Applications In Quantum Cryptography Research Articles

Polymeric Integrated Optics for Measuring Quantum-Entangled Photon States

Quantum-entangled photons have drawn considerable attention for application in quantum cryptography and quantum computers. The optical systems used for measuring polarization-entangled states mostly consist of free-space optical components, which are bulky and sensitive to environmental changes and requires persistent optical alignment. In this study, we propose a solution for the stable measurement of the quantum entanglement of photons based on polymeric waveguide integrated optics. The proposed system consists of two quarter-wave plates inserted in a polymeric optical waveguide, an asymmetric X-junction optical waveguide, four birefringence modulators, and two polarizing beam splitters. The basic performance of the integrated optic device has been confirmed using a 1550-nm distributed feedback laser. High polarization conversion and splitting efficiencies are demonstrated, which are important for the measurement of entangled photon states.

Characterization of an underwater channel for quantum communications in the Ottawa River.

We examine the propagation of optical beams possessing different polarization states and spatial modes through the Ottawa River in Canada. A Shack-Hartmann wavefront sensor is used to record the distorted beam's wavefront. The turbulence in the underwater channel is analysed, and associated Zernike coefficients are obtained in real-time. Finally, we explore the feasibility of transmitting polarization states as well as spatial modes through the underwater channel for applications in quantum cryptography.

Perovskites for Laser and Detector Applications

Perovskite materials have triggered a renewed interest in photovoltaic research in the recent years. They display crystal forms with 0D, 1D and 2D, 3D motifs, and several chemical forms, namely inorganic (titanates, rubidiates, nobiates, tantalates etc.), organic/inorganic metal halides with single to multiple cations, and even organic polymer or quantum dot‐infused hybrids. Each crystal type and chemical form are endowed with specific physicochemical, optical, electronic, and morphological properties. These unique properties render them suitable for targeted applications, namely photovoltaics, LEDs, photocatalysis/electrolysis/solar fuels/solar and Li‐ion batteries, gas‐sensors, ferroelectrics, capacitors, transistors and memristors, photodetectors, and lasers, for advanced quantum cryptography and outer space applications. At first, the crystal and material types, and physicochemical, morphological, and optoelectronic properties of perovskite materials are discussed. Particularly, we focus on those properties which cumulatively contribute to their application in the abovementioned fields. Simultaneously, a comprehensive discussion about the advances in each field is presented. Structure/property/application relationships with key advances demonstrate the versatility of perovskites in modern optoelectronic technologies.

Two new constructions of approximately symmetric informationally complete positive operator-valued measures

A symmetric informationally complete positive operator-valued measure (SIC-POVM) is a POVM in [Formula: see text] consisting of [Formula: see text] positive operators of rank one such that all of whose Hermite inner products are equal. SIC-POVMs are important in quantum information theory, which have many applications in quantum state tomography, quantum cryptography and basic research in quantum mechanics. However, it is very difficult to construct SIC-POVMs. Therefore, many scholars have focused on approximately symmetric informationally complete positive operator-valued measures (ASIC-POVMs) for which the Hermite inner products are close to equal. In this paper, two new constructions of ASIC-POVMs are provided by using character sums and some special functions over finite fields.

Multiparameter QKD authentication protocol design over optical quantum channel

Quantum cryptography is the first application of quantum physics at the single photon level. The most important application of quantum cryptography is Quantum Key Distribution (QKD). One of the biggest problems of QKD implementation is enormous number of possible attacks, which puts out specific need for more refined simulation strategies in bridging the gap between theoretic models and their implementation. In this work we have introduced generalized optical architecture which can provide various solutions of some actual problems for two mostly used QKD protocols: BB84 and B92 protocols. Simulations, which included the influence of optical losses over a quantum channel with concrete realistic lengths, have confirmed validity and high level of provable security of the proposed generalized QKD authentication architecture. Due to simplicity of the proposed architecture and obtained QKD B92 protocol communication efficiency, we believe that it can be implemented, solving out some of the most relevant implementation problems which are common for both QKD protocols.

Spontaneous parametric down-conversion

ABSTRACTSpontaneous Parametric Down-Conversion (SPDC), also known as parametric fluorescence, parametric noise, parametric scattering and all various combinations of the abbreviation SPDC, is a non-linear optical process where a photon spontaneously splits into two other photons of lower energies. One would think that this article is about particle physics and yet it is not, as this process can occur fairly easily on a day to day basis in an optics laboratory. Nowadays, SPDC is at the heart of many quantum optics experiments for applications in quantum cryptography, quantum simulation, quantum metrology but also for testing fundamentals laws of physics in quantum mechanics. In this article, we will focus on the physics of this process and highlight a few important properties of SPDC. There will be two parts: a first theoretical one showing the particular quantum nature of SPDC, and the second part, more experimental and in particular focusing on applications of parametric down-conversion. This is clearly a non-exhaustive article about parametric down-conversion as there is a tremendous literature on the subject, but it gives the necessary first elements needed for a novice student or researcher to work on SPDC sources of light.

