DE102020207644A1 - Quantum-assisted communication network and method for operating a quantum-assisted communication network - Google Patents

Abstract

A quantum assisted communication network (100; 200) is provided, comprising:
a plurality of network nodes (10-1, 10-2);
wherein at least two, preferably more than two or all, network nodes (10-1, 10-2) are connected by means of classic network connections (20-12) and are connected by means of quantum network connections (30-12) by means of which quantum states can be transmitted;
each two network nodes (10-1, 10-2) connected via a quantum network connection (30-12) being connected to a quantum source (40-12) of the communication network (100; 200) assigned to the node, which is designed for this purpose is to provide the associated network nodes (10-1, 10-2) interleaved qubits;
wherein control devices (12-1, 12-2) are also designed to recognize phases of low network load of the classic network connection (20-12) between network nodes (10-1, 10-2) and to identify them in a phase of low network load To control quantum sources (40-12) in order to use the phase of low network load to provide the network nodes (10-1, 10-2) with entangled qubits.

Description

TECHNICAL AREA

The invention relates to a quantum-supported communication network and a method for operating such a network.

TECHNICAL BACKGROUND

The use of entangled quantum bits (so-called qubits) to transmit or convey information is known per se and is the subject of studies on the development of quantum-based communication structures. Fundamental is the knowledge that entangled particles (so-called Einstein-Podolsky-Rosen pairs or EPR pairs) can be generated which - regardless of their spatial distance - assume the same state when one of the two particles is measured.

A possible transmission of information at faster than light speed, since the measurement is simultaneous due to the entanglement of the entangled particles, is practically prevented by the fact that the entangled particles must already be present as entangled qubits at the transmitter and receiver at the time of the information transmission, and the measurement results are complete are random. Such entangled qubits are used up when a signal is transmitted with them.

In one possible implementation, a quantum source (or: qubit source) is arranged between every two network nodes of a quantum network and assigned to this network node. This quantum source generates entangled qubits and makes them available to the respective assigned network nodes.

Such a quantum network is, for example, in the scientific publication of D. Siddharta et al., "Robust quantum network architectures and topologies for entanglement distribution", Physical Review A 97, No. 1 (January 29, 2018) described. Methods for generating entangled qubits over long distances have been described, for example, in Hofmann, et al., "Heralded entanglement between widely separated atoms.", Science 337.6090 (2012): 72-75 and described there as “heralded entanglement”, in German for example: “announced entanglement”.

However, such quantum networks always have the disadvantage that they are heavily dependent on the availability of entangled qubits and thus on their generation and provision.

The creation of new connections in such a system by means of “entanglement swapping” is described, for example, in the scientific publication by Schoute et al., “Shortcuts to quantum network routing”, arXiv: 1610.05238. However, since more qubits are consumed by such entanglement swapping than when using a direct connection, such a method in principle increases the existing disadvantages of the quantum-supported communication network as a whole.

SUMMARY OF THE INVENTION

On the basis of this known prior art, one of the objects of the present invention is to provide a quantum-assisted communication network and an associated operating method which improve classical networks with quantum technology.

One of the special advantages of this approach is that it can already be implemented with existing technology, and existing classic networks (i.e. networks that exchange normal signals that are not based on entangled qubits) can be expanded in their capacity and / or made more secure or robust be able.

Accordingly, according to a first aspect of the present invention, a quantum-assisted communication network having the features of claim 1 is provided.

• eine Vielzahl von Netzwerkknoten;
• wobei mindestens zwei, bevorzugt mehr als zwei oder alle, Netzwerkknoten mittels Klassische-Netzwerk-Verbindungen verbunden sind und mittels Quanten-Netzwerk-Verbindungen verbunden sind, mittels welchen Quantenzustände übertragen werden können;
• wobei je zwei über eine Quanten-Netzwerk-Verbindung verbundene Netzwerkknoten mit einer den Knoten zugeordneten Quantenquelle des quantenunterstützten Kommunikationsnetzwerks verbunden sind, welche dazu ausgebildet ist, den zugeordneten Netzwerkknoten verschränkte Qubits bereitzustellen;
• wobei die Netzwerkknoten Quanten-Speichereinrichtungen zum Speichern von den zugeordneten Quantenquellen bereitgestellten verschränkten Qubits zum Verwenden in den Quanten-Netzwerk-Verbindungen aufweisen;
• wobei die Netzwerkknoten jeweils eine Steuereinrichtung aufweisen, welche dazu ausgebildet ist, das Empfangen und Versenden von Daten durch den jeweiligen Netzwerkknoten zu steuern;
• wobei die Steuereinrichtungen außerdem dazu ausgebildet sind, Phasen geringer Netzwerkauslastung der Klassische-Netzwerk-Verbindung zwischen Netzwerkknoten zu erkennen und dazu eingerichtet sind, in einer erkannten Phase geringer Netzwerkauslastung zugeordnete Quantenquellen zu steuern, um die Phase geringer Netzwerkauslastung dazu zu verwenden, den Netzwerkknoten verschränkte Qubits bereitzustellen.

Such a quantum-assisted communication network includes:

• a variety of network nodes;
• wherein at least two, preferably more than two or all, network nodes are connected by means of classic network connections and are connected by means of quantum network connections by means of which quantum states can be transmitted;
• two network nodes connected via a quantum network connection being connected to a quantum source of the quantum-supported communication network assigned to the node, which is designed to provide entangled qubits to the assigned network node;
• wherein the network nodes have quantum storage devices for storing entangled qubits provided by the associated quantum wells for use in the quantum network connections;
• wherein the network nodes each have a control device which is designed to control the receiving and sending of data by the respective network node;
• wherein the control devices are also designed to recognize phases of low network load of the classic network connection between network nodes and are set up to control associated quantum sources in a recognized phase of low network load in order to use the phase of low network load to Qubits entangled in the network nodes provide.

