50 results about "Spontaneous parametric down-conversion" patented technology

A narrow-band single-photon source (10) is disclosed, along with a QKD system (200) using same. The single-photon source is based on spontaneous parametric downconversion that generates signal and idler photons (PS and PI) as an entangled photon pair. Narrow-band signal photons are generated by selectively narrow-band-filtering the idler photons. This results in a non-local filtering of the signal photons due to the time-energy entanglement of the photon pair. Subsequent detection of the filtered idler photon establishes the narrow-band signal photon. The narrow-band single-photon source is particularly useful in a QKD system, wherein the narrow-band signal photons are used as quantum signals to mitigate the adverse effect of chromatic dispersion on QKD system performance.

The invention discloses a compressed-sensing-based entangled light imaging method against the background of strong interference. According to the technical scheme, a laser 1 generates laser; spontaneous parametric down conversion is carried out on the laser by a BBO crystal 2 to obtain signal light and idle light; the signal light passes through a to-be-imaged object 3 and a first single-photon detector 6 successively to obtain signal light passing through the first single-photon detector 6; a lens 4 collects the idle light to obtained collected idle light and sends the collected idle light to a spatial light modulator5; the spatial light modulator 5 carries out amplitude modulation on the collected idle light and then the modulated light passes through a second single-photon detector7; the light is sent to a coincidence counter 8; the coincidence counter 8 records coincidence counting of the signal light passing through the first single-photon detector 6 and the idle light passing through the second single-photon detector7 to obtain a measurement matrix and a coincidence counting column vector; and a data processing module 9 obtains an imaging result of the to-be-imaged object 3 based on the measurement matrix and the coincidence counting column vector.

A single-photon generator for generating a single photon with high efficiency at a constant frequency. A CW semiconductor laser (1) emits a laser beam of wavelength 780 nm. A photon of wavelength 780 nm is divided into two photons of wavelengths 1550 and 1570 nm by means of a non-degenerate waveguide PPLN (2). A dichroic mirror (6) separates the two photons. A gate-operation single-photon detector (4) detects one of the photons and generates a detection signal. An LN polarization modulator is operated with the detection signal. An optical switch (5) composed of the LN polarization modulator and a polarized beam splitter rotates the polarization of the other photon by 90° and outputs the photon in a given direction. With this, only one photon can be taken out in the direction of the travel at a frequency of several hundreds of kilohertz. Two photons of different wavelengths are produced by spontaneous parametric down-conversion by a non-degenerate waveguide PPLN, the photons are separated by a dichroic mirror, one of the photons is detected by a gate-operation single-photon detector, and the output of the other photon is controlled by a high-speed LN polarization modulator. Therefore, a single photon can be efficiently produced at a constant frequency.

A photonic chip based on periodical poling and waveguides circuits in ferroelectric crystals, the method is based on the integration of waveguide circuits, periodical poling and electro-optic modulator (EOM). The chip is illustrated by FIG. 1. The waveguide circuits guide the photons and makes linear operations like the beam splitting, filtering etc. on the photons. The periodical poling enables the efficient spontaneous parametric down conversion (SPDC), resulting the generation of entangled photons. The EOM controls the phase of photons dynamically. The following directional coupler distributes the entangled photons and the quantum interference takes place, resulting different types of path-entangled states by controlling the voltage of EOM insides the chip.

The invention discloses a simple and reliable method for preparing any Werner state, comprising a step of preparing an entanglement light source, in which photon pairs are entangled by using laser topump nonlinear crystals to generate a spontaneous parametric down conversion process, and a step of constructing a controllable depolarized channel, in which a completely mixed state is introduced byacting the controllable depolarized channel on one photon. Sandwich-shaped crystals are adopted for the nonlinear crystals and comprise two BBO crystals and a real zero-order half-wave plate disposedbetween the two BBO crystals. The controllable depolarized channel is composed of a Sagnac ring, a complete destructive phase channel and a state superposition portion, the Sagnac ring is of a rectangular structure, and a half-wave plate is disposed between two reflectors thereof; the complete destructive phase channel is composed of two destructive phase crystals and a half-wave plate therebetween; and the state superposition portion comprises a BS. The simple and reliable method is convenient to adjust and high in feasibility, and can be applied to the fields of quantum information processing and quantum communication.

