DE102022118548B3 - Method and device for generating entangled photons - Google Patents

Abstract

What is proposed is a method for generating entangled photons (12), preferably for use in optical communication, quantum cryptography and/or quantum information technology, the method comprising the following steps: i) generating a pump beam (11), preferably in a pump device (1), ii) generation of entangled photons (12) by pumping a non-linear entanglement element (4) with the pump beam (11), iii) distribution of the entangled photons based on their wavelength into several outputs of a wavelength selection device (5). What is essential here is that that in step i) a photon beam (10) is first generated by amplified spontaneous emission, preferably in a photon source (2) of the pump device (1), and that in step i) the photon beam (10) is then filtered to generate the pump beam (11). is, preferably in a filter device (3) of the pump device (1).

Description

The invention relates to a method for generating entangled photons according to the features of the preamble of claim 1 and a device for generating entangled photons according to the features of the preamble of claim 14.

Entangled photons are used for quantum communication, for example for quantum key distribution (QKD). Quantum communication and quantum cryptography are far superior to classical communication and classical encryption because the security of this type of communication and encryption is not based on a mathematical calculation, but on physical natural laws of the process and the system, such as the entanglement of photon pairs.

In known sources for generating entangled photons, polarization-entangled photon pairs are usually generated by pumping a non-linear element with a pump laser beam. Longitudinal single-mode lasers with high spatial coherence are used for pumping, which have high wavelength stability and are therefore correspondingly cost-intensive. These lasers are used to enable a stable source, i.e. both stable in time in terms of generation rate and in terms of wavelength stability of the entangled photons generated. The wavelength of the entangled photons is influenced by the pump laser beam and the properties of the nonlinear element. Since the properties of the non-linear element do not normally change abruptly, known sources rely on a stable longitudinal single-mode pump laser with high spatial coherence for stable generation of entangled photons.

In known sources, entangled pairs of photons are sent to two receivers. With two receivers, an economical transmission rate is possible with known sources of entangled photons. For quantum communication or quantum cryptography between more than two receivers, the transmission rate in known sources is significantly reduced because the entangled photon pairs in these sources are divided among the multiple receivers by spectral multiplexing. This leads to a reduction in the transmission rate that is no longer economical.

From the document US 2015 / 0 261 058 A1 an integrated optical photon source is known for generating path-entangled photon pairs, which are generated in one of two interferometer arms in identical photon pair sources. The photon pair sources are pumped using a pump laser beam that is first amplified and then filtered in an amplified spontaneous emission (ASE) filter.

The present invention is based on the object of providing a more cost-effective, stable, easy-to-adjust and flexible method for generating entangled photon pairs and a corresponding device.

The object is achieved according to the invention by a method for generating entangled photons according to the features of claim 1.

1. i) Erzeugung eines Pumpstrahls, vorzugsweise in einer Pumpvorrichtung,
2. ii) Erzeugung von verschränkten Photonen durch Pumpen eines nicht-linearen Verschränkungs-Elements mit dem Pumpstrahl,
3. iii) Aufteilung der verschränkten Photonen anhand ihrer Wellenlänge auf mehrere Ausgänge einer Wellenlängenselektionsvorrichtung. Wesentlich dabei ist, dass in Schritt i) zuerst ein Photonenstrahl durch verstärkte spontane Emission erzeugt wird, vorzugsweise in einer Photonenquelle der Pumpvorrichtung, und

dass in Schritt i) anschließend der Photonenstrahl zur Erzeugung des Pumpstrahls gefiltert wird, vorzugsweise in einer Filtervorrichtung der Pumpvorrichtung.According to the invention, a method for generating entangled photons is proposed, preferably for use in optical communication, quantum cryptography and/or quantum information technology, the method comprising the following steps:

1. i) generating a pump jet, preferably in a pump device,
2. ii) generation of entangled photons by pumping a non-linear entanglement element with the pump beam,
3. iii) Division of the entangled photons based on their wavelength into several outputs of a wavelength selection device. What is essential here is that in step i) a photon beam is first generated by amplified spontaneous emission, preferably in a photon source of the pump device, and

that in step i) the photon beam is then filtered to generate the pump beam, preferably in a filter device of the pump device.

Furthermore, the object is achieved according to the invention by a device for generating entangled photons according to the features of claim 14.

According to the invention, a device for generating entangled photons is proposed, preferably for use in optical communication, quantum cryptography and/or quantum computing, wherein the device has a pump device for generating a pump beam, a non-linear entanglement element and a wavelength selection device, and
the non-linear entanglement element is arranged after the pump device for generating entangled photons by pumping the non-linear entanglement element with the pump beam, and
the wavelength selection device is arranged after the non-linear entanglement element for dividing the entangled photons based on their wavelength into several outputs of the wavelength selection device, and
the pump device has a photon source and a filter device. What is essential here is that the photon source has one or more optically active elements and/or a superluminescent diode SLED for generating a photon beam through amplified spontaneous emission, and that the filter device has one or more filters for filtering the photon beam to generate the pump beam.

The advantage of the method according to the invention and the device according to the invention lies in the generation of the photon beam by amplified spontaneous emission (Amplified spontaneous emission ASE) and the subsequent filtering to the desired wavelength and spectral width of the pump beam, which is then used to generate entangled photons.

The advantage is that enhanced spontaneous emission is very robust against external influences, i.e. thermal or mechanical stabilization of the device and method is not necessary.