Although a distinction is made here between classical network connections and quantum network connections for reasons of better understanding and a more precise description, it goes without saying that these can also be implemented, for example, in, or by means of, one and the same physical carrier, for example through a physical fiber optic connection. Alternatively, however, the classic network connection and the quantum network connection can also be implemented physically separately. For example, quantum network connections could be implemented using fiber optic connections and the classic network connections using copper lines or the like.

Instead of the use of classical network connections and quantum network connections, when using the same physical carrier (e.g. fiber optics), classical network protocols / quantum network protocols or classical - Talking about network information technology / quantum network information technology or the like. It is then possible to speak of a connection between two (or more than two, or all) network nodes by means of a line which is set up to transmit messages both with classical network protocols and with quantum network protocols.

As many network nodes as possible are preferably connected to one another both via a classic network connection and via a quantum network connection, not every network node having to be connected to every other network node. It goes without saying that in a communication network all network nodes are at least indirectly connected to all other network nodes. Therefore, when a classic network connection between two network nodes or a quantum network connection is explicitly mentioned here, a direct connection should be meant in particular, i.e. implemented, for example, by a fiber optic line between the two network nodes and without additional network nodes lying on the way.

The transfer of quantum states means that a dedicated measurement (i.e. influencing) of a part of an entangled qubit at one network node results in a corresponding, absolutely similar influence on the other part of the same entangled qubit at another network node. If, for example, two photons are entangled with each other at a transmitter (network node) or are already generated as an entangled pair, one photon can be sent from this pair to a receiver (network node), e.g. via fiber optic cables with or without a repeater, and the second photon can remain with the sender. If the transmission mechanism is ideal, the sender and receiver will share an entangled pair of photons. The setting of a specific quantum number (e.g. polarization direction) on one of the photons then causes the same quantum number to be set on the other of the photons.

In the case of the quantum wells and the quantum storage devices, any techniques known in the prior art can be used, for example those described in Siddharta et al. or the techniques described therein.

The respective quantum source can be arranged, for example, between the network nodes to which it is assigned and for which it generates the entangled qubits. The quantum source can, however, also be arranged at a network node, generate entangled pairs there, and from there transmit half of the entangled pairs generated to potential recipients of messages from this network node. A separate quantum source can be arranged at the sending network node for each potential recipient network node, or a quantum source can be designed to generate entangled qubits for all recipient network nodes. In particular, announced entanglement (“heralded entanglement”) can be used to generate entangled qubits over long distances. In other words, with a quantum source arranged on or in a network card (as a transmitting network node), entangled particles or entangled qubits can be generated directly on the network card and would then only be for the other end of a line, i.e. exactly one receiver. Network card (receiver network node) determined.

• Erstens sollte das Speichern von verschränkten Qubits über einen Zeitraum hinweg möglich sein, der groß ist im Vergleich zu typischen Verarbeitungszeiten im jeweiligen Anwendungsfall. Für den Austausch von Quantenzuständen mittels Photonen wurden Techniken beispielsweise in Körber et al., „Decoherence-protected memory for a single-photon qubit.“, Nature Photonics 12.1 (2018): 18 , beschrieben. Um dem Verlust von gespeicherten verschränkten Qubits entgegenzuwirken, sollten außerdem die Relaxationszeiten und Kohärenzzeiten der gespeicherten verschränkten Qubits im Vergleich zu den typischen Verarbeitungszeiten lang sein.

The quantum storage devices can be implemented using a variety of techniques, with only a few basic requirements:

• First, it should be possible to store entangled qubits over a period of time that is long compared to typical processing times in the respective application. For the exchange of quantum states by means of photons, techniques were for example in Körber et al., "Decoherence-protected memory for a single-photon qubit.", Nature Photonics 12.1 (2018): 18 described. In order to counteract the loss of stored entangled qubits, the relaxation times and coherence times of the stored entangled qubits should also be long compared to the typical processing times.

Second, the quantum storage devices should be able to store as many entangled qubits as possible in comparison to how many entangled qubits (or entangled pairs) are used to execute a communication protocol.

Third, the quantum storage devices should not require physical proximity to one another. In quantum-assisted communication networks, which establish the quantum network connections using optical fibers, the rate of photon loss scales exponentially with the length of the fibers, so that quantum repeaters are usually used to transmit quantum information over long distances (i.e. to exchange quantum states over long distances). One possibility is to generate a qubit in the form of an entangled pair (e.g. of photons) locally (i.e. at close range) and then to increase the distance between the particles of the pair, for example by means of entanglement swapping through quantum repeaters, as shown for example in Munro et al., "Inside quantum repeaters." IEEE Journal of Selected Topics in Quantum Electronics 21.3 (2015): 78-90 is described. Alternatively, entangled qubits can also be distributed using "fiying qubits", for example via satellite, such as in Yin et al., "Satellite-based entanglement distribution over 1200 kilometers." Science 356.6343 (2017): 1140-1144 has been described.

The control devices can comprise conventional computer elements, for example one or more central processors (CPUs), one or more graphics processors (GPUs), one or more application-specific integrated circuits ("application-specific integrated circuit", ASIC), one or more field-programmable logic gates ("field -programmable gate array ", FPGA), input and output interfaces, a working memory, a non-volatile computer-readable data memory (eg a solid-state memory," solid state drive ", SSD) and / or the like. The control devices can be arranged or integrated in or on the respective network nodes, but they can also be implemented entirely or partially by means of cloud computing.

The phases of low network load can be defined, for example, when the current network load falls below a specified (or dynamically changeable or specifiable) threshold value. The principle of using the existing transmission capacities of the quantum network connection (or a fiber optic cable that realizes both the classic and the quantum network connection) in phases of low network load in order to generate interlaced qubits "in reserve", as it were significant importance, because in this way the existing network infrastructure is optimally used at all times: to transmit messages (high utilization) and / or to generate entangled qubits (with comparatively low utilization). This principle is also referred to as “generate entanglement when idle” (GEWI), for example: “generate entanglement when idle”.

