scholarly journals Parameter regimes for surpassing the PLOB bound with error-corrected qudit repeaters

Quantum ◽  
2019 ◽  
Vol 3 ◽  
pp. 216 ◽  
Author(s):  
Daniel Miller ◽  
Timo Holz ◽  
Hermann Kampermann ◽  
Dagmar Bruß
Keyword(s):  
Secure Communication ◽  
Quantum Communication ◽  
Quantum Repeater ◽  
Long Distance ◽  
Quantum Networks ◽  
Quantum Capacity ◽  
Higher Dimensional ◽  
Quantum Repeaters ◽  
New Applications ◽  
Provably Secure

A potential quantum internet would open up the possibility of realizing numerous new applications, including provably secure communication. Since losses of photons limit long-distance, direct quantum communication and wide-spread quantum networks, quantum repeaters are needed. The so-called PLOB-repeaterless bound [Pirandola et al., Nat. Commun. 8, 15043 (2017)] is a fundamental limit on the quantum capacity of direct quantum communication. Here, we analytically derive the quantum-repeater gain for error-corrected, one-way quantum repeaters based on higher-dimensional qudits for two different physical encodings: Fock and multimode qudits. We identify parameter regimes in which such quantum repeaters can surpass the PLOB-repeaterless bound and systematically analyze how typical parameters manifest themselves in the quantum-repeater gain. This benchmarking provides a guideline for the implementation of error-corrected qudit repeaters.

scholarly journals Experimental quantum conference key agreement

2021 ◽  
Vol 7 (23) ◽  
pp. eabe0395
Author(s):  
Massimiliano Proietti ◽  
Joseph Ho ◽  
Federico Grasselli ◽  
Peter Barrow ◽  
Mehul Malik ◽  
...  
Keyword(s):  
Secure Communication ◽  
Key Agreement ◽  
Quantum Communication ◽  
Quantum Information Processing ◽  
Global Scale ◽  
Low Noise ◽  
Long Distance ◽  
Quantum Networks ◽  
High Brightness ◽  
Ghz States

Quantum networks will provide multinode entanglement enabling secure communication on a global scale. Traditional quantum communication protocols consume pair-wise entanglement, which is suboptimal for distributed tasks involving more than two users. Here, we demonstrate quantum conference key agreement, a cryptography protocol leveraging multipartite entanglement to efficiently create identical keys between N users with up to N-1 rate advantage in constrained networks. We distribute four-photon Greenberger-Horne-Zeilinger (GHZ) states, generated by high-brightness telecom photon-pair sources, over optical fiber with combined lengths of up to 50 km and then perform multiuser error correction and privacy amplification. Under finite-key analysis, we establish 1.5 × 106 bits of secure key, which are used to encrypt and securely share an image between four users in a conference transmission. Our work highlights a previously unexplored protocol tailored for multinode networks leveraging low-noise, long-distance transmission of GHZ states that will pave the way for future multiparty quantum information processing applications.

scholarly journals Entangling single atoms over 33 km telecom fibre

2022 ◽  
Author(s):  
Tim van Leent ◽  
Matthias Bock ◽  
Florian Fertig ◽  
Robert Garthoff ◽  
Sebastian Eppelt ◽  
...  
Keyword(s):  
Large Scale ◽  
Quantum Communication ◽  
Frequency Conversion ◽  
Single Atom ◽  
Quantum Network ◽  
Low Loss ◽  
Quantum Repeater ◽  
Long Distance ◽  
Quantum Networks ◽  
Network Links

Abstract Heralded entanglement between distant quantum memories is the key resource for quantum networks. Based on quantum repeater protocols, these networks will facilitate efficient large-scale quantum communication and distributed quantum computing. However, despite vast efforts, long-distance fibre based network links have not been realized yet. Here we present results demonstrating heralded entanglement between two independent, remote single-atom quantum memories generated over fibre links with a total length up to 33 km. To overcome the attenuation losses in the long optical fibres of photons initially emitted by the Rubidium quantum memories, we employ polarization-preserving quantum frequency conversion to the low loss telecom band. The presented work represents a milestone towards the realization of efficient quantum network links.

scholarly journals Quantum dot technology for quantum repeaters: from entangled photon generation towards the integration with quantum memories

2021 ◽  
Author(s):  
Julia Neuwirth ◽  
Francesco Basso Basset ◽  
Michele B. Rota ◽  
Emanuele Roccia ◽  
Christian Schimpf ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Quantum Communication ◽  
Special Focus ◽  
Quantum Repeater ◽  
Long Distance ◽  
Quantum Networks ◽  
Pair Generation ◽  
The One ◽  
Photon Generation ◽  
High Degree

Abstract The realization of a functional quantum repeater is one of the major research goals in long-distance quantum communication. Among the different approaches that are being followed, the one relying on quantum memories interfaced with deterministic quantum emitters is considered as one of the most promising solutions. In this work, we focus on the hardware to implement memory-based quantum-repeater schemes that rely on semiconductor quantum dots for the generation of polarization entangled photons. Going through the most relevant figures of merit related to efficiency of the photon source, we select significant developments in fabrication, processing and tuning techniques aimed at combining high degree of entanglement with on-demand pair generation, with a special focus on the progress achieved in the representative case of the GaAs system. We proceed to offer a perspective on integration with quantum memories, both highlighting preliminary works on natural-artificial atomic interfaces and commenting a wide choice of currently available and potentially viable memory solutions in terms of wavelength, bandwidth and noise-requirements. To complete the overview, we also present recent implementations of entanglement-based quantum communication protocols with quantum dots and highlight the next challenges ahead for the implementation of practical quantum networks.

