We describe a fiber-based telecom-band polarization-entangled photon-pair source. Preliminary experimental
results of tomographic reconstruction of all four Bell states generated by this source are presented. They show
that a fiber source is an excellent producer of entangled photon-pairs for practical quantum communications.
We present a fiber based source of entangled photon-pairs in the 1550 nm telecom band that can be integrated into the existing fiber network and is well suited for quantum information processing. With this source we have demonstrated the generation, storage, and long-distance distribution of polarization entanglement in standard optical fiber. We have also investigated the origin of the large number of accidental coincidences in the experiments, which has been proved to be Raman scattering, and discussed how to suppress the Raman scattering to improve the quality of the fiber source.
We present the design and construction of a high-speed telecom-band (1.5 μm) single-photon counting system based on an InGaAs/InP avalanche photodiode (APD) operating in the gated Geiger mode. The detector can be gated at high speeds (we examine its performance up to 25 MHz) to maximize the counting rate in long-distance, telecom-band, fiber-optic quantum communication applications. Narrow gate pulses (250 ps full width at half maximum) are used to reduce the dark-count and the after-pulse probability. In order to count the avalanche events, we employ a high-speed comparator to sample the unfiltered and unamplified avalanche photocurrent. The APD and all the associated electronics are integrated onto a printed circuit board with a computer interface. In addition, we cool the APD to -27°C to reduce the dark-count probability.
We will describe keyed communication in quantum noise (KCQ) and how it can be used for either data encryption or key generation. Specifically, we will focus on the AlphaEta protocol for data encryption where the role of quantum noise will be discussed. Additionally, the potential of using classical noise to enhance security via deliberate signal randomization (DSR) will be investigated. We will also investigate the effect of unwanted impairments, such as nonlinearities in a wavelength-division-multiplexed fiber transmission system, and how they affect the ultimate allowable propagation distance. Our simulations and experiments suggest that AlphaEta-protocol based physical-layer encryption is compatible with long-haul optical transmission systems operating at Gb/s data rates.
We demonstrate quantum-noise protected data encryption over a 200km-long inline optically-amplified fiber line at 650Mbps rate using off-the-shelf components. In contrast to our previous implementation, this demonstration uses phase-encoded coherent states, resulting in a polarization independent system that is compatible with the existing WDM infrastructure. Security calculations are presented for individual attacks on both the encrypted data as well as the secret key. This demonstration paves the way for widespread deployment of quantum cryptography in WDM networks.
We demonstrate high-speed (0.25Gbps) data encryption over 50km of
telecom fiber using coherent states of light. For the parameter
values used in the experiment, the demonstration is secure against
individual ciphertext-only eavesdropping attacks near the
transmitter with ideal detection equipment. While other quantum
cryptographic schemes require the use of fragile quantum states
and ultra-sensitive detection equipment, our protocol is loss
tolerant, uses off-the-shelf components, and is optically