Free-space Quantum Cryptography Research Articles

Faint laser pulses versus a single-photon source in free space quantum cryptography

In this letter we present estimates for the distance of secret key transmission through free space for three different protocols of quantum key distribution: for BB84 and phase time-coding protocols in the case of a strictly single-photon source, and for the relativistic quantum key distribution protocol in the case of faint laser pulses.

On a two-pass scheme without a faraday mirror for free-space relativistic quantum cryptography

The stability of destructive interference independent of the input polarization and the state of a quantum communication channel in fiber optic systems used in quantum cryptography plays a principal role in providing the security of communicated keys. A novel optical scheme is proposed that can be used both in relativistic quantum cryptography for communicating keys in open space and for communicating them over fiber optic lines. The scheme ensures stability of destructive interference and admits simple automatic balancing of a fiber interferometer.

Electrically driven polarized single-photon emission from an InGaN quantum dot in a GaN nanowire

In a classical light source, such as a laser, the photon number follows a Poissonian distribution. For quantum information processing and metrology applications, a non-classical emitter of single photons is required. A single quantum dot is an ideal source of single photons and such single-photon sources in the visible spectral range have been demonstrated with III-nitride and II-VI-based single quantum dots. It has been suggested that short-wavelength blue single-photon emitters would be useful for free-space quantum cryptography, with the availability of high-speed single-photon detectors in this spectral region. Here we demonstrate blue single-photon emission with electrical injection from an In0.25Ga0.75N quantum dot in a single nanowire. The emitted single photons are linearly polarized along the c axis of the nanowire with a degree of linear polarization of ~70%.

Electroluminescence from isolated single indium gallium nitride quantum dots up to 150 K

AbstractWe present light emitting diode structures with InGaN quantum dots (QDs) as active material grown by metal‐organic vapor‐phase epitaxy. The devices reveal a threshold voltage of 3.15 V at room temperature, or 8.8 V at 4 K, respectively. At room temperature, the electroluminescence intensity is still as high as 28% of the intensity at 4 K, the emission covering the spectral region from 2.3 to 2.7 eV at 4 K (2.2–2.6 eV at 300 K). Electrically driven luminescence from spectrally isolated single InGaN QDs emitting in the green spectral region is demonstrated with a thermal stability of up to 150 K. These results are an important step towards applications like electrically driven single photon emitters at elevated temperatures, which are desirable as a basis for communication techniques incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.

Gaussian mixture prior distribution on artifactual current for MEG inverse problem

Quantum cryptography is a new technique that uses the laws of physics to transmit information securely. In such systems, the vehicle to transfer quantum information is a single photon. However, the transmission distance is limited by the absorption of photons in an optical fiber in which the maximum demonstrated range is about 100 km. Free-space quantum cryptography between a ground station and a satellite is a way of sending the quantum information further distances than that with optical fibers since there is no birefringence effect in the atmosphere. At the National Institute of Information and Communications Technology (NICT), the laser communication demonstration between the NICT optical ground station and a low earth orbit satellite was successfully conducted in 2006. For such space communication links, free-space quantum cryptography is considered to be an important application in the future. We have developed a prototype system for free-space quantum cryptography using a weak coherent light and a telecom communication channel. The preliminary results are presented.

Electroluminescence from a single InGaN quantum dot in the green spectral region up to150 K

We present electrically driven luminescence from single InGaN quantum dots embeddedinto a light emitting diode structure grown by metal–organic vapor-phase epitaxy. Singlesharp emission lines in the green spectral region can be identified. Temperature dependentmeasurements demonstrate thermal stability of the emission of a single quantum dot up to150 K. These results are an important step towards applications like electrically drivensingle-photon emitters, which are a basis for applications incorporating plasticoptical fibers as well as for modern concepts of free space quantum cryptography.

Free-space quantum cryptography with quantum and telecom communication channels

Quantum cryptography is a new technique that uses the laws of physics to transmit information securely. In such systems, the vehicle to transfer quantum information is a single photon. However, the transmission distance is limited by the absorption of photons in an optical fiber in which the maximum demonstrated range is about 100km. Free-space quantum cryptography between a ground station and a satellite is a way of sending the quantum information further distances than that with optical fibers since there is no birefringence effect in the atmosphere. At the National Institute of Information and Communications Technology (NICT), the laser communication demonstration between the NICT optical ground station and a low earth orbit satellite was successfully conducted in 2006. For such space communication links, free-space quantum cryptography is considered to be an important application in the future. We have developed a prototype system for free-space quantum cryptography using a weak coherent light and a telecom communication channel. The preliminary results are presented.

Low cost and compact quantum key distribution

We present the design of a novel free-space quantum cryptography system, complete with purpose-built software, that can operate in daylight conditions. The transmitter and receiver modules are built using inexpensive off-the-shelf components. Both modules are compact allowing the generation of renewed shared secrets on demand over a short range of a few metres. An analysis of the software is shown as well as results of error rates and therefore shared secret yields at varying background light levels. As the system is designed to eventually work in short-range consumer applications, we also present a use scenario where the consumer can regularly ‘top up’ a store of secrets for use in a variety of one-time-pad (OTP) and authentication protocols.

