Method for quantum key generation by multiple recipients

Abstract

A method for quantum key generation using entangled photon pairs between at least four receivers (4) is proposed, comprising the following steps: i) Generation of entangled photon pairs; ii) splitting the signal photons and the idler photons into quantum channels based on their wavelength and transmitting the signal photons and the idler photons via a splitter (6) and / or switch (7); iii) detection of the signal photons and the idler photons at the respective receivers (4); iv) Quantum key generation between the receivers (4). It is essential that for the quantum key generation between all receivers (4) several time periods are formed, with steps i) to iii) being carried out in each time period, and that in each time period before and / or during step ii) only between two or more connections V jan adjustment of the entanglement property is carried out, which can be adjusted independently of each other, and that the time periods differ in such a way that at least one connection V j through another connection V j is exchanged in order to carry out a quantum key generation between all receivers (4) over the several time periods.

Description

The invention relates to a method for quantum key generation between at least four receivers according to the features of the preamble of claim 1 and to a system for quantum key generation between at least four receivers according to the features of the preamble of claim 13.Networks for quantum key generation with interdigitated photon pairs are known. In these networks, a plurality of receivers are connected to one another, for example, via a source. In such a network, the number of physical connections, i.e. the quantum channels between the receivers, increases only over the relation i(i-1) / 2, where i is the number of receivers. In contrast, in direct connection networks between all receivers, a plurality of additional quantum channels are necessary.In networks for quantum key generation having a plurality of receivers which are connected to one another via a source, a plurality of photon pairs which are interlaced in an interlace property are generated in the source and are assigned to the individual receivers, for example, in accordance with the wavelength. Quantum keys can be generated between all receivers based on the interdigitated photon pairs.For quantum key generation, the connection between the two receivers of the interleaved photon pairs must be matched with respect to the selected interleaving property. This means that both receivers agree on a common frame of reference of the interlace property. This entanglement property can represent, for example, the polarization, the time and / or the mode of the photons, wherein in the case of the polarization the matching of the connection takes place, for example, in a fiber via a polarization control.Such a matching is always carried out between two receivers in known systems. In known systems with several receivers, all receivers are balanced with one reference system. The problem here is that the simultaneous matching between a plurality of receivers interferes with one another and this is only possible by means of repeated matching steps between all receivers in order to approach one another in steps, since the plurality of receivers partially use the same fiber. In known networks, this interference is accepted, resulting in a lower quality of connection between all receivers, greatly reducing the generation rate of quantum key generation. Furthermore, such a simultaneous matching between a plurality of receivers is very time-consuming and very resource-intensive.It is an object of the present invention to provide an improved, more efficient, faster and more robust method for quantum key generation between at least four receivers and a corresponding device.According to the invention, the object is achieved by a method for quantum key generation between at least four receivers according to the features of claim 1.According to the invention, a method for quantum key generation with interleaved photon pairs between at least four receivers is proposed, wherein in each case two receivers of an interleaved photon pair form a connection V j for quantum key generation, having the following steps: i) generation of interleaved photon pairs in a source, wherein each photon pair has a signal photon and an idle photon which are interleaved with one another in an interleaved property; ii) splitting the signal photons and the idle photons on the basis of their wavelength onto quantum channels of the plurality of receivers and transmitting the signal photons and the idle photons via quantum channels forming connections V j from the source to the receivers; iii) Detection of the signal photons and the idle photons at the respective receivers; iv) Quantum key generation between the receivers of the interleaved photon pairs.It is essential here that a plurality of time periods are formed for quantum key generation between all receivers, steps i) to iii) being carried out in each time period, and that in each time period, before and / or during step ii), only between two or more connections V j a matching of the entanglement property is carried out, which can be matched independently of one another in order to enable quantum key generation in these two or more connections V j and that the time periods differ in such a way that in each case at least one connection V j is replaced by another connection V j in which quantum key generation was not yet possible in order to carry out quantum key generation between all receivers by the plurality of time periods, and in that the transmission in step ii) takes place via a splitter and / or switch in the quantum channel.Furthermore, the object is achieved according to the invention by a system for quantum key generation with interdigitated photon pairs between at least four receivers according to the features of claim 13.According to the invention, a system for quantum key generation with interleaved photon pairs between at least four receivers is proposed, wherein the system has a source, a frequency multiplexer, a plurality of quantum channels and the plurality of receivers, wherein the plurality of receivers are connected to the source via a respective quantum channel, wherein the source is designed to generate interleaved photon pairs with a respective signal photon and an idle photon, which are interleaved with one another in an interleaved property, wherein the quantum channels of two receivers of an interleaved photon pair respectively form a connection V j for quantum key generation, wherein the frequency multiplexer is arranged in or after the source, which is designed