A Quantum Repeater Based on Entanglement Purification and Entanglement Swapping

2013 ◽  
Vol 302 ◽  
pp. 607-611
Author(s):  
Zhen Zhu Zhou ◽  
Wei He ◽  
Chun Dan Zhu ◽  
Ying Wang
Keyword(s):  
Quantum Communication ◽  
Entanglement Swapping ◽  
High Fidelity ◽  
Quantum Repeater ◽  
Long Distance ◽  
Entanglement Purification ◽  
Photon Pairs ◽  
The Common ◽  
Entangled Photon Pairs ◽  
Epr Pair

We discuss a long-distance quantum communication system based on entangled photon pairs, which apply entanglement as its fundamental resource. For distances longer than the coherence length of a counterpart noisy quantum channel, the fidelity of transmission is ordinarily so low that standard purification processes are not applicable. The quantum repeater stretches the length of the entangled photon pairs. And the high fidelity entanglement of photons between sender and receiver is obtained by entanglement purification and entanglement swapping. We compare the nested repeater with the common repeater and show that it outperforms the latter, which is built an EPR pair in less time.

scholarly journals One-hour coherent optical storage in an atomic frequency comb memory

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yu Ma ◽  
You-Zhi Ma ◽  
Zong-Quan Zhou ◽  
Chuan-Feng Li ◽  
Guang-Can Guo
Keyword(s):  
Optical Fibers ◽  
Large Scale ◽  
Quantum Communication ◽  
Frequency Comb ◽  
Quantum Memory ◽  
Spin Coherence ◽  
Quantum Repeater ◽  
Long Distance ◽  
Alternative Solutions ◽  
Atomic Frequency

AbstractPhoton loss in optical fibers prevents long-distance distribution of quantum information on the ground. Quantum repeater is proposed to overcome this problem, but the communication distance is still limited so far because of the system complexity of the quantum repeater scheme. Alternative solutions include transportable quantum memory and quantum-memory-equipped satellites, where long-lived optical quantum memories are the key components to realize global quantum communication. However, the longest storage time of the optical memories demonstrated so far is approximately 1 minute. Here, by employing a zero-first-order-Zeeman magnetic field and dynamical decoupling to protect the spin coherence in a solid, we demonstrate coherent storage of light in an atomic frequency comb memory over 1 hour, leading to a promising future for large-scale quantum communication based on long-lived solid-state quantum memories.

scholarly journals Experimental realization of entangled qutrits for quantum communication

2004 ◽  
Vol 4 (2) ◽  
pp. 93-101
Author(s):  
R. Thew ◽  
A. Acin ◽  
H. Zbinden ◽  
N. Gisin
Keyword(s):  
Quantum Communication ◽  
Fiber Optic ◽  
Quantum Systems ◽  
Entangled States ◽  
Fringe Visibility ◽  
Long Distance ◽  
Experimental Realization ◽  
3 Dimensional ◽  
Higher Dimensional ◽  
Maximally Entangled States

We have experimentally realized a technique to generate, control and measure entangled qutrits, 3-dimensional quantum systems. This scheme uses spontaneous parametric down converted photons and unbalanced 3-arm fiber optic interferometers in a scheme analogous to the Franson interferometric arrangement for qubits. The results reveal a source capable of generating maximally entangled states with a net state fidelity, F = 0.985 $\pm$ 0.018. Further the control over the system reveals a high, net, 2-photon interference fringe visibility, V = 0.919 $\pm$ 0.026. This has all been done at telecom wavelengths thus facilitating the advancement towards long distance higher dimensional quantum communication.

scholarly journals Quantum repeaters based on concatenated bosonic and discrete-variable quantum codes

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Filip Rozpędek ◽  
Kyungjoo Noh ◽  
Qian Xu ◽  
Saikat Guha ◽  
Liang Jiang
Keyword(s):  
Continuous Variable ◽  
Quantum Codes ◽  
Discrete Variable ◽  
Long Distance ◽  
Concatenated Code ◽  
Different Types ◽  
Optical Modes ◽  
Distance Communication ◽  
Quantum Repeaters ◽  
Quantum Error

AbstractWe propose an architecture of quantum-error-correction-based quantum repeaters that combines techniques used in discrete- and continuous-variable quantum information. Specifically, we propose to encode the transmitted qubits in a concatenated code consisting of two levels. On the first level we use a continuous-variable GKP code encoding the qubit in a single bosonic mode. On the second level we use a small discrete-variable code. Such an architecture has two important features. Firstly, errors on each of the two levels are corrected in repeaters of two different types. This enables for achieving performance needed in practical scenarios with a reduced cost with respect to an architecture for which all repeaters are the same. Secondly, the use of continuous-variable GKP code on the lower level generates additional analog information which enhances the error-correcting capabilities of the second-level code such that long-distance communication becomes possible with encodings consisting of only four or seven optical modes.

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