Patent Application: US-85983410-A

Abstract:
photonic signals are tagged with a pre - selected modification , such as a polarization signature to carry data across an obstructed path between sender and receiver . communication authentication through polarization variation allows for yuen - kumar or entangled photon quantum communication protocols to propagate through environmental scattering media such as air , smoke , fog , rain , and water . while ultraviolet light photons are well suited as a carrier for quantum communication signals scattered in air , it is appreciated that visible wavelengths have longer propagation paths in water to convey non - line - of - sight data . a secure signal is scattered by the media and simultaneously communicated to a single recipient or multiple recipients exposed to scattered signal portions . a process of solving the scattering processes through a random scattering media is provided to reconstruct a quantum keyed message at a receiver . the scattering of the signal is utilized herein to provide non - line - of - sight and intentional short - range communication .

Description:
the present invention has utility as a secure short range quantum communication scheme that is operative independent of a direct line of sight between a sender and receiver . the scatter caused by the environment to a light beam is the basis of non - line - of - sight communication . the manipulation of photons as a carrier for quantum communication data is provided by a polarization signature as the basis for the inventive non - line of sight secure , short range communication . the present invention has applications for communication within mobile small networks that optionally have a need for simultaneous multicasting to multiple recipients . as used herein “ short - range ” communication is defined as the ability to send a signal between a sender and receiver separated by up to several kilometers , within an outside range of ten kilometers . it is appreciated that ultraviolet ( uv ) radiation is well suited for non - line - of - sight quantum communication in air ; specific wavelengths will have different scattering characteristics under a given set of environmental conditions illustratively including humidity , particulate and turbulence . in a preferred embodiment , a uv light source , such as uv laser is provided with multiple laser lines is used with the ability to change carrier wave wavelength to achieve a desired range of signal propagation through the scattering medium . the present invention is also operative with water as the scattering media with the recognition that longer wavelengths of visible blue - green light have greater propagation distances in water relative to ultraviolet wavelengths . as such , a water based intentionally short - range non - line - of - sight quantum communication system uses a blue - green carrier wavelength of between 440 and 560 nanometers for maximal range . it is appreciated that the present invention is also operative in transmission through solid substance such as ice , soil , and rock with resort to a propagation wavelength that is scattered by the solid media , yet transmissive through the volume of solid to be traverse by the message . communication through a solid typically involves infrared and longer wavelengths of more than 800 nanometers . radiation is subject to absorption and scattering in media . the media is characterized by absorption and scattering parameters . a light ray scattering can be characterized by mueller matrices which also handle partial absorption . on the other , hand scattering of discrete photons results in absorption , or a form of scattering depending on the state of the photon and atoms . to understand light propagation through a random medium , resort is made to maxwell &# 39 ; s equation . environmental media such as air , water , smoke and fog are well approximated as random media . maxwell &# 39 ; s equations can be put in the following form typically suitable for scattering considerations [ 1 ]. for scattering purposes the version of the equations that are uses assume no sources and currents . the material properties are provided by the relations where ε ( r ) and μ ( r ) are in the form of scalars for isotropic media and otherwise are in the form of tensors . substituting the isotopic media scalar forms of these equations into maxwell &# 39 ; s equations yields the equation needs to be solved subject to boundary conditions and a radiation condition [ 1 ]. usually these equations apply scattering to single particles . however a t matrix method can be used to average over the orientations of ensembles of particles [ 1 ]. however , other solutions are possible . the equation subject to random parameters is subjected