A quantum repeater based on decoherence free subspaces

2008 ◽  
Vol 8 (5) ◽  
pp. 468-488
Author(s):  
U. Dorner ◽  
A. Klein ◽  
D. Jaksch
Keyword(s):  
Quantum Communication ◽  
Waiting Times ◽  
Entanglement Swapping ◽  
Quantum Gates ◽  
Quantum Repeater ◽  
Decoherence Free Subspace ◽  
Decoherence Free Subspaces

We study a quantum repeater which is based on decoherence free quantum gates recently proposed by Klein {\it et al.} [Phys. Rev. A, {\bf 73}, 012332 (2006)]. A number of operations on the decoherence free subspace in this scheme makes use of an ancilla qubit, which undergoes dephasing and thus introduces decoherence to the system. We examine how this decoherence affects entanglement swapping and purification as well as the performance of a quantum repeater. We compare the decoherence free quantum repeater with a quantum repeater based on qubits that are subject to decoherence and show that it outperforms the latter when decoherence due to long waiting times of conventional qubits becomes significant. Thus, a quantum repeater based on decoherence free subspaces is a possibility to greatly improve quantum communication over long or even intercontinental distances.

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.

Long distance two-party quantum crypto made simple

2012 ◽  
Vol 12 (5&6) ◽  
pp. 448-460
Author(s):  
Iordanis Kerenidis ◽  
Stephanie Wehner
Keyword(s):  
Quantum Communication ◽  
Oblivious Transfer ◽  
Difficult Problem ◽  
Entanglement Swapping ◽  
Quantum States ◽  
Large Network ◽  
Long Distance ◽  
Computational Problem ◽  
Cryptographic Primitive

Any two-party cryptographic primitive can be implemented using quantum communication under the assumption that it is difficult to store a large number of quantum states perfectly. However, achieving reliable quantum communication over long distances remains a difficult problem. Here, we consider a large network of nodes with only neighboring quantum links. We exploit properties of this cloud of nodes to enable any two nodes to achieve security even if they are not directly connected. Our results are based on techniques from classical cryptography and do not resort to technologically difficult procedures like entanglement swapping. More precisely, we show that oblivious transfer can be achieved in such a network if and only if there exists a path in the network between the sender and the receiver along which all nodes are honest. Finally, we show that useful notions of security can still be achieved when we relax the assumption of an honest path. For example, we show that we can combine our protocol for oblivious transfer with computational assumptions such that we obtain security if either there exists an honest path, or, as a backup, at least the adversary cannot solve a computational problem.

scholarly journals Teleportation of entanglement over 143 km

2015 ◽  
Vol 112 (46) ◽  
pp. 14202-14205 ◽  
Author(s):  
Thomas Herbst ◽  
Thomas Scheidl ◽  
Matthias Fink ◽  
Johannes Handsteiner ◽  
Bernhard Wittmann ◽  
...  
Keyword(s):  
Direct Consequence ◽  
Building Blocks ◽  
Entanglement Swapping ◽  
Entangled State ◽  
Quantum Repeater ◽  
Long Distance ◽  
Entanglement Purification ◽  
Classical Communication ◽  
High Loss ◽  
La Palma

As a direct consequence of the no-cloning theorem, the deterministic amplification as in classical communication is impossible for unknown quantum states. This calls for more advanced techniques in a future global quantum network, e.g., for cloud quantum computing. A unique solution is the teleportation of an entangled state, i.e., entanglement swapping, representing the central resource to relay entanglement between distant nodes. Together with entanglement purification and a quantum memory it constitutes a so-called quantum repeater. Since the aforementioned building blocks have been individually demonstrated in laboratory setups only, the applicability of the required technology in real-world scenarios remained to be proven. Here we present a free-space entanglement-swapping experiment between the Canary Islands of La Palma and Tenerife, verifying the presence of quantum entanglement between two previously independent photons separated by 143 km. We obtained an expectation value for the entanglement-witness operator, more than 6 SDs beyond the classical limit. By consecutive generation of the two required photon pairs and space-like separation of the relevant measurement events, we also showed the feasibility of the swapping protocol in a long-distance scenario, where the independence of the nodes is highly demanded. Because our results already allow for efficient implementation of entanglement purification, we anticipate our research to lay the ground for a fully fledged quantum repeater over a realistic high-loss and even turbulent quantum channel.