A further advantage is that the wavelength of the pump beam can be adjusted by the filter device of the photon beam in such a way that the pump beam can be selected and generated within the spectrum of the photon beam in order to produce the desired wavelengths of the entangled photons.

In contrast, a laser has an active medium, a pump and a resonator. In the laser, the resonator is absolutely necessary to generate the laser beam by amplifying the stimulated emission. Essential to generating the laser beam is the exceeding of the laser threshold through feedback in the resonator and the resulting suppression of the amplified spontaneous emission. Through this feedback we also obtain the desired narrow spectrum of the wavelength of the laser beam. Increased spontaneous emission is undesirable in a laser because it leads to power losses and power fluctuations. In order to generate a stable longitudinal single-mode laser beam with high spatial coherence and high temporal coherence, thermal and mechanical stabilization is necessary.

Amplified spontaneous emission means a photon beam generated by spontaneous emission, which has been optically amplified by stimulated emission in the optically active medium. The photon beam generated by spontaneous emission has spatial coherence but only low temporal coherence. The advantage of enhanced spontaneous emission lies in the larger optical bandwidth of the emitted radiation, i.e. the larger spectral width of the photon beam.

It can be provided that in step i) the photon beam is generated by amplified spontaneous emission in one or more optically active elements and/or in a superluminescent diode SLED.

It can be provided that the photon beam is generated by amplified spontaneous emission by suppressing and/or preventing a laser process in the one or more optically active elements and/or the superluminescent diodes SLED. It can be provided that a laser threshold is not exceeded in order to generate the photon beam. For a laser process, i.e. exceeding the laser threshold, a resonator is necessary in addition to an active medium and a pump. In contrast, the one or more optically active elements and/or the superluminescent diodes SLED do not have a resonator or are not arranged in a resonator.

It can be provided that the suppression and/or prevention of the laser process takes place through low reflection and/or high transmission and/or scattering, preferably Rayleigh scattering, and/or through optical isolation of the photon beam. It can be provided that, to suppress and/or prevent the laser process, one or more optical elements with low reflection and/or one or more optical elements with high transmission and/or one or more optical elements for scattering, preferably Rayleigh scattering, and / or one or more optical isolators are arranged in the photon source, preferably arranged in the beam path of the photon beam. It can be provided that the laser process is suppressed and/or prevented by optical switches, preferably with a pulsed photon beam. It can be provided that in order to suppress and/or prevent the laser process, one or more optical switches, preferably electro-optical modulators and/or acousto-optical modulators, are arranged in the photon source, preferably arranged in the beam path of the photon beam, preferably for a pulsed photon beam.

It can be provided that in step i) the one or more optically active elements are pumped to generate the photon beam through enhanced spontaneous emission. Pumping can be done optically or electronically. It may be provided that the photon source has a photon beam pump laser or photon beam pump electronics that pumps the one or more optically active elements to generate the photon beam by amplified spontaneous emission.

It can be provided that the photon beam pump laser is designed to be temporally unstable and/or spectrally multi-mode for pumping the one or more optically active elements. The advantage of such an embodiment is that the photon beam pump laser of this type is very cost-effective in contrast to temporally stable and/or spectrally single-mode lasers.

It can be provided that the one or more optically active elements are designed as a solid, liquid and/or gas. It can be provided that the one or more optically active elements are designed as a doped solid and/or doped fiber, preferably a rare earth-doped fiber. The advantage of a doped solid and/or a doped fiber is the robustness and resistance to external influences. The advantage of doped fibers is that they are easy to integrate into an optical system using fiber connectors without the need to adjust the system.

It can be provided that the photon beam is amplified by several optically active elements. It can be provided that several optically active elements are formed in the pump device to amplify the photon beam. It can be provided that several optically active elements are formed next to one another in order to generate several photon beams, preferably that the several photon beams are then bundled into one photon beam.

It can be provided that the photon beam in step i) is generated with a broad wavelength spectrum, preferably that the broad wavelength spectrum of the photon beam is at least 1 nm wide, preferably at least 10 nm, most preferably at least 30 nm. The advantage of such a broad wavelength spectrum The reason for the photon beam is that, together with the subsequent filtering, the generation of the pump beam is extremely robust against external influences. It is essential that the wavelength spectrum of the photon beam contains all of the filtered wavelengths of the pump beam.

It can be provided that the wavelength spectrum of the photon beam is formed in the range between 250 nm and 600 nm, or is formed in the range between 600 nm and 1200 nm.

It can be provided that one or more filters are used for filtering in step i). It can be provided that the filter device has one or more filters.

It can be provided that the one or more filters are designed as free-jet elements and/or as fiber elements.

It can be provided that the filtering takes place through reflection and/or transmission. It can be provided that the one or more filters are used as a reflection filter and/or as a transmission filter and/or as a fiber Bragg filter and/or as an etalon and/or as a volume Bragg grating and/or as a dielectric reflection grating and/or as dielectric transmission grid and / or are designed as a prism.

It can be provided that the filtering in step i) is carried out step by step by several filter steps carried out one after the other, preferably that the spectral width of the photon beam is reduced step by step in the several filters arranged one after the other. It can be provided that several filters are arranged one after the other in the filter device, preferably that the filters are designed with a gradually reduced spectral width.

It can be provided that the one or more filters of the filter device are arranged in and/or after the photon source. It can be provided that in a filter device with several filters, individual filters are arranged in the photon source and further filters are arranged after the photon source. It can be provided that the one or more filters are arranged in the optically active element and/or in the superluminescent diode SLED and/or after the optically active element and/or after the superluminescent diode SLED.