Исследование статистики регистрации одиночных фотонов двумя фотодетекторами для применений в квантовой криптографии

Исследование статистики регистрации одиночных фотонов двумя фотодетекторами для применений в квантовой криптографии

Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities

A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

Monitoring of continuous-variable quantum key distribution system in real environment.

How to guarantee the practical security of continuous-variable quantum key distribution (CVQKD) system has been an important issue in the quantum cryptography applications. In contrast to the previous practical security strategies, which focus on the intercept-resend attack or the Gaussian attack, we investigate the practical security strategy based on a general attack, i.e., an arbitrated individual attack or collective attack on the system by Eve in this paper. The low bound of intensity disturbance of the local oscillator signal for eavesdropper successfully concealing herself is obtained, considering all noises can be used by Eve in the practical environment. Furthermore, we obtain an optimal monitoring condition for the practical CVQKD system so that legitimate communicators can monitor the general attack in real-time. As examples, practical security of two special systems, i.e., the Gaussian modulated coherent state CVQKD system and the middle-based CVQKD system, are investigated under the intercept-resend attacks.

Multipartite Gaussian steering: Monogamy constraints and quantum cryptography applications

We derive laws for the distribution of quantum steering among different parties in multipartite Gaussian states under Gaussian measurements. We prove that a monogamy relation akin to the generalized Coffman-Kundu-Wootters inequality holds quantitatively for a recently introduced measure of Gaussian steering. We then define the residual Gaussian steering, stemming from the monogamy inequality, as an indicator of collective steering-type correlations. For pure three-mode Gaussian states, the residual acts a quantifier of genuine multipartite steering, and is interpreted operationally in terms of the guaranteed key rate in the task of secure quantum secret sharing. Optimal resource states for the latter protocol are identified, and their possible experimental implementation discussed. Our results pin down the role of multipartite steering for quantum communication.

Editorial

“One day, Sir, you may tax it.” This sentence is Michael Faraday's purported reply to William Gladstone then British Cancellor of the Exchequer (Minister of Finance) when asked of the practical value of electricity. Even if this episode never took place it, nevertheless, identifies in a striking way the impact of fundamental research on economic growth. The research discoveries of today will be the revenue of tomorrow. Around the time of its birth the laser was called “a solution looking for a problem”. Today there is hardly any problem that cannot be solved by a laser and our economy with a wealth of applications relies on this fact. Without quantum mechanics the laser would not exist. Moreover, the global positioning system relies in its electronic parts on quantum mechanics but it would not work without the subtle corrections of general relativity. “The new quantum technology is largely still in the basic research stage thus making quantum physical effects usable in the new generation of quantum technology requires even greater research efforts. … Although many of the basic discoveries of the new generation of quantum technology have taken place in Germany, so far no company in the country has attempted to commercially exploit the new quantum physical effects.” In the year 2016 the European Community as well as the Federal Government of Germany have recognized the importance of this emerging field and have initiated the Flagship Quantum Technology and a German initiative to propel quantum technologies and foster the transfer from the research environment to the industrial application. In this spirit we have dedicated the cover page of Fortschritte der Physik for the year 2017 to quantum technologies by presenting a magneto-optical trap for lithium. This device is only one of many representatives of the exciting possibilities offered by quantum cryptography, quantum computing, and many more applications we cannot even begin to imagine at the moment. We wish our readers, authors and referees a Healthy, Successful and Happy New Year 2017!

Quantum cryptography and its applications over the internet

Quantum computing can effectively and efficiently perform dense coding, teleportation, prime factoring, and database search methods. Quantum cryptography can be used in secret sharing, secure computation, and secure direct communications. Cloud computing and e-commerce are also ensured by applying quantum computation. In this article we introduce existing solutions and possible quantum cryptography applications over the Internet.

Single-photon emitting diode in silicon carbide.

Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide an ideal material to build such devices. Here, we demonstrate the fabrication of bright single-photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of >300 kHz) and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single-photon source is proposed. These results provide a foundation for the large scale integration of single-photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.

Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond

The negatively charged nitrogen-vacancy colour center (NV− center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis. Here, we report on a micro-concave waveguide antenna design, which can effectively direct single photons from any emitter into either free space or into waveguides in a narrow cone angle with more than 80% collection efficiency irrespective of the dipole orientation. The device also enhances the spontaneous emission rate which further increases the number of photons available for collection. The waveguide antenna has potential applications in quantum cryptography, quantum computation, spectroscopy and metrology.

Generation of N00N State With Orbital Angular Momentum in a Twisted Nonlinear Photonic Crystal

We investigate wavefront engineering of photon pairs generated through spontaneous parametric down conversion in lithium niobate-based nonlinear photonic crystals (NPCs). Due to the complexity of domain structures, it is more convenient to describe photon interaction based on the nonlinear Huygens-Fresnel principle than conventional quasiphase matching regime. Analytical expressions are obtained to describe the transverse properties of down-converted photon states. The convenience of domain engineering in LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystals provides a potential platform for flexible wavefront manipulation of multiphoton states. The generation of N00N state with orbital angular momentum in a twisted NPC is studied utilizing this method. The obtained state is of great value in quantum cryptography, metrology, and lithography applications.

