The decoy-state method substantially improves the performance of quantum key distribution (QKD) and perfectly solves crucial issues caused by multiphoton pulses. In recent years, the decoy-state method has occupied a key position in practicality, and almost all the QKD systems have employed the decoy-state method. However, the imperfections of traditional intensity modulators limit the performance of the decoy-state method and bring side-channels. In this work, a special intensity modulator and its accompanying modulation method are designed and experimentally verified for the secure, stable and high-performance decoy-state QKDs. The experimental result indicates that its stable and adjustable intensities, convenient two-level modulation, inherently high speed, and compact structure is extremely fit the future trends and will help the decoy-state method to be perfectly applied to QKD systems.
Recently, a source-independent quantum random number generator (SI-QRNG), which can generate secure random numbers with untrusted sources, has been realized. However, the measurement loopholes of the trusted but imperfect devices used in SI-QRNGs have not yet been fully explored. Here, we point out and evaluate the security loopholes of practical imperfect measurement devices in SI-QRNGs. We also provide corresponding countermeasures to prevent these information leakages by recalculating the conditional minimum entropy and adding a monitor. Furthermore, by taking into account the finite-size effect, we show that the influence of the afterpulse can exceed that of the finite-size effect with the large number of sampled rounds. Our protocol is simple and effective, and it promotes the security of SI-QRNG in practice as well as the compatibility with high-speed measurement evices, thus paving the way for constructing ultrafast and security-certified commercial SI-QRNG systems.
We investigate a quantum random number generation (QRNG) based on backward spontaneous Raman scattering (SpRS) in standard single-mode fiber, where the randomness of photon wavelength superposition and arrival time are simultaneously utilized. The experiment uses four avalanche photodiodes working in gated Geiger mode to detect backward Raman scattering photons from four different wavelength channels and a time-to-digital converter placed behind the detectors to record their arrival time.
There is an increasing demand for multiplexing of quantum key distribution with optical communications in a single fiber in consideration of high costs and practical applications in the metropolitan optical network. Here, we realize the integration of quantum key distribution and Optical Transport Network of 80 Gbps classical data at 15 dBm launch power over 50 km of the widely used standard (G.652 Recommendation of the International Telecom Union Telecom Standardization Sector) telecom fiber. A secure key rate of 11 kbps over 20 km is obtained. By tolerating a high classical optical power up to 18 dBm of 160 Gbps classical data on single mode fiber our result shows the potential and tolerance of quantum key distribution being used in future large capacity transmission systems, such as metropolitan area networks and data center. The quantum key distribution system is stable and practical which is insensitive to the polarization disturbance of channels by using phase coding system based on Faraday-Michelson interferometer. We also discuss the fundamental limit for quantum key distribution performance in the multiplexing environment.
An integrated Single photon detector (SPD) module that combines a single-photon avalanche photodiode (APD) cooled
by thermoelectric cooler and auxiliary circuits has been demonstrated at 1550 nm. We have employed two coaxial
cables to suppress the spike noise and introduce the timing gates to extract avalanche signals. In a typical condition of
such SPDs, the dark count probability was reduced to 4.7E-5 per pulse, without affecting the detection efficiency (11%)
at 218K.
Quantum Key Distribution (QKD) networks allow multiple users to generate and share secret quantum keys with
unconditional security. Although many schemes of QKD networks have been presented, they are only concentrated on
the system realization and physical implementations. For the complete practical quantum network, a succinct theoretic
model that systematically describes the working processes from physical schemes to key process protocols, from
network topology to key management, and from quantum communication to classical communication is still absent. One
would hope that research and experience have shown that there are certain succinct model in the design of
communication network. With demonstration of the different QKD links and the four primary types of quantum
networks including probability multiplexing, wavelength multiplexing, time multiplexing and quantum multiplexing, we
suggest a layer model for QKD networks which will be compatible with different implementations and protocols. We
divide it into four main layers by their functional independency while defining each layer's services and responsibilities
in detail, orderly named quantum links layer, quantum networks layer, quantum key distribution protocols process layer,
and keys management layer. It will be helpful for the systematic design and construction of real QKD networks.
The imperfect components of a quantum key distribution (QKD) system will degrade its security. The highly attenuated
weak coherent laser source used in today's QKD system is vulnerable to PNS attacks due to multi-photon optical pulses.
Decoy State QKD, which is capable of beating PNS attacks and providing unconditional security, has been an attractive
scheme recently. We have used a one way Faraday-Michelson phase modulated QKD system to implement 123km
decoy state QKD in the lab. Furthermore a field decoy state QKD experiment of 32km dark fiber in Beijing is fulfilled.
The optical pulse repetition rate is 1MHz and the final secure key is 9.59×10-7 (6.784×10-6) bit per pulse for 123km
(32km). The experiment result indicates that the decoy state scheme can be successfully used in real-life metropolitan
QKD sessions.
We have demonstrated a gated-mode single-photon detector at 1550 nm using two thermoelectrically cooled InGaAs/InP
avalanche photodiodes (APDs). Balanced outputs from the two APDs were used to cancel the charge and discharge
spikes, which were attributable to capacitive behavior in a gated mode. The avalanche signals were not attenuated during
the spike cancellation, which enable one to reduce the bias voltage applied to the APDs and thus reduce the dark count
probability. We obtained a quantum efficiency of 10.5% with a dark count probability of 4.8E-5 per gate at 212 K. A
single photon detector module that integrated APD and all necessary circuits into a compact bin has been performed.
In the paper, the foundation requirement of a quantum key distribution network is described. According to the requirement, a kind of star topology quantum key distribution network is introduced. The core of this quantum network is a "router" which is composed of less than N wavelength division multiplexers. Based on the "router", a four nodes quantum key distribution network has been set up, the measurement results shown us that it is suitable for simple purpose of quantum key distribution over many users and the crosstalk is weak enough.
An experimental setup for quantum key distribution (QKD) in special optical fiber at the wavelength of 850nm was presented. The system employs the B92 protocol to establish a secret key between Alice and Bob. The key is encoded in the phase of very weak laser of average photon number 0.1 per pulse. The measured error rate is lower than 8%, the effective transmission rate is about 17bit/s.
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