It can be provided that the photon beam is filtered in step i) such that the pump beam has a narrow wavelength spectrum, preferably that the narrow wavelength spectrum of the pump beam is smaller than 1 nm, preferably smaller than 50 pm, most preferably smaller than 1 pm.

It can be provided that in step i) a pump beam with a wavelength λ _n is generated, with n = 1. This can also be done as individual lines Source can be referred to. The individual line refers to the one wavelength λ _n with n = 1 of the pump beam.

It can be provided that in step i) a pump beam with several wavelengths λ _n is generated, with n = 1, ..., i and i = 2, 3, .... This can also be referred to as a multi-line source become. The multiple lines refer to the multiple wavelengths λ _n with n = 1, ..., i and i = 2, 3, .... of the pump beam.

It can be provided that the laser process in the one or more optically active elements and/or the superluminescent diode SLED is suppressed by the one or more filters. It can be provided that the optical components for suppressing and/or preventing the laser process are simultaneously designed as filters.

It can be provided that the photon source and the filter device are connected to one another by optical components, preferably by one or more fibers and/or one or more beam splitters and/or one or more circulators and/or one or more wave selection elements.

It can be provided that in step i) the wavelength λ _n of the photon beam and/or the pump beam is shifted by a non-linear wavelength shift process, preferably shifted in the range between 250 nm and 600 nm or in the range between 600 nm and 1200 nm. This can preferably be done in the pump device. The wavelength shift by the non-linear process is performed when the wavelength of the photon beam and/or the pump beam is outside the range for generating entangled photons, that is, outside the 250 nm and 600 nm or the range of 600 nm and 1200 nm .

It can be provided that after step i) the wavelength λ _n of the pump beam is shifted by a non-linear wavelength shift process, preferably shifted in the range between 250 nm and 600 nm or in the range between 600 nm and 1200 nm. This can be done after the pumping device and before the non-linear entanglement element. The wavelength shift by the non-linear process is performed when the wavelength of the photon beam and/or the pump beam is outside the range for generating entangled photons, that is, outside the 250 nm and 600 nm or the range of 600 nm and 1200 nm .

It can be provided that one or more non-linear wavelength shifting elements are arranged in and/or after the pump device in order to shift the wavelength of the photon beam and/or the wavelength of the pump beam by one or more non-linear wavelength shifting processes. It can be provided that one or more non-linear wavelength shifting elements are arranged after the filter device in order to shift the wavelength of the pump beam through one or more non-linear wavelength shifting processes.

It can be provided that only the wavelength of the photon beam is shifted by one or more non-linear wavelength shifting elements or that only the wavelength of the pump beam is shifted by one or more non-linear wavelength shifting elements or that both the wavelength of the photon beam and The wavelength of the pump beam is also shifted by one or more non-linear wavelength shift elements.

It can be provided that the non-linear wavelength shift process of the one or more non-linear wavelength shift elements is frequency doubling and/or sum frequency generation and/or difference frequency generation and/or parametric process and/or four-wave mixing. It can be provided that the one or more non-linear wavelength shift elements are designed for frequency doubling and/or sum frequency generation and/or difference frequency generation and/or parametric process and/or a four-wave mixture.

It can be provided that the entangled photons are entangled in polarization, and/or time (time-bin) and/or orbital angular momentum.

It can be provided that in step ii) the entangled photons are generated by a non-linear entanglement process in the non-linear entanglement element, preferably by parametric fluorescence (spontaneous parametric down-conversion SPDC) or spontaneous four-wave mixing (Spontaneous Four-Wave Mixing SFWM). The nonlinear entanglement element may be arranged in a Sagnac configuration, linear configuration, BBO configuration or in a four-wave mixing configuration with a cavity to generate entangled photons.

It can be provided that the non-linear entanglement element has one or more non-linear crystals or one or more non-linear waveguides.

It can be provided that the entangled photons are designed as entangled photon pairs or as entangled photon triplets or as entangled multiple photons. By pumping the non-linear entanglement element with the pump beam, several entangled photon pairs or entangled photon triples or entangled multi-photons formed one after the other are generated.

It can be provided that the photons of an entangled photon pair or an entangled photon triple or an entangled multi-photon each have spectrally separated photons. Spectrally separated photons are understood here to mean that the photons of an entangled photon pair or an entangled photon triplet or an entangled multiple photon each have different wavelengths, ie, for example, for an entangled photon pair with a signal photon with wavelength λ _s and an idler photon with the Wavelength λ _i holds that λ _s ≠ λ _i . This is also referred to as a non-degenerated photon pair and is obtained by the dependence of the wavelengths of the entangled photons on both the pump wavelength and the properties of the non-linear entanglement element.

It can be provided that the entangled photons have a wavelength in the range between 500 nm and 2 μm.

It can be provided that the entangled photons have a wavelength in the range between 500 nm and 1000 nm. The advantage of this range is that silicon-based single photon detectors can be used, which can be manufactured easily and inexpensively and have a high detection efficiency in the range between 500 nm and 1000 nm.

It can be provided that the entangled photons have a wavelength between 1260 nm and 1360 nm (O-band) and/or between 1360 nm and 1460 nm (E-band) and/or between 1460 nm and 1530 nm (S-band). and/or between 1530 nm and 1565 nm (C-band) and/or between 1565 nm and 1625 nm (L-band). An advantage of these wavelength ranges is the low absorption and/or low dispersion in fiber optic cables for transmitting photons in a fiber over long distances.