The invention discloses a self-collimating high-stability entanglement source module and a system thereof, comprising a dual-color polarization beam splitter DPBS, a two-color half-wave plate DHWP, afirst plane mirror M1, a second concave mirror CM2, a first concave mirror CM1 and a second plane mirror M2 which are sequentially arranged and form an optical loop, wherein a periodically polarized crystal is disposed on the optical path between the first concave mirror CM1 and the second concave mirror CM2. An advantage of the invention is that both the focusing of the pump beam and the collimation of the generated spontaneous parametric down-converting photons can be achieved by using the first concave mirror and the second concave mirror. The focusing lens of the pumping light and the fiber collimator required for photon collection may be omitted, which greatly simplifies the complexity of the optical path, and highly integrates and miniaturizes the entangled source module.

The invention belongs to the technical field of quantum information science and discloses an energy-time entangled two-photon generating method. The method includes: step one, emitting pump light; step two, adjusting the pump light, and sending to second-order nonlinear crystal or crystal waveguide to realize a second-order nonlinear process of cascade optical frequency doubling and spontaneous parametric down conversion in the second-order nonlinear crystal or crystal waveguide to generate energy-time entangled two-photon pairs, wherein adjusting the pump light includes adjusting pump light power and polarization direction and filtering; step three, subjecting light emitted by the second-order nonlinear crystal or crystal waveguide to spectral filtering and wavelength selection, and separating residual pump photons from the energy-time entangled two-photon pairs generated in the step two; step four, separating and extracting signal photons and idler frequency photons from the energy-time entangled two-photon pairs filtered out in the step three. A light source prepared according to the method has advantages of high efficiency, small size, practicality, easiness in integration withoptical fiber systems and the like.

A compact source of polarization-entangled photons includes a laser source, producing a laser beam, a pair of nonlinear crystals, in optical contact with each other, with one of the pair of nonlinear crystals having an input face, with the laser beam incident on the input face, and another of the pair of nonlinear crystals rotated 90°, along an axis perpendicular to the input face, with respect to each other and a fiber coupling point, configured to receive a pair of single-mode fibers. Pairs of polarization-entangled photons are produced through spontaneous parametric down conversion of the laser beam and provided to the fiber coupling point.

Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. An optical conversion generation unit including two second-order nonlinear optical media disposed on opposite sides of a half-wave plate in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light. The optical components can be optimized for operation at this wavelength without the need to consider the shorter wavelength of the up-converted light.

A quantum digital signature (QDS) method using a labeled single photon source (HSPS) is divided into a preparation phase of the HSPS, a key distribution phase using a QDS scheme of the HSPS, and a signed message phase. Firstly, HSPS is obtained through down-conversion of spontaneous parameters, and after the marking effect is achieved, most of vacuum pulses are effectively eliminated. A key distribution protocol (KGP) is then performed on this basis such that participants in the signature protocol all obtain signed key strings. Finally, the transmission, verification and receiving (refusal) process of the signature information is carried out, and on the premise that the security of non-repudiation, unforgeability and transferability of the QDS protocol is met, whether the signature is valid or not is judged by comparing the mismatching rate between the key strings of the two parties. Compared with an existing QDS scheme using a weak coherent light source (WCS), the scheme has the advantages that the vacuum state proportion is reduced to a greater extent, the safe transmission distance is greatly increased, the method is efficient, feasible, simple and easy to operate, and a certainreference value is provided for the practicability of quantum cryptology.