to divide the signal photons and idle photons by means of their wavelength into the quantum channels of the plurality of receivers, each receiver having a detection module which has a measurement module and at least one detector which are designed to detect the entanglement property of the photons for quantum key generation, the system having matching devices which are arranged in the receivers or in the quantum channels to the receivers and are designed to perform a matching of the entanglement property of the entangled photon pairs with respect to two receivers.It is essential here that the system additionally has a control device and the control device is connected to each matching device, and that the control device is designed to control the matching devices in a plurality of time periods for quantum key generation between all receivers, preferably for carrying out the method for quantum key generation according to steps i) to iv), wherein the control device is designed to control only the matching devices between two or more connections V j in each time period, which matching devices can be matched independently of one another in order to enable quantum key generation in these two or more connections V j wherein the control device is designed to control the device, in each time period, the control of the matching device of at least one connection V j in each case is replaced by the control of the matching device of another connection V j in which quantum key generation has not yet been possible in order to carry out quantum key generation between all receivers by means of the plurality of time periods, and in that two or more receivers are connected to the source via a splitter and / or a switch via a common quantum channel.An advantage of the method and the system according to the invention is that a supply of quantum keys is generated between all receivers by the rotation over time of the calibration and thus for quantum key generation in the time periods. After passing through the plurality of time periods, all receivers are served with interleaved photon pairs, wherein, according to the invention, each connection has been matched at least once between each receiver for quantum key generation in at least one time period.In the method and system of the invention, quantum keys are generated at all receivers by the passing of the connections V j so that after the plurality of time periods each receiver has generated a quantum key with each other receiver.It is advantageous in this case that by the matching of the interlocking properties in each case only between independent connections in the periods of time, the method and the system are optimized in such a way that, by the temporal classification of the matching according to the invention, a better generation rate for the quantum key generation between all receivers is obtained. The better generation rate is obtained because the method and the system according to the invention allow the connections V j to be matched more precisely and quickly. This is because, according to the invention, a plurality of connections V j are simultaneously balanced, but only mutually independent connections V are simultaneously balanced, as a result of which the balancing does not interfere with one another.It is also advantageous that the quantum key generation according to the invention can be carried out more quickly and therefore more precise and quick environmental effects such as temperature fluctuations or vibrations can be compensated for, since the balances do not interfere with one another. Due to the lack of mutual interference of the matching of the plurality of connections V j no iterative matching steps between a plurality of connections V j are necessary.In addition, it is advantageous that the system according to the invention can be made available cost-effectively, since fewer matching devices are necessary, since only one matching device is required for each connection V j.A further advantage of the method and network according to the invention is the direct connection of the source to each receiver in each case by a quantum channel. As a result, the number of physical connections, i.e. of the quantum channels, increases only via the relation i(i-1) / 2.The method and system for quantum key generation comprise at least four receivers, preferably i receivers E p with the number i equal to or greater than a natural number equal to 4 and with the numbering p equal to a natural number.Two receivers E p of an interleaved photon pair form a compound V j with the numbering j equal to a natural number. Overall, connections V j are possible between all receivers s, r connections V j are matched in each time interval t k with the number r equal to a natural number greater than 2 and less than s.The method and system for quantum key generation use multiple time periods t k, preferably q time periods t k with the number q equal to or greater than a natural number and with the numbering k equal to a natural number. This means that within the plurality of, preferably the q, time periods t k quantum key generation is carried out between all receivers. Here, the execution of quantum key generation with the q time periods t k can also be referred to as a complete rotation.The method and the system according to the invention result in an improved temporal efficiency factor for generating quantum keys with the temporal efficiency factor in this case describes the increase in the generation rate to a method and a system in which a quantum key is generated only between two receivers at a time. Comparison with a method and system in which all connections are simultaneously aligned differs greatly by the respective quality of the alignment between all connections.It is essential that for quantum key generation in a specific time period t k only the connections V j are used in which the matching has taken place.At least four receivers, preferably between i receivers E p with i equal to or greater than a natural number 4 and with p equal to a natural number, is understood here to mean that the quantum key generation is carried out between four receivers, or five receivers, or six receivers, or seven receivers or multiple receivers.Quantum key generation between all receivers is understood to mean that each of these two or more receivers, which are connected to the source via a splitter and / or a switch via a common quantum channel, can generate quantum keys with all other receivers, but not with the one or more receivers, which likewise receive photons via the splitter and / or switch. It is essential here that these two or more receivers, which are connected to the source via a splitter and / or a switch via a common quantum