It can be provided that the wavelength selection device has one or more dichroic mirrors and/or one or more gratings and/or one or more volume Bragg gratings and/or one or more fiber Bragg gratings and/or one or more prisms and/or or has a wavelength demultiplexer.

It can be provided that the multiple outputs of the wavelength selection device are connected through the outputs of the one or more dichroic mirrors and/or the one or more gratings and/or the one or more volume Bragg gratings and/or the one or more Fiber Bragg grating and / or the one or more prisms and / or the wavelength demultiplexer are formed.

As already described above, it can be provided that in step i) a pump beam with several wavelengths λ _n is generated, with n = 1, ..., i and i = 2.3, .... This can also be done as Multi-line source are called. The multiple lines refer to the multiple wavelengths λ _n with n = 1, ..., i and i = 2.3, .... of the pump beam. The previously described explanations of the generation of the photon beam, the generation of the entangled photons and the division of the entangled photons also apply to a pump beam with several wavelengths λ _n , ie to a multi-line source, as for a single-line source.

In a multi-line source it can be provided that in step i) a pump beam with several wavelengths λ _n is generated by filtering the photon beam.

In a multi-line source it can be provided that one or more filters are arranged in the filter device to generate a pump beam with several wavelengths λ _n . It can be provided that the one or more filters are used as a reflection filter and/or as a transmission filter and/or as a fiber Bragg filter and/or as an etalon and/or as a volume Bragg grating and/or a dielectric reflection grating and/or a dielectric transmission grating and/or prism are formed. By using appropriate filters, for example fiber Bragg gratings, the broad wavelength spectrum of the photon beam can be filtered to a pump beam with several wavelengths λ _n . In this exemplary embodiment as a multi-line source, the pump beam with several wavelengths λ _n is generated by filtering from the spectrum of the photon beam.

In a multi-line source it can be provided that the photon beam has the multiple wavelengths λ _n of the pump beam.

In a multi-line source it can be provided that in step i) a pump beam with several wavelengths λ _n is generated by shifting the photon beam, preferably by several non-linear wavelength shifting processes. In this exemplary embodiment, a different wavelength λ _n of the pump beam can be generated by the multiple non-linear wavelength shift processes in the different non-linear wavelength shift elements. In a multi-line source, it can be provided that several non-linear wavelength shift elements are designed to generate a pump beam with several wavelengths λ _n . By using several non-linear wavelength shift elements arranged one after the other, preferably each with different properties, the shift occurs to different extents. It should be noted that a non-linear wavelength shift process results in a shift for only part of the photon beam and the non-shifted portion of the photon beam is shifted in the non-linear wavelength shift element arranged afterwards. The displacement depends on the properties of the respective second non-linear element, ie the polarity and/or the temperature of the second non-linear element.

It can be provided that the generation of a pump beam with multiple wavelengths λ _n takes place through a combination of one or more filters and/or one or more non-linear wavelength shift elements.

In a multi-line source it can be provided that the multiple wavelengths λ _n of the pump beam are formed spectrally separate from one another.

In a multi-line source it can be provided that the multiple wavelengths λ _n of the pump beam are spatially formed in a beam path. In a multi-line source it can be provided that the multiple wavelengths λ _n of the pump beam are each spatially separated from one another in their own beam path, preferably that the spatial separation takes place through the filtering and/or the displacement. It can be provided that two or more of the multiple beam paths are combined to form a beam path with multiple wavelengths λ _n , preferably in the pump device. The advantage of a common beam path is that only one non-linear entanglement element can be used to generate the entangled photons. The advantage of the separate beam path is the possibility of subsequent further filtering.

In a multi-line source it can be provided that the multiple wavelengths λ _n of the pump beam are formed spectrally separated from one another by at least 0.01 nm, preferably at least 0.1 nm, most preferably at least 0.5 nm. By separating the spectra in this way The multiple wavelengths λ _n of the pump beam can ensure that the entangled photons generated are also spectrally separated. The advantage of such a large spectral separation lies in the low-loss division of the entangled photons in the wavelength selection device.

In a multi-line source it can be provided that the photon beam is filtered and/or shifted in step i) in such a way that the pump beam has several narrow wavelength spectra λ _n , preferably that the narrow wavelength spectra λ _n of the pump beam are less than 1 nm, preferably smaller 50 pm, most preferably less than 1 pm. The advantage of a pump beam with the narrowest possible wavelength spectra λ _n is that the entangled photons generated also have a narrow wavelength spectrum.

In a multi-line source it can be provided that the multiple wavelengths An of the pump beam are completely spectrally separated from one another.

In a multi-line source it can be provided that the multiple wavelengths An of the pump beam are spectrally separated in such a way that at most 5% of the spectrum of the pump beam overlap, preferably at most 1%, most preferably 0.01%. The advantage of a pump beam with the largest possible spectral separation of the multiple wavelengths λ _n of the pump beam is that the multiple spectrally separated entangled photons generated also have a large spectral separation, whereby the individual photons of the photon pairs or photon triples or multi-photons can be used in a simple manner for quantum communication can be separated by their wavelength. This ensures spectral division without major losses, which leads to a higher transmission rate.