Theoretical Study of Quantum Bit Rate in Free-Space QuantumCryptography

The quantum bit rate is an important operating parameter in free-spacequantum key distribution. We introduce the measuring factor and thesifting factor, and present the expressions of the quantum bit ratebased on the ideal single-photon sources and the single-photon sourceswith Poisson distribution. The quantum bit rate is studied in thenumerical simulation for the laser links between a ground station and asatellite in a low earth orbit. The results show that it is feasible toimplement quantum key distribution between a ground station and asatellite in a low earth orbit.

The quantum cryptograpy: Communication and computation

Nowadays there are two secure ways of encrypting information, the public key cryptography (PKC), and the symmetric cryptography (SC). With the arrival of the quantum computation, both methods become vulnerable, thanks to its exponential-growing calculation capacity. To solve this lack of security, quantum physics nowadays offers us two satisfactory methods which have been proposed successfully from a theoretical point of view: the two non-commuting observables, based on the Bennet and Brassard protocol, and the quantum entanglement combined with the Bell's inequality theorem, based on the Ekert protocol. Since some experiments have demonstrated the viability of the conduction of free space quantum cryptography at the surface of the Earth, we propose that this could be a boost for secure ground-to-satellite or satellite-to-satellite communications.

Ultrafast superconducting single-photon optical detectors and their applications

We present a new class of ultrafast single-photon detectors for counting both visible and infrared photons. The detection mechanism is based on photon-induced hotspot formation, which forces the supercurrent redistribution and leads to the appearance of a transient resistive barrier across an ultrathin, submicrometer-width, superconducting stripe. The devices were fabricated from 3.5-nm- and 10-nm-thick NbN films, patterned into 10% for 405-nm radiation to 3.5% for 1550-nm photons. The detector response time and jitter were /spl sim/100 ps and 35 ps, respectively, and were acquisition system limited. The dark counts were below 0.01 per second at optimal biasing. In terms of the counting rate, jitter, and dark counts, the NbN single-photon detectors significantly outperform their semiconductor counterparts. Already-identified applications for our devices range from noncontact testing of semiconductor CMOS VLSI circuits to free-space quantum cryptography and communications.

Squeezed light from microstructured fibres: towards free-space quantum cryptography

Amplitude squeezed pulsed light has been produced using a microstructured silica fibre. By spectrally filtering after the nonlinear propagation in the fibre a squeezing value of -1.7dB has been measured. A quantum key distribution scheme based on squeezed light from such microstructured fibres is proposed.

Secure free-space key exchange to 1.9 km and beyond

Abstract We have designed and built a free space quantum cryptography system. It operates using weak laser pulses with polarization modulation by acousto-optic switching. The system also incorporates full key sifting and error correction between computers connected by a serial port. We have used this system to exchange keys over ranges up to 1.9km with absolute security. The system is robust against transmission (and diffraction) losses up to 20 dB. Building from this initial result we analyse the feasibility of exchanging keys to a low earth orbit satellite.

Secure free-space key exchange to 1.9km and beyond

We have designed and built a free space quantum cryptography system. It operates using weak laser pulses with polarization modulation by acousto-optic switching. The system also incorporates full key sifting and error correction between computers connected by a serial port. We have used this system to exchange keys over ranges up to 1.9km with absolute security. The system is robust against transmission (and diffraction) losses up to 20 dB. Building from this initial result we analyse the feasibility of exchanging keys to a low earth orbit satellite.

Call for papers Special issue on “Quantum interference and cryptographic keys: novel physics and advancing technologies"

The collective phenomena of quantum interference, including wave particle duality and apparent non-locality, have intrigued the physics community for many years. It is only recently that we have begun to turn these somewhat counter intuitive quantum phenomena to good use. A leading force in that direction is quantum cryptography - absolute secure key exchange encoding data on the polarisation or phase of individual photons, or using the quantum correlations between pairs of particles. Technologies are now implemented to bring the various forms of quantum cryptography to commercial application. At the same time the possibility of communications applications has stimulated the study of a variety of novel quantum interference phenomena. Quantum information experiments involving two, three and four photons are planned and a novel Field of continuous variable (many photon) quantum information has emerged. These various aspects of quantum cryptography are considered in the conference “QUICK: Quan- tum interference and cryptographic keys: novel physics and advancing technologies", taking place in Cargese from April 7 to 13, 2001. Following that conference, we invite submission of original papers to a special issue of the European Physical Journal D, on the following topics: - quantum cryptography technologies, - quantum cryptography systems, - free space quantum cryptography and satellites, - pair-photon sources and multiphoton interference, - single photon sources, - continuous variable quantum information, - security aspects, - cryptographic protocols, - entanglement purification in cryptographic schemes, - novel physics and quantum gates for photonic qubits. The submitted articles should be sent to the EPJ D Editorial Office in Orsay. The deadline is July 15, 2001. We look forward to a stimulating special issue.