Displacement measurement systems, measurement methods and EUV lithography machines for quantum meta-structure elements are disclosed, which include: an entangled state light source generator, a meta-device, a collimating lens, a polarizing beam splitter, and a computing section. Left-rotation photon and the right-rotation photon are projected to the polarizing beam splitter, and the correlation between output ports of two polarizing beam splitters is counted for reading to measure the displacement of the meta-device element. The displacement of the meta-structure element is measured in a manner that realizes the correlation between the left-rotation photons and the right-rotation photons.

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 multi-wavelength entangled photon pair generation device includes: a multi-mode pump laser that radiates a broadband pump laser beam in an ultraviolet wavelength range including multiple Gaussian-distributed wavelengths; a nonlinear crystal that generates a multi-wavelength de-multiplexed entangled photon pair in a near-infrared wavelength range including multiple wavelength components corresponding to multiple Gaussian-distributed wavelengths of the broadband pump laser beam, respectively; a temperature controller that adjusts a temperature of the nonlinear crystal; and an output optical system that filters out the broadband pump laser beam from light output through the nonlinear crystal and passes the multi-wavelength de-multiplexed entangled photon pair.

Bright entangled photon sources including an alignment-free, fiber-based, mechanically-rugged and generic interferometric module are disclosed. The inherent phase-stability of a Sagnac interferometer is deployed. High down-conversion efficiency of periodically poled nonlinear-waveguides is combined with the optical gain of semiconductor optical amplifiers and immunity of fiber optics. A single compact interferometric engine combines these attributes, allowing highly stable, integrable and bright polarization entangled-photon sources operating at room temperature. Using a minimum number of in-line optical parts, the compact module is based on a novel method that enhances the long-term stability and efficiency without compromising the entanglement quality. Besides energy entanglement, polarization entanglement is presented and set through the operational conditions. An optional periodically poled nonlinear waveguide can be hosted to achieve the desired spectral bandwidth and photons generation rate. The result is a zero-maintenance, lightweight, low-power consumption engine of compact and fully-integrable bright polarization-entangled photon sources.

A stream of photons from an optical source at a source wavelength are converted into entangled photon pairs via a spontaneous parametric down-conversion process. This produces time-synchronized signal and idler photon pairs which share a nominal wavelength, twice the source wavelength, a common polarization. The signal and idler individually have wavelengths that are equally offset above and below their nominal wavelength. The photons segregated into two paths based on wavelength via a wavelength division multiplexer. A phase modulator in the signal path alters the phase of the signal photon, while the idler photon's phase remains unchanged. By applying a modulation signal to the phase modulator, a quantum message is encoded on the photon pair. A multi-channel wavelength division multiplexer may be used to support multiple channels, each carrying signal-idler pairs conveying a quantum encoded message.

A quasi-deterministic single-photon source and method of generating single photons on demand are disclosed. The single-photon source includes photon pair generation for generating a heralding and heralded photon in a frequency-correlated photon pair, a single-photon spectrometer adapted to detect the heralding photon and to generate an output signal that is indicative of the frequency of the detected heralding photon, a pulse shaper arrangement for reshaping a broadband pulse, and an optical frequency conversion means for converting, upon irradiation with a reshaped pulse, a heralded photon into a single output photon with deterministic source frequency. The pulse shaper arrangement is configured to select, based on the spectrometer output signal, only frequency components of the broadband pulse that substantially coincide with the heralding photon frequency or with a constant detuning thereof.

Wavelength-tunable source of pulsed laser radiation for VIS-NIR spectroscopy which consists of a pump source (1) forming bursts of picosecond pulses of high pulse repetition rate, and a synchronously pumped optical parametric oscillator (2). The pump source (1) comprises a solid-state regenerative amplifier (31) having one or two electro-optical switches (32,33) inside its resonator (44). The switches create partial transmission of the resonator for a time interval longer than a resonator roundtrip time, and eject a part of energy of a pulse circulating inside. Bursts of 5-10 ns duration are formed, which are filled with high peak power picosecond pulses. Pulse repetition rate of the order of GHz of pump pulses allows the construction of a compact optical parametric oscillator. The whole set of parameters ensures high energy efficiency, stability and an ability to provide output pulse bursts repeating at up to 10 kHz repetition rate.

A photonic circuit with at least one nonlinear amplitude thresholder for correcting errors produced by linear photonic logic. One or more photonic input gates of the photonic circuit receive one or more input signals and generate one or more photonic signals based on the one or more photonic input signals. A first set of one or more photonic gates of the photonic circuit generates one or more intermediate photonic signals based on the one or more photonic signals. The at least one nonlinear amplitude thresholder generates at least one photonic thresholding signal based on the one or more intermediate photonic signals, the at least one nonlinear amplitude thresholder operating in a first operating regime, second operating regime, and/or third operating regime. A second set of one or more photonic gates of the photonic circuit generates one or more photonic output signals based on the at least one photonic thresholding signal.

An optical nonlinearity measurement method according to the present disclosure utilizes photon pair generation through a spontaneous four-wave mixing process, to observe photon pairs using an optical waveguide loaded with a two-dimensional material. Compared with the Z-scan method, the influence of free carriers on nonlinear refractive indexes is only indirect. With a parameter being the length of the attached two-dimensional material in the optical waveguide direction, a theoretical value of the coincidence rate of the photon pairs based on the coupled wave equation is fitted to a measured value of the coincidence rate of the photon pairs. For the coincidence rate of the photon pairs, the theoretical value based on the coupled wave equation is fitted to the measured value in a state reflecting the structure of the optical waveguide loaded with the two-dimensional material, and nonlinear coefficients .sub.1 and .sub.2 at that time are obtained.

A photonic integrated circuit comprising one or more waveguides comprising a second order non-linearity configured to operate on optical pulses each having a pulse length shorter than 1000 optical cycles, as measured at their full width at half maximum. The circuit is configured to generate one or more quantum states carried by one or more of the optical pulses, manipulate one or more of the quantum states, and/or measure one or more of the quantum states.