In a multi-line source it can be provided that in step ii) several spectrally separated entangled photons are generated by the multiple wavelengths λ _n of the pump beam, preferably entangled photon pairs, entangled photon triples or entangled multi-photons.

In a multi-line source it can be provided that the photons are each entangled photo nenpair or each entangled photon triple or each entangled multiple photon each have spectrally separated photons. What is meant here by spectrally separated photons is that the photons of an entangled photon pair or an entangled photon triplet or an entangled multiple photon each have different wavelengths. For example, in a multi-line source, each entangled photon pair has a signal photon with wavelength λ _sn and an idler photon with wavelength λ _in , which are generated by pumping the non-linear entanglement element with wavelength An of the pump beam become. The wavelength of the signal photons and the idler photons when generating entangled photon pairs is determined by the respective wavelength λ _n of the pump beam and/or the properties of the non-linear entanglement element, such as the polarity of the crystal, the temperature and/or or the k-vector. For example, several spectrally separated entangled photon pairs here mean that, on the one hand, the signal λ _sn and idler photons λ _in a photon pair have different wavelengths, that is, λ _sn ≠ λ _in regardless of which wavelengths λ _n of the pump beam generate the photon pair became. This is also referred to as a non-degenerated photon pair and is obtained by the dependence of the wavelengths of the pump beam as well as the properties of the non-linear entanglement element. In addition, for the several spectrally separated entangled photon pairs, the wavelengths of the signal photons, generated by the different wavelengths λ _n , differ spectrally from one another, that is, λ _sn ≠ λ _s(n+1) . This also applies accordingly to the idler photons, that is, in addition, the wavelengths of the idler photons, generated by the different wavelengths λ _n , differ spectrally from one another, that is, λ _in ≠ λ _i(n+1) .

• 1: schematische Darstellung der erfindungsgemäßen Vorrichtung zur Erzeugung von verschränkten Photonen;
• 2: schematische Darstellung eines ersten Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit einem Filter;
• 3: schematische Darstellung eines zweiten Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit einem Reflektions-Element;
• 4: das zweite Ausführungsbeispiel der 3 mit Faserverbindungen;
• 5: schematische Darstellung eines dritten Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit einem Faser-Bragg Gitter;
• 6: das dritte Ausführungsbeispiel der 5 mit Faserverbindungen;
• 7: schematische Darstellung eines vierten Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit einem Faser-Bragg Gitter für mehrere Wellenlängen λ_n des Pumpstrahls;
• 8: das vierte Ausführungsbeispiel der 7 mit Faserverbindungen;
• 9: schematische Darstellung eines fünften Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit einem Prisma;
• 10: schematische Darstellung eines sechstes Ausführungsbeispiels einer erfindungsgemäßen Pumpvorrichtung mit zwei optisch aktiven Elementen;
• 11: das sechste Ausführungsbeispiel der 11 mit Faserverbindungen;
• 12: zweites Ausführungsbeispiel der erfindungsgemäßen Vorrichtung mit mehreren nicht-linearen Wellenlängenverschiebungs-Elementen;
• 13: drittes Ausführungsbeispiel der erfindungsgemäßen Vorrichtung mit mehreren Wellenlängen λ_n des Pumpstrahls durch Filterung;
• 14: viertes Ausführungsbeispiel der erfindungsgemäßen Vorrichtung mit mehreren Wellenlängen λ_n des Pumpstrahls durch mehrere nicht-lineare Wellenlängenverschiebungs-Elemente;
• 15: schematische Darstellung der Wellenlänge des Photonenstrahls und eines Pumpstrahls mit drei Wellenlängen λ_1,λ₂ und λ₃.

Further embodiments of the invention are shown in the figures and described below. The figures show an example of a possible embodiment of the invention. This embodiment serves to explain a possible implementation of the invention and should not be understood as limiting. Show:

• 1 : Schematic representation of the device according to the invention for generating entangled photons;
• 2 : Schematic representation of a first exemplary embodiment of a pump device according to the invention with a filter;
• 3 : Schematic representation of a second exemplary embodiment of a pump device according to the invention with a reflection element;
• 4 : the second embodiment of the 3 with fiber connections;
• 5 : Schematic representation of a third exemplary embodiment of a pump device according to the invention with a fiber Bragg grating;
• 6 : the third embodiment of the 5 with fiber connections;
• 7 : Schematic representation of a fourth exemplary embodiment of a pump device according to the invention with a fiber Bragg grating for several wavelengths λ _n of the pump beam;
• 8th : the fourth embodiment of the 7 with fiber connections;
• 9 : Schematic representation of a fifth exemplary embodiment of a pump device according to the invention with a prism;
• 10 : Schematic representation of a sixth exemplary embodiment of a pump device according to the invention with two optically active elements;
• 11 : the sixth embodiment of the 11 with fiber connections;
• 12 : second embodiment of the device according to the invention with several non-linear wavelength shift elements;
• 13 : third embodiment of the device according to the invention with several wavelengths λ _n of the pump beam by filtering;
• 14 : fourth embodiment of the device according to the invention with several wavelengths λ _n of the pump beam through several non-linear wavelength shift elements;
• 15 : schematic representation of the wavelength of the photon beam and a pump beam with three wavelengths λ _1, λ ₂ and λ ₃ .

1 shows the device according to the invention for generating entangled photons, which has a pump device 1, a non-linear entanglement element 4 and a wavelength selection device 5.

