Quantum information science in integrated photonics technology

Quantum information science provides new paradigms of communication, computation and measurement; such as perfectly secure quantum key distribution, intrinsic parallel computation and increased precision measurement by beating the standard quantum limit. The first implementation of optical quantum circuits whose performance exceeds that required for fault tolerance quantum computation is presented. Near- unit fidelity non-classical interference and entangling operations are demonstrated in integrated photonic waveguides fabricated on silica on silicon chips. Improvement of about 5% in the measured performance is the result of perfectly indistinguishable photon pairs produced from an SPDC source. These integrated devices, combined with high efficiency single photon sources and detectors, will be the building block for future demonstrations of quantum information. Operation of quantum optics circuits with superconducting nanowire single photon detectors (SNSPD) is reported. The lower jitter of SNSPDs compared to silicon single photon avalanche photodiodes (SPADs) enables the measurement of higher visibility non-classical interference on directional couplers, CNOT gates and Mach-Zehnder interferometer. SSPDs are fast, low noise and can detect single photons in a broad range of wavelengths. Recent studies show very high detection efficiency making these devices promising for future photonic quantum information processing. Quantum interference in multi-mode interference (MMI) devices is reported for the first time. These devices allow the design of NxM splitters with superior performances, excellent tolerance to polarization and wavelength variations and relaxed fabrication requirements compared to the other main beam splitting technology, the directional couplers. However, to date, there have been no demonstrations of quantum interference in MMI devices (one may be concerned that multi-mode operation could prevent or perturb such interference). It is found that that the quantum interference visibility is significantly lower than that of a directional coupler with the same source. A major reason for the reduced visibility is the coherence length of the photons, which is set by the large-band interference filters. Since the different modes see different effective refractive indices within the interferometer, a jitter is 'introduced which allows distinguishability between the photons. To overcome this problem a narrower filter was introduced in one of the channels between the device and the detector, i.e. not affecting the source. This quantum erasure technique increases the detected indistinguishability of the photons, showing a high visibility and confirming that timing jitter limits quantum interference with large filters. The first observation of quantum walks of two indistinguishable particles is reported. Quantum walks offer new tools for simulating physical, chemical and biological systems, performing universal quantum computation and studying generalized quantum interference. Experimental demonstrations to date have shown single particle quantum walks; the observable dynamics of which can be fully explained with classical wave mechanics and experimentally mimicked using, for example, bright laser light. To observe uniquely quantum mechanical correlations in quantum walks, the propagation of two single, indistinguishable photons in an array of 21 waveguides in a silicon oxynitride chip is measured. The simultaneous walk of two photons on a graph simulate the walk of a single photon on a larger graph; the graph growing exponentially when linearly increasing the number of photons. These results violate classical bounds and cannot be efficiently simulated or described using classical mechanics. It is shown that the output strongly depends on the input state. Previous quantum optical work has highlighted the promise of monolithic integrated optics for quantum information science. This demonstration takes advantage of the intrinsic stability of photonic waveguide circuits to perform two-photon interference on a large scale. The results presented in this Thesis demonstrate the potential of integrated quantum photonic technology for quantum information applications, in particular quantum computation and quantum simulation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo