Photonic integrated circuits (PICs) are key to advancing quantum technologies for secure communications. They offer inherent stability, low losses, and compactness compared to standard fiber-based and free-space systems. Our research demonstrates PICs' effectiveness in enhancing quantum communications; we implement a three-state BB84 protocol with a decoy-state method, and we employ an integrated receiver and superconducting nanowire single-photon detectors to achieve technological advancements. One of the most notable results is the extraction of a secret key over a 45 dB channel attenuation. This achievement in the maximum covered distance signifies the potential of integrated photonics to advance the field of quantum communication.
Photonic integrated circuits (PICs) are key to advancing quantum technologies for secure communications. They offer inherent stability, low losses, and compactness compared to standard fiber-based and free-space systems. Our research demonstrates PICs' effectiveness in enhancing quantum communications; we implement a three-state BB84 protocol with a decoy-state method, and we employ an integrated receiver and superconducting nanowire single-photon detectors to achieve technological advancements. One of the most notable results is the extraction of a secret key over a 45 dB channel attenuation. This achievement in the maximum covered distance signifies the potential of integrated photonics to advance the field of quantum communication.
Photonic integrated circuits (PICs) are key in advancing quantum technologies for secure communications. They offer inherent stability, low losses and compactness compared to standard fiber-based and free-space systems. Our reasearch demonstrates PIC's effectivness in enhancing quantum communications, implementing a three-state BB84 protocol with decoy-state method. We employ an integrated receiver and superconducting nanowire single photon detectors (SNSPDs) to achieve technological advancements. One of the most notable results is the extraction of a secret key over a record-breaking 45 dB channel attenuation. Our results demonstrate a remarkable 220% boost in key rate compared to our prototype fiber-based receiver over a 10 dB channel attenuation. This improvement in the secret key rate (SKR) signifies the potential of integrated photonics to advance the field of quantum communication.
Advances in quantum computing pose significant threats to the security of conventional encryption standards. Although quantum key distribution systems offer inherent security, they face challenges in achieving practical secret-key rates over long transmission distances. Photonic Integrated Circuit technologies provide scalability and system efficiency for high key rates using multiplexed time-bin protocols. We present the architecture of a 16-channel multiplexed QKD system at a GHz clock rate realized on integrated photonic chips, promising further scalability. The sender module revolves around an indium-phosphide chip featuring tunable lasers, modulators, and combiners. On the receiver side, low fiber-to-chip coupling loss and waveguide-integrated superconducting nanowire single-photon detectors on silicon nitride provide the necessary detection efficiency.
Quantum communication promises unconditional security by leveraging the fundamental laws of quantum physics, which make eavesdropping detectable through the disturbance it introduces in quantum states. A cornerstone of this technology is quantum key distribution (QKD), enabling the distribution of a shared secret key between distant users with information- theoretic security, rather than relying on assumptions about an eavesdropper’s computational power, as in classical cryptography. However, current QKD systems rely largely on bulk-optical solutions, which limits scalability, stability, and integration into existing telecommunication infrastructures. Photonic integrated circuits (PICs) offer a promising platform to overcome these challenges by providing compact, stable, and CMOS-compatible architectures. This PhD work investigates integrated photonic platforms for practical quantum communication at telecommunication wavelengths, with a focus on demonstrating QKD protocols across three different encoding schemes: time-bin, frequency-bin, and path. First, a time-bin QKD receiver using a borosilicate-glass integrated imbalanced Mach–Zehnder interferometer (iMZI) is developed and compared with a fiber-based receiver, showing enhanced phase stability and improved long-distance secure key rates. Next, frequency-bin entanglement-based QKD is implemented using silicon microring resonators, demonstrating high-visibility quantum interference and active phase-stabilization techniques. Finally, a chip-to-chip path-entangled QKD link is realized using silicon photonic spiral sources, representing a crucial step toward fully integrated quantum transceivers. Across these experiments, this PhD thesis establishes a unified experimental framework for integrated QKD and evaluates performance in terms of quantum bit error rate, secure key rate, and system stability under realistic operating conditions. Together, the results provide a proof-of-concept demonstration of scalable, high-performance quantum communication using PIC technology, advancing toward practical deployment in future quantum networks and laying foundations for multidimensional and fully integrated quantum communication nodes.
Long distance quantum key distribution links are essential for the development of a widely spread fiber-based quantum network. For instance, it would allow for two remote users to communicate securely without the need for a trusted intermediate node. In this work, we focus on enhancing the receiver side of a quantum key distribution system, deploying state-of-the-art superconducting nanowire single photon detectors with ultra low dark count (< 1Hz) and very high efficiency (> 90%), achieving a secure key distribution over a 55 dB losses channel with 0.6 bps rate. This result opens new possibilities for long distance secure communications.
For the establishment of secure communication as well as a future quantum internet, technologies like Quantum Key Distribution (QKD) must become smaller in size, cost-effective in production and more performant. Since attacks like store-now-decrypt-later are already a threat for sensitive data, research in this area must be pushed towards a higher practicality. In this work we show the feasibility of using a photonic integrated circuit (PIC) for application as a QKD transmitter. The PIC (provided by Eindhoven University of Technology) comprises a ring laser source, a Mach-Zehnder interferometer (MZI) with integrated RF phase modulators used for pulse carving and phase modulation as well as an attenuator section. This indium phosphide (InP) chip enables us to generate the necessary states for a 4-state time-bin-phase BB84 protocol [1] implementation. After characterization of all the photonic components and preliminary testing, we were able to generate a secret key rate of approximately 89kbps for 50MHz signal repetition rate with a QBER of 1.3% (in Z-Basis) in a back-to-back configuration.
Continuous-Variable Quantum Key Distribution (CV-QKD) and Quantum Random Number Generation (CV-QRNG) are critical technologies for secure communication and high-speed randomness generation, exploiting shot-noise-limited coherent detection for their operation. Integrated photonic solutions are key to advancing these protocols, as they enable compact, scalable, and efficient system implementations. In this work, we introduce Femtosecond Laser Micromachining (FLM) on borosilicate glass as a novel platform for producing Photonic Integrated Circuits (PICs) realizing coherent detection suitable for quantum information processing. We exploit the specific features of FLM to produce a PIC designed for CV-QKD and CV-QRNG applications. The PIC features fully adjustable optical components that achieve precise calibration and reliable operation under protocol-defined conditions. The device exhibits low insertion losses (≤ 1.28 dB), polarization-insensitive operation, and a Common-Mode Rejection Ratio (CMRR) exceeding 73 dB. These characteristics allowed the experimental realization of a source-device-independent CV-QRNG with a secure generation rate of 42.74 Gbps and a QPSK-based CV-QKD system achieving a secret key rate of 3.2 Mbit/s. Our results highlight the potential of FLM technology as an integrated photonic platform, paving the way for scalable and high-performing quantum communication systems.