Quantum networks are expanding, yet scalability challenges remain. Full-mesh connectivity requires quantum state routing, not point to point links. We demonstrate field tests of secure entanglement-based networking enabling trustless full connections between users.

Realizing a global quantum internet relies on the deployment of robust satellite-based entanglement distribution links. While pioneering demonstrations have established the feasibility of such links, the transition to operational infrastructure demands the validation of robust, integrated space-to-ground architectures. Here, we report on a free-space Quantum Key Distribution experiment conducted over a 1.8 km free-space link using an engineering model of the quantum payload onboard the SpeQtre satellite and the Abu Dhabi Quantum Optical Ground Station. By implementing a BBM92 protocol with polarization-entangled photons, a secret key rate of approximately 7.56 kbps with a mean quantum bit error rate of 4.78

We demonstrate a high-performance SOI-based heralded photon-pair source with tunable pair-generation rate, achieving a coincidence-to-accidental ratio (CAR) of ∼ 38000, heralded self-correlation g H (2) (0)~10 −3 , and a raw coincidence rate of 43 kHz.

We present a method for characterizing polarization fiber channels carrying broadband quantum signals, where narrowband filtering would waste photon flux. Wavelength-dependent polarization mode dispersion (PMD) maps each input state to a trajectory on the Poincaré sphere; we show that the singular value decomposition of the band-averaged rotation matrix yields, in closed form, the optimal input states, the mutually unbiased measurement bases, and their infidelities. The three singular values provide a compact, bandwidth-dependent channel signature that separates first- from higher-order PMD, and the resulting 5

We report on the design and field validation of a fully connected entanglement-based quantum key distribution (QKD) network employing a time-shared photon-pair source and reconfigurable optical switching. The system eliminates the need for trusted relay nodes and enables any-to-any secure connectivity among users over metropolitan-scale fiber infrastructure. We present a three-node prototype network operating in the O-band $(1310 / 1316 \text{nm})$ which demonstrates key generation sufficient to provide pairwise 10 G encrypted connections between 32 users, and confirming practical feasibility for telecom integration.

Quantum key distribution (QKD) via satellite links is widely regarded as a viable near-term 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. Here, inspired by the concept of distributed secret sharing and the imminent projected launch of several QKD-equipped satellites, we propose a parallel trusted node approach, in which key distribution is mediated by several satellites in parallel. This has the effect of distributing the trust, removing single points of failure and reducing the necessary assumptions. In addition, we discuss 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.

Quantum Random Number Generators provide true physical randomness based on quantum processes, essential for cryptographic and scientific applications. However, practical implementations face challenges in robustness and verifiability: ensuring that the entropy source remains secure and stable over time, and enabling independent confirmation of randomness quality without compromising security. We present a system based on a simple looped beam splitter architecture that uses only passive optical components. The device features an intrinsic self-testing mechanism derived from the stability of detection-probability ratios, allowing continuous validation of correct operation. In addition, the same physical process generates two independent random sequences with identical entropy: a private sequence, used for secure applications, and a public one, enabling external statistical verification with zero mutual information between them. This approach demonstrates that robust, self-testing, and publicly verifiable quantum randomness can be achieved with minimal optical complexity without jeopardizing security.

With the growing number of satellite-based Quantum Key Distribution (QKD) payload launches, it becomes essential to ensure compatibility across different platforms for satellite tracking and quantum signal acquisition. In this paper, the Technology Innovation Institute (TII) presents the development of the Abu Dhabi Quantum Optical Ground Station (ADQOGS) for secure free-space optical communications. With the know-how of GA-Synopta's experienced engineering team, we have developed a versatile multi-wavelength quantum acquisition and tracking system tailored to support various upcoming space-based QKD missions, crucial for the practical implementation of global quantum communication networks. This system is capable of handling multiple wavelengths, ranging from 600 nm to 1560 nm for downlink beacons and 1530 nm to 1610 nm for uplink beacons. It includes a free-space quantum module adequate to detect QKD signals at 780±10 nm and 850±3 nm and offers spatial and spectral filtering capabilities along with a motorized polarization correction system.

The polarization mode dispersion (PMD) in optical fibers poses a major challenge for maintaining the fidelity of quantum states for quantum communications. In this work, a comprehensive model linking the probability of quantum measurement errors (infidelity) to PMD is developed and validated by experimental measurements of differential group delay and quantum bit error rate (QBER). Our research proposes effective methods to mitigate PMD effects for broadband entangled photons and evaluates the impact of higher-order PMD effects. The model provides an experimentally verified framework for the optimization of commercial quantum key distribution systems in deployed fiber-optic lines.

Quantum Key Distribution (QKD) technologies are on the way to becoming a practical solution for quantum-secured communication networks. One of the major issues pointed out by governmental agencies [1], [2] is the high cost of equipment needed to build large scale connected quantum networks. To overcome distance limitations, one can use satellites as a trusted node or backbone quantum networks depending on distance and fiber availability. Nevertheless, both solutions are not well-suited for connecting end users to a quantum network. In this work, we use passive state preparation to make the QKD transmitter as simple as possible. Combined with an optical switch, the receiver can share time among multiple transmitters, allowing us to build optimal quantum networks. An additional advantage of the passive state approach is the reduced number of critical elements affecting engineering vulnerabilities since active elements are harder to test.

