Parcels of Universe or why Schr"odinger and Fourier are so relatives?

This paper is about the surprising connection between the Fourier heat equation and the Schr\"odinger wave equation. In fact, if the independent "time" variable in the heat equation is replaced by the time variable multiplied by $i=\sqrt{-1}$, the he…

Authors: Marco Frasca, Alfonso Farina

Parcels of Universe or why Schr"odinger and Fourier are so relatives?
> REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 1  This p aper is about the s urprising connection between the Fourier heat equation and the Schrödinger wave equation. In fact, if t he independent “time” variable in the heat equation is replaced by the time variable multiplied by     , the heat equation becomes t he Schrö dinger equation. T wo quite different phys ical phe nomena ar e put in clo se connection: the heat diff usion in a material and the probability a mplitude o f particles in a n atom. It is a fact of life that t he movements of a small particle f loating randoml y in a f luid, th e w ell- known Brownian motion, is regulated by the Fourier equation while the probabilistic b ehavior of the matter ar ound us, the quantum world, is dr iven b y the Schröd inger equation b ut no known stochastic proce ss seems at work here . The appar ent simplicity of the formal connection by a “time - rotation”, a Wick rotation as it is co mmonly kno wn, seems to po int otherwise. Why t his connection? I s there any physical intuitive explanation? Is there an y practical v alue ? I n this pap er, the authors atte mpt to shed some light o n the above questio ns. T he recent concept of volume q uantization in nonco mmutative geometry, due to Connes, Cha mseddine and M ukhanov, points again to stochastic pro cesses also under lying the q uantum world making Fourier and Sch rödi nger strict relatives. I. I NT RODUCTI ON In reference [ 1], it is shown that the n umbers alon g a ro w of a Tartaglia-Pascal triangle goes to fit a Gau ssian function. In t he paper [2], the authors obtain a kind of quantum Tartaglia - Pascal triangle that appears to be the “square root” of the classical one. A square ro ot could entail also imaginary values and it is here where the deep connection bet ween B rownian motion and quantum world starts. The diffusion heat (Fourier) equation is generally written in the form           where  is the di ffusion coefficient and  the prob ability distribution of the B rownian motion 1 . The Schrodinger equation is w ritten in the form               Marco Frasca is currentl y wo rking in MBDA Italia S.p .A. at Seeker Division (Rome) . Alfonso Farina was Senior VP S elex-Sistemi I ntegrati (retired), now consultant of L and&Naval Div ision of L eonardo Company (Rome). 1 I n Ref.[1] th e hea t equatio n w as written in the form where  was equivalent to our  and represe nted th e distributio n of the temperature in a body a nd  was the diffusion constant in the given b ody . In this paper,  is given by the microscopic motion of atoms colliding with a Brownian particle as devised b y Einstein [4]. where  is the wave f unction ,  the Planck constant d ivided by  and  th e m ass of the par ticle. T hese equations are formally ver y similar a nd can be transfor med i nto each other provided w e ch ange the ti me variable to    , what physicists call a W ick rotation [3 ]. This apparently innocu ous modification is i ndeed a drastic change as no w  is a complex function while  is a well-behaving real probability distribution. So, a questio n naturally arises : Where does the imaginary time co me from? The so lution of t he Fo urier equation, describi ng a probabilistic effect as the scatter ing of a small p article by the molecules of a fluid 2 , has a t ypical Gaussian for m that ar ises naturall y from the asymptotic form of the binomial co efficients, t h e Tartaglia-Pascal trian gle. As sho wn in [2], a Gaussi an probability distribu tion in a quantu m world represents a well- localized p article that, evolving i n time, loses such a precise localization, but this Gaussian pdf is the square of the wave function. Therefore , we can connect the bino mials of the Fourier equation with the square roo t of the probability distribution of a m oving free particle in a quantum world. However, this entails complex values. T his mapping 3 was proved in [2] and is the startin g point for a new view on stochastic processes and a p arceled world. So, the rather stunning conclusion is that there exists a square root of the Tartaglia -Pascal triangle, a q uantum