Multi-photon quantum information science and technology in integrated optics

Fundamental quantum physics and quantum information science has found great experimental success with the implementation of single photons. To date, however, the majority of quantum optical experiments use large scale (bulk) optical elements bolted down to an optical bench; an approach that ultimately limits the complexity and stability of quantum circuits required for quantum science and technology (QST). Here, a series of experiments are reported in the emerging field of integrated quantum photonics that show monolithic waveguide chips to be a suitable platform for realising the next generation of quantum optical circuits. The thesis begins by reporting high quality Hong-Ou-Mandel interference-a phenomena that is central to nearly all photonic QST -in directly written waveguide structures. We then observe multi-photon quantum interference in lithographically fabricated waveguide circuits to implement the following demonstrations relevant to quantum computation, quantum metrology and analogue quantum simulation: (i) a compiled version of Shor's quantum algorithm is performed to factorize 15, using a number of integrated single- and two-qubit gates; (ii) a reconfigurable circuit is used to observe super-sensitive quantum interference fringes by manipulating two- and four-photon number-path entanglement; (iii) high quality quantum interference is observed in the reconfigurable device, indicating use as a building block for arbitrary reconfigurable circuits and (iv) a scheme for heralding two- and four-photon entanglement is implemented using projective measurement of auxiliary photons. The capabilities of integrated quantum photonics are extended beyond those of bulk quantum optics with two further demonstrations using arrays of evanescently coupled waveguide: (v) continuous quantum interference of two photons in a 21 mode quantum walk is realised, demonstrating generalisation of the Hong-OuMandel effect and (vi) the symmetry and quantum correlations of two polarisation entangled photons injected into a waveguide array are used to directly simulate quantum interference of fermions, bosons and a continuum of fractional behaviour exhibited by anyons. The latter demonstration is shown to generalise simulation of quantum interference in any mode transformation and to simulate quantum interference of any number of particles. For both demonstrations, implementing such unitary evolution with bulk optics would require hundreds of individual elements in a large interferometric structure which in practice is beyond the abilities of conventional quantum optics. The results presented in this thesis report elementary integrated circuits for future quantum devices and presents quantum experiments realised in integrated photonics, that cannot be realised with bulk optical components. These demonstrations are foundational in developing a new quantum photonic platform necessary for studying fundamental quantum physics and for advancing quantum information science and technology.EThOS - Electronic Theses Online ServiceGBUnited Kingdo