party counterfactual entanglement distri-bution based on entanglement swapping and quantum dots are proposed.The success probability and implementation issues are further analyzed such that the viability is ver-ified.With the rapid development of quantum technology,I believe that these results could pave the way towards more secure quantum information processing.