Ultrafast and Fault-Tolerant Quantum Communication across Long Distances

Abstract

Quantum repeaters (QRs) provide a way of enabling long distance quantum communication by establishing entangled qubits between remote locations. In this Letter, we investigate a new approach to QRs in which quantum information can be faithfully transmitted via a noisy channel without the use of long distance teleportation, thus eliminating the need to establish remote entangled links. Our approach makes use of small encoding blocks to fault-tolerantly correct both operational and photon loss errors. We describe a way to optimize the resource requirement for these QRs with the aim of the generation of a secure key. Numerical calculations indicate that the number of quantum memory bits at each repeater station required for the generation of one secure key has favorable poly-logarithmic scaling with the distance across which the communication is desired.PACS numbers: 03.67. Dd, 03.67.Hk, 03.67.Pp. Quantum communication across long distances (10 3 -10 4 km) can significantly extend the applications of quantum information protocols such as quantum cryptography [1] and quantum secret sharing [2, 3] which can be used for the creation of a secure quantum internet [4]. Quantum communication can be carried out by first establishing a remote entangled pair between the sender and the receiver and using teleportation to transmit information faithfully. However, there are two main challenges that have to be overcome. First, fiber attenuation during transmission leads to an exponential decrease in entangled pair generation rate. Second, several operational errors such as channel errors, gate errors, measurement errors and quantum memory errors severely degrade the quality of entanglement used for secure key generation. In addition, quantum states cannot be amplified or duplicated deterministically in contrast to classical information [5]. Establishing quantum repeater (QR) stations based on entanglement distribution is the only currently known approach to long-distance quantum communication using conventional optical fibers without exponential penalty in time and resources.A number of schemes have been proposed for long distance quantum communication using , most of which could be broadly classified into three classes. The first class of QRs [6][7][8][9] reduces the exponential scaling of fiber loss to polynomial scaling by introducing intermediate QR nodes. However, this scheme for long distance quantum communication is relatively slow [13], even after optimization [14], limited by the time associated with two-way classical communication between remote stations required for the entanglement purification process needed to correct operational errors [15]. In contrast, the second class of QRs introduce quantum encoding and classical error correction to replace the entanglement purification with classical error correction, handling all operational errors [10,16]. As a consequence, the entanglement generation rate further improves from 1/O(poly(L tot )) to 1/O(poly(log(L tot ))) where L tot is the total distance of communicat...

Role of syndrome information on a one-way quantum repeater using teleportation-based error correction

“…In our simple error model we assume the error rate to be symmetric in the sense that the qubit bit error is e z = e and the qubit phase error is also e x = e. Similar analysis can be performed for a depolarizing channel [12].…”

“…Although the loss in the bosonic channel has the dominating impact on the quantum repeater performance, there will also be finite errors associated with controlling matter qubits in the intermediate stations [12]. As an effective error model, we assume that all errors are induced through the channel and the operations in intermediate stations are perfect.…”

“…An open question is whether there are other simple intermediate stations facilitating quantum repeater behavior. Recently, various quantum repeater architectures have been studied [11][12][13][14]. Ultimately, one-way schemes with a teleportation-based error correction (TEC) approach [15,16] have an advantage in terms of achievable rates.…”

“…In Ref. [12], the syndrome measurement was used to flag success or failure events, and to reduce the effective errors in the success case. The secret key rate was then analyzed by calculating the probability that all intermediate stations show success events and by calculating the expected remaining error rates.…”

An efficient quantum light–matter interface with sub-second lifetime

“…There are many quantum repeater schemes proposed so far [6][7][8][9][10][11]. Considering the experimental capabilities, the memory-photon entanglement based schemes [6] are much more feasible than the error correction based schemes [6][7][8][9][10][11]. Towards a first quantum repeater based on memory-photon entanglement, significant progresses have made in improving performances of the building blocks [6].…”