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Abstract:A quantum photonic circuit with the ability to produce continuous variable quantum vortex states is proposed. This device produces two single-mode squeezed states which go through a Mach-Zehnder interferometer where photons are subtracted by means of weakly coupled directional couplers towards ancillary waveguides. The detection of a number of photons in these modes heralds the production of a quantum vortex. Likewise, a measurement system of the order and handedness of quantum vortices is introduced and the performance of both devices is analyzed in a realistic scenario by means of the Wigner function. These devices open the possibility of using the quantum vortices as carriers of quantum information.

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Single photon or biphoton states propagating in optical fibers or in free space are affected by random perturbations and imperfections that disturb the information encoded in such states and accordingly quantum key distribution is prevented. We propose three different systems for autocompensating such random perturbations and imperfections when a measurement-device-independent protocol is used. These systems correspond to different optical fibers intended for space division multiplexing and supporting collinear modes, polarization modes or codirectional modes such as few-mode optical fibers and multicore optical fibers. Accordingly, we propose different Bell-states measurement devices located at Charlie system and present simulations that confirm the importance of autocompensation. Moreover, these types of optical fibers allow the use of several transmission channels, which compensates the reduction of the bit rate due to losses.

We present a system based on phase conjugation in optical fibers for autocompensating highdimensional quantum cryptohraphy. Phase changes and coupling effects are auto-compensated by a single loop between Alice and Bob. Bob uses a source of coherent states and next Alice attenuate them up to a single photon level and thus 1-qudit states are generated for implementing a particular QKD protocol, for instance the BB84 one, together with decoy states to detect eavesdropping attacks.

Ion-exchanged glass as a platform for quantum photonics is proposed. Quantum projectors are implemented with integrated optical directional couplers fabricated by ion-exchange K + /Na + in soda-lime glass. We consider devices composed of concatenated directional couplers which implement N -dimensional quantum projective measurements, and concomitantly the production of 1-qudit states. The fundamental units of these devices are 2 × 2 directional couplers that are experimentally studied in order to obtain, through an optical characterization, empiric relationships between fabrication and optical parameters of such couplers. Likewise, a two-dimensional quantum projector is demonstrated so that projective measurements are obtained for the states of bases X (diagonal) and Y (circular).Index Terms-Integrated quantum passive elements, integrated quantum projective meters, ion-exchanged glass platform. I. INTRODUCTIONI NTEGRATED quantum photonic devices can implement different quantum operations for quantum communications, quantum computation, quantum metrology, and so on, with the inherent advantages associated to integrated optics. Different platforms have been proposed and used to develop these integrated quantum devices, including silicon-on-insulator (as SiO 2 ), Lithium Niobate, and Gallium Arsenide [1]-[3]. However, to our knowledge, ion-exchanged glass (IExG) platform has not been used as an integration technology for quantum photonics, despite the fact that it is present in many classical optical communications systems and optical sensors, and has been

We present an autocompensating quantum cryptography technique for Measurement-Device-Independent quantum cryptography devices with different kind of optical fiber modes. We center our study on collinear spatial modes in few-mode optical fibers by using both fiber and micro-optical components. We also indicate how the obtained results can be easily extended to polarization modes in monomode optical fibers and spatial codirectional modes in multicore optical fibers.