channel, cannot generate a quantum key among one another.Advantageously, this results in a simpler and more cost-effective network, since only a single quantum channel is necessary for connecting these two or more receivers to the source. A splitter can be designed, for example, as a beam splitter, which randomly splits the photons to one of its output channels. A switch can be designed, for example, as a movable mirror or plug-in connection, as a result of which the photons are directed to one of the output channels depending on the position of the mirror or the plug-in connection. The splitters and / or switches may constitute an access node (or service node), or a relay node (relay nodes) or a user node (user node). Such an embodiment enables a more cost-effective connection of a plurality of receivers to one another. For example, multiple user nodes and their associated access nodes may form a QKD access network (QAN) suitable for covering rooms of buildings. And multiple relay nodes may form a QKD backbone network (QBN) to connect multiple QANs for wide area coverage.Quantum key generation between all of the at least four receivers is to be understood in particular to mean that, for example, in the case of four receivers having the first receiver E 1 and the second receiver E 2 behind a switch and the third receiver E 3 and the fourth receiver E 4 behind a switch, a quantum key is in each case between the first receiver E 1 and the third receiver E 3, and the first receiver E 1 and the fourth receiver E 4, and the second receiver E 2 and the third receiver E 3, and the second receiver E w and the fourth receiver E 4 are generated.Furthermore, quantum key generation between all of the at least four receivers is to be understood in particular as meaning that a quantum key is generated between these at least four receivers, as described above. Further receivers in the system may be connected to the source which do not generate a quantum key in the periods at the time of quantum key generation between the four receivers, but which are also a participating receiver in a quantum key generation carried out thereafter.The generation of a plurality of interleaved photon pairs in the source and in step i) is to be understood to mean that a plurality of interleaved photon pairs can be generated simultaneously and / or successively in the source. Simultaneously, this means that a plurality of interleaved photon pairs are generated at the same or approximately the same time, wherein the wavelengths of these interleaved photon pairs differ from one another. In this case, sequential means that a plurality of interleaved photon pairs can be generated successively in time, wherein these photon pairs can have the same wavelength or different wavelengths. The interlaced photon pairs with the same wavelength generated successively in time increase the length of the quantum key between two specific receivers. Interdigitated photon pairs with different wavelengths allow quantum key generation between multiple different receivers of multiple links V j. This applies in the same way to steps ii), iii) and iv), wherein in step ii) simultaneously and / or successively a plurality of signal photons and Idler photons from different interleaved photon pairs are split between the quantum channels and transmitted therein, and in step iii) simultaneously at a plurality of receivers or successively at one or more receivers the photons are detected and in step iv) simultaneously and / or successively a plurality of quantum keys are generated between a plurality of receivers.A method for quantum key generation with interdigitated photon pairs is understood to mean that steps i), ii) and iii) are passed through one after the other for each interdigitated photon pair, but steps i), ii) and iii) can also be passed through simultaneously for a plurality of photon pairs having different wavelengths.Matching the entanglement property means that the reference system of the entanglement property for measuring a photon pair in the detection module in the detection in step iii) is matched to each other at the two corresponding receivers. For example, in the case of photon pairs which are interlaced in polarization, the polarization in the respective detection modules is coordinated with one another with a transmission via the corresponding connection V j as reference system, wherein any polarization rotation, for example by the transmission of the photons in fibers or arrangement of the elements of the system, can be compensated for by so-called polarization controllers. For this purpose, for example, in the case of a first receiver, a laser beam having a defined polarization is transmitted in a base, for example horizontally polarized, to a second receiver, and the polarization of the laser beam is measured in this base in the case of the second receiver. The quantum channel in the first base can be matched, for example, by minimizing the laser beam at the second receiver during a measurement in the vertical polarization. This minimization is carried out in a further step for a second base which is orthogonal to the first base, for example for the + / - 45° horizontally polarized laser beam. When the photon pairs are interlaced in time, phase matching is performed in the respective interferometers of the receivers. It is furthermore essential that in the method and the system according to the invention, in each individual time period t k only connections V j are balanced for which an independent balancing is possible, i.e. which do not interfere with or influence one another. This allows the matching to be made much more precise and faster, resulting in a higher generation rate of the quantum key. Only between two or more connections V j means that at least two connections V j and at most all further possible connections V j are balanced in a time period which can be balanced independently of one another.Matching the link V j independently of each other in a time period t k means that the matching of the reference system of the receivers and the links V j does not interfere or influence each other in this time period t k. This can substantially improve the quality of the transmission and detection of the photons, which leads to a higher generation rate of the quantum key. For example, in the case of four receivers, the connection V 1 between the first receiver E 1 and the second receiver E 2 can be matched independently of the connection V 2 between the third receiver E 3 and the fourth receiver E 4. Further by way of example, in the case of four receivers, the connection V 1 between the first receiver E 1 and the second receiver E 2 can be matched independently of the connection V 2 between the first