T artaglia - Pascal trian gle (QT PT), that represents a co mpletely new complex-valued four dimensional fig ure (x, y,z,t) that lives in the realm of quantum mecha nics 4 . Our universe, as we currently understand it, has a peculiar mathematical str ucture. It is a Rie mann manifold with the Hausdorff property [5] . One can always have open sets without inter section with points inside. No patholog y whatsoever. A Rie mann m anifold is dee ply con nected to stochastic processes. In t wo dimensions, it can be always reconstructed from B rownian motion [6] . However , there is a deeper connection as shown b y Alain Connes, Ali Chamseddine and Viatc heslav Mu khanov. In esse nce a 2 Note that t he effect arises b y the averaged squared velocity of the molecule s that gives the ove rall temper ature of the fluid itsel f. 3 The mapp ing we proved states: “ There exists a discrete mapping onto the wave function that solves the Schrödinger equatio n for a free p article via the Tartaglia-Pascal triangle. Such a mapping gives complex-valued probability amplitudes wh ose squares are t he binomial c oefficients .” 4 Th e correspondence, as given i n [ 2], is b etwe en the binomial coefficient 󰇡   󰇢 and the quantum analog  󰇡   󰇢      󰇭 󰇡   󰇢              󰇮 . Parcels of Universe or why Schrödinger and Fourier are so relatives? Marco Frasca, Al fonso Farina LFellow, IEEE > REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 2 Riemann manifold ca n b e rec onstructed by two sets of small volumes [7 ]-[8]. So, motion between s uch par cels, by a particle th at is able to sense them , can be ass imilated to a Brownian motion. Where do suc h small volumes come from? T he idea comes out from the nonco mmutative geo metry uncovered by Alain Connes in the last cen tury [9]. The idea behind noncommutative geometr y can b e traced back to the de ep connection b etween algebr a and geometry as initially conceived by Descartes. It is well -known that whatever algebraic expression one consider s there is a correspo nding geometrical object of it. E.g. , the equation        represents a circle on a Cartesian plane. Neverthele ss, all this works fine because complex numbers have the proper ty to commute ea ch other. We lear ned over the last ce ntury t hat our world does not seem to agree with this pro perty at its foundations. Werner Heisenberg initially co nceived this and it is now our understanding o f the b ehavior of ele mentary particles. In th is case, we have what Paul D irac called q - numbers and m omentum  and position  do n ot comm ute yielding the famous equation      (otherwise stated 󰇟    󰇠   where 󰇟  󰇠 is the commutator) fro m which th e uncertainty principle derives. T he reason is that such q - numbers are matrices with an infinite number of eleme nts or, better stated, op erators acting on a Hilbert spac e. Why such no ncommutative b ehavior changes the behavior of particles? W e know that dyna mics can be r epresented on geometric object called phase space where both momenta a nd positions ar e taken into acco unt. Dynamics i s d escribed by a trajectory o n such a spa ce. In add ition, when energy is conserved, on a p hase space the motion happens on a given geometrical objec t like a torus or a sphere. T herefore, there is a d eep connection bet ween Newton mechanics a nd geometry in a phase space. W illiam Rowan Ha milton discovered this two ce nturies ago. Therefore, what does it make deter ministic the Newton mechanics? This comes out fro m t he commutativity of momenta and positions. Other wise , we ha ve quantum mechanics and the structure of the p hase space changes dra matically. Quantu m mechanics is the conseque nce of the noncommutative geometr y of the phase space and one has to cope with operators and Hilbert spaces that are n ot properly geometric obj ects as our intuitio n lear ned from ordinary experience. One w orks with small volumes in the quantum phase space. T he order of magnitude i s given by  . As oppo site to the co ntinuity in the classical Newtonian phase space. As sta ted above, a Riemann manifold is characterized by a metric t hat d etermines the geodesic curves 5 on it. It is a differentiable ma nifold. This me ans that the d erivative is well defined on fu nctions d efined on the ma nifold. We can make a correspondence between the points on a Riemann m anifold and an algebra of functions defined on it that w e can call maps. These fu nctions can re present the manifold itself as the geometric concept of a point d oes. Stated in a simpler way, we 5 A geode