Resource-effective quantum key distribution: a field trial in Padua city center

Abstract

Field-trials are of key importance for novel technologies seeking commercialization and wide-spread adoption. This is certainly also the case for Quantum Key Distribution (QKD), which allows distant parties to distill a secret key with unconditional security. Typically, QKD demonstrations over urban infrastructures require complex stabilization and synchronization systems to maintain a low Quantum Bit Error (QBER) and high secret key rates over time. Here we present a field-trial which exploits a low-complexity self-stabilized hardware and a novel synchronization technique, to perform QKD over optical fibers deployed in the city center of Padua, Italy. In particular, two techniques recently introduced by our research group are evaluated in a real-world environment: the iPOGNAC polarization encoder was used for the preparation of the quantum states, while the temporal synchronization was performed using the Qubit4Sync algorithm. The results here presented demonstrate the validity and robustness of our resource-effective QKD system, that can be easily and rapidly installed in an existing telecommunication infrastructure, thus representing an important step towards mature, efficient and low-cost QKD systems.

Cross-encoded quantum key distribution exploiting time-bin and polarization states with qubit-based synchronization

“…The iPOGNAC offers fast polarization modulation with longterm stability, and a low intrinsic error rate, and, contrary to previous solutions, generates predetermined polarization states with a fixed reference frame in freespace. Moreover, it has also been tested in a field trial in an urban environment [6]. This polarization encoder relies on an unbalanced Sagnac interferometer containing a lithium-niobate phase modulator, and with the BS replaced by a fiber-based PBS with a polarizationmaintaining (PM) optical fiber input and outputs.…”

“…1), where N D (N A ) is the number of counts in the detector associated with |D (|A ). This algorithm, described in [14], was developed for polarization tracking in polarization-encoded fiber links, and was tested in an urban QKD field trial [6]. It starts operating without interrupting the QKD when the QBER exceeds 1%, and stops when it becomes smaller than 1%.…”

“…QKD is characterized by a consolidated composable security framework [1,2] and by rapid and continuous technical advancements [3]. In fact, several QKD field trials are being performed to demonstrate the real-world applicability of this technology [4][5][6][7] and several start-ups and university spin-offs are being created to intercept the growing market demands.…”

Qubit-Based Clock Synchronization for QKD Systems Using a Bayesian Approach

“…However, this introduces additional hardware requirements and increases the cost and complexity of the setup. One way to avoid these additional resource requirements is to use the quantum channel itself to transmit the information necessary to perform the synchronization [17][18][19][20]. One such qubit-based synchronization protocol was introduced and demonstrated by Calderaro et al [17].…”

Security bounds for decoy-state QKD with arbitrary photon-number statistics

“…Since its first proposal, the decoy-state method [1] has had a major impact on the practicality of quantum key distribution (QKD), having eased many of its technical achievements [2,3] and, recently, its implementations in field trials [4,5]. By countering the photon-numbersplitting (PNS) attack [6], it has enabled the use of practical light sources in QKD and it has been object of many studies including implementation proposals and security proofs.…”