to the decomposition method to model the information reconstruction as a receiver subsequent to scatter . [∇ 2 + k 2 ( r )] e ( r )= g ( r ) in cartesian coordinates . here k 2 ( r ) is considered to be a random variable with outcomes prescribed by a probability density function . the equation is solved as l x e + l y e + l z e + k 2 ( x , y , z ) e = g ( x , y , z ) now the system of equations is put into the triplicate form by shifting the operators l x e =− l y e − l z e − k 2 ( x , y , z ) e + g ( x , y , z ) l y e =− l x e − l z e − k 2 ( x , y , z ) + g ( x , y , z ) l z e =− l x e − l y e − k 2 ( x , y , z ) + g ( x , y , z ). each equation is capable of a separate solution given suitable boundary conditions . however in this form it is possible to average the solutions at each step and obtain a different approximation or convergence rate . l x − 1 l x e =− l x − 1 l y e − l x − 1 l z e − l x − 1 k 2 ( x , y , z ) e + l x − 1 g ( x , y , z ) e ( x , y , z )= e ( 0 , y , z )+ xe x ( 0 , y , z )− l x − 1 l y e − l x − 1 l z e − l x − 1 k 2 ( x , y , z ) e + l x − 1 g ( x , y , z ) e ( x , y , z )= e ( x , 0 , z )+ ye y ( x , 0 , z )− l y − 1 l y e − l y − 1 l z e − l y − 1 k 2 ( x , y , z ) e + l y − 1 g ( x , y , z ) e ( x , y , z )= e ( x , y , 0 )+ ze z ( x , y , 0 )− l z − 1 l y e − l z − 1 l z e − l z − 1 k 2 ( x , y , z ) e + l z − 1 g ( x , y , z ) e 0 ( x , y , z )= e ( 0 , y , z )+ xe x ( 0 , y , z )+ l x − 1 g ( x , y , z ) e 0 ( x , y , z )= e ( x , 0 , z )+ ye y ( x , 0 , z )+ l y − 1 g ( x , y , z ) e 0 ( x , y , z )= e ( x , y , 0 )+ ze z ( x , y , 0 )+ l z − 1 g ( x , y , z ) at the next step the partial solutions are averaged or integrated separately to find e 1 ( x , y , z ). resulting from the scattered collection of photons is a beam that spreads because of scattering in turbid media , which is analogous to a diffusion or markov process [ 6 ]. the dispersion in the atmosphere depends on the wavelength [ 7 ]. while many of the photons of the beam change polarization , some of the photons do not have polarization changes , and some have only small polarization changes . over small distances the polarization of most photons does not change very much , although some photons will have significant changes in polarization . experimental results on beam breakdown caused by aerosols at 266 nm have also been presented [ 8 ]. these types of data can be compared against longer wavelength energy loss . atmospheric propagation losses at the longer wavelength of 523 nm are known [ 9 ]. in the atmosphere , ozone and oxygen are the major absorbers [ 10 , 11 ]. radiation is scattered by molecules , according to the rayleigh scattering process [ 12 ], and by aerosols , according to general mie scattering principles [ 13 ]. in the case of the atmosphere or any fluid , the density and corresponding index of refraction time - space variability create beam spreading called optical turbulence [ 14 , 15 ]. in the atmosphere there is far more scattering for uv than for visible light . because atmospheric density decreases quickly with height , in the ideal atmosphere there is less turbulence - induced scattering for uv vertical beams than for horizontal beams . in non - storm conditions the turbulence near the ground tends to have more thermal , moisture , and terrain forcing . the atmosphere has temperature and density inversions as a function of height . these inversions create channeling ; ducting , and reflecting of signals due to density patterns . the inversions often signal pollution layers . these concentrations have their own scattering and absorption properties [ 16 - 18 ]. in addition meteorological clouds may be present . these clouds provide extra scattering properties . the density of the atmosphere decreases rapidly with height , and under ideal conditions uv for light detection and ranging ( lidar ) can propagate many kilometers in the vertical [ 19 ]. results of a uv 351 nm guidestar system working out to 20 km from the ground have been documented [ 20 ]. stand - off remote raman lidar using 266 nm light for ranges up to 60 m [ 21 ] have been documented . a study predicts the character of 200 m pulse propagation for 220 - 440 nm laser pulses [ 22 ]. non - poisson quantum fluctuations in an invariance regime can propagate farther than coherent laser speckle . in such situations the non - poissonian statistics survive over long distances [ 23 ]. lodhal shows that the spatial correlations of quantum light have “ infinite ” range and remain intact after moving through random media . the non - poisson aspects of a quantum system in having a long linear extent relative to classical beam coherence is invoked in the present invention to for authentication and increased transmission range beyond the