According to the invention, the pump device 1 has a photon source 2, which generates a photon beam 10. What is essential here is that the photon beam 10 in the photon source 2 is generated by increased spontaneous emission, for example by an optically active element 21 (not shown in 1 ) or a superluminescent diode is generated. The optically active element 21 can be pumped optically or electronically. The wavelength spectrum of the photon beam 10 generated by amplified spontaneous emission is broad.

Furthermore, the pump device 1 has a filter device 3, in which the photon beam 10 is filtered into a pump beam 11 with one or more wavelengths λ _n . The pump beam 11 is then used to pump the non-linear entanglement element 4 to generate entangled photons 12.

After being generated in the wavelength selection device 5, the entangled photons 12 are divided into one output of the wavelength selection device 5 based on their wavelength. In the exemplary embodiment 1 entangled photon pairs, each with a signal photon 13 and an idler photon 14, are generated by a pump beam 11 with a wavelength λ ₁ . What is important here is that the wavelength of the signal photon 13 and the idler photon 14 is designed differently in order to enable a division of the signal photons 13 and the idler photons 14 based on their wavelength in the wavelength selection device 5. This can be done by selecting the pump wavelength and the properties of the non-linear entanglement element 4.

2 shows a first exemplary embodiment of the pump device 1 according to the invention with a photon source 2 with a photon source pump laser 20, which generates a photon source pump beam 25 for optically pumping the optically active element 21. The photon beam 10 generated in this way is then filtered in the filter device 3 to generate the pump beam 11. In the exemplary embodiment 2 the filter device 3 is designed as a transmission filter 30.

3 shows a second embodiment of the pump device 1 according to the invention with photon source 2 with the photon source pump laser 20 and the optically active element 21, a circulator 41 being arranged between the photon source pump laser 20 and the optically active element 21.

The photon source pump beam 25 of the photon source pump laser 20 is in 3 from the first input/output of the circulator 41 to the second input/output of the circulator 41 and then optically pumps the optically active element 21. The photon beam 10 generated thereby is in the filter device 3, which in the exemplary embodiment 3 is formed as a reflection element 31 directly after the optically active element 21, filtered by reflection of the desired wavelength λ ₁ to the pump beam 11. The pump beam 11 is guided after the optically active element 21 from the second input/output of the circulator 41 to the third input/output of the circulator 41.

4 shows the second exemplary embodiment of the pump device 1 according to the invention 3 , whereby 4 of the 3 only differs in that instead of the photon source pump beam 25 and the photon beam 10, the fibers 40 are shown between the photon source pump laser 20, the circulator 41 and the optically active element 21 for beam guidance of the photon source pump beam 25 and the photon beam 10. The rays are in for clarity 4 not shown. The beam guidance is as in 3 described. In this exemplary embodiment, the optically active element 21 can be particularly advantageously designed as a doped fiber.

5 shows a third exemplary embodiment of the pump device 1 according to the invention. The exemplary embodiment of 5 differs from the exemplary embodiment 3 only in that the reflection element 31 of the filter device 3 for generating the pump beam 11 is designed at a distance from the optically active element 21.

6 shows the third exemplary embodiment of the pump device 1 according to the invention from the 5 , whereby 6 of the 5 only differs in that instead of the photon source pump beam 25, the photon beam 10 and the pump beam 11, the fibers 40 between the photon source pump laser 20, the circulator 41 and the optically active element 21 for beam guidance of the photon source pump beam 25, the photon beam 10 and of the pump beam 11 are shown and that the reflection element 31 of 5 is designed as a fiber Bragg grid 32. The rays are in for clarity 6 not shown. The beam guidance is as in 5 described. In this exemplary embodiment, the optically active element 21 can be particularly advantageously designed as a doped fiber.

7 shows a fourth exemplary embodiment of the pump device 1 according to the invention. The exemplary embodiment of 7 differs from the exemplary embodiment 5 only in that several reflection elements 31 are designed one behind the other as a filter device 3 for generating the pump beam 11 with several wavelengths λ _n .

8th shows the fourth exemplary embodiment of the pump device 1 according to the invention from the 7 , whereby 8th of the 7 only differs in that instead of the photon source pump beam 25, the photon beam 10 and the pump beam 11, the fibers 40 are shown between the photon source pump laser 20, the circulator 41 and the optically active element 21 for beam guidance of the photon source pump beam 25 and the photon beam 10 are and that the several reflection elements 31 arranged one behind the other 7 are designed as a fiber Bragg grating 32. The fiber Bragg grid 32 of the 8th is designed in such a way that it reflects the multiple wavelengths λ _n . This corresponds to a so-called discretely chirped fiber Bragg grating. The rays are in for clarity 8th not shown. The beam guidance is as in 7 described. In this exemplary embodiment, the optically active element 21 can be particularly advantageously designed as a doped fiber.

9 shows a fifth exemplary embodiment of the pump device 1 according to the invention. The exemplary embodiment of 9 differs from the exemplary embodiment 2 only in that instead of the filter 30 in 2 a prism 33 as a filter device 3 in 9 is trained. Through the prism 33, several wavelengths λ _n of the pump beam 11 are each formed spatially separated from one another in their own beam path, as in 9 shown. In this exemplary embodiment, additional filters can be arranged in each beam path or several beam paths can be combined into one beam path using additional optical components.

10 shows a sixth exemplary embodiment of the pump device 1 according to the invention. In this exemplary embodiment, the photon source 2 is designed with two optically active elements 21.