sic cu rve is a generalization of the concept of “straight line” of the Euclidean sp ace to curved s paces as the shortest path joining two points. are moving fro m a picto rial representation to its algebraic elements as for the phase spac e we move fro m the geometrical structure of the motion like an orbit to functions rep resenting it like coordinates and momenta. W hen one moves from such functions to oper ators (or q -numbers a la Dirac as Heisenberg did) one gets a nonco mmutative Riemann manifold. Connes, Cha mseddine and Mukhanov proved that such a noncommutative ma nifold comes out made by t wo kinds o f elementary volumes and it is from here that the d eep connection w ith stochastic proce sses starts. This m eans t hat the relation bet ween Fourier and Schr ödinger eq uations , formally given b y a Wick rotation, has a deep physical meaning. Mathematicall y, it entail s the introd uction of a new class of stoc hastic processes: the fractional powers of a Wiener process [10]. In summary, the relat ion bet ween t he Fourier and the Schrödinger equations, thro ugh a Wic k ro tation, is not merely a mathematical curiosit y but rather has deep physic al implications a s the w orld is struct ured as a nonco mmutative Riemann manifold on which the particles, able to feel its quantization, perfor m B rownian motion with a pro cess equation, which is exactly t he Schrödinger eq uation. T his means t hat the analo gy between these famous eq uations rel ies on the kind of atoms one co nsiders: For Fourier, it is the matter being parceled while for Schrödinger, it is the space being made by ele mentary volumes ac ting like t he atoms in the matter. Ho wever , geometry is con tinuous in the for mer and discretized in the latter . Conse quently, in a lattice world, if one moves randomly between the sites of the la ttice, one obtains the so lution to the Fourier equation. In a quantum wor ld, represented - for instance - by a quantum T artaglia -Pascal triangle [2] , one has that the space on which the particle moves is discretized and so, moving o n such a space yields t he solution to the Schrödinger e quation. The quantum Tartaglia triangle is, in a se nse, the square r oot of the classical o ne [2] and this is the root o f the “i” factor 4 . In the re maining part of the p aper, we will d iscuss this deep connection showin g how the emerg ence o f a quantum w orld comes out from a quantized space. II. T HE WO RLD IN PA RCELS As sho wn b y Cha mseddine i n [11], we ca n always define a set of functions           to cover a volume with the condition 󰇛  󰇜   󰇛  󰇜     󰇛  󰇜    . These r epresent spheres i n    dimensions. We c an co ver t he volume o f a given manifold with such spher es so that the y beco mes a wa y to “measure” t he manifold itself . Ho wever, unfortunatel y, we will find holes e verywhere in our covering notwithstanding the manifold w e started with was simply connected. Therefore, w e ca nnot cl aim we are able to fully recover the original manifold fro m smaller volumes. In o rder to overcome t his di fficulty, le t us return to the case of quantum mechanics. As we stated above, in this case , we are studying t he motion of a particle in a particular m anifo ld > REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 3 represented through the coordinates 󰇛  󰇜 w ith  being the position and  the momentum and this ea sily generalize s to the  dim ensional case. This is wh at physicists call phase space . W illiam Rowan Ha milton intr oduced this co ncept earlier in the XIX century b y reformulating Ne wton eq uations of motion in this way [12]. Fig. 1 . A par celed manifold 6 . Furthermore, Heisenberg noticed that the coord inates in phase space do not co mmute at all and the reason of t he no n- commutation must be attr ibuted to the existence of the Planck constant  [1 3]-[14]. T his is generally stated in the form 󰇟    󰇠   . So, one can ask if there exists a solution to this equation in such a way to formulate t he d ynamics of a particle that moves on suc h noncom mutative pha se space. T oday, we know the answer is affirmative, provided  and  are not ordinary c(omplex) -numbers but rat her q (uantum) -numbers that is, sel f-adjoint operators that act on a Hilbert space o f functions. So, we ha ve a so- called “triple”, in the nomenclature due to Alain C onnes, for med by an al gebra of operators, a Hilbert space of functions on which they ac t upon and we ca n postulate a spectral (Dirac) operator to measure distances i n such a noncommutative phase space that acts o n the functions i n the Hilbert sp ace. T o define the Dirac operato r one could use e.g. the Schrödinger equation that determines the way a particle m oves ar ound se nsing dista nces. We see that we ha ve built a geometr y without recurring to any ordinary concept of p oint, geodesic and similar but our definition o f a nonco mmutative pha se sp ace, a geo metric concept anywa y, is purely a lgebraic i n a per fect Cartesian spirit. 