A phase of low network load can be defined, for example, by the fact that no classic messages to be transmitted are waiting in a buffer for transmission. In other words: the system can be set up to always generate or send as many qubits as it can, unless the quantum storage device for entangled particles is full. The qubits sent are then used either to transmit messages (if there are currently messages in the buffer) or, otherwise, to generate entanglement.

If the entanglement memory is full, the lifetime of the entangled pairs can be used to read when they must be deleted (this value is determined, for example, by the coding) and the memory can then be started again in advance.

Interleaved qubits are preferably generated in blocks, since it would normally be less efficient to change the coding method within a (data) frame, because frames only occur in certain standardized lengths and because each system usually only supports a finite number of coding rates. The system then needs a time X (Y) to generate a block of Y interlaced qubits.

The system can therefore advantageously be set up with the following rule: If a block of size Y has to be deleted in X (Y) time units (e.g. due to expiry of the lifetime), and if there are no messages in the buffer waiting for transmission, then create a block with a larger block Y-size qubits.

The time can be divided into individual time units, an entangled qubit being generated whenever there is no message to be sent at a network node within such a time unit.

Further advantages emerge from the subclaims and from the description with reference to the figures.

According to some preferred embodiments, variants or developments of embodiments, the control devices are designed to exchange information about the network load and / or information about the number of stored interleaved qubits via link state packages (LSP). The exchange comprises sending the information (or the connection status packets) to one another and receiving the information (or the connection status packets) from one another. Each sending of a connection status packet does not necessarily have to go hand in hand with receiving a connection status packet, and in some embodiments this may well be the case. The control devices are advantageously also set up to control the network nodes based on the information received (i.e. based on the connection status packets received).

In particular, according to some preferred embodiments, variants or developments of embodiments, the control devices can be set up to exchange entangled qubits between network nodes based on the information received (or connection status packets) via entanglement swapping, in particular to exchange entangled qubits of network nodes (or network node pairs) ) with currently comparatively low utilization of network connections with currently relatively higher utilization.

It can be seen that the utilization of the existing network infrastructure can be improved even more in this way. For example, if a large amount of data is to be transmitted between network node A and network node B, the entangled qubits between A and B may soon be used up. At the same time, it can be the case that both network node A and network node B in the quantum-supported communication network are connected to a further network node C which currently has no messages to transmit. In other words, in this example, the network load between network node A and network node B is currently high, and the network load between network node A and network node C and the network load between network node B and network node C are low.

While the communication load is on connection A <-> B, interleaved qubits are thus provided by the control devices on connections A <-> C and C <-> B, which each have a low network load. Through entanglement swapping (in German, for example: Entanglement exchange), the entangled qubits of connection A <-> C and connection B <-> C (or, more simply, connection A <-> C <-> B) can now be used to transfer data quantum-based between A and B. transferred to. The example can easily be transferred to other existing network nodes, with the quantum-based transfer from network node A to network node B then also being carried out via entanglement swapping through further indirect connections A <-> X <> ... <-> Y <-> B can. The transfer of qubits required for swapping takes place entirely on connections A <-> X <-> ... <> Y <-> B, but not on route A <-> B.

The resource costs for entanglement swapping can, for example, also be used in a cost function on which the routing in the quantum-supported communication network is based.

According to some preferred embodiments, variants or developments of embodiments, the control devices are designed to control the network nodes to send messages in a high-bandwidth mode, at least also by means of quantum network connections, if there are enough entangled qubits between the network nodes for sending are available for the respective message. The control device can optionally also be set up to send the message in the high bandwidth mode exclusively by means of classic network connections if insufficiently entangled qubits are available for a message. In this way, the available bandwidth is primarily used to transmit the data, be it quantum-based or in a classic way. Messages can thus be transmitted particularly quickly.

A transmission “at least also by means of a quantum network connection” is to be understood as meaning that the transmission takes place either exclusively by means of a quantum network connection or by using both a quantum network connection and a classic network connection . For example, “superdense coding” can be used, whereby two classic bits can be transmitted by transmitting a single qubit. Such “superdense coding” for quantum-supported communication via classic network connections is, for example, in Bennett et al., "Entanglement-assisted classical capacity of noisy quantum channels." Physical Review Letters 83.15 (1999): 3081 described.

In the high bandwidth mode, quantum-supported communication using the quantum network connection is used as long as entangled qubits are available for this purpose, ie as long as the number of qubits remaining in the quantum storage device and entangled between sender and receiver is greater is the number C of the entangled qubits consumed per quantum-assisted (or: entanglement-assisted) transmission. Quantum network connections, provided they are physically separate from the classic network connections, are usually also used for traditional message transmission, for example when there are currently no entangled qubits. In such a case, both the physical carrier (i.e. the line) for the classic network connection and the physical carrier for the quantum network connection can thus be used consistently in the high bandwidth mode.

According to some preferred embodiments, variants or developments of embodiments, the control devices are designed to control the network nodes, to send messages in a high security mode exclusively at least using quantum network connections if there are enough entangled qubits for between the network nodes the sending of the respective message are available, and, if there are not enough interlaced qubits available, to wait until sufficient qubits are available before sending them.

A transmission "exclusively using quantum network connections" is to be understood as meaning that a transmission only takes place if a message is completely quantum-based (i.e. via the quantum network connection) or through a combination of quantum-based and classic ( ie classic network connection) Communication can be transmitted, but not if it can only be transmitted via the classic network connection, ie classic. In particular, the quantum-based generation of key pairs is considered here as part of the message transmission.

The high bandwidth mode, the high security mode and / or any other modes can, for example, be permanently or temporarily set or for the entire quantum-supported communication network, for a specific combination of network nodes, or only for a specific message can be determined dynamically. For example, a message to be sent can contain meta-information which specifies the mode in which the message is to be sent through the quantum-supported communication network.