Robust Quantum Gates in Decoherence-Free Subspaces with Josephson Charge Qubits

2012 ◽  
Vol 51 (7) ◽  
pp. 2282-2290 ◽  
Author(s):  
Zhi-Bo Feng ◽  
Run-Ying Yan ◽  
Chunli Zhang ◽  
Libo Fan
Keyword(s):  
Quantum Gates ◽  
Charge Qubits ◽  
Decoherence Free Subspaces

scholarly journals Efficient quantum communication under collective noise

2013 ◽  
Vol 13 (3&4) ◽  
pp. 290-323
Author(s):  
Michael Skotiniotis ◽  
Wolfgang Dur ◽  
Barbara Kraus
Keyword(s):  
Quantum Information ◽  
Discrete Group ◽  
Quantum Communication ◽  
Communication Protocol ◽  
Transmission Rate ◽  
Collective Noise ◽  
Cyclic Groups ◽  
Time Encoding ◽  
Decoherence Free Subspace ◽  
Quantum Communication Protocol

We introduce a new quantum communication protocol for the transmission of quantum information under collective noise. Our protocol utilizes a decoherence-free subspace in such a way that an optimal asymptotic transmission rate is achieved, while at the same time encoding and decoding operations can be efficiently implemented. The encoding and decoding circuit requires a number of elementary gates that scale linearly with the number of transmitted qudits, $m$. The logical depth of our encoding and decoding operations is constant and depends only on the channel in question. For channels described by an arbitrary discrete group $G$, i.e.~with a discrete number, $\lvert G\rvert$, of possible noise operators, perfect transmission at a rate $m/(m+r)$ is achieved with an overhead that scales at most as $\mathcal{O}(d^r)$ where the number of auxiliary qudits, $r$, depends solely on the group in question. Moreover, this overhead is independent of the number of transmitted qudits, $m$. For certain groups, e.g.~cyclic groups, we find that the overhead scales only linearly with the number of group elements $|G|$.

scholarly journals Quantum repeaters with individual rare-earth ions at telecommunication wavelengths

Quantum ◽  
2018 ◽  
Vol 2 ◽  
pp. 93 ◽  
Author(s):  
F. Kimiaee Asadi ◽  
N. Lauk ◽  
S. Wein ◽  
N. Sinclair ◽  
C. O'Brien ◽  
...  
Keyword(s):  
Photon Emission ◽  
Entanglement Swapping ◽  
Rare Earth Ions ◽  
Atomic Ensemble ◽  
Purcell Factor ◽  
Quantum Repeater ◽  
Erbium Ions ◽  
Long Term Storage ◽  
Telecommunication Wavelength ◽  
Entanglement Distribution

We present a quantum repeater scheme that is based on individual erbium and europium ions. Erbium ions are attractive because they emit photons at telecommunication wavelength, while europium ions offer exceptional spin coherence for long-term storage. Entanglement between distant erbium ions is created by photon detection. The photon emission rate of each erbium ion is enhanced by a microcavity with high Purcell factor, as has recently been demonstrated. Entanglement is then transferred to nearby europium ions for storage. Gate operations between nearby ions are performed using dynamically controlled electric-dipole coupling. These gate operations allow entanglement swapping to be employed in order to extend the distance over which entanglement is distributed. The deterministic character of the gate operations allows improved entanglement distribution rates in comparison to atomic ensemble-based protocols. We also propose an approach that utilizes multiplexing in order to enhance the entanglement distribution rate.

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.

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