6 This figure was inspired b y a talk given by Al ain Connes in Castiglioncell o (Italy) o n 2014. What are the co nsequence s of ha ving such a nonco mmutative structure for the phase space? So, let us consider a particle of unitary mass moving under the ef fect of an ela stic spri ng. It is everyday experience that such a particle undergoes oscilla tor motion. T his is true if t he p hase space is a standard geo metric object. In such a case, the manifold on which the particle moves in phase space ha s the form o f an el lipsoid , degenerating to a n e llipse in t w o dimensions, g eometricall y characterized by the ener gy available to the p article. The effect of the Heisenberg commutation relation changes this dramatically as we get a fully quantized m anifold in small volumes having a well-defined magnitude. This is standard material in quantu m mechanics textbooks (e. g. see [15] ). Specifically, if the a vailable ener gy is  , we will have a number of quanta  propor tional to it a nd eac h quantum is measured by the pro duct of  multiplied by the pulsation  of the oscillatio n of the clas sical particle. Then, we can e valuate the volume o f the quantized ellipsoid that in this simple case is just given b y  , being     and       its semi-axes. Now, using energy quantization, the volume of the noncommutative manifold will be 2  󰇛  󰇜 and the phase space is q uantized i n small volumes ea ch o ne o f dimension propor tional to the Planck constant. T urning b ack to the Chamsedd ine’s exa mple, one can always try to co ver a given manifo ld with small volumes usi ng spheres but t he covering will always be unsatis factory. However, looking at quantum mechanics, we see that t he Heisenberg quantization conditi on gra nts us that a p erfect covering of a noncommutative manifold can be o btained. So, Chamseddine’s example can be made at work moving t o a noncommutative manifold. But, wh at should the quantizati on condition b e i n t his ca se? To understand t his, let us co nsider the case of a circle of radius 1. In this case, we can cover the circle with phase changes     and we can choose an arbitrary angle to ob tain the co vering with even smaller angles. A dista nce could be given b y  󰇛    󰇜        󰆒     sin 󰇡  󰆒  󰇢 . Now, i f  is the derivative with re spect to the angle and promote the angle to a position op erator, it is not difficult to observe that   󰇟    󰇠   ap pears to be fully analogous to t he Hei senberg quantization condition u se d above. T he q uantum prob lem informs us t hat the solution has a spectrum o f integers for  . If we try to extend thi s to a generic one-di mensional Riemann mani fold  , for  unitar y as for t he circle, t he q uantization conditio n   󰇟    󰇠   will give a so lution for  provided the length of the manifold satisfies      , that is the Riema nn manifold is quantized exactly as happened for the oscillator manifold. We have again a triple made b y an operator algebra, a Hilbert sp ace and a “Dirac” oper ator describing it. No w, we are cover ing a noncommutative manifold and the problem with an o rdinary manifold applies no more. These ideas ca n be generalized to arbitrar y di mensions and what Connes, Chamsed dine and Muk hanov proved w as that the quantization co ndition that w e have introd uced w ith the example of the circle can be consistentl y ap plied in 4 > REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 4 dimensions. This permits the introduction of a fundamental experimental fact ob served in nature: For each particle seen in nature, there is it s anti -particle [1 6]. T his fact is widely known as the matter-a ntimatter parad igm. However, for sure, the Universe would not exist the way we know and are ab le to observe without this double nature of the matter. T o descr ibe this, one h as to introduce complex numbers. The effect of complex conjugation and time reversal moves the descriptio n from matter to anti-matter. T his has a dee p geo metrical origin as shown in noncommutative geo metry, as we need to consider a complex Riemann manifold to fit m atter and anti - matter in