• Bereitstellen eines quantenunterstützten Kommunikationsnetzwerks mit einer Vielzahl von Netzwerkknoten,
• wobei mindestens zwei, bevorzugt mehrere oder sogar alle, Netzwerkknoten mittels Klassische-Netzwerk-Verbindungen verbunden sind und mittels Quanten-Netzwerk-Verbindungen verbunden sind, mittels welchen Quantenzustände übertragen werden können;
• wobei je zwei über eine Quanten-Netzwerk-Verbindung verbundene Netzwerkknoten mit einer den Knoten zugeordneten Quantenquelle des quantenunterstützten Kommunikationsnetzwerks verbunden sind, welche dazu ausgebildet ist, den zugeordneten Netzwerkknoten verschränkte Qubits bereitzustellen;
• Erzeugen von verschränkten Qubits mittels der Quantenquellen;
• Speichern der erzeugten Qubits in den Quanten-Speichereinrichtungen zum Verwenden in der Quanten-Netzwerk-Verbindung;
• Erkennen von Phasen geringer Netzwerkauslastung der Klassische-Netzwerk-Verbindung zwischen Netzwerkknoten;
• Steuern, in erkannten Phasen geringer Netzwerkauslastung, von Quantenquellen, um die jeweilige Phase geringer Netzwerkauslastung dazu zu verwenden, den Netzwerkknoten verschränkte Qubits bereitzustellen.

Furthermore, according to a further aspect of the present invention, a method for operating a quantum-supported communication network having the features of claim 6 is provided. The procedure consists of the following steps:

• Provision of a quantum-supported communication network with a large number of network nodes,
• wherein at least two, preferably several or even all, network nodes are connected by means of classic network connections and are connected by means of quantum network connections by means of which quantum states can be transmitted;
• two network nodes connected via a quantum network connection being connected to a quantum source of the quantum-supported communication network assigned to the node, which is designed to provide entangled qubits to the assigned network node;
• Generating entangled qubits by means of the quantum wells;
• Storing the generated qubits in the quantum storage devices for use in the quantum network connection;
• Detection of phases of low network load of the classic network connection between network nodes;
• Control of quantum sources in identified phases of low network load in order to use the respective phase of low network load to provide the network nodes with entangled qubits.

According to some preferred embodiments, variants or developments of embodiments, the method also comprises the steps: exchanging, including sending and receiving, connection status packets, which contain information about the network load and / or information about the number of stored interleaved qubits, between the network nodes; and controlling the network nodes based on the information obtained.

According to some preferred embodiments, variants or developments of embodiments, the method additionally includes the step: exchanging entangled qubits between network nodes by means of entanglement swapping based on the information received, in particular about entangled qubits from network nodes with currently comparatively low utilization at network nodes with currently comparatively higher utilization provide.

According to some preferred embodiments, variants or developments of embodiments, the method additionally comprises the steps: checking how many interlaced qubits are currently present between two network nodes; and sending messages in a high bandwidth mode, at least also using quantum network connections, if there are enough entangled qubits available between the network nodes for sending the respective message, and exclusively using classic network connections, if for a message does not have enough entangled qubits available.

According to some preferred embodiments, variants or developments of embodiments, the method additionally comprises the steps: checking how many interlaced qubits are currently present between two network nodes; and sending messages, in a high-security mode, exclusively at least using quantum network connections, if sufficient entangled qubits are available between the network nodes for sending the respective message, and if insufficiently entangled qubits are available delay sending until enough qubits are available.

The checking of how many entangled qubits are currently present between two network nodes is advantageously always carried out by means of non-destructive quantum measurements.

The method can also include steps for setting the high security mode, the high bandwidth mode or also other modes, for example based on a user input at least one network node, based on meta information of a message to be sent, based on a table with properties (for example trustworthiness values) of the network nodes and / or the like.

The above configurations and developments can be combined with one another as desired, provided that it makes sense. The variants and developments described for the method according to the invention can all be applied to the quantum-supported communication network according to the invention, and vice versa.

Further possible configurations, developments and implementations of the invention also include combinations, which are not explicitly mentioned, of features of the invention described above or below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

Unless explicitly or implicitly described otherwise, numbering of method steps is used for better clarity and not necessarily to show a mandatory sequence, even if, according to some embodiments, the steps can be carried out, for example, in the sequence in which they are numbered. In general, however, the steps can in particular also be carried out simultaneously or at least partially overlapping, and in each case one or more times.

Figure list

• 1 ein schematisches Blockdiagramm eines erfindungsgemäßen quantenunterstützten Kommunikationsnetzwerks gemäß einer Ausführungsform der vorliegenden Erfindung;
• 2 eine Schemazeichnung zum Erläutern von Details des Kommunikationsnetzwerks gemäß 1;
• 3 ein schematisches Blockdiagramm eines erfindungsgemäßen quantenunterstützten Kommunikationsnetzwerks gemäß einer weiteren Ausführungsform der vorliegenden Erfindung; und
• 4 eine Schemazeichnung zum Erläutern von Details des Kommunikationsnetzwerks gemäß 3.

The present invention is explained in more detail below with reference to the exemplary embodiments specified in the schematic figures. It shows:

• 1 a schematic block diagram of an inventive quantum-assisted communication network according to an embodiment of the present invention;
• 2 a schematic drawing for explaining details of the communication network according to FIG 1 ;
• 3 a schematic block diagram of an inventive quantum-assisted communication network according to a further embodiment of the present invention; and
• 4th a schematic drawing for explaining details of the communication network according to FIG 3 .

The accompanying figures are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the advantages mentioned emerge with a view to the drawings. The elements of the drawings are not necessarily shown to scale with one another. Directional terminology such as "above", "below", "left", "right", "above", "below", "horizontal", "vertical", "front", "rear" and similar information are only used for explanatory purposes Used for purposes and not to restrict the generality to specific configurations as shown in the figures.

In the figures of the drawing, identical, functionally identical and identically acting elements, features and components - unless stated otherwise - are each provided with the same reference symbols.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

1 shows a schematic block diagram of a quantum-assisted communication network according to the invention 100 according to an embodiment of the present invention.

The quantum-supported communication network 100 comprises a large number of network nodes 10-1 , 10-2 , ... 10-N (collectively also referred to as 10-i), of which in 1 representing two network nodes 10-1 , 10-2 are shown. It goes without saying that the following explanations also apply analogously to quantum-supported communication networks with three or more, preferably ten or more, particularly preferably a hundred or thousand or even more network nodes 10-i are applicable.