receiver E 1 and the third receiver E 3 if the matching of the connection V 1 takes place at the second receiver E 2 and the matching of the connection V 2 takes place at the third receiver E 3, wherein, on the other hand, matching the connection V 1 at the second receiver E 2 and matching the connection V 2 at the first receiver E 1 would interfere with the matching of the connection V 1 or would not be possible due to a splitter or switch.At least one link V j is to be replaced with another link V j+x, with x as an integer, that only one link V j of the preceding time period t k is replaced and replaced with one link V j+x in which quantum key generation has not yet been possible, or that two links V j, V j+1 of the preceding time period t k are replaced and replaced with two links V j+x1, V j+x2 in which quantum key generation has not yet been possible, and so on for three, four and more links, or all connections of the preceding time period t k are exchanged and replaced by the corresponding number of connections in which quantum key generation was not yet possible.A compound V j, in which quantum key generation was not yet possible, means that for this compound V j steps i) to iii) have not yet been passed through, while this compound V j was independently balanced before and / or during step ii). This means that, within the meaning of the method and system mentioned here, quantum key generation between two receivers is only referred to as possible if the corresponding connection V j has been and / or is equalized before and / or during the transmission of the photons in step ii). If a calibration does not take place, photons can be measured, but no common key can be generated by the different reference systems of the receivers.In order to carry out quantum key generation between all receivers by the plurality of time periods t k means that steps i), ii), iii) and iv) have been passed through for all possible connections between all receivers after the plurality of time periods t k and that a matching has taken place for all connections V j before and / or during step ii) in at least one time period t k in this case.It can be provided that the plurality of time periods are repeated a plurality of times, preferably are repeated a plurality of times in succession, preferably a second time, or a third time, or a fourth time or more. This means that one complete rotation is repeated one after the other. As a result, quantum keys can be generated between all receivers over a longer period of time.It can be provided that the time periods t k are carried out sequentially for quantum key generation. This means that for quantum key generation, the time periods t k are formed directly in succession. In this context, directly following one another means that no other connections are used therebetween. Directly following one another furthermore means that no connections V j are operated between the time periods t k in a time window, for example in order to carry out maintenance work. This advantageously results in simple generation of the quantum keys between all receivers.It can be provided that the time periods t k are not carried out sequentially for quantum key generation. This means that for quantum key generation, the time periods t k are not formed directly in succession. Thus, between two time periods t k other connections can be served. Other connections can be understood to mean one or more connections V j from one of the plurality of time periods t k or a plurality of connections which cannot be matched independently of one another. A non-sequential execution advantageously results in that specific connections V j can be operated multiple times, for example if there is an increased need for quantum keys between two specific receivers. In the case of connections V j which can furthermore also be independently balanced, the higher quality and generation rate furthermore advantageously results. Thus, in a non-sequential execution after one of the plurality of time periods t k one of the time periods t k may be repeated or a new time period may be inserted in which connections V j are served which may be independently aligned. If necessary, connections between two time periods can also be operated which cannot be adjusted independently of one another, wherein an increased adjustment requirement or a poorer generation rate results in these connections.It can be provided that in step i) the interdigitated photon pairs are generated by a non-linear process, preferably by parametric fluorescence (down-conversion), or spontaneous parametric fluorescence (spontaneous parametric down-conversion), or four-wave mixing (four-wave mixing). It can be provided that the source comprises one or more non-linear crystals which are configured to generate entangled photon pairs by a non-linear process, preferably by parametric fluorescence (down conversion), or spontaneous parametric fluorescence (spontaneous parametric down conversion), or four-wave mixing (four-wave mixing). These non-linear processes make it possible to generate entangled photon pairs in different wavelength ranges in a simple manner.It can be provided that the interleaved photon pairs are interleaved in time, and / or polarization, and / or in the path angular momentum, and / or in the spin angular momentum. The advantage of using time-interleaved photon pairs is robust interleaving. The advantage of using polarization-entangled photon pairs is simple generation and simple matching, as well as possible automation of the matching. The advantage of using photon pairs interlaced in the web angular momentum and / or in the spin angular momentum is the possible high dimensions of the photon pairs.It can be provided that for the adjustment of photon pairs interlaced in polarization, a polarization rotation in the connection V j is compensated. It can be provided that the polarization-entangled photon pair matching device has one or more wavelength plates, and / or fiber squeezers (fiber squeezers), and / or polarization controllers, and / or liquid crystals. The plurality of components can also be combined with one another, whereby an even more precise adjustment is possible. The advantage of such a design lies in the easily controllable adjustment, which can also be automated, and the cost-effective components.It can be provided that a time interval in the connection V j is compensated for the adjustment of photon pairs interlaced in time. It can be provided that the adjusting device for photon pairs interlaced in time has one or more optical delay means. The advantage of such a design lies in the very precise and simple checking of the alignment.It can be provided that for the adjustment of photon pairs interlaced