Search

CN-121986299-A - Method for generating entangled photons

CN121986299ACN 121986299 ACN121986299 ACN 121986299ACN-121986299-A

Abstract

The present invention relates to a method for generating entangled photon pairs by propagating a laser beam having a wavelength lambda p through a crystal, preferably a crystal having a C 3v or D 3 or D 3h symmetry class.

Inventors

  • F. Alan Berger
  • T. Perch
  • F. Setzpfant
  • M. Weissflog
  • S. Saravi

Assignees

  • 弗劳恩霍夫应用研究促进协会
  • 耶拿弗里德里希·席勒大学

Dates

Publication Date
20260505
Application Date
20241002
Priority Date
20231009

Claims (17)

  1. 1. A method for producing entangled photon pairs by propagating a laser beam of wavelength lambda p through a crystal, preferably a crystal having a C 3v or D 3 or D 3h symmetry class.
  2. 2. A method according to claim 1, characterized in that the crystal is arranged on the substrate in a suspended or embedded optical system such that a laser beam, preferably a linearly polarized or elliptically polarized or circularly polarized laser beam, having a wavelength λ p propagates through the crystal.
  3. 3. The method according to claim 1 or 2, wherein the propagation is along the Z-axis.
  4. 4. A method according to any one of claims 1to 3, characterized in that the generation of entangled photon pairs is achieved by superimposing two non-linear paths in the tensor, which are indistinguishable by the choice of crystal symmetry.
  5. 5. Method according to any of claims 1 to 4, characterized in that the entanglement state is selected by polarization rotation of the laser field, preferably a laser beam.
  6. 6. Method according to any one of claims 1 to 5, characterized in that the degree of entanglement is selected by polarization, preferably the ellipticity of the incident polarization, preferably steplessly, preferably by the polarization of the laser beam.
  7. 7. Method according to claims 5 and 6, characterized in that the crystal has triple rotational symmetry, preferably about the laser beam propagation axis.
  8. 8. The method according to any one of claims 1 to 7, wherein entanglement occurs in a polarization-wavelength phase space.
  9. 9. The method according to any one of claims 1 to 8, wherein the generated photon pairs co-propagate along a direction predetermined by the laser.
  10. 10. A method according to any one of claims 1 to 9, characterized in that at the output, the remaining laser radiation and possibly parasitic radiation are filtered out.
  11. 11. An apparatus for generating entangled photon pairs, the apparatus comprising a laser for generating a laser beam and a crystal, preferably a crystal arranged in the laser beam, preferably a crystal having a C 3v or D 3 or D 3h symmetry class.
  12. 12. The apparatus of claim 11, wherein the crystal has a symmetry of the C 3v or D 3 or D 3h symmetry class or similar symmetry.
  13. 13. The apparatus according to claim 11 or 12, wherein the crystal has a second order nonlinearity and/or a third order nonlinearity.
  14. 14. The device according to any of claims 11 to 13, characterized in that the crystal has no fluorescence transitions in the relevant wavelength range and/or that a filter for laser radiation and/or parasitic radiation is arranged after the crystal.
  15. 15. The apparatus according to any of claims 11 to 14, characterized in that the laser and/or the crystal are designed to be rotatable for the selection of the entangled state, or that an optical element for polarization rotation, preferably a wave plate, is arranged between the laser and the crystal.
  16. 16. An apparatus according to any one of claims 11 to 15, characterized in that one or more optical elements, preferably wave plates, are arranged before the crystal in order to select entanglement.
  17. 17. The apparatus according to claims 15 and 16, characterized in that the crystal has a triple rotational symmetry, preferably about the axis of propagation of the laser beam.

Description

Method for generating entangled photons Technical Field The present invention relates to a method for generating entangled photon pairs according to the features of the preamble of claim 1 and to an apparatus for generating entangled photon pairs according to the features of the preamble of claim 11. Background Entangled photon sources (english, ENTANGLED PHOTON SOURCES, EPS) are important quantum photonic devices. Entangled photon sources are required for many approaches in quantum technology, including quantum key distribution, quantum imaging, quantum spectroscopy, and quantum information technology approaches, such as those used for boson sampling or quantum computer interconnects. The most common method of generating entangled photons is to utilize a spontaneous parametric down-conversion (SPDC) process, also known as parametric fluorescence, in which a high energy (short wavelength) "parent photon" is split into two lower energy (longer wavelength) child photons in a χ (²) nonlinear crystal. The two photons are correlated, that is, they have a common dual particle wave function. Although this process occurs locally, only photon pairs in which all participating sources constructively interfere can be observed macroscopically. If this process occurs in a homogeneous medium, it is called phase matching of plane wave pairs (English, PHASE MATCHING, PM) and if it occurs in a structured medium, it is broadly called pattern matching of pattern pairs. To generate entangled photon pairs from photon pairs, the crystal and optical system must be coordinated with each other so that two independent and indistinguishable SPDC paths lead to the same mode pair. If the paths are indistinguishable, then the paths will interfere and entangled photons can be emitted. A number of light source types are known from such prior art to implement this concept. There can be broadly divided into two categories, common path entangled photon sources (CP-EPS) and split path entangled photon sources (DP-EPS). DP-EPS has two independent channels in which photon pairs are generated. In a second step, these photon pairs are superimposed by means of a coherent mixer. For example, the sagnac loop light source is of this type, where the paths are separated by the propagation direction and superimposed by a beam splitter. Likewise, resonator comb light sources are of this type, in which photon pairs are generated in different wavelength modes and are superimposed in a single sideband by means of a mixer (modulator). The structure of DP-EPS is often very complex and requires a large number of highest quality photonic components. However, the phase-matching PM, pattern-matching MM, and conversion efficiency on each channel can all be optimized separately, as compared to the CP-EPS. Thus, the DP-EPS performance is generally more powerful. CP-EPS eliminates independent conversion and re-superposition along both modes. Instead, the CP-EPS uses two independent nonlinear channels along one pattern or pair of patterns that are spatially indistinguishable (at least in the far field). The most common case here is polarization entanglement of plane waves along a common wave vector. Such a system, while conceptually simpler, must be able to achieve phase matching PM (or pattern matching MM) of two independently propagating photons, and furthermore, must synchronize the SPDC efficiency along both channels in the same system. This is generally only applicable for a specific crystal class and needs to be achieved with fixed polarization along a specific propagation axis under very tightly controlled PM or MM conditions, which in turn require tightly controlled environmental conditions (e.g. temperature). Thus, CP-EPS is generally technically less important because it is technically difficult to control despite its subtle concept. One way to circumvent the phase matching condition (PM condition) or the mode matching condition (MM condition) is to thin the crystal to a scale smaller than the wavelength of the light (more precisely: smaller than the coherence length). It has been shown that, for example, in thin gallium phosphide crystals (but with different crystal symmetry than described herein), one form of polarization entangled photon pairs can be generated. However, tunability of different maximum entangled polarization states is thereby not achieved, but rather requires the special crystal symmetry described herein. Heretofore, no polarization entangled light source has been studied and is not known that can produce different maximum entangled photon pairs in a manner that can be tuned based on only special crystal symmetry and without the need for other optical elements, or additionally produce photon pairs with adjustable entanglement in the same system. Disclosure of Invention It is an object of the present invention to provide an improved method for generating entangled photon pairs and to provide a correspondingly improved device for generating e