The photon source 2 of the exemplary embodiment 10 has the photon source pump laser 20, which generates a photon source pump beam 25. The photon source pump beam 25 is first split to a beam splitter 22 and guided to an upper and a lower wave selection element 24. Both wave selection elements 24 are designed such that the photon source pump beam 25 is guided to the respective optically active element 21.

In the upper optically active element 21 the 10 the photon beam 10 is generated by optically pumping the optically active element 21 with the photon source pump beam 25. By reflecting the photon beam 10 at the end of the optically active element 21, the photon beam 10 is directed in the direction of the wave selection element 24 and then in the direction of an insulator 23. Both the low reflection of the photon beam 10 at the end of the optically active element 21 and the insulator 23 in the beam path prevent a laser process in the optically active element 21 and thus enable the generation of the photon beam 10 through increased spontaneous emission. After the isolator 23, the photon beam 10 is guided from a first input/output of the upper circulator 41 to the second input/output of the upper circulator 41 and then filtered in the filter device 3, designed as a reflection element 31, to generate the pump beam 11. The pump jet 11 is guided from the second input/output of the upper circulator 41 to the third input/output of the upper circulator 41 to a first input/output of the lower circulator 41.

In the lower optically active element 21 the 10 the photon beam 10 is generated by optically pumping the optically active element 21 with the photon source pump beam 25. Behind the lower optically active element 21, a reflection element 31 is designed as a filter device 3, in which the pump beam 11 is generated by filtering the photon beam 10. The pump beam 11 is guided through the lower optically active element 21 to the lower wave selection element 24 and from there to the second input/output of the lower circulator 41.

In the lower circulator 41, the two pump jets 11 are combined and led to the third input/output of the lower circulator 41.

The exemplary embodiment of the 10 with two optically active elements 21 can be used to, firstly, generate a pump beam 11 with a wavelength λ ₁ with higher intensity, since two optically active elements are used to generate the photon beam 10, or secondly, a pump beam 11 with multiple wavelengths λ _n generate.

11 shows the sixth exemplary embodiment of the pump device 1 according to the invention from the 10 , whereby 11 of the 10 The only difference is that instead of the photon source pump beam 25, the photon beam 10 and the pump beam 11, the fibers 40 are shown between the individual optical components for beam guidance and that the reflection elements 31 of the 10 is designed as a fiber Bragg grid 32. The rays are in for clarity 11 not shown. The beam guidance is as in 10 described. In this exemplary embodiment, the two optically active elements 21 can be particularly advantageously designed as a doped fiber. Furthermore, the reflection in the upper optically active element 21 can take place through the fiber end of the doped fiber.

12 shows a second exemplary embodiment of the device according to the invention with a non-linear wavelength shift element 6.

The exemplary embodiment of the 12 differs from the exemplary embodiment 1 only in that the non-linear wavelength shift element 6 is arranged between the photon source 2 and the filter device 3 in order to shift the wavelength spectrum of the photon beam 10 using a non-linear wavelength shift process in such a way that the desired wavelength λ ₁ of the pump beam 11 is contained in the photon beam 10 before filtering. The pump beam 11 with the desired wavelength λ ₁ is then filtered from the photon beam 10 in the filter device 3.

By way of example, a second non-linear wavelength shift element 6 is dashed between the filter device and the non-linear entanglement element 4 in 12 shown. This can be used to shift the wavelength of the pump beam 11 to the desired wavelength λ ₁ through a non-linear wavelength shifting process. The spectral shift in the non-linear wavelength shift process depends on the properties of the respective second non-linear wavelength shift element 6, for example the polarity or the temperature.

It is also possible to use the non-linear wavelength shift elements 6 12 between the photon source 2, the filter device 3 and the non-linear entanglement element 4.

13 shows a third embodiment of the device according to the invention. The exemplary embodiment of the 13 differs from the exemplary embodiment 1 only in that a pump beam 11 with several wavelengths λ _n is generated in the photon source 2. This corresponds to a multi-line source. Such a pump beam 11 with several wavelengths λ _n can, for example, as in a photon source 2 in the 7 until 11 shown are generated, or by arranging several non-linear wavelength shift elements 6 with different properties in front of the non-linear entanglement element 4 as for 12 described.

Due to the multiple wavelengths λ _n of the pump beam 11, several spectrally separated entangled photons 12 are generated in the non-linear entanglement element 4. The photons, each with different wavelengths, are assigned to 5 different outputs in the wavelength selection device, as in 13 shown. In the example of 13 This means that both the wavelength of the signal photon 13 and the idler photon 14 of a pair, as well as the wavelength of the signal photons 13 of different pairs and the wavelength of the idler photons 14 of different pairs differ from one another.

14 shows a fourth embodiment of the device according to the invention. The exemplary embodiment of the 14 differs from the exemplary embodiment 13 only in that the pump beam 11 with multiple wavelengths λ _n is generated in the photon source 2 by arranging multiple non-linear wavelength shift elements 6 with different properties.

15 shows an exemplary spectrum of the photon beam 10 (dashed line) and, as an example, three wavelengths λ ₁ , λ ₂ and λ ₃ of a pump beam 11 filtered therefrom.