in the path angular momentum and / or in the spin angular momentum, an angular momentum change in the connection V j is compensated. It can be provided that the matching device for photon pairs interlaced in the path angular pulse and / or in the spin angular pulse has one or more wavelength plates, and / or spatial light modulator (SLM). The advantage of such a design lies in the easily controllable adjustment, which can also be automated.It can be provided that each receiver or each quantum channel of a receiver has a matching device. Advantageously, this results from the fact that not all matching devices are required for matching all possible connections V j for the method and the system according to the invention, and a fail-safe system is thus provided in which the matching in a failed matching device can be replaced by a matching device that has not yet been used. It is important that for the method according to the invention and the system according to the invention for the balancing of all connections V j only i-1 balancing devices are necessary, in a method and a system with i receivers. It can be provided that the system has only i-1 matching devices. A cost-effective system can thus be provided.It can be provided that the matching per connection V j before and / or during step ii) takes place only by a matching device, arranged at one of the two receivers or in one of the two quantum channels. Advantageously, the arrangement of the source, the receivers and the quantum channels results in the fact that, in such an embodiment, the balancing of the entire connection V j can be carried out by a single balancing device which is arranged somewhere between those in receivers. Thus, the matching process is simplified. A matching device which is arranged directly at the respective receiver is protected in particular from influencing from the outside, i.e. attempted manipulation and interference, since no additional communication between the receiver and the matching device via public channels is necessary for the adjustment.It can be provided that the adjustment is carried out, monitored and / or regulated before and / or in step ii) by a control device which is connected to all adjustment devices. It can be provided that the control device is arranged at one of the receivers. It can be provided that the control device is designed as a computer or integrated circuit (IC), preferably as an FPGA element (field programmable gate array). It can be provided that the computer or integrated circuit (IC), preferably as an FPGA element (field programmable gate array), comprises a storage medium which comprises instructions which, when executed by the computer or integrated circuit (IC), preferably as an FPGA element (field programmable gate array), cause the latter to carry out the alignment before and / or during step ii). Advantageously, such a configuration results in a possible automation of the method.It can be provided that in step i) interlaced photon pairs are generated with wavelengths which are randomly distributed over a broad spectrum or are generated in a targeted manner interlaced photon pairs with specific wavelengths. It can be provided that in step i) interlaced photon pairs are generated in each time period t k for all possible connections V j or that in step i) interlaced photon pairs are generated in each time period t k only for the connections V j also matched therein. The advantage of generating photons in a broad spectrum is the cost effective provision of the interdigitated photon pairs to a plurality of receivers. The advantage of generating photons with specific wavelengths is that for each compound V j in the corresponding time period t k photons can be generated specifically for these compounds V j whereby the generation rate for the quantum key generation can be increased.It can be provided that the photons generated in step i) are generated in a signal wavelength range and an idle wavelength range that are spectrally separated from one another. Here, spectrally different from each other is to be understood as meaning that the wavelengths of the signal photon and of the idle photon of the pairs differ from each other, and that the wavelengths of the pairs differ from each other. This results in the advantage of a simpler and less loss-free division of the photons in step ii).It can be provided that the photon pairs generated in step i) are formed for each connection V in a j spectrally separated manner from one another. Spectrally separated interleaved photon pairs is understood here to mean that, on the one hand, the signal and idle photons of a photon pair have different wavelengths, i.e. λ sx ≠λ ix. applies. This is also referred to as a nondegenerate (nondegenerate) photon pair. In addition, for the plurality of spectrally separated interleaved photon pairs, the wavelengths of the signal photons of the photon pairs are spectrally different from one another, i.e. λ sx ≠ λ s(x+1). This also applies correspondingly to the idle photons, i.e. in addition the wavelengths of the idle photons differ spectrally from one another, i.e. λ ix ≠λ i(x+1). applies. It is essential here that a plurality of the spectrally separated photon pairs can also be generated successively in time in order to generate a longer quantum key.It can be provided that the frequency multiplexer is designed to perform the splitting of the signal photons and the idle photons in step ii).Preferably, assigning the signal and idle photons by their wavelength to the quantum channels in step ii) and by the frequency multiplexer means that the source generates signal and idle photons with different wavelengths and the photons are transmitted to the frequency multiplexer, preferably in a spatial mode. The frequency multiplexer divides the signal and idle photons according to their wavelength into the different quantum channels.It can be provided that one or more or all quantum channels are designed as glass fibre channels and / or have glass fibre links. Glass fiber paths are understood to mean that not all the transmission takes place through a glass fiber, but that free-beam paths are also possible over subareas. The advantage of such an embodiment lies in the cost-effective and simple structure of the network.It can be provided that the detection in step iii) takes place at each receiver by a detection module. It can be provided that each detection module has one or more detectors and a measurement module. The measuring module and the detectors can be used to determine the entanglement property of the photons for quantum key generation and the time of the detection of the photon.It can be provided that the at least one detector or the plurality of detectors are formed