James A. Grieve

We demonstrated a configurable on-chip entangled photon source for BBM92 quantum key distribution (QKD) networks. Built on a scalable silicon-on-insulator (SOI) platform, our design incorporates tunable ring resonators. These allow precise, on-chip adjustment of the quality factor (Q-factor), which is central to optimizing the brightness and noise of the source. Our extensive characterization shows this source achieves a coincidence-to-accidental ratio (CAR) of 48239, $g^2(0)$ of $6.8\times10^{-4}$ and raw coincidence rate of 212k counts/second. This exceeds performance reported in the literature. This performance directly translates to higher secure key rates, lower QBER and QKD robustness. The ability to fine-tune source parameters provides flexibility, allowing adaptation to diverse network conditions and optimization for specific QKD applications. This research marks a step toward creating compact, efficient, and reconfigurable entangled sources for practical and scalable quantum communication.

Quantum communication protocols, offering information-theoretic security, position satellite-based quantum key distribution (QKD) as a pivotal enabler for secure global communication networks. To ensure practical utility for end-users, the placement of optical ground stations (OGSs) must be strategically determined based on the topology of terrestrial quantum networks. Importantly, the site selection criteria recognize that free-space channels, unlike astronomical sites, are not optimized for such applications. Therefore, a comprehensive characterization of free-space channels in diverse environments is essential for designing and implementing a robust global quantum network. In this study, we present a measurement-based characterization of the atmospheric channel at the Abu Dhabi Quantum Optical Ground Station (ADQOGS). Two complementary experimental setups were employed: a ground-based weather station, which continuously monitors key atmospheric parameters, and a quantum acquisition and tracking system that integrates single-photon detectors, mounted on an RC telescope. These setups enable the simultaneous acquisition of classical and quantum signals, both of which are critical for assessing satellite QKD links. We report the experimental results acquired at the ADQOGS site, focusing on key atmospheric parameters impacting satellite-ground quantum communication. Specifically, we show measurements of atmospheric turbulence and background light. The results were analyzed to evaluate their impact on link availability and overall QKD performance in different scenarios. Our findings offer valuable insights for optimizing satellite-ground quantum links, enhancing link stability, and informing the design of future large-scale quantum-secure communication networks. This work contributes to the ongoing efforts toward establishing a robust global quantum communication infrastructure.

Quantum networks are moving rapidly from research laboratories to practical applications. Most quantum networks are based on the trusted node approach because the distance for quantum key distribution (QKD) is limited by photon loss. Shorter distances quantum networks providing any to any connectivity require N(N-1)/2 dark fiber lines, where N is the number of users. Telecom operators, which are the most active players in quantum networks today, can become trusted node owners, which may be an additional barrier to the adoption of quantum networks. An alternative solution is to use entanglement in quantum networks at the city level. In our work we have demonstrated it on a network with three nodes. The center of the network is the PPLN-based source for polarization entangled photon pairs at 1310 and 1316nm. The outputs of the source are connected to a 2x32 optical switch to which any two users can be connected in pairs. To make the receiver suitable for measuring both photons, we have assembled a 2-wavelength Bragg filter that enables the measurement of photons in both wavelengths with a bandwidth of 2 nm. The receivers are designed to be completely passive - the fiber is connected to the BBM92 polarization projection system in free space box, followed by single photon detectors and a time tagger. Polarization distortion is compensated with a fiber-based polarization controller on the source side using the publicly announced QBER. The key is followed by the standard procedures of sifting, cascade error correction and finite key e=10-10 privacy amplification. The derived keys are uploaded to 10G L2/L3 encryption systems, which are able to establish quantum-safe VPN tunnels between any participants. List below describes results of a key rate for 3 node network when the entangled source is connected to a 2x32 optical switch and its outputs are connected to receivers A1(direct) and A2, A3 with 10 km fiber spools each. All secret key tares include finite key size effects A2 (10 km) - A1 (direct). QBER ~2.8%, Secret key rate ~125 b/s A3 (10 km) - A2 (10km). QBER ~4.9%, Secret key rate ~50 b/s A3 (10 km) - A1 (direct). QBER ~3.9%, Secret key rate ~100 b/s