Single-photon sources (SPSs) are directly applicable in quantum key distribution (QKD) because they allow the implementation of the canonical BB84 protocol. To date, QKD implementations using SPSs are not widespread because of the need for cryogenic operation, or frequency conversion to a wavelength efficiently transmitted over telecommunication fibers. We report an observation of polarization-encoded QKD using a room-temperature telecom SPS based on a GaN defect. A field test over 3.5 km of deployed fiber with 4.0-dB loss yielded a quantum bit error rate (QBER) of 5.0% and a secure key rate of 585.9 bps. Further testing in a 32.5-km fiber spool (attenuation of 11.2 dB), which exhibited substantially lower polarization mode dispersion, yielded a QBER of 3.2% and a secure key rate of 50.4 bps. These results illustrate the potential of the GaN defects for supporting polarization-encoded quantum communication.

Random Number Generators are critical components of modern cryptosystems. Quantum Random Number Generators (QRNG) have emerged to provide high-quality randomness for these applications. Here we describe a scheme to extract random numbers using balanced detection of shot noise from an LED in a commercially available off-the-shelf package. The balanced detection minimizes classical noise contributions from the optical field, improving the isolation of the quantum noise. We present a detailed description and analyze the performance of a QRNG that can be easily integrated into existing systems without the requirement of custom components. The design is optimised for manufacturability, cost, and size.

Randomness is a critical resource of modern cryptosystems. Quantum mechanics offers the best properties of an entropy source in terms of 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.

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 random number-based applications where an honest user needs to publicly demonstrate that the random bits they are using pass the statistical tests without the bits being revealed. Here, 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.

A high-quality heralded single photon source is realized on silicon-on-insulator (SOI) platform. With the help of specially designed ultra- low loss fiber-chip edge couplers, the heralding efficiency of the single photon source system is 56%, after calibrating for a 38% detector efficiency. Compared with the state of the art, this measured heralding efficiency marks a new milestone for integrated, on-chip silicon sources.

We study Polarization Mode Dispersion (PMD) in fiber-based Quantum Key Distribution (QKD) using a broad-spectrum polarization-entangled photon source. We analyze wavelength-dependent polarization transformations over 10 km deployed fiber channels, with measurements spanning one year of evolution. By examining the rotation of polarization states on the Poincare sphere and projecting them along a PMD trajectory onto a predefined state within a measurement basis, we derived a simple new formula that accurately links the measurement error probability to finite signal bandwidth and the observed differential group delay (DGD). Finally, we propose strategies to mitigate the PMD effect for entangled-based QKD by optimizing the orientation of the measurement bases and by performing the optimal spectral filtering of the source.

In prepare-and-measure quantum key distribution systems, careful preparation of quantum states within the transmitter device is a significant driver of both complexity and cost. Moreover, the security guarantees of such systems rest on the correct operation of high speed quantum random number generators (QRNGs) and the high-fidelity modulation of weak optical signals by high-speed optoelectronic devices, all of which must be hardened against a variety of known side-channel attacks. A fully passive state preparation approach elegantly resolves these problems by combining state preparation and QRNG stages into a single optical instrument. By using pairs of optical pulses from a gain-switched laser diode as ready-to-use qubits, the QKD transmitter can be radically simplified, eventually comprising a single laser and local phase tomography stage. We demonstrate our simplified transmitter by establishing a QKD link over a 10 km fiber, generating a secret key rate 110 bits/s, sufficient for practical deployment in "last mile" urban quantum networks. Our results show promise in making QKD simpler and more accessible, closing a critical technology gap in building a secure quantum communication infrastructure.

We report a stable, low loss method for coupling light from silicon-on-insulator (SOI) photonic chips into optical fibers. The technique is realized using an on-chip tapered waveguide and a cleaved small core optical fiber. The on-chip taper is monolithic and does not require a patterned cladding, thus simplifying the chip fabrication process. The optical fiber segment is composed of a centimeter-long small core fiber (UHNA7) which is spliced to SMF-28 fiber with less than -0.1 dB loss. We observe an overall coupling loss of -0.64 dB with this design. The chip edge and fiber tip can be butt coupled without damaging the on-chip taper or fiber. Friction between the surfaces maintains alignment leading to an observation of ±0.1 dB coupling fluctuation during a ten-day continuous measurement without use of any adhesive. This technique minimizes the potential for generating Raman noise in the fiber, and has good stability compared to coupling strategies based on longer UHNA fibers or fragile lensed fibers. We also applied the edge coupler on a correlated photon pair source and observed a raw coincidence count rate of 1.21 million cps and raw heralding efficiency of 21.3%. We achieved an auto correlation function gH(2)(0) as low as 0.0004 at the low pump power regime.

We report a stable, low loss method for coupling light from silicon-on-insulator (SOI) photonic chips into optical fibers. The technique is realized using an on-chip tapered waveguide and a cleaved small core optical fiber. The on-chip taper is monolithic and does not require a patterned cladding, thus simplifying the chip fabrication process. The optical fiber segment is composed of a centimeter-long small core fiber (UHNA7) which is spliced to SMF-28 fiber with less than -0.1 dB loss. We observe an overall coupling loss of -0.64 dB with this design. The chip edge and fiber tip can be butt coupled without damaging the on-chip taper or fiber. Friction between the surfaces maintains alignment leading to an observation of ±0.1 dB coupling fluctuation during a ten-day continuous measurement without use of any adhesive. This technique minimizes the potential for generating Raman noise in the fiber, and has good stability compared to coupling strategies based on longer UHNA fibers or fragile lensed fibers. We also applied the edge coupler on a correlated photon pair source and observed a raw coincidence count rate of 1.21 million cps and raw heralding efficiency of 21.3%. We achieved an auto correlation function g H(2)(0) as low as 0.0004 at the low pump power regime.