312 research outputs found
Recursive quantum repeater networks
Internet-scale quantum repeater networks will be heterogeneous in physical
technology, repeater functionality, and management. The classical control
necessary to use the network will therefore face similar issues as Internet
data transmission. Many scalability and management problems that arose during
the development of the Internet might have been solved in a more uniform
fashion, improving flexibility and reducing redundant engineering effort.
Quantum repeater network development is currently at the stage where we risk
similar duplication when separate systems are combined. We propose a unifying
framework that can be used with all existing repeater designs. We introduce the
notion of a Quantum Recursive Network Architecture, developed from the emerging
classical concept of 'recursive networks', extending recursive mechanisms from
a focus on data forwarding to a more general distributed computing request
framework. Recursion abstracts independent transit networks as single relay
nodes, unifies software layering, and virtualizes the addresses of resources to
improve information hiding and resource management. Our architecture is useful
for building arbitrary distributed states, including fundamental distributed
states such as Bell pairs and GHZ, W, and cluster states.Comment: 14 page
QuISP: a Quantum Internet Simulation Package
We present an event-driven simulation package called QuISP for large-scale
quantum networks built on top of the OMNeT++ discrete event simulation
framework. Although the behavior of quantum networking devices have been
revealed by recent research, it is still an open question how they will work in
networks of a practical size. QuISP is designed to simulate large-scale quantum
networks to investigate their behavior under realistic, noisy and heterogeneous
configurations. The protocol architecture we propose enables studies of
different choices for error management and other key decisions. Our confidence
in the simulator is supported by comparing its output to analytic results for a
small network. A key reason for simulation is to look for emergent behavior
when large numbers of individually characterized devices are combined. QuISP
can handle thousands of qubits in dozens of nodes on a laptop computer,
preparing for full Quantum Internet simulation. This simulator promotes the
development of protocols for larger and more complex quantum networks.Comment: 17 pages, 12 figure
Fast and reliable entanglement distribution with quantum repeaters: principles for improving protocols using reinforcement learning
Future quantum technologies such as quantum communication, quantum sensing,
and distributed quantum computation, will rely on networks of shared
entanglement between spatially separated nodes. In this work, we provide
improved protocols/policies for entanglement distribution along a linear chain
of nodes, both homogeneous and inhomogeneous, that take practical limitations
such as photon losses, non-ideal measurements, and quantum memories with short
coherence times into account. For a wide range of parameters, our policies
improve upon previously known policies, such as the
``swap-as-soon-as-possible'' policy, with respect to both the waiting time and
the fidelity of the end-to-end entanglement. This improvement is greatest for
the most practically relevant cases, namely, for short coherence times, high
link losses, and highly asymmetric links. To obtain our results, we model
entanglement distribution using a Markov decision process, and then we use the
Q-learning reinforcement learning (RL) algorithm to discover new policies.
These new policies are characterized by dynamic, state-dependent memory cutoffs
and collaboration between the nodes. In particular, we quantify this
collaboration between the nodes. Our quantifiers tell us how much ``global''
knowledge of the network every node has. Finally, our understanding of the
performance of large quantum networks is currently limited by the computational
inefficiency of simulating them using RL or other optimization methods. Thus,
in this work, we present a method for nesting policies in order to obtain
policies for large repeater chains. By nesting our RL-based policies for small
repeater chains, we obtain policies for large repeater chains that improve upon
the swap-as-soon-as-possible policy, and thus we pave the way for a scalable
method for obtaining policies for long-distance entanglement distribution.Comment: Version 2, title changed, some typos fixed. 27 pages, 18 figures and
3 tables. Comments are welcom
On the Bipartite Entanglement Capacity of Quantum Networks
We consider the problem of multi-path entanglement distribution to a pair of
nodes in a quantum network consisting of devices with non-deterministic
entanglement swapping capabilities. Multi-path entanglement distribution
enables a network to establish end-to-end entangled links across any number of
available paths with pre-established link-level entanglement. Probabilistic
entanglement swapping, on the other hand, limits the amount of entanglement
that is shared between the nodes; this is especially the case when, due to
architectural and other practical constraints, swaps must be performed in
temporal proximity to each other. Limiting our focus to the case where only
bipartite entangled states are generated across the network, we cast the
problem as an instance of generalized flow maximization between two quantum end
nodes wishing to communicate. We propose a mixed-integer quadratically
constrained program (MIQCP) to solve this flow problem for networks with
arbitrary topology. We then compute the overall network capacity, defined as
the maximum number of EPR states distributed to users per time unit, by solving
the flow problem for all possible network states generated by probabilistic
entangled link presence and absence, and subsequently by averaging over all
network state capacities. The MIQCP can also be applied to networks with
multiplexed links. While our approach for computing the overall network
capacity has the undesirable property that the total number of states grows
exponentially with link multiplexing capability, it nevertheless yields an
exact solution that serves as an upper bound comparison basis for the
throughput performance of easily-implementable yet non-optimal entanglement
routing algorithms. We apply our capacity computation method to several
networks, including a topology based on SURFnet -- a backbone network used for
research purposes in the Netherlands
Quantum NETwork: from theory to practice
The quantum internet is envisioned as the ultimate stage of the quantum
revolution, which surpasses its classical counterpart in various aspects, such
as the efficiency of data transmission, the security of network services, and
the capability of information processing. Given its disruptive impact on the
national security and the digital economy, a global race to build scalable
quantum networks has already begun. With the joint effort of national
governments, industrial participants and research institutes, the development
of quantum networks has advanced rapidly in recent years, bringing the first
primitive quantum networks within reach. In this work, we aim to provide an
up-to-date review of the field of quantum networks from both theoretical and
experimental perspectives, contributing to a better understanding of the
building blocks required for the establishment of a global quantum internet. We
also introduce a newly developed quantum network toolkit to facilitate the
exploration and evaluation of innovative ideas. Particularly, it provides dual
quantum computing engines, supporting simulations in both the quantum circuit
and measurement-based models. It also includes a compilation scheme for mapping
quantum network protocols onto quantum circuits, enabling their emulations on
real-world quantum hardware devices. We showcase the power of this toolkit with
several featured demonstrations, including a simulation of the Micius quantum
satellite experiment, a testing of a four-layer quantum network architecture
with resource management, and a quantum emulation of the CHSH game. We hope
this work can give a better understanding of the state-of-the-art development
of quantum networks and provide the necessary tools to make further
contributions along the way.Comment: 36 pages, 33 figures; comments are welcom
A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot
A quantum-light source that delivers photons with a high brightness and a
high degree of entanglement is fundamental for the development of efficient
entanglement-based quantum-key distribution systems. Among all possible
candidates, epitaxial quantum dots are currently emerging as one of the
brightest sources of highly entangled photons. However, the optimization of
both brightness and entanglement currently requires different technologies that
are difficult to combine in a scalable manner. In this work, we overcome this
challenge by developing a novel device consisting of a quantum dot embedded in
a circular Bragg resonator, in turn, integrated onto a micromachined
piezoelectric actuator. The resonator engineers the light-matter interaction to
empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator
manipulates strain fields that tune the quantum dot for the generation of
entangled photons with fidelities up to 0.96(1). This hybrid technology has the
potential to overcome the limitations of the key rates that plague current
approaches to entanglement-based quantum key distribution and
entanglement-based quantum networks. Introductio
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