Electroluminescence from localized defects in zinc oxide: toward electrically driven single photon sources at room temperature.

Single photon sources are required for a wide range of applications in quantum information science, quantum cryptography, and quantum communications. However, the majority of room temperature emitters to date are only excited optically, which limits their proper integration into scalable devices. In this work, we overcome this limitation and present room temperature electrically driven light emission from localized defects in zinc oxide (ZnO) nanoparticles and thin films. The devices emit in the red spectral range and show excellent rectifying behavior. The emission is stable over an extensive period of time, providing an important prerequisite for practical devices. Our results open possibilities for building new ZnO-based quantum integrated devices that incorporate solid-state single photon sources for quantum information technologies.

Orbital angular momentum entanglement via fork-poling nonlinear photonic crystals.

We report a compact scheme for the generation and manipulation of photon pairs entangled in the orbital angular momentum (OAM) from the fork-poling quadratic nonlinear crystal. The χ(2)-modulation in this crystal is designed for fulfilling a tilted quasi-phase-matching geometry to ensure the efficient generation of entangled photons as well as for transferring of topological charge of the crystal to the photon pairs. Numerical results show that the OAM of photon pair is anti-correlated and the degree of OAM entanglement can be enhanced by modulating the topological charge of crystal, which indicates a feasible extension to high-dimensional OAM entanglement. These studies suggest that the fork-poling nonlinear photonic crystal a unique platform for compact generation and manipulation of high-dimensional and high-order OAM entanglement, which may have potential applications in quantum communication, quantum cryptography and quantum remote sensing.

Electroluminescence from a diamond device with ion-beam-micromachined buried graphitic electrodes

Focused MeV ion microbeams are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk, as demonstrated in previous works with the fabrication of multi-electrode ionizing radiation detectors and cellular biosensors. In this work we investigate the suitability of the fabrication method for the electrical excitation of color centers in diamond. Differently from photoluminescence, electroluminescence requires an electrical current flowing through the diamond sub-gap states for the excitation of the color centers. With this purpose, buried graphitic electrodes with a spacing of 10μm were fabricated in the bulk of a detector-grade CVD single-crystal diamond sample using a scanning 1.8MeV He+ micro-beam. The current flowing in the gap region between the electrodes upon the application of a 450V bias voltage was exploited as the excitation pump for the electroluminescence of different types of color centers localized in the above-mentioned gap. The bright light emission was spatially mapped using a confocal optical microscopy setup. The spectral analysis of electroluminescence revealed the emission from neutrally-charged nitrogen-vacancy centers (NV0, λZPL=575nm), as well as from cluster crystal dislocations (A-band, λ=400–500nm). Moreover, an electroluminescence signal with appealing spectral features (sharp emission at room temperature, low phonon sidebands) from He-related defects was detected (λZPL=536.3nm, λZPL=560.5nm); a low and broad peak around λ=740nm was also observed and tentatively ascribed to Si-V or GR1 centers. These results pose interesting future perspectives for the fabrication of electrically-stimulated single-photon emitters in diamond for applications in quantum optics and quantum cryptography.

Realisation of orbital angular momentum sorter of photons based on sagnac interferometer

Orbital angular momentum (OAM) of photons has both classical and quantum applications due to its feature of optical vortex and infinite dimension. OAM discrimination is one of the basic problems, which has been paid much attention recently. Here we present an interferometer method in which a Sagnac interferometer with a Dove prism is placed on each arm to separate the different OAM of photons into different output ports, namely, OAM sorters. We demonstrate experimentally the feasibility of OAM sorter by dividing different OAM states into different output ports. Using the cascade interferometers, we also sort the superposition state successfully. Experimental results are in good agreement with the theoretical predictions. Compared with other methods, this method is more stable and can be used to separate superposition states into single photon levels. Furthermore, this method can also be used to couple OAM modes with spatial modes, a very important method for manipulating OAM states. It is a useful method and has potential applications in high-capacity optical communication, quantum entanglement, quantum cryptography, quantum computation and quantum information.

Framework for Wireless Network Security Using Quantum Cryptography

Data that is transient over an unsecured wireless network is always susceptible to being intercepted by anyone within the range of the wireless signal. Hence providing secure communication to keep the user information and devices safe when connected wirelessly has become one of the major concerns. Quantum cryptography provides a solution towards absolute communication security over the network by encoding information as polarized photons, which can be sent through the air. This paper explores on the aspect of application of quantum cryptography in wireless networks. In this paper we present a methodology for integrating quantum cryptography and security of IEEE 802.11 wireless networks in terms of distribution of the encryption keys.