Reference symbol list

1

Pumping device

2

photon source

3

Filter device

4

non-linear entanglement element

5

Wavelength selection device

6

non-linear wavelength shift element

10

photon beam

11

Pump jet

12

entangled photons

13

Signal photon

14

Idler Photon

20

Photon source pump laser

21

optically active element

22

Beam splitter

23

insulator

24

Wave selection element

25

Photon source pump beam

30

Transmission filter

31

Reflection element

32

Fiber Bragg grid

40

fiber

41

Circulator

Claims (15)

Method for generating entangled photons (12), preferably for use in optical communication, quantum cryptography and/or quantum computing, the method comprising the following steps: i) generation of a pump beam (11), preferably in a pump device (1), ii) generation of entangled photons (12) by pumping a non-linear entanglement element (4) with the pump beam (11), iii) dividing the entangled photons based on their wavelength into several outputs of a wavelength selection device (5), characterized in that in step i ) first a photon beam (10) is generated by amplified spontaneous emission, preferably in a photon source (2) of the pump device (1), and that in step i) the photon beam (10) is then filtered to generate the pump beam (11), preferably in a filter device (3) of the pump device (1). Procedure according to Claim 1 , characterized in that in step i) the photon beam (10) is generated by amplified spontaneous emission in one or more optically active elements (21) and / or in a superluminescent diode SLED. Procedure according to one of the Claims 1 or 2 , characterized in that the photon beam (10) is generated by amplified spontaneous emission by suppressing and/or preventing a laser process in the one or more optically active elements (21) and/or the superluminescent diode SLED, preferably for generating the Photon beam (10) a laser threshold is not exceeded. Procedure according to Claim 3 , characterized in that the suppression and/or prevention of the laser process occurs through low reflection and/or high transmission and/or scattering, preferably Rayleigh scattering, and/or through optical isolation of the photon beam (10). Procedure according to one of the Claims 1 until 4 , characterized in that the photon beam (10) is generated in step i) with a broad wavelength spectrum, preferably that the broad wavelength spectrum of the photon beam (10) is at least 1 nm wide, preferably at least 10 nm, most preferably at least 30 nm. Procedure according to one of the Claims 1 until 5 , characterized in that one or more filters are used for filtering in step i), preferably that the filtering is carried out by reflection and / or transmission, most preferably that the laser process is optically active in the one or more optically active through the one or more filters Elements and / or the superluminescent diode SLED is suppressed. Procedure according to one of the Claims 1 until 6 , characterized in that the filtering in step i) is carried out step by step by several filter steps carried out one after the other, preferably that the spectral width of the photon beam (10) is reduced step by step in the several filters arranged one after the other. Procedure according to one of the Claims 1 until 7 , characterized in that the photon beam (10) is filtered in step i) such that the pump beam (11) has a narrow wavelength spectrum, preferably that the narrow wavelength spectrum of the pump beam (11) is less than 1 nm, preferably less than 50 pm, most preferably less than 1 pm. Procedure according to one of the Claims 1 until 8th , characterized in that in step i) the wavelength λ _n of the photon beam (10) and / or the pump beam (11) is shifted by a non-linear wavelength shift process, preferably shifted in the range between 250 nm and 600 nm or in the range between 600 nm and 1200 nm, and/or that after step i) the wavelength λ _n of the pump beam (11) is shifted by a non-linear wavelength shift process, preferably shifted in the range between 250 nm and 600 nm or in the range between 600 nm and 1200 nm. Procedure according to one of the Claims 1 until 9 , characterized in that in step ii) the entangled photons (12) are generated by a non-linear entanglement process in the non-linear entanglement element (4), preferably by parametric fluorescence (Spontaneous parametric down-conversion SPDC) or spontaneous Four-wave mixing (Spontaneous Four-Wave Mixing SFWM). Procedure according to one of the Claims 1 until 10 , characterized in that in step i) a pump beam (11) with a wavelength λ _n is generated, with n = 1, preferably that in step i) a pump beam (11) with several wavelengths λ _n is generated, with n = 1 , ..., i and i = 2, 3, .... Procedure according to Claim 11 , characterized in that in step i) a pump beam (11) with several wavelengths λ _n is generated by filtering the photon beam (10), and / or that in step i) a pump beam (11) with several wavelengths λ _n by shifting the Photon beam (10) is generated, preferably by several non-linear wavelength shift processes. Procedure according to one of the Claims 11 or 12 , characterized in that the multiple wavelengths λ _n of the pump beam (11) are formed spectrally separate from one another. Device for generating entangled photons (12), preferably for use in optical communication, quantum cryptography and/or quantum computing, the device comprising a pump device (1) for generating a pump beam (11), a non-linear entanglement element (4) and has a wavelength selection device (5), and the non-linear entanglement element (4) is arranged after the pump device (1) for generating entangled photons (12) by pumping the non-linear entanglement element (4) with the pump beam ( 11), and the wavelength selection device (5) is arranged after the non-linear entanglement element (4) for dividing the entangled photons based on their wavelength into several outputs of the wavelength selection device (5), and the pump device (1) is a photon source (2) and a filter device (3), characterized in that the photon source (2) has one or more optically active elements (21) and / or a superluminescent diode (SLED) for generating a photon beam (10) by amplified spontaneous emission, and that Filter device (3) has one or more filters for filtering the photon beam (10) to generate the pump beam (11). Device according to Claim 14 , characterized in that to suppress and/or prevent the laser process, one or more optical elements with low reflection and/or one or more optical elements with high transmission and/or one or more optical elements for scattering, preferably Rayleigh scattering, and/ or one or more optical isolators are arranged in the photon source (2), preferably arranged in the beam path of the photon beam (10).

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