as single photon detectors, preferably as germanium or silicon detectors, or single photon avalanche diodes or indium gallium arsenide detectors, or superconducting nanowire single photon detectors, or silicon avalanche photodiodes.It can be provided that the measurement module has a polarizer, and / or an unsymmetrical interferometer, and / or a spatial light modulator (SLM).It can be provided that the receiver has a plurality of detection modules. It can be provided that the plurality of detection modules of a receiver detect photons in different wavelength ranges. It can be provided that in step iii) one or more receivers simultaneously detects a plurality of signal photons and / or idle photons having different wavelengths. This allows the receiver to simultaneously generate quantum keys with several other receivers, since photons with different wavelengths can be detected simultaneously. It can be provided that frequency filters are arranged in front of the plurality of detection modules in order to enable quantum key generation with a plurality of receivers simultaneously by splitting the photons into the detection modules on the basis of their wavelength. As a result, a respective partner receiver can be assigned for each detection module of a receiver. It can be provided that the frequency filter is designed as a dichroic mirror, or as a grating, or as a filter.It can be provided that in step iv) for quantum key generation from the detected photons in step iii) a raw key is generated at both receivers. Furthermore, it can be provided that a screening (senting) of the raw key is carried out after the generation of the raw key. For visualization, after the measurement of the photons, information is exchanged between the two receivers. This information is, for example, the time stamps of the measured photons. Thereafter, each receiver performs the vision process on its own raw key. It can be provided that further steps, such as a fault determination and / or fault correction and / or a privacy amplification (privacy amplification), are additionally carried out after the inspection. Due to the visualization and the possible further steps, a common key can be generated in both receivers by quantum key generation.It can be provided that a transmission rate of entangled photons between two or more receivers is at least 1 kHz, preferably at least 100 kHz, most preferably at least 10 MHz.It can be provided that the quantum key generation in step iv) for the connections of a time period t k takes place in each case during and / or after the corresponding time period t k. While means that steps i) to iv) are carried out in each time period. After this, means that steps i) to iii) are carried out in each time period, and step iv) takes place after the respective time period. The generation of the quantum key from the raw key can also start during the respective time period and only be concluded in a next time period. It is essential that by detecting the photons in step iii) a raw key for quantum key generation can already be generated, which is used for generating the common key. The execution of step iv) enables complete quantum key generation in the respective time period, wherein a quantum key can already be generated from the already detected photons during the generation of further photons.It can be provided that in each time period t k for at least two compounds V j steps i) to iii) are carried out with the adjustment, preferably steps i) to iv). This is to be understood as meaning that in each time period t k for two compounds V j steps i) to iii), preferably steps i) to iv), are carried out with the calibration, or for three compounds V j steps i) to iii), preferably steps i) to iv), are carried out with the calibration, or for four compounds V j steps i) to iii), preferably steps i) to iv), are carried out with the calibration, and so on. The more links V j are aligned in each time period t k the greater the generation rate of the quantum keys for all receivers.It can be provided that in each time period t k a receiver is contained at most once in the connections V j of the respective time period t k. It can thus be ensured in a simple manner that the matching of the connections V j of this time period t k takes place independently of one another.It can be provided that in each time period t k a receiver is contained in several of the connections V j of the respective time period t k. It is essential here that the balancing of all connections V j of this time interval t k continues to take place independently of one another. However, a receiver which has a high communication requirement can thus be operated a plurality of times at a higher rate of quantum key generation.It can be provided that each time interval t k is at least 1 s, preferably at least 1 min, preferably at least 5 min or more. It can be provided that the length of the time periods t k differs from one another. This advantageously results in the fact that for connections V j which have a higher or lower key requirement, the time periods t k can be adapted to the respective requirement.In the following examples, for ease of understanding, receivers E 1, E 2 etc. are referred to as receivers A, B, etc.As a non-exclusive first example, a method and system for quantum key generation with four receivers (A 1, A 2, B 1, B 2) is given here. In this method and system, all A i receivers can perform quantum dish generation with all B i receivers. However, quantum key generation between the two receivers A 1 and A 2 and between the two receivers B 1 and B 2 is not possible.Due to the four receivers (A 1, A 2, B 1, B 2) and the communication possibility, s=4 connections result from this by the number of receivers A i multiplied by the number of receivers B i with A 1 B 1, A 1 B 2, A2B1and A2B2.In this nonexclusive first example, steps i) to iii), preferably steps i) to iv), of these compounds are divided into q=2 periods, each period t having k r=2 compounds V j with, for example, the following division:Two further classifications are given here by way of example:In all cases, the temporal efficiency factor isAs a non-exclusive second example, a method and system for quantum key generation with five receivers (A 1, A 2, A 3, B 1, B 2) is given here. In this method and system, all A i receivers can perform quantum dish generation with all B i receivers. Quantum key generation between receivers A 1, A 2 and A 3 and between the two receivers B 1 and B 2 is not possible.Due to the five receivers (A 1, A 2, A 3, B 1, B 2) and the communication possibility, s=6 connections result from the number of receivers A i multiplied by the number of receivers B i with A 1 B 1, A 1 B2, A2B1, A2B2, A 3 B 1 and A 3 B 2,In