Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.
We review our efforts in integrating optical hardware for quantum key distribution onto photonic chips and in engineering the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.
We report the development of an optical assembly and driving electronics for a low-SWaP polarization encoder design for use in satellite-to-ground quantum communication. The optical design multiplexes multiple lasers, which are selectively excited to produce a polarization encoded output. This implementation is intrinsically stable due to the use of only polarization maintaining fiber in the combining optics. The transmitter, provides a low-cost, low-power and high-speed platform to produce polarization encoded pulses. We use the transmitter to generate 4 polarization states with 2 intensity levels via multiplexing of 8 pulsed light sources. The module can generate the polarization states H, V, D and A, which correspond to polarization angles of 0, 90, 45 and -45 degrees respectively, forming two mutually unbiased bases. The transmitter is characterized via a polarization decoder over a free-space link within a laboratory setting. We characterize the source for varying optical channel loss which is introduced between the transmitter and receiver. The transmitter employs the T12 decoy-state BB84 protocol. We explore the performance of the system with commercially available single photon detectors for two clock rates of 500 MHz and 1 GHz. We find a similar secure key rate for both repetition rates, despite the expected 3 dB gain at 1 GHz. This is a result of detector jitter hindering the performance of the QKD system, resulting in a larger QBER when detection events leak into the adjacent time bins and ultimately reduces the secure key rate.
Quantum key distribution (QKD) offers the highest possible levels of communication secrecy. Using the laws of quantum mechanics, QKD protocols allow two distant parties to establish symmetric encryption keys that can be proven information theoretically secure. In order to make this technology accessible to a wide range of sectors, it is essential to address the questions of cost, volume production and compatibility with standard Telecom/Datacom infrastructures. While over the last few years, a number of works were devoted to the demonstration of photonic integrated circuits for quantum communications, a practical solution to interface these chips in a complete system remained an elusive goal. We review our efforts in integrating the core optical functions of quantum key distribution onto quantum photonic chips and in demonstrating the first standalone photonic integrated QKD system. Our approach tackles various system integration challenges related to packaging, optoelectronic design and power consumption. The quantum hardware is assembled in pluggable interconnects that guarantee efficient thermal management and forward compatibility of a same host electronics with successive generations of chips. Autonomous operation and long-term stability are demonstrated in realistic operation conditions. Our work offers new pathways for practical implementations of QKD and its viable deployment at large scales.
Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Here, we introduce a novel wavelength-multiplexed stabilisation scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. In our work, we develop a setup that provides key rates over a record fibre distance of 605 km and increases the secure key rate at long distances by two orders of magnitude to values of practical significance.
Integrated photonics presents an opportunity for low-cost, lightweight and highly-reproducible quantum cryptographic systems. We show that incorporating integrated photonics within pluggable modules a chip-based QKD system operating in real time and with highly competitive secure key rates can be realised with room temperature single photon detectors. The pluggable modules also benefit from their ability to be easily upgraded and replaced so that as the technology matures the system performance can be further enhanced. We also show that our system can be used with standard classical cryptography systems enabling secure data transfer at 100G.
A complete chip-based quantum communication system is demonstrated. The core functions of quantum transmitter, quantum receiver and quantum random number generator are implemented onto photonic integrated circuits (PICs) of different materials. For the first time, these PICs are all interfaced in a compact optoelectronic assembly where they operate synchronously to distribute information theoretically secure encryption keys in real-time. After reviewing the challenges of system integration for quantum photonic circuits, we present our development of plug-and-play quantum communication modules that are practical, scalable, power efficient and perform with high stability under real-life conditions.
Time gating for SPADs is exploited either for increasing their maximum count rate or for detecting faint signals hidden by strong unwanted light pulses. Here we describe two short-gate techniques for high-speed photon counting with InGaAs/InP SPADs: i) a sinusoidal gating system at about 1.3 GHz, with very low afterpulsing and high count rate; ii) a SiGe integrated circuit for sub-nanosecond gating with < 200 ps rising/falling edges.
The practical combination of quantum cryptography and classical communications will require convergence of their technologies. In this pivotal time where both fields are transitioning towards photonic integrated architectures, it is essential to develop devices that fully leverage their hardware compatibilities, while still addressing the key issues of cost reduction, miniaturization and infrastructure energetic footprint, essential for future high- bandwidth, low-latency networks. Here, we address these issues by developing an on-chip transmitter consisting of just 3 building blocks but capable of transmitting both quantum encrypted photons and classical multi-level modulation signals. By combining optical injection locking and direct phase modulation we are able to encode pulse trains with multiple levels of differential phase, without the need of high-speed electro-optic modulators and their associated power footprint. We generate return-to-zero differential phase shift keying signals with up to 16 distinct levels. Moreover, we demonstrate multi-protocol quantum key distribution delivering state-of-the-art secure key rates. Our on-chip transmitter will facilitate the flexible combination of quantum and classical communications within a single, power-efficient device that can readily be integrated in existing high connectivity networks.
The capability to achieve high count rates has become an imperative in the most areas where near-infrared single-photon counters are required to detect photons up to 1.7 μm. Hence, afterpulsing mitigation is a dominant theme in recent works concerning systems based on InGaAs/InP SPADs. Given the challenges inherent in reducing the density of defects that give rise to the carrier trapping events causing afterpulsing, the only viable approach is to reduce the potential number of carriers that can be trapped by limiting the charge flow per avalanche event. In this paper we present a sine-wave gating system based on the balanced detector configuration. The gate frequency is programmable in a wide range (1.0 – 1.6 GHz) for allowing synchronization with an external laser system and for exploring the best trade-off between afterpulsing and photon detection efficiency. The long-term stability can be achieved with a stable cancelation of the gate feedthrough. In this work this is guaranteed by a feedback loop that continuously monitors the residual output power at the gate frequency and adjusts the amplitude and phase of the two sinusoids fed to the SPAD-dummy couple.
CMOS SPADs are nowadays an established imaging technology for applications requiring single-photon sensitivity in a compact form-factor (e.g. three-dimensional LIDAR imaging and fluorescence lifetime FLIM microscopy). However, we aimed at further enhance overall SPAD performances, by exploiting smart power technologies, such as the BCD (Bipolar-CMOS-DMOS) one. We achieved the present state-of-the-art SPADs fabricated in the 0.16 μm BCD technology by STMicroelectronics, attaining >60% photon detection efficiency at 500 nm, dark count rate density < 0.2 cps/μm2, and less than 30 ps FWHM timing jitter.
We present a new InGaAs/InP Single-Photon Avalanche Diode (SPAD) with high detection efficiency and low noise,
which has been employed in a sinusoidal-gated setup to achieve very low afterpulsing probability and high count rate.
The new InGaAs/InP SPAD has lower noise compared to previous generations thanks to the improvement of Zinc
diffusion conditions and the optimization of the vertical structure. A detector with 25 μm active-area diameter, operated
in gated-mode with ON time of tens of nanoseconds, has a dark count rate of few kilo-counts per second at 225 K and
5 V of excess bias, 30% photon detection efficiency at 1550 nm and a timing jitter of less than 90 ps (FWHM) at 7 V of
excess bias.
In order to reduce significantly the afterpulsing probability, these detectors were operated with a sinusoidal gate at 1.3
GHz. The extremely short gate ON time (less than 200 ps) reduces the charge flowing through the junction, thus
reducing the number of trapped carriers and, eventually, lowering the afterpulsing probability. The resulting detection
system achieves a maximum count rate higher than 650 Mcount/s with an afterpulsing probability of about 1.5%, a
photon detection efficiency greater than 30% at 1550 nm and a temporal resolution of less than 90 ps (FWHM).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.