place. T his implies t hat a noncommutative Riemann manifold splits up in two kind s of a large number of parcels making up its volume as dep icted in Fig. 1. We assu me that these can be distributed in a r andom way because all the configurations are ad missible for the build ing of the manifold yielding a n identical result for the volume . So, we will be a ble to o btain a nonco mmutative Riemann manifold b ack pro vided we co nsider small parcels with volu me 1 an d  , the two fundamental unities in the world of mathematics. III. M OVING AROUND T HE PARCELS We can i magine that, for a p article with a given ener gy, moving on a manifold like that in Fig.1 means perfor ming a kind o f B rownian motion. Indeed, we ca n get a set of equivalent m anifolds, each one with the same volumes but with the parcels differentl y dispo sed. Fig. 2. Brow nian motion on a parce led manifold. To understand what is going on, w e extend the case of t he circle in the pr eceding section to the sphere. I n this case we have to introduce two d ifferent op erators   and   in f ull analogy with the case o f the circle o f the p receding section . We would like also to have a manifold t hat co uld be quantized consistently. This is generall y p ossible only i f one makes use of a Clifford algebra [ 16] . A Clifford algebra is a trick y way to take t he square root of the wave equation. T his wa s uncovered by Paul Dirac that in this way obtai ned the correct equation to d escribe the electro n and a p rope r generalization of the Sc hrödinger equatio n that co uld accou nt for t he relativity d iscovered by Albert Einstein [17]. The Dirac equation is essential in noncommutative geometr y to measure distances. Consider the wave equatio n on the surface o f the sphere o f radius 1. T his can be written as:           󰇛 󰇜        . Taking t he square root means t hat we have to use the nab la o perator  and w e do this by i ntroducing three new o bjects   ,   and   to be defined below. Then, let us consider the ne w (Dirac) operato r built as             where we have set    󰇛     󰇜 . One gets, taking the square   , that t he wave equatio n is full y recovered provided σs have the properties              and            w hen    . T his is what we call a Clifford algebra and the lower non-t ri vial di mensionality for the σ are 2x2 matrices firstly i ntroduced by Wolfgang P auli to describ e the spin of particles [ 18]. G iven this C lifford algeb ra of σ matrices , we ca n build a quantized manifold by considering the map                  ob tained by a nalogy from the square ro ot of the wave eq uation and the case o f t he circle in the preceding sectio n . Here we have introd uced a new Clifford al gebra, the same as above, but indep endent of it as this applies now to the “coor dinates”   ,   and   . This is the rea son why we called t hese matrices γ rather than σ . T hen, as Connes, Mu khanov and Ch amseddine proved, a manifold gets q uantized with respect to the conjugate operator  provided the Heisenberg-like quantization conditi on  󰇛 󰇟  󰇠 󰇟   󰇠󰇟   󰇠󰇜 =   σ holds, b eing    and σ a 2x2 matrix [7] -[8]. T he trace is over the γ matrices . T his quantization condition , which we have seen to arise natura lly from the ca se of the circle of the p receding sect ion , represent s a generalization o f the well -known Heisenberg condition 󰇟    󰇠   we discussed in the introduction for quantu m mechanics and the phase sp ace. The triple product o f 󰇟   󰇠 is due to the d imensionality of the manifold we are now considering. What Connes, M ukhanov a nd Chamsedd ine sho w is that this quantizatio n condit ion admits a solution, i.e.   ,   and   exist, i f and only if the volume is quantized. This is true given t wo kinds of small volumes (parcels): One has volume 1 and the other volu me i . The question i s how will a particle move on such a manifold? What will its eq uation of motion be? T he answer was given in a recent paper by o ne of t he authors [19] . To understand this, it is i mportant to notice th at this n oncommutative man ifold will have randoml y d istributed parcels that make it as, whatever co nfiguration we will choo se, t he volu me of the manifold will remai n the sa me. This situation is reall y si milar to the Brownian motion o f a particle in a fluid wh ose theory was put forward by Albert Einstein i n 190 5 [ 4]. He showed that the motion of a p article, under the effect o f t he scattering of the molecule s co mposing t he fluid, is r uled by t he Fourier heat eq uation. T his means tha t this