Two network nodes each 10-1 , 10-2 are by means of classic network connections 20-12 connected (in general: network node 10-i and 10-i are by means of a classic network connection 20-ij connected). There are also two network nodes each 10-1 , 10-2 also by means of quantum network connections 30-12 connected in general: network nodes 10-i and 10-i are connected by means of quantum network connection 30-ij), by means of which quantum states can be transmitted.

Two each via a quantum network connection 30-12 connected network nodes 10-1 , 10-2 are with a quantum source assigned to the node 40-12 of the quantum-supported communication network 100 connected, which is designed to the associated network node 10-1 , 10-2 provide entangled qubits. In a layer model such as the Internet protocol family, the generation and provision of the entangled qubits (and thus also the quantum source 40-12 per se) can be assigned to the network access layer ("link layer"). This is particularly the case because no routing is required to generate the entangled qubits and the higher layers of the quantum-supported communication network remain unaffected by how the entangled qubits are generated and distributed.

In the present case, it is assumed for the description that the quantum source 40-12 for the quantum network connection 30-12 between the first network node 10-1 and the second network node 10-2 at the first network node 10-1 is arranged, the entangled qubits are generated there and one half of the entangled pairs are generated at the second network node 10-2 transmitted, for example by means of announced entanglement.

The network nodes 10-1 , 10-2 also have quantum storage devices 11-1 , 11-2 for storing from the assigned quantum wells 40-12 provided entangled qubits for use in the quantum network connections 30-12 on. The network nodes 10-1 , 10-2 each also include a control device 12-1 , 12-2 , which is designed to receive and send data by the respective network node 10-1 , 10-2 both over the classic network connection 20-12 as well as via the quantum network connection 30-12 to control.

The control devices 12-1 , 12-2 are also designed to deal with phases of low network load on the classic network connection 20-12 between network nodes 10-1 , 10-2 to recognize and set up, in a recognized phase of low network load, assigned quantum sources 40-12 in order to use the phase of low network load to the network node 10-1 , 10-2 provide entangled qubits.

A sliding window protocol, for example, can be used to reliably distribute qubits to the network nodes, as is shown below with reference to the network nodes 10-1 , 10-2 is described:

When a frame with qubits is transmitted, the qubits (or halves of the EPR pairs) are first sent one by one to the receiving network node 10-2 sent, whereby at the sender network node 10-1 a time measurement is started with the last qubit in the frame. Each frame is given a sequence number. After the frame has been sent out, the sender network node waits 10-1 for a predetermined period of time for an acknowledgment from the recipient network node 10-2 . If the acknowledgment is received during the predetermined time, the halves of the EPR pair will be at the sender network node 10-1 saved. If no acknowledgment is received within the predetermined time, the sender network node discards 10-1 its halves from this frame. At the receiving network node 10-2 the frame is checked for the fulfillment of acceptance criteria and, if these are met, the EPR pair halves are stored there and the confirmation is sent out. This can be done, for example, via the classic network connection.

2 illustrates various scenarios that can occur with the sliding window protocol. The time course is drawn vertically, from top to bottom. The left vertical line relates to events at the sender network node 10-1 , and the right vertical line to events on the receiving network node 10-2 . The panels at the left and right end each illustrate whether interlaced qubits have been saved.

Read from top to bottom: First, the quantum source is used 40-12 three frames with entangled qubits generated and temporarily stored, for example in a short-term quantum memory of the quantum source 40-12 of the first network node 10-1 (hereinafter referred to as the sender network node 10-1 designated).

The sending network node 10-1 a start signal 5 sent out, with which the start of the transmission of entangled qubits is indicated. The receiving network node 10-2 responds to this with a response signal 6th , which indicates that the recipient network node 10-2 is ready to receive the entangled qubits.

The transmitter network node then transmits 10-1 three frames, which are designated with 0, 1, and 2, with interlaced qubits to the recipient network node 10-2 . With the first three frames, all three frames arrive at the receiving network node 10-2 (three arrows from left to diagonally right below). The corresponding entangled qubits are stored in the quantum storage device 11-2 of the receiving network node 10-2 saved, which is represented by the three crosses in the upper right panel.

The receipt of each of the three frames is confirmed by an acknowledgment signal from the receiving network node 10-2 to the transmitter network node 10-1 is acknowledged, these confirmation signals from the sender network node 10-1 can also be received (three arrows from right to diagonally below left). Accordingly, according to the sliding window protocol, the entangled qubits transmitted with the confirmed three frames 0, 1, 2 are stored in the quantum storage device 11-1 of the sender network node 10-1 saved, which is illustrated by three crosses in the upper left panel.

The transmitter network node then transmits 10-1 three further frames 0, 1, and 2 with interlaced qubits, whereby in this example the first frame with the designation 0 for some reason not, or not completely, or not with sufficient properties, at the receiving network node 10-2 arrives. The sender network node 10-1 therefore only sends out confirmation signals for frames 1 and 2, and also only saves the interlaced qubits from frames 1 and 2, illustrated by the right middle panel: the first field in the second line remains empty, but there are crosses in the following two fields of the second line.

The sender network node 10-1 started a time measurement with the sending of the last interleaved qubit in the first frame with the designation 0 as described above. Within the predetermined period of time T, the transmitter network node receives 10-1 no acknowledgment signal for this frame with the designation 0; therefore, also in the quantum memory device 11-1 of the sender network node 10-1 no entangled qubits stored from this frame (left middle panel, middle row).

The sender network node 10-1 now sends three more frames with the designations 0, 1 and 2. This time the receiving network node receives 10-2 every 3 frames, but for some reason the acknowledge signal for the frame labeled 1 is lost. As the sender network node 10-1 again within the predetermined time period T after the transmission of the last entangled qubit of the frame with the designation 1 does not receive a corresponding confirmation signal, are stored in the quantum memory device 11-1 of the sender network node 10-1 now only the interlaced qubits from the frames with the designations 0 and 2 are saved (lower left panel, last row: middle field empty).

The receiving network node 10-2 who does not know anything about the loss of the confirmation signal for the frame with the designation 1, however, saves the entangled qubits of all received frames (lower right panel, last row: all fields occupied). The entangled qubits from the frame labeled 1 in the quantum storage device 11-2 of the receiving network node 10-2 will eventually become invalid or overwritten with a new entangled qubit. The sender network node 10-1 however, knows at the software level that these entangled qubits cannot be used.

Finally, the receiving network node sends 10-2 the sender network node 10-1 a stop signal 7th , which indicates that the recipient network node 10-2 now stops accepting frames until it receives a new start signal 5 receives.

As mentioned earlier, the receiving network node checks 10-2 the received entangled qubits for the fulfillment of predetermined acceptance criteria. Another scenario, not shown, is that the sender network node 10-1 Receives a frame, but one or more of the entangled qubits received does not meet the acceptance criteria. In this case, the recipient becomes a network node 10-2 both storing the corresponding entangled qubits in its quantum storage device 11-2 as well as sending an acknowledgment signal for this frame to the sender network node 10-1 fail. The sender is thus also the network node 10-1 informs that the entangled qubits of the said frame cannot be used for communication.

Gleitendes-Fenster-Protokoll: 

The sliding window report can also be displayed as follows, whereby comments are printed in / * ... / *:

 Sliding Window Log: 

Input: A predetermined entanglement fidelity Fmin, a total number N of entangled pairs and a number T of qubits for testing foreign fidelity. It is assumed that a handshake protocol for initiating the transfer of interleaving frames was established while the transmission buffer on the sender (network node) side was empty. When a frame is retransmitted, the quantum memory (short-term quantum memory or quantum memory device) that holds the qubits in this frame at the sender network node is cleared of it.

At this point it should be added that each frame is advantageously provided with a unique (either absolute, or at least within a predetermined time window) serial number, which is between the transmitter network nodes 10-1 and receiving network nodes 10-2 is transmitted. This makes it easier to find the halves of the entangled pairs in the respective quantum storage devices 11-1 , 11-2 to be assigned to the respective counterparts. In addition, the actual physical storage of the halves in the quantum storage devices 11-1 , 11-2 become irrelevant. Within each frame, the entangled qubits contained therein can easily be sorted according to the "first in - first out" principle.

The following is an operation of the quantum-assisted communication network 100 described in a high-bandwidth mode, other operating modes of course also being possible. The case is again only described as an example that a message from the first network node 10-1 to the second network node 10-2 is to be sent.

The first network nodes 10-1 to the second network node 10-2 messages to be sent from the first network node 10-1 receive. It is then determined (for example, checked by means of non-destructive measurement, or calculated on the basis of known data, e.g. the lifetime of entangled pairs) how many entangled qubits for the quantum-supported communication (i.e. for the quantum network connection 30-12) between the first network node 10-1 ("Send network node") and the second network node 10-2 ("Receiver network node") are available.

Since, according to the designation, the highest possible bandwidth or transmission rate is to be achieved in the high bandwidth mode, the existing interleaved qubits are first used to exclusively, or at least support, the classic network connection 20-12 who have favourited Quantum Network Connection 30-12 to use for transmission. For example, quantum superdense coding can be used to achieve a transmission rate of 2 classic bits per transmitted qubit. There are also other transmission methods in which an even higher, theoretically even infinitely high, increase in the transmission rate is possible through the qubits. Superdense coding is mentioned here as just one example of many possibilities.

The mentioned transmission exclusively (or at least also) using the quantum network connection 30-12 is continued until there are no longer enough entangled qubits available for the quantum transmission protocol used. Then the transmission is carried out using the classic network connection 20-12 continued until there are enough interlaced qubits between sender network nodes 10-1 and receiving network nodes 10-2 be available.

As in this example the classic network connection 20-12 is fully utilized, there will be no network capacity available to generate further interleaved qubits in accordance with the GEWI principle. Thus, for this exemplary transmission of large amounts of data, further entangled qubits will only be established again by entanglement swapping. This can be based on, for example a cost function, with which it is calculated whether the advantages of entanglement swapping overall outweigh the disadvantages, in particular the increased consumption of additional entangled qubits. For example, the priority level of the message to be transmitted, an increased need to keep certain network nodes free, can be included in the calculation 10-1 , 10-2 or something like that.

For example, certain network nodes 10-1 , 10-2 be intended for emergency messages only; in this case, a need to keep this network node free 10-1 , 10-2 be chosen so high that the cost function results only for messages with a very high (or the highest) priority level that these network nodes should be involved in entanglement swapping. In this way a particularly reliable connection can be guaranteed.

Modes other than the aforementioned high-bandwidth mode, for example the high-security mode or other modes, can also be used, but do not require any further explanation here.

3 shows a quantum-assisted communication network 200 according to a further embodiment of the present invention. With the quantum-supported communication network 200 it is a variant of the quantum-supported communication network 100 according to 1 so that elements that remain the same are not described again.

Based 3 an advantageous further development of the quantum-supported communication network according to the invention or the method according to the invention is explained, which consists in the entangled qubits between two network nodes 10-1 , 10-2 to balance.

Assume that, as in 3 shown, both the first network node 10-1 a quantum source 40-12 for generating entangled qubits between the first network node 10-1 and the second network node 10-2 as well as the second network node 10-2 a quantum source 40-21 for generating entangled qubits between the second network node 10-2 and the first network node 10-1 having. The communication links between the network nodes 10-1 , 10-2 are unidirectional in this example.

This means that there is a first quantum network connection 30-12 for sending data from the first network node 10-1 to the second network node 10-2 as well as a second quantum network connection 30-21 for sending data from the second network node 10-2 to the first network node 10-1 . The entangled qubits for sending using the first quantum network connection 30-12 are stored in a first quantum storage device 11-1-12 of the first network node 10-1 as well as in a first quantum storage device 11-2-12 of the second network node 10-2 stored while the entangled qubits for sending by means of the second quantum network connection 30-21 in a second quantum storage device 11-1-21 of the first network node 10-1 as well as in a second quantum storage device 11-2-21 of the second network node 10-2 get saved.

There is also a first classic network connection 20-12 for sending data from the first network node 10-1 to the second network node 10-2 as well as a second classic network connection 20-21 for sending data from the second network node 10-2 to the first network node 10-1 .

It can now be the case that the first network node 10-1 Messages to the second network node 10-2 sends, but vice versa the second network node 10-2 rather seldom messages to the first network node 10-1 sends. According to the GEWI principle, this means, especially in the high-bandwidth mode, that the number of entangled qubits in the quantum storage devices 11-1-12 and 11-2-12 will be quickly exhausted or generally at a low level, while the number of entangled qubits in the quantum storage devices 11-1-21 and 11-2-21 will often be at the upper limit or generally at a higher level.

4th shows such a state schematically, where the crosses stand for the number of stored frames with interlaced qubits. The vertical lines indicate possible upper and lower threshold values W1 , W2 . That is, once a pair of quantum storage devices 11-1-12 , 11-2-12 fewer frames than the lower threshold W1 can be made to send frames from the pair of inverted quantum storage devices 11-1-21 , 11-2-21 being transformed. It can also be provided that as soon as a pair of quantum storage devices 11-1-21 , 11-2-21 more frames than the upper threshold W2 has, frames are delivered to the quantum memory device in the reverse direction.

This can be carried out by means of an entanglement balance protocol according to the invention, which will be explained below. Expressions like “if X” and the like refer to Boolean queries. “If” corresponds to the query usually referred to as “if”, and “otherwise” corresponds to the command usually referred to as “else”.

Another possible improvement arises when, for routing in the Internet or network layer, the bandwidth of the quantum-supported communication link between network nodes 10-1 , 10-2 can be specified. In the communication networks 100 , 200 According to the present invention, the bandwidth can to a certain extent carry out a phase jump, namely from a fixed bandwidth via the classic network connection 20-12 in the case of missing or insufficient interlaced qubits, to an increased (and potentially unlimited) bandwidth as soon as sufficient interlaced qubits are available.

In the following, a bandwidth estimation protocol is described which provides a bandwidth value which can be guaranteed for a given V connection. This means that the bandwidth value can also be smaller than the exact bandwidth at the actual time of transmission. The basic idea of the bandwidth estimation protocol is a statistical evaluation of the average communication rate (bandwidth) by monitoring the number of transmissions and their use of entangled qubits.

For this purpose there is a quantum network connection at each end 30-12 a network node 10-1 , 10-2 used, each of which has a known maximum quantum processing rate Pmax. At the beginning when the network nodes 10-1 , 10-2 to the quantum-supported communication network 100 , 200 are added, the network nodes 10-1 , 10-2 the bandwidth of your classic network connection 20-12 announce (broadcast). Over time, the network nodes become 10-1 , 10-2 Generate entangled qubits and use them to generate the classic bandwidth through additional (or sole) use of the quantum network connection 30-12 raise. An average effective bandwidth can be determined from this. As soon as sufficient statistics have been generated, for example as soon as a fluctuation in the determined effective bandwidth remains within a predetermined tolerance channel, the network nodes can 10-1 , 10-2 the quantum-supported communication network 100 , 200 inform (update) about this bandwidth.

As has already been described several times, is the number of entangled qubits available for a quantum network connection 30-12 according to the GEWI principle depending on the number of time units with low (or no) network load of the classic network connection 20-12 . Since the ability of the quantum-assisted communication network 100 , 200 , the classic bandwidth of the classic network connection 20-12 to increase, is directly related to the number of interleaved qubits available, the effective bandwidth is therefore also dependent on the number of time units with low network utilization. This means that if there was a sudden surge in traffic, the bandwidth could drop dramatically. The network nodes 10-1 , 10-2 can advantageously monitor the arrival of data packets to be transmitted in their respective message buffer and thus detect a sharp increase in data packets to be transmitted. In this case, the network nodes 10-1 , 10-2 immediately to the classic bandwidth as the bandwidth to be announced for the communication link between the network nodes 10-1 , 10-2 fall behind.

(One possible) bandwidth estimation protocol:
Input: maximum number of violations NV, window size WS, maximum number RS of the samples to be taken, percentage which quantifies a tolerance between the announced and actual bandwidth; optional incr and decr

"LSP" stands for link state packages, which can thus contain information about the network load and / or information about the number of stored interlaced qubits.

(One possible) expected bandwidth protocol:

#A protocol for determining the bandwidth of a quantum-supported communication link that transmits classic information
Input: Two quantum-supported network nodes 10-1 , 10-2 (here designated as “r” and “s” for receiver / s and sender / s), ie network nodes 10-1 , 10-2 , which can store / buffer and process quantum information, whereby the network nodes 10-1 , 10-2 through a quantum network connection 30-12 are connected, which transmits a stream of classic data either via superdense coding or purely classic; an acceptable bandwidth fluctuation BufFluc; a burn-in value BurnIn, which specifies a number of transmissions to be discarded in the bandwidth calculation at the beginning of the calculation; a delay time D according to which there is a wait between data requests; a maximum buffer growth rate Buf _lim , which can be reached before falling back to the classic bandwidth; and a value dBand, which indicates how much the bandwidth has to change before the quantum-supported communication network has to be informed (updated) about the change.

In the preceding detailed description, various features have been summarized in one or more examples to improve the stringency of the presentation. It should be clear, however, that the above description is merely illustrative and in no way restrictive in nature. It serves to cover all alternatives, modifications and equivalents of the various features and exemplary embodiments. Many other examples will be immediately and immediately apparent to the person skilled in the art on the basis of his technical knowledge in view of the above description.