We present the Abu Dhabi Quantum Optical Ground Station (ADQOGS), a versatile optical ground station designed for diverse satellite-based quantum key distribution (QKD) missions. As the first of its kind in the Middle East, ADQOGS’s primary goal is to connect the UAE to global quantum-secured communication networks, thus overcoming the limited reach of terrestrial, fiber-based, QKD lines. The ability of the station to accommodate the reception and emission of multiwavelength optical signals promotes the diversification of space-based trusted nodes and allows a novel parallel trusted node approach to space QKD.

Random number generators are critical components for modern cryptosystems. Deterministic methods of producing random numbers cannot guarantee true randomness due to their susceptibility to external perturbations and deterministic origins. Quantum mechanics due to its probabilistic nature can be used to generate random numbers that cannot be predicted. Here we describe the design of a compact, inexpensive, and manufacturable QRNG based on balanced detection of shot noise from an LED in a commercially available off-the-shelf package which can be integrated into existing devices.

Randomness is a critical resource of modern cryptosystems. Quantum mechanics offers the best properties of an entropy source for unpredictability. However, these sources are often fragile and can fail silently. Therefore, statistical tests on their outputs should be performed continuously. Testing a sequence for randomness can be very resource-intensive, especially for longer sequences, and transferring this to other systems can put the secrecy at risk. In this paper, we present a method that allows a third party to publicly perform statistical testing without compromising the confidentiality of the random bits by connecting the quality of a public sequence to the private sequence generated using a quantum process. We implemented our protocol over two different optical systems and compared them.

Quantum key distribution (QKD) via satellite links is the only currently viable solution to create quantum-backed secure communication at a global scale. To achieve intercontinental coverage with available technology one must adopt a “flying trusted node” paradigm, in which users fully trust the satellite platform. The major part of the poster will focus on our latest work where inspired by the concept of distributed secret sharing and the imminent projected launch of several QKD-equipped satellites, we proposed a parallel trusted node approach, in which key distribution is mediated by several satellites in parallel. This distributes the trust, removes single points of failure, and reduces the necessary assumptions. In addition, we discussed the versatility that an optical ground station should provide to execute such a protocol and, in general, to be fully integrated into a multi-party global quantum network. Finally, one last section of the poster will focus on how we will implement the idea of versatility and adaptability at the Abu Dhabi Quantum Optical Ground Station from a hardware perspective.

One of the most important requirements for the correct operation of the BB84 protocol is the preparation of the true random state. Most realizations follow this logic: Alice prepares random quantum states, measures them to extract random numbers, and then uses them to modulate the state of the transmitted light. The alternative approach is passive state preparation. It was proposed in 2010 and recently studied for security aspects. The idea is to use the natural phase randomness of the laser pulses to prepare random states. This approach can help to solve the security problem of correlating the state modulation voltage. Originally, the focus was on preparing the polarization state. This required two lasers or an additional intensity modulator. In this work, we use a laser that generates random phase pairs of subsequent pulses as a ready-to-use qubit. This allows us to simplify the Alice device. To perform a full phase characterization, we split a portion of the signal, convert it to polarization, and perform polarization tomography where we postselect four BB84 states. Without a decoy state, this QKD system is well suited for the last mile of a star quantum network with a loss budget of up to 10 dB. We have experimentally demonstrated passive state QKD over 10km deployed and spool fiber obtaining 10-100 bps of secret key correspondingly.

Verifying the quality of a random number generator involves performing computationally intensive statistical tests on large data sets commonly in the range of gigabytes. Limitations on computing power can restrict an end-user's ability to perform such verification. There are also applications where the user needs to publicly demonstrate that the random bits they are using pass the statistical tests without the bits being revealed. We report the implementation of an entanglement-based protocol that allows a third party to publicly perform statistical tests without compromising the privacy of the random bits.