is a stocha stic process with > REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 5 a given pro bability di stribution functio n. In o ur case, there is something different as the m otion of the particle, although random as well, can hit b oth rea l and complex valued volumes randomly. This i mplies that o ur stochastic process cannot be a real one but, rather, a co mplex valued stochastic pro cess. In order to have a stoc hastic pro cess producing t he values 1 and i , we start with a Bernoulli process B that describes the tossing o f a coin, yielding a rando m sequence with +1 and -1. From this we can introd uce the p rocess         that will yield a si milar sequence with 1 and i . It is not dif ficult to observe that     . Then, the par ticle will move arou nd the maps Y tha t m ake the ma nifold and these are me mbers o f a Clifford algebra as we have seen. T herefore, this is a Wiener process but also means that the Bernoulli process B is n ot independent but will originate from the signs of the s ingle Brownian steps. Using the typical notation of stochastic calculus, where steps are written like differe ntials, the case o f our sphere will take a form l ike (see [19 ])   󰇟  󰇛             󰇜     󰇛             󰇜      󰇛        󰇜 󰇠 where the condition     must be understood and a, b, c , e, f, g and k, m a re numbers . W e used index es on the various Berno ulli pro cesses to distinguish their contributions on t he differe nt maps as shown in [10] and [19]; we are j ust extracting the s quare root of a W iener p rocess. This entails t he use o f a Cliffor d algeb ra ( the Dirac’s trick) as happened for the wave eq uation. So, summing everything up, we have seen th at a Riemann manifold can be quantized if it is noncommutative and, to accommodate the matter-antimatter paradig m experimentally, this quantization has parcels of unitary volu mes 1 and i . Moving on it entails a complex stoc hastic process that i s nothing else than the square roo t of the well-kno wn Bro wnian motion (see Fig. 2) . Now, we should as k what is the equivalent o f the Fourier heat equation for t his case as t his i s a characteristic of whatever stochastic process. The s urprising answer is that now, for a co mplex stoc hastic process, we ha ve a complex Fourier equation. T he magic happened and we are back to Schrödinger. IV. T HE SURPRI SING RELATION BETW EEN THE S CHRÖDI NGER AND F OURIER EQUATI ONS From the discussion given above it appea rs that t he Schrödinger equatio n is a Fourier equation in disg uise. They both represent a stochastic process es but one has to move from real sto chastic p rocesses to complex ones. Anyhow, the relation is deeper as one ari ses ta king a formal square root of the oth er. In the end, one has a diffusion equation for the random proce ss but, in a q uantum world, the equi valent of the probability distribution function is not real and one has to struggle working with m odulus square of w hat is commonly called a wave function that is now the p robability distribution function to consider for nat ural proce sses. This can be put at test very ea sily with a numerical computation. We compute a Brownian m otion and take its square root. The former has a histogra m rec overing the Fourier kernel, a Gaussia n distribution. We can Wick rotate the numerical data of the sq uare roo t yielding a Ga ussian curve agai n, the Wic k-rotated Schrödinger kernel, as e xpected by our co nnection [ 19]. T he result i s given i n Fig. 3 and is in excellent agreement with expectations. Fig.3. Compariso n between the Fourier ker nel of a Bro wnian motion and the Wick-rotated Schrödinger kernel of its square root. So, the formal change of the ti me variab le    , introduced by W ick, hides a deep physical fact: The ordinar y B rownian motion described by the Fourier equation changes into the motion on a par celed universe, w here matter a nd antimat ter exist, particles spin and th e Sch rödinger equation describes what is going on. But now, w e are w orking with complex quantities w hose only the modulus square can m ake s ense. Fig. 4 depicts this rel ation b etween Fourier and Schrö dinger equations and related physical conseque nces. Fig. 4. How Fourier and Schrödinger speak each other and Wick invented a communication w ay . V. C ONCLUSION S We have seen how a simple formal r elation between two famous equations entails a deep m athematical concept with new stochastic p rocesses underl ying it. A new mathematical technique also forecasts a wealth of possible app lications. > REