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Quantum digital signatures apply quantum mechanics to the problem of guaranteeing message integrity and non-repudiation with information-theoretical security, which are complementary to the confidentiality realized by quantum key distribution. Previous experimental demonstrations have been limited to transmission distances of less than 5-km of optical fiber in a laboratory setting. Here we report the first demonstration of quantum digital signatures over installed optical fiber as well as the longest transmission link reported to date. This demonstration used a 90-km long differential phase shift quantum key distribution system to achieve approximately one signed bit per second - an increase in the signature generation rate of several orders of magnitude over previous optical fiber demonstrations.

NOON state interference (NOON-SI) is a powerful tool to improve the phase sensing precision, and can play an important role in quantum sensing and quantum imaging. However, most of the previous NOON-SI experiments only investigated the center part of the interference pattern, while the full range of the NOON-SI pattern has not yet been well explored.In this Letter, we experimentally and theoretically demonstrate up to six-photon NOON-SI and study the properties of the interference patterns over the full range.The multi-photons were generated at a wavelength of 1584 nm from a PPKTP crystal in a parametric down conversion process.It was found that the shape, the coherence time and the visibility of the interference patterns were strongly dependent on the detection schemes.This experiment can be used for applications which are based on the envelope of the NOON-SI pattern, such as quantum spectroscopy and quantum metrology., Comment: 5 pages, 3 figures

Quantum optical amplification that beats the noise addition limit for deterministic amplifiers has been realized experimentally using several different nondeterministic protocols. These schemes either require single-photon sources, or operate by noise addition and photon subtraction. Here we present an experimental demonstration of a protocol that allows nondeterministic amplification of known sets of coherent states with high gain and high fidelity. The experimental system employs the two mature quantum optical technologies of state comparison and photon subtraction and does not rely on elaborate quantum resources such as single-photon sources. The use of coherent states rather than single photons allows for an increased rate of amplification and a less complex photon source. Furthermore it means that the amplification is not restricted to low amplitude states. With respect to the two key parameters, fidelity and amplified state production rate, we demonstrate, without the use of quantum resources, significant improvements over previous experimental implementations., Comment: 21 pages, 4 figures

Digital signatures are widely used to provide security for electronic communications, for example in financial transactions and electronic mail. Currently used classical digital signature schemes, however, only offer security relying on unproven computational assumptions. In contrast, quantum digital signatures (QDS) offer information-theoretic security based on laws of quantum mechanics (e.g. Gottesman and Chuang 2001). Here, security against forging relies on the impossibility of perfectly distinguishing between non-orthogonal quantum states. A serious drawback of previous QDS schemes is however that they require long-term quantum memory, making them unfeasible in practice. We present the first realisation of a scheme (Dunjko et al 2013) that does not need quantum memory, and which also uses only standard linear optical components and photodetectors. To achieve this, the recipients measure the distributed quantum signature states using a new type of quantum measurement, quantum state elimination (e.g. Barnett 2009, Bandyopadhyay et al 2013). This significantly advances QDS as a quantum technology with potential for real applications., Comment: 18 pages, 4 figures. Vesrion accepted in PRL. In v3 small change of title and substancial rewriting of parts of the paper following suggestion of referee. Part of the security analysis included in the appendix (supplementary material) for completeness, is similar to the one in our earlier paper arXiv:1309.1375, since it uses similar methods applied to a different setting

Digital signatures are frequently used in data transfer to prevent impersonation, repudiation and message tampering. Currently used classical digital signature schemes rely on public key encryption techniques, where the complexity of so-called "one-way" mathematical functions is used to provide security over sufficiently long timescales. No mathematical proofs are known for the long-term security of such techniques. Quantum digital signatures offer a means of sending a message which cannot be forged or repudiated, with security verified by information-theoretical limits and quantum mechanics. Here we demonstrate an experimental system which distributes quantum signatures from one sender to two receivers and enables message sending ensured against forging and repudiation. Additionally, we analyse the security of the system in some typical scenarios. The system is based on the interference of phase encoded coherent states of light and our implementation utilises polarisation maintaining optical fibre and photons with a wavelength of 850 nm., Comment: Final version submitted for publication. Some slight changes were made to the structure of the text and figures before publication. Includes Supplementary Information

We present the application of quantum key distribution technologies to fiber-based broadband passive optical access networks. This application is based on our 850 nm wavelength gigahertz clock-rate single-receiver system, is compatible with existing telecommunications fiber and exploits a wavelength band not currently utilized in access networks. The developed quantum key distribution networks are capable of transmitting over distances consistent with the span of access links for metropolitan networks (10 km), at clock frequencies ranging up to 3 GHz., Comment: 9 pages, PDF only

A fibre-based quantum key distribution system operating up to a clock frequency of 3.3GHz is presented. The system demonstrates significantly increased key exchange rate potential and operates at a wavelength of 850nm., Comment: Presented at ECOC 05, Glasgow, UK, (September 2005)

In recent years quantum information research has lead to the discovery of a number of remarkable new paradigms for information processing and communication. These developments include quantum cryptography schemes that offer unconditionally secure information transport guaranteed by quantum-mechanical laws. Such potentially disruptive security technologies could be of high strategic and economic value in the future. Two major issues confronting researchers in this field are the transmission range (typically <100km) and the key exchange rate, which can be as low as a few bits per second at long optical fiber distances. This paper describes further research of an approach to significantly enhance the key exchange rate in an optical fiber system at distances in the range of 1-20km. We will present results on a number of application scenarios, including point-to-point links and multi-user networks. Quantum key distribution systems have been developed, which use standard telecommunications optical fiber, and which are capable of operating at clock rates of up to 2GHz. They implement a polarization-encoded version of the B92 protocol and employ vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, as well as silicon single-photon avalanche diodes as the single photon detectors. The point-to-point quantum key distribution system exhibited a quantum bit error rate of 1.4%, and an estimated net bit rate greater than 100,000 bits- per second for a 4.2 km transmission range., Comment: Presented at SPIE Symposium on Microtechnologies for the New Millennium, Sevilla, Spain (May 2005)

Two multi-user approaches to fiber-based quantum key distribution systems operating at gigahertz clock frequencies are presented, both compatible with standard telecommunications fiber., Comment: IEEE LEOS Summer Topical 2006 - Quantum Communications in Telecom Networks - July 17-19 2006 - Quebec City, Canada

Comparison is made between the results obtained from a state-of-the-art flow and radiative model and bow shock vacuum ultraviolet (VUV) data obtained the recent Bow Shock 2 Flight Experiment. An extensive data set was obtained from onboard rocket measurements at a reentry speed of 5 km/sec between the altitudes of approximately 65-85 km. A description of the NO photoionization cell used, the data, and the interpretation of the data will be presented. The primary purpose of the analyses is to assess the utility of the data and to propose a radiation model appropriate to the flight conditions of Bow Shock 2. Theoretical predictions based on flow modeling discussed in earlier work and a new radiation model are compared with data.