this nonexclusive second example, steps i) to iii), preferably steps i) to iv), of these compounds are divided into q=2 periods, each period t having k r=3 compounds V j with, for example, the following division:The temporal efficiency factor isIt should be noted here that in this case the matching of the entanglement property can be performed solely by the receivers with the larger number, i.e. here by the A i receivers. This means that in the case of the B i receivers, a device for adjusting the interlace property does not necessarily have to be formed.Further embodiments of the invention are illustrated in the figures and described below. The figures show, by way of example, a possible configuration of the invention. This embodiment serves to explain a possible implementation of the invention and should not be understood as limiting. The following are shown: FIG. 1 : shows a schematic illustration of a system according to the invention with four receivers and two splitters in the quantum channels; FIGS. 2 to 4 show a schematic illustration of the system from FIG. 1 with the possible connections V j; FIG. 5 shows a schematic illustration of a system according to the invention having six receivers, two splitters and two switches in the quantum channels; FIG. 6 shows a schematic illustration of a system according to the invention having six receivers, three splitters and one switch in the quantum channels; FIG. 7 : shows a schematic illustration of the system from FIG. 1 with a control device.FIG. 1 shows a schematic representation of an embodiment of a system 1 according to the invention for quantum key generation with interdigitated photon pairs between four receivers A 1, A 2, B 1 and B 2. The receivers A 1 and A 2( or B 1 and B 2) are each connected via a separate quantum channel 5 to a splitter 6 and via this to the source 2 via a common quantum channel 5. It is essential here that in this exemplary embodiment the two receivers 4A 1 and A 2( or B 1 and B 2), which are connected via a splitter 6 via a common quantum channel 5 to the source 2, cannot generate a quantum key among one another. Quantum key generation between all receivers 4 is understood to mean that each of these two receivers A 1 and A 2( or B 1 and B 2), which are connected via a splitter 6 via a common quantum channel 5 to source 2, can generate quantum keys with all other receivers 4 B 1 and B 2( or A 1 and A 2) but not with one another. In this exemplary embodiment, a frequency multiplexer 3 is arranged in the source 2, which is designed to divide the signal photons and idle photons of the interleaved photon pairs by means of their wavelength into the quantum channels 5 of the plurality of receivers 4.In the exemplary embodiment of FIG. 1, the receivers 4A 1 and A 2 each have a matching device 8. Optionally, only or also the receivers 4B 1 and B 2 have a calibration device 8, as shown in dashed lines. The matching means 8 match the reference systems with respect to the interleaving property of the different receivers 4.FIGS. 2, 3 and 4 show the system 1 according to the invention for quantum key generation from FIG. 1, wherein the matching devices 8 are not shown in FIGS. 2, 3 and 4 for the sake of better clarity. FIGS. 2, 3 and 4 show the possible connections between the receivers 4 for quantum key generation and their division into the plurality of time periods t k.FIG. 2 shows a first possible classification of the connections by quantum key generation between receivers A 1 and B 2 and receivers A 2 and B 2( dashed arrows) in a first time interval t 1 with the connection being matched. In a second time period t 2 quantum key generation takes place between the receivers A 1 and B 1 and the receivers A 2 and B 1( dotted arrows) with matching of the connection.FIG. 3 shows a second possible classification of the connections by quantum key generation between receivers A 2 and B 1 and receivers A 2 and B 2( dashed arrows) in a first time interval t 1 with the connection being matched. In a second time period t 2 quantum key generation takes place between the receivers A 1 and B 1 and the receivers A 1 and B 2( dotted arrows) with matching of the connection. The difference from the connections of FIG. 2 is that for FIG. 2 the matching devices 8 at the receivers A 1 and A 2 are sufficient, and for FIG. 3 the matching devices 8 at the receivers B 1 and B 2 can be arranged.FIG. 4 shows a third possible classification of the connections by quantum key generation between receivers A 1 and B 2 and receivers A 2 and B 1( dashed arrows) in a first time interval t 1 with the connection being matched. In a second time period t 2 quantum key generation takes place between the receivers A 1 and B 1 and the receivers A 2 and B 2( dotted arrows) with matching of the connection.FIGS. 5 and 6 show two further exemplary embodiments of the system 1 according to the invention for quantum key generation having six receivers 4.In these exemplary embodiments, the source 2 is connected to the six receivers 4 via a plurality of quantum channels 5, splitters 6 and switches 7. In this case, FIGS. 5 and 6 differ only in that in FIG. 5 the receivers A 1, A 2, A 3 and A 4 are first connected to the source 2 via a splitter 6 and then a further splitting by two switches 7 takes place and in FIG. 6 the receivers A 1, A 2, A 3 and A 4 are first connected to the source 2 via a switch 7 and then a further splitting by two splitters 6 takes place.The quantum key generation takes place in both exemplary embodiments analogously to the exemplary embodiment of FIGS. 1 to 4.FIG. 7 shows the quantum key generation system 1 from the exemplary embodiment of FIG. 1, wherein the control device 9 is additionally illustrated in FIG. 7. In this exemplary embodiment, the control device 9 (key management system) is connected to the balancing devices 8 via lines and the respective receiver 4.List of reference characters1 System for quantum key generation 2 Source 3 Frequency multiplexer 4 Receiver 5 Quantum channel 6 Splitter 7 Switch 8 Matching device 9 Control device

Claims