The exemplary embodiments were selected and described in order to be able to illustrate the principles on which the invention is based and their possible applications in practice as well as possible. This enables those skilled in the art to optimally modify and use the invention and its various exemplary embodiments with regard to the intended use. In the claims and the description, the terms “including” and “having” are used as neutral-language terms for the corresponding terms “comprising”. Furthermore, the use of the terms “a”, “an” and “an” should not fundamentally exclude a plurality of features and components described in this way.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Non-patent literature cited

• D. Siddharta et al., "Robust quantum network architectures and topologies for entanglement distribution", Physical Review A 97, No. 1 (January 29, 2018) [0005]
• Hofmann, et al., "Heralded entanglement between widely separated atoms.", Science 337.6090 (2012): 72-75 [0005]
• Körber et al., "Decoherence-protected memory for a single-photon qubit.", Nature Photonics 12.1 (2018): 18 [0018]
• Munro et al., "Inside quantum repeaters." IEEE Journal of Selected Topics in Quantum Electronics 21.3 (2015): 78-90 [0020]
• Yin et al., "Satellite-based entanglement distribution over 1200 kilometers." Science 356.6343 (2017): 1140-1144 [0020]
• Bennett et al., “Entanglement-assisted classical capacity of noisy quantum channels.” Physical Review Letters 83.15 (1999): 3081 [0035]

Claims (10)

A quantum assisted communication network (100; 200) comprising: a plurality of network nodes (10-1, 10-2); wherein at least two, preferably more than two or all, network nodes (10-1, 10-2) are connected by means of classic network connections (20-12) and are connected by means of quantum network connections (30-12) by means of which quantum states can be transmitted; wherein two network nodes (10-1, 10-2) connected via a quantum network connection (30-12) are each connected to a quantum source (40-12) of the quantum-supported communication network (100; 200) assigned to the node, which for this purpose is designed to provide interleaved qubits to the assigned network nodes (10-1, 10-2); wherein the network nodes have quantum storage means (11-1, 11-2) for storing entangled qubits provided by the associated quantum wells (40-12) for use in the quantum network connections (30-12); wherein the network nodes (10-1, 10-2) each have a control device (12-1, 12-2) which is designed to receive and send data by the respective network node (10-1, 10-2) to control; wherein the control devices (12-1, 12-2) are also designed to recognize phases of low network load of the classic network connection (20-12) between network nodes (10-1, 10-2) and are set up in to control quantum sources (40-12) assigned to a recognized phase of low network utilization in order to use the phase of low network utilization to provide the network nodes (10-1, 10-2) with entangled qubits. Quantum-assisted communication network (100; 200) according to Claim 1 , wherein the quantum network connection (30-12) and the classic network connection (20-12) are each implemented via the same physical conductor, in particular a fiber optic line. Quantum-assisted communication network (100; 200) according to Claim 1 or 2 , wherein the control devices (12-1, 12-2) are designed to exchange information about the network load and / or information about the number of stored interleaved qubits via connection status packets, comprehensively send to each other and receive from each other, and wherein the control devices (12 -1, 12-2) are further set up to control the network nodes (10-1, 10-2) based on the information received. Quantum-assisted communication network (100; 200) according to Claim 3 , the control devices (12-1, 12-2) being set up to exchange entangled qubits between network nodes (10-1, 10-2) based on the information received via entanglement swapping, in particular to exchange entangled qubits from network nodes (10-1 , 10-2) with currently comparatively low utilization at network nodes (10-1, 10-2) with currently relatively higher utilization. Quantum-assisted communication network (100; 200) according to one of the Claims 1 until 4th , wherein the control devices (12-1, 12-2) are designed to control the network nodes, to send messages in a high-bandwidth mode at least also by means of quantum network connections (30-12), if between the network nodes (10-1, 10-2) sufficiently entangled qubits are available for sending the respective message. Quantum-assisted communication network (100; 200) according to one of the Claims 1 until 5 , wherein the control devices (12-1, 12-2) are designed to control the network nodes (10-1, 10-2), in a high security mode messages exclusively using at least quantum network connections ( 30-12) if there are enough entangled qubits available between the network nodes (10-1, 10-2) for sending the respective message and, if there are not enough entangled qubits available, to wait before sending them, until sufficient qubits are available. Quantum-assisted communication network (100; 200) according to one of the Claims 1 until 6th , wherein the control devices (12-1, 12-2) are designed to estimate an available bandwidth based on a number of stored interleaved qubits and a number or rate of incoming messages and to communicate this to the quantum-supported communication network (100). A method for operating a quantum-supported communication network (100; 200), comprising the steps of: providing a quantum-supported communication network (100) with a plurality of network nodes (10-1, 10-2), wherein at least two network nodes (10-1, 10-2 ), preferably more than two or all, are connected by means of classic network connections (20-12) and are connected by means of quantum network connections (30-12) by means of which quantum states can be transmitted; each two network nodes (10-1, 10-2) connected via a quantum network connection (30-12) g are connected to a quantum source (40-12) of the quantum-supported communication network which is assigned to the node and is designed to provide the to provide associated network nodes (10-1, 10-2) with entangled qubits; Generating entangled qubits by means of the quantum wells (40-12); Storing the generated qubits in the quantum storage devices (11-1, 11-2) for use in the quantum network connection (30-12); Detection of phases of low network load of the classic network connection (20-12) between network nodes (10-1, 10-2); Control, in identified phases of low network utilization, of quantum sources (40-12) in order to use the respective phase of low network utilization to provide the network nodes (10-1, 10-2) with entangled qubits. Procedure according to Claim 8 , comprising: exchanging, including sending and receiving, connection status packets which contain information about the network load and / or information about the number of stored interleaved qubits, between the network nodes (10-1, 10-2); and controlling the network nodes based on the information obtained. Procedure according to Claim 9 , comprising: Exchanging entangled qubits between network nodes (10-1, 10-2) by means of entanglement swapping based on the information received, in particular about entangled qubits from network nodes (10-1, 10-2) with currently comparatively low utilization at network nodes ( 10-1, 10-2) with currently comparatively higher utilization.

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