ICACT20240378 Slide.22
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Thanks for your attention! Now, Floor is open for QnA. Welcome any comment or question.
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ICACT20240378 Slide.21
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Here are the references.
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ICACT20240378 Slide.20
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We propose Q-PSBA, a reliable routing protocol for entanglement distribution in quantum networks.
Q-PSBA utilizes the service availability of quantum repeater nodes to deal with limited resources and existing multiple requests. Q-PSBA uses link-disjoint multipath in prevention of potential failure or memory shortage. Simulation results show that Q-PSBA provides higher throughput and ideal fidelity for entanglement distribution requests with time stability. We are now working on an optimal, load-balanced resource allocation algorithm to deterministically meet the bandwidth requirements of requests under limited resources.
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ICACT20240378 Slide.19
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Finally it comes to the conclusion and future work.
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ICACT20240378 Slide.18
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To study the sustainability of our method, we randomly generate 25 rounds of requests with S-D pair distance of 5 hops, with 4 requests in each round. The performance of requests with different sequences (i.e. arrival time) is shown in Fig.6. We found that the difference in average fidelity and throughput between requests with different sequences is within 0.04 and 3, thus the stability with time indicated.
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ICACT20240378 Slide.17
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the S-D pair distance is defined as the Manhattan distance between the source node and the destination node. Under the experimental setup described above, 100 requests were generated randomly and finished with paths selected by Q-PSBA and Q-CAST. All available qubits are utilized in nodes on each path, and the fidelity of every successfully constructed target entanglement is measured.
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ICACT20240378 Slide.16
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Without loss of generality, we also set some random parameters in the network. First, we randomly select an initial fidelity from a Gaussian distribution N = (0.8, 0.03^2) for each edge and assume the fidelity of multiple entangled pairs generated along the same edge to be identical. Then we defined a random request generator, which simulates a request flow following a Poisson distribution with a mean inter-arrival time of 50ms. Each request in the flow has random, non-adjacent source and destination nodes. Except for entanglement establishment and entanglement swapping, necessary entanglement purification on a single link is engaged based on the end-to-end fidelity calculation model in [12] to ensure that the final entanglement’s fidelity is above 0.5.
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ICACT20240378 Slide.15
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In addition to routing algorithms, several protocols were deployed on each node to simulate qubit resource management and quantum operations.
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ICACT20240378 Slide.14
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Section 3 is the simulation of our methods and the results.
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ICACT20240378 Slide.13
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Introducing multi-path methods in the entanglement distribution routing process can reduce the storage capacity requirements for individual quantum repeater nodes. Also, it allows for a more efficient utilization of resources from different nodes to handle probabilistic failures that may occur on some certain paths, improving the overall robustness. We adopt a link-disjoint multi-path algorithm Q-PSBA(Path Selection Based on Availability), to avoid resource contention on a single link caused by different paths of the same request. It is achieved by an extended multi-round Dijkstra algorithm with our composite metric K, where the edges associated with the optimal path are deleted between rounds.
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ICACT20240378 Slide.12
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Then we come to the routing algorithm. Compared to the original Dijkstra algorithm, we introduced innovative routing metrics with nodes’ resource availability and links’ entanglement quality along the path included. To maximally loosen the requirement for qubit coherence time, an end-to-end entanglement generation will be started when all nodes on the path are prepared. Therefore, resource availability is depicted by the minimum node qubit capacity Ci and the maximum node availability Ti among the repeater nodes of a path. The entanglement quality is represented by both the product of fidelity on every link, and the sum of classical communication delay on each edge of the path. Finally we get the composite metric K of a path by the following formula, where k sub 1, k sub 2, k sub 3 ≥ 0 are parameters to adjust the routing strategy.
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ICACT20240378 Slide.11
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Since both the resource demand and the service time vary from specific request r, neither the service rate nor the queue length is accurate in representing a repeater node’s service capability. Instead, we use the whole waiting time of current requests in a node to characterize its availability. Using time parameters in the previous page, the departure time of requests being serviced currently can be sequentially predicted, revealing the next task to be completed and the number of qubits it will release. Afterwards, the moment when the next task is able to enter the system is determined according to its resource demand, and then its departure time is also confirmed by service time. This process is repeated until the completion time of all tasks is obtained, the latest time among which is the availability attribute.
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ICACT20240378 Slide.10
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As mentioned earlier, quantum network nodes possess much less memory capacity compared with nodes in classical networks, resulting in severe resource contention under multi-request circumstances. It’s likely for a newly arrived request to find all repeaters unavailable, making it necessary to distinguish the availability of those busy nodes.