extent of laser speckle or other coherence associated with the light source . a variation of the polarization amplitude or timing allows yuen - kumar [ 3 ] quantum communication ( qc ) as an authentication of the signal . qc in the presence of scattering has implications in quantum microdevices , such as quantum dots used for quantum computing and qc as well as in the macro environment . free - space uv qc is more stealthy than many other forms of visible light optical communication . if the uv is in the solar blind region then there are far fewer competing external noise photons from the sun . the source beam is absorbed by the atmosphere after a propagation distance and will thus be shielded from long - distance surveillance . also , because of the small natural background of uv solar blind noise photons , a smaller source strength can be used and hence lower power . the quantum encoding presents secure encryption capability . tagging a photon modeled by scatter from a random media with a polarization or an entanglement with another photon signature provides a method of communicating information by way of a scattered photon . a quantum key encryption technique according to the present invention preferably invokes yuen - kumar coherent states of different amplitudes that are linearly independent and span infinite dimensional space denoted as qumodes . in a single - mode realization , m possible coherent states | α t are represented by where α 0 2 is the observable probability as to the occurrence of the state and the angle between two neighboring states is 2π / m [ 2 ]. in a two - mode realization , for example , the prior art yuen - kumar free - space scheme is presented in fig1 , where the states are a product of two different coherent states as defined by the qumodes are optionally associated with polarization , time , or frequency . as depicted in prior art fig1 ( left ), m points uniformly distributed on a fixed great circle on the poincaré sphere are used for m / 2 possible bases . the opposite points on a diameter correspond to two orthogonal states of a basis , representing the 0 and 1 bit value for that basis . the two neighbors of each point on the circle are taken to represent a different bit value . a secret key is used to select a specific basis for each qumode between users a and b , as well as a polarity bit that is added to the data bit for randomizing the polarity of the basis . a long running key k ′ for such selection is obtained as the output from a standard encryption mechanism operating on a basic shorter key k , as depicted in fig1 ( right ). for each data bit , a total of 1 + log 2 ( m / 2 ) bits from k ′ is used to determine the polarity bit and the selection of m / 2 possible bases . yuen [ 3 , 4 ] has shown that , granting an eavesdropper e a perfect copy of the ciphered bit but without knowing the secret key , the probability of error is p e ˜ ½ , when m & gt ;& gt ; α 0 , while p e ˜ e − α 0 2 for b , since the secret key is known to b . thus even with perfect eavesdropping , that is , getting a perfect copy of the ciphered bit , e &# 39 ; s probability of making correct decisions is the same as pure guessing . in application a secret key is used to synchronize the qumode variable . preferably , the qumode variable is polarization of a light source even though , through the use of a frequency modulating crystal or a chopper , frequency or pulse time qumode variables , respective are used . it is appreciated in the case of polarization that a large number of polarization keys are available as defined by the poincaré sphere . a light source as used herein is appreciated to include both coherent sources and non - poisson statistical sources . a light source is considered a coherent ( or poisson ) light source when it satisfies at least criterion of : constant intensity , intensity fluctuation but only a small fraction of the output is used to transmit data , intensity fluctuations are rapid ( temporal incoherence ), perfect monochromaticity ( spatially and temporally coherent ), and quantum mechanically coherent state . a light source is considered an incoherent ( or non - poisson ) light source when it satisfies at least criterion of : slow intensity fluctuations , is quasi - thermal , or the light produced is from an ensemble of light source elements . a properly functioning laser operating as a poissonian light source is appreciated to be a convenient , high flux source of photons is preferred for the practice of the present invention . however , as detailed above , non - poissonian sources do afford advantages over poissonian sources in terms of longer transmission distances and signal authenitication . a communication system according to the present invention is shown in fig2 and