A photon pair generator includes a light source configured to emit light, and a nonlinear optical element configured to receive the light radiated from the light source and generate a quantum-entangled photon pair through spontaneous parametric down-conversion (SPDC), the nonlinear optical element including a polar material layer and a nonlinear material layer provided on the polar material layer.

The invention relates to a hybrid integrated optical communication waveband on-chip quantum entanglement source, which comprises a laser generation and amplification module and a nonlinear optical module, the nonlinear optical module is formed by connecting two sections of nonlinear waveguides through a second harmonic filter; under the action of optical communication waveband pump light, second harmonic generation and spontaneous parametric down-conversion processes successively occur in the two sections of nonlinear waveguides, so that quantum entanglement two-photon generation is realized. The second harmonic filter connected with the two waveguides can effectively restrain residual pump light, and noise is prevented from being introduced into entangled two photons in the spontaneous Raman scattering process. All devices required by the on-chip quantum entanglement source are integrated on the same substrate material, so that the volume of the quantum entanglement source is effectively reduced. The hybrid integrated optical communication waveband on-chip quantum entanglement source provided by the invention has the characteristics of high integration level, high brightness and low noise, can be realized through an advanced micro-nano processing and packaging technology, and is beneficial to the integration and practical development of quantum light sources.

The invention provides a method for manipulating a two-photon quantum interference curve. The method comprises two main steps of preparation of a parametric light source and improvement of a manipulative two-photon quantum interference light path, wherein the preparation of the parametric light source is achieved through spontaneous parametric down conversion of laser pumping beta-barium metaborate crystals, and parametric light is transmitted into the quantum interference light path by using single mode fiber; the improvement of the two-photon quantum interference light path is achieved through two polarization beam splitters and a half-wave plate, wherein the fast-axis angle of the half-wave plate is 2.5 degrees. In two output ports of the second polarization beam splitter, the manipulation of the two-photon quantum interference curve can be achieved through the placement of two interference filters, the implementation is simple and feasible, the interference filters of different bandwidths can be combined and used, the better interference visibility can be achieved, the introduced counting error can be controlled, and the better experiment effect is obtained. The method for manipulating the two-photon quantum interference curve has the advantages that the method is simple and feasible, and the adjustment is convenient, and an experiment platform is stable and reliable.

The present invention provides a novel entanglement source generation device and a preparation method thereof, the spontaneous parametric down-conversion process is realized by utilizing the periodically poled lithium niobate film ridge waveguide, and the entanglement source is collected by virtue of the single-mode optical fiber, so that a fundamental mode matched with the single-mode optical fiber is allowed to be output in the spontaneous parametric down-conversion process; and the entanglement source is coupled into the single-mode optical fiber in a mode matching manner by virtue of a spatial light path, so that the entanglement source with high efficiency, high brightness and high quality is realized by virtue of extremely high single-mode coupling efficiency. Meanwhile, in the scheme for preparing the entanglement source through the optical fiber/waveguide-space-optical fiber coupling mode, high coupling, interference and filtering efficiency can be achieved in a simple and mature mode, and the quality of the entanglement source is further improved.

The invention provides a mixed-state preparation method with adjustable parameters. The method comprises an entangled light source preparation part, a weight-adjustable shunt part and decoherence channel parts of all paths, and is characterized in that the entangled light source preparation part is used for preparing entangled photon pairs through a spontaneous parametric down-conversion process generated by using a laser pumping nonlinear crystal; the weight-adjustable shunt part realizes the controllable weight of each path by using a BD crystal network, and a BD crystal divides a non-polarized light beam into two parallel orthogonal polarized light beams; the decoherence channel part of each path introduces a complete mixed state to one path of the entangled photon pair through a controllable decoherence channel. According to the method, a two-photon entangled light source is generated by using BBO crystal spontaneous parametric down-conversion. Through the cascade calcite network,two-bit mixed-state preparation of any parameter can be realized only by adjusting the rotation angle of the half-wave plate. The method is easy to implement. Compared with a mixed state prepared by aSagnac ring interferometer, the method is more stable, more convenient to cascade and modular.