Method for quantum key generation with interleaved photon pairs between at least four receivers (4), wherein in each case two receivers (4) of an interleaved photon pair form a connection V j for quantum key generation, having the following steps: i) generation of interleaved photon pairs in a source (2), wherein each photon pair has a signal photon and an idle photon which are interleaved with one another in an interleaved property; ii) splitting the signal photons and the idle photons on the basis of their wavelength onto quantum channels of the plurality of receivers (4) and transmitting the signal photons and the idle photons from the source (2) to the receivers (4) via quantum channels forming connections V j ; iii) Detection of the signal photons and the idle photons at the respective receivers (4); iv) quantum key generation between the receivers (4) of the interleaved photon pairs; characterized in that a plurality of time periods are formed for quantum key generation between all receivers (4), steps i) to iii) being carried out in each time period, and in that in each time period, before and / or during step ii), only between two or more connections V j an adjustment of the interleaving property is carried out, which can be adjusted independently of one another in order to enable quantum key generation in these two or more connections V j and in that the time periods differ in such a way, in each case at least one connection V j is exchanged for another connection V j in which quantum key generation has not yet been possible in order to carry out quantum key generation between all receivers (4) by means of the plurality of periods, and in that the transmission in step ii) takes place via a splitter (6) and / or switch (7) in the quantum channel (5).Method according to Claim 1, characterized in that the matching per connection V j before and / or during step ii) takes place only by a matching device (8), arranged at one of the two receivers (4) or in one of the two quantum channels.Method according to claim 2, characterised in that the adjustment before and / or in step ii) is carried out, monitored and / or regulated by a control device (9) which is connected to all adjustment devices (8).Method according to one of the preceding claims, characterized in that in step iii) one or more receivers (4) simultaneously detect a plurality of signal photons and / or idle photons having different wavelengths.Method according to one of the preceding claims, characterized in that the quantum key generation in step iv) for the connections of a time period t k takes place in each case during and / or after the corresponding time period t k.Method according to one of the preceding claims, characterized in that the plurality of time periods are repeated a plurality of times.Method according to one of the preceding claims, characterized in that in each time period t k a receiver (4) is contained at most once in the connections V j of the respective time period t k or in that in each time period t k a receiver (4) is contained in a plurality of the connections V j of the respective time period t k.Method according to one of the preceding claims, characterized in that in step i) interlaced photon pairs are generated in each time period t k for all possible connections V j or in that in step i) interlaced photon pairs are generated in each time period t k only for the connections V j also matched therein.Method according to one of the preceding claims, characterized in that in step i) interlaced photon pairs with wavelengths are generated which are randomly distributed over a broad spectrum, or selectively interlaced photon pairs with specific wavelengths are generated.Method according to one of the preceding claims, characterized in that the interleaved photon pairs are interleaved in time, and / or polarization, and / or in the web angular momentum, and / or in the spin angular momentum.Method according to Claim 10, characterized in that a polarization rotation in the connection V j is compensated for in order to balance photon pairs which are interlaced in the polarization, and / or in that a time period in the connection V j is compensated for in order to balance photon pairs which are interlaced in the time, and / or in that a rotation pulse change in the connection V j is compensated for in order to balance photon pairs which are interlaced in the path rotation pulse and / or in the spin rotation pulse.Method according to one of the preceding claims, characterized in that in step i) the interdigitated photon pairs are generated by a non-linear process.A system (1) for quantum key generation with interleaved photon pairs between at least four receivers (4), wherein the system (1) has a source (2), a frequency multiplexer (3), a plurality of quantum channels and the plurality of receivers (4), wherein the plurality of receivers (4) are connected to the source (2) via a respective quantum channel (5), wherein the source (2) is configured to generate interleaved photon pairs each having a signal photon and an idle photon which are interleaved with one another in an interlace property, wherein the quantum channels of two receivers (4) of an interleaved photon pair each form a connection V j for quantum key generation, wherein the frequency multiplexer (3) is arranged in or after the source (2), which is configured to generate a frequency multiplexer (3), the signal photons and idle photons are divided by their wavelength into the quantum channels of the plurality of receivers (4), each receiver (4) having a detection module which has a measurement module and at least one detector which are designed to detect the entanglement property of the photons for quantum key generation, the system (1) having matching devices (8) which are arranged in the receivers (4) or in the quantum channels to the receivers (4) and are designed to perform a matching of the entanglement property of the entangled photon pairs with respect to two receivers (4), characterized in that the system (1) additionally has a control device (9) and the control device (9) is connected to each matching device (8), and in that the control device (9) is designed to control the matching devices (8) in a plurality of time periods for quantum key generation between all receivers (4), preferably to carry out the method for quantum key generation according to steps i) to iv), wherein the control device (9) is designed to control in each time period only the matching devices (8) between two or more connections V j which can be matched independently of one another in order to enable quantum key generation in these two or more connections V j wherein the control device (9) is designed to replace the control of the matching device (8) of in each case at least one connection V j in each time period by the control of the matching device (8) of another connection V j, in which quantum key generation has not yet been possible to perform quantum key generation between all receivers (4) by the plurality of periods, and two or more receivers are connected to the source via a splitter and / or a switch via a common quantum channel.The system (1) according to claim 13, characterized in that each receiver or quantum channel (5) of a receiver (4) comprises a matching means (8), or that the system (1) comprises only i - 1 matching means (8).

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