uses an ultraviolet laser as a light source 12 in an air medium as a photonic source . a polarizer 14 receives a light source output 13 and is set to a preselected modifcation key value relative to a receiver shown generally at 20 . it is appreciated that the effective communication range is decreased by insertion of a filter into the optical intermediate between the light source 12 and a receiver 20 . an optical amplitude or phase modulator 16 receives the polarized quantum communication photonic signal 18 and creates an arbitrarily modulated quantum communication photonic signal 22 that proceeds to scatter through a light scattering medium denoted a . exemplary polarization phase modulators illustratively include liquid crystals , kerr cells , and pockel cells . preferably , a series of two liquid crystal devices and a quarter wave plate are used to achieve arbitrary polarization . a scattered portion 23 of the arbitrarily modulated quantum communication photonic signal 22 has scattered around an obstacle denoted at b . it is appreciated that the scatter that affords the non - line - of - sight capability of the present invention also limits the distance at which the arbitrarily modulated quantum communication photonic signal 22 is detectable . a receiver 20 includes an optical phase or amplitude modulator 24 of the same type as that in place in the transmitter modulator 14 , with the modulator 24 configured as a demodulator . a polarizer 26 is set to the same poincaré sphere setting as polarizer 16 and represents the shared key . the resulting signal 28 then contacts a polarization beam splitter 32 . preferably beam splitter 32 is a 50 / 50 splitter . the orthogonal signals 34 and 34 ′ are incident on photon detectors 36 and 36 ′ that count incident photon receipt and report a counting event to temporal coincidence electronics 40 as a series of zeroes and ones . photon detectors operative herein illustratively include single photon counting modules and conventional photon - intensity detectors such as charge coupled devices and gated photon counters . optionally , lenses 42 are interposed within the receiver 20 to collimate optical signals to subsequent components . it is appreciated that beam on additional splitters or filters along an optical path further facilitates signal attenuation in the event of a signal of excessive intensity . a second receiver 20 ′ is also depicted in fig2 with like components relative to receiver 20 and modulator 24 ′ and polarizer 26 ′ to illustrate the multi - cast nature of the present invention . it is appreciated that short range , non - line - of - sight quantum communication is also performed with a dual photon entangled pair carrier . as shown in fig3 , where like numerals correspond to those detailed with respect to fig2 , a type - i nonlinear crystal 60 receives an optical output 13 from light source 12 . the crystal 60 generates entangled photon pairs with near collinearity 61 . the entangled photon pairs with near collinearity 61 is scattered by medium a to generate a scattered signal 63 that scatters around an obstacle b and to a receiver , shown collectively at 80 . preferably , the crystal 60 is tuned for non - degenerative down conversion with regard to dichroic mirrors 62 and 62 ′. narrow band filters 64 and 64 ′ are used to provide shared quantum keys after optical signals are transmitted through optional lenses 42 to photon detectors 36 , 36 ′, 37 and 37 ′ before a signal is fed to electronics 40 . although the stochastic - energy - based entanglement technique is not theoretically resistant to eavesdropping on shared quantum keys , because of the possibility of cloning , in practice it is difficult to eavesdrop on because of timing constraints . this method can be used as a research model system and can be used to generate shared random keys in an environment where eavesdropping is not a threat . optionally , the insertion of poincaré sphere aligned polarizers 16 and 26 afford a secure communication system . f . m . kahnert , “ numerical methods in electromagnetic scattering theory ,” j . of quantitative spectroscopy & amp ; radiative transfer 79 - 80 ( 2003 ), 775 - 824 . g . barbosa , e . corndorf , p . kumar , h . yuen , “ quantum cryptography in free space with coherent - state light ,” proceedings spie vol . 4821 , 2002 . h . yuen , “ quantum versus classical noise cryptography ”, quantum communications and measurements ii , ed . p . kumar et al ., plenum press , 2000 . h . yuen , “ anonymous key quantum cryptography ,” quantum communications , computations , and measurements iii , ed . p . tomesi , et al ., plenum press , 2001 . j . yen , p . poirier , and m . o &# 39 ; brien , “ intentionally short - 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