The invention discloses a wide spectrum self-calibration absolute spectrum radiometer based on spontaneous parametric down-conversion. The wide spectrum self-calibration absolute spectrum radiometer comprises a correlated photon source module, a rotating scanning reflecting mirror, a no-focus telescope light path module, a dichroscope, a double-channel pump light suppression light path module, a signal light acquisition light path module, a free light acquisition light path module, a double-path conforming device and a control computer. The correlated photon source module provides "no-tracing"calibration based on the I-class spontaneous parametric down-conversion effect. The rotating scanning reflecting mirror is clockwise rotated for 90 degrees to realize switching of the self-calibration function and the target radiation information observation function, and the self-calibration absolute spectrum radiometer is realized according to the design concept. The self-calibration absolute spectrum radiometer has important application prospect in light radiation measurement and light radiation measurement standard transmission.

The invention belongs to the field of integration quantum optics, and provides an electric pumping Bragg reflection waveguide integration correlated photon pair source. The correlated photon pair source can generate pumping laser with the wavelength being about 0.65 micrometer, spontaneous parametric down-conversion achieving phase matching is achieved inside the device, correlated photon pairs with the wavelength being about 1.3 micrometers are generated, and an effective technical path is provided for the integration correlated photon pair source with the wavelength being about 1.3 micrometers. Accordingly, due to the adopted technical scheme, the correlated photon pair source based on a GaInP/AlGaInP material system is composed of a quantum well and a Bragg reflection waveguide, electric injection excitation is applied to the quantum well, the quantum well radiates pumping laser, the pumping laser excites the Bragg reflection waveguide, by means of the material nonlinear characteristic of the Bragg reflection waveguide, spontaneous parametric down-conversion is achieved, and the correlated photon pairs are generated. The invention mainly relates to designing and manufacturing ofthe correlated photon pair source.

The invention relates to a quantum interference detection chip, which comprises a coupling grating, an input directional coupler, a grating mode beam splitter, an output directional coupler and a superconducting nanowire single-photon detector. The coupling grating is used for respectively coupling an entangled photon pair generated by off-chip spontaneous parametric down-conversion into two inputports of the on-chip input directional coupler; the input directional coupler is used for converting the input entangled photon pair into a transverse electric fundamental mode photon and a transverse electric second-order mode photon; the grating mode beam splitter has a light splitting characteristic on incident transverse electric fundamental mode light and transverse electric second-order mode light, so that two-photon interference in mode is realized; the output directional coupler is used for transmitting a pair of photons which are simultaneously in a transverse electric fundamental mode or a transverse electric second-order mode and are subjected to mode interference to a certain output port; and the superconducting nanowire single-photon detector absorbs a pair of photons at a low temperature and converts the photons into current signals to be detected by peripheral test equipment. According to the invention, the density of an integrated quantum optical path can be improved.

The invention provides a quantum battery for solving the problem that the batteries of existing electronic products and new energy resource communication media are poor in performance, small in electric capacity and short in endurance or continuous usage time, cannot meet the product consumption needs of consumers and is long in charging time traditionally and the like. The quantum battery comprises a positive pole, a negative pole, a charging medium layer and a housing. The charging medium layer comprises a quantum entanglement state preparation facility, the quantum entanglement state preparation facility can be a facility for preparing quantum entanglement through conversion under spontaneous parameters or a facility for preparing quantum entanglement state in quantum electrodynamics (QED) or a facility for preparing quantum entanglement state in an ion trap. By adopting a quantum battery technology, the energy storage capacity of one-time charging can be greatly increased, the current usage time for full charging at a time of a notebook computer, a tablet personal computer and a mobile phone is remarkably shortened, meanwhile the travelling distances of an electric automobile and an electric bicycle can be remarkably increased, and the environment can be protected and ecological balance can be maintained by utilizing an atomic energy level physical principle.