Therefore, we model every quantum repeater node as a multi-server queuing system where both the arrival time and the service time of customers follow general distribution, and the number of servers is equal to the number of memory qubits in the node. Every node request r is regarded as 𝑛 sub 𝑟 customers arrive at the system and need to be serviced simultaneously. The graph shows the 3 stages of the request’s service process with their time consumed in order.
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ICACT20240378 Slide.09
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Our entanglement distribution scheme utilizes the “on-demand generation” model, in which the link level entangled pairs are generated after path exploration to save qubit resources and avoid decoherence in quantum memories. A remote entanglement generation request will experience path selection and resource allocation phase in order, finally be converted to requests on the source node, the destination node and several repeater nodes. Producing pairwise entanglement concurrently enables simultaneous entanglement swapping along the entire path with minimal delay to combat limited memory lifetimes.
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ICACT20240378 Slide.08
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In our work, we model the service process of quantum repeater nodes which support link-level entanglement establishment, multi-round purification and entanglement swapping, and derive their service availability based on the concept of queuing theory. Then, we propose a link-disjoint multi-path routing algorithm in the prevention of potential failure or memory shortage, with repeaters’ availability, links’ fidelity and classical delay taken into consideration. Besides, we develop a simulation platform to analyze the performance of quantum communication networks based on a discrete event simulation engine.
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ICACT20240378 Slide.07
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Laszlo Gyongyosi proposes the first quantum routing method where the service rate of quantum repeaters are derived and utilized. However, the work is limited to a given set of incoming and outcoming entangled connections, and the complete service process is not considered.
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ICACT20240378 Slide.06
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Axel Dahlberg et al., 2019 propose the first physical and link layer protocols that turn ad-hoc physics experiments producing heralded entanglement between quantum processors into a well-defined and robust service. They also discuss different use cases: measure directly, create and keep, etc. Later in 2022, relevant experimental demonstration was reported with two NV center based quantum nodes separated by 2m. Hereafter we shall regard link layer entanglement distribution as a robust service. Further, to develop a network layer protocol for quantum communication network, efficient routing algorithm is desirable.
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ICACT20240378 Slide.05
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To achieve highly reliable remote entanglement distribution, many efforts have been done.
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ICACT20240378 Slide.04
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Entanglement swapping is utilized to establish entanglement between non-adjacent quantum nodes, for hop by hop mechanism is impossible because of the non-cloning theorem. Noted that every time quantum teleportation is conducted, the pre-shared entanglement will be collapsed, or say, consumed. Therefore, the 3 main challenges of remote entanglement distributions are: limited resources, severe decoherence and low success rate, where the latter two factors even aggravate the shortage of resources.
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ICACT20240378 Slide.03
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Generally, quantum states are encoded with photons to be transmitted through quantum channels built by optical fibers, but this method suffers from severe loss and the success rate drops exponentially.
Entanglement is a phenomenon in quantum mechanics where two or more particles become correlated as a indivisible entity, regardless of how distant they are physically separated. Based on the characteristic of entanglement, the quantum teleportation protocol was developed to overcome the photon loss problem and send a qubit state magically: first let Alice and Bob share an entanglement, then Alice operates and measures on the arbitrary qubit to be sent and half of the entangled pair, transmit the measurement results to Bob through classical channel, finally Bob perform necessary alternation on his qubit and actually gets the original arbitrary state.
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ICACT20240378 Slide.02
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Due to its powerful parallel computing capability, quantum computing will likely lead a new round of information technology revolution. However, the development of monolithic quantum processors is limited by crosstalk in the past years. Although each classical computer is equipped with storage of several terabits, the first quantum computing platform with more than 1000 qubits was just reported In October 2023. Quantum communication provides an alternative method to enable large-scale distributed quantum computing. Besides, quantum communication also guarantees more secure communication through quantum key distribution, more accurate clock synchronization and distributed sensing.
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ICACT20240378 Slide.01
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The outline of our presentation is as follows: first, a brief introduction about quantum network and remote entanglement distribution will be given. Second, we will discuss several related work and our proposed method. Then, the simulation and results. Finally, the conclusion of our paper and the future work.
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ICACT20240378 Slide.00
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Hi everybody, my name is Tianzhu Hu. Today, I'm going to present our paper about a solution for entanglement distribution in quantum communication networks under the title " A Reliable Routing Method for Remote Entanglement Distribution under Limited Resources“.
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