A method of generating a random symbol sequence using quantum opto-electronic devices A and B with device-independent security is disclosed. The method is characterized by the two sources each producing entangled two-beam, pulsed multiphoton quantum states of light and sending one beam to a quantum interference and measurement device C. Before being sent, the beams are multiplexed with coherent beams. Quantum interference and measurement device C demultiplexes them and uses coherent beams for compensating the fluctuations in the quantum beams. Then, it interferes quantum beams on a beam splitter, measures the output and sends results back. Subsequently, A and B share an entangled state. They interfere local beams with coherent light on beam splitters and measure on detectors. A fraction of measurements are kept secret and used as the source of symbols forming the cryptographic key, while others are used to establish the security using an entanglement test.

A fundamental new effect in nonlinear photonic systems is disclosed herein, called n-photon bound states in the continuum, which can be applied to deterministically create large Fock states, as well as very highly intensity-squeezed states of light. The effect is one in which destructive interference gives a certain quantum state of light an infinite lifetime, despite coexisting in frequency with a radiative continuum. For Kerr nonlinear systems, that state is an n-photon (Fock) state of a particular and tunable n. Experimentally-realizable examples are shown which are capable of producing n-photon Fock states, and states with very large intensity squeezing, such as greater than 10 dB. The effect requires only Kerr nonlinearity and linear frequency-dependent (non-Markovian) dissipation, and is, in principle, applicable at any frequency. The theory and concepts are also immediately applicable to nonlinear bosons besides photons, and thus may be implemented in many other disciplines.

The invention belongs to the technical field of nonlinear synthetic crystals, and particularly relates to a method for improving the intense laser-induced damage resistance of nonlinear synthetic crystals. The method comprises: electrifying nonlinear synthetic crystals by means of a stabilized DC power supply under a certain atmosphere. The invention can effectively decrease the density of pinpoint damage in nonlinear synthetic crystals by means of an electrification method, thus optimizing the intense laser-induced damage resistance of the nonlinear synthetic crystals and particularly fulfilling a more obvious improvement effect on defects with a greater damage threshold. The electrification method provided by the invention is expected to further reduce the damage probability in a case where an ultraviolet nanosecond pulse laser fluence with a wavelength of 355 nm or 351 nm is greater than 8J/cm.sup.2 to improve the damage resistance of crystals. The electrification method further implemented based on laser conditioning provided by the invention is a novel comprehensive method for improving the damage resistance of crystals and has a great has a great economical advantage.

Embodiments can include a photonic structure comprising: a substrate; a waveguide formed over the substrate; an insulator layer formed over the waveguide, wherein the waveguide is formed of nonlinear optical material; and a tuning structure integrally formed on the photonic structure with the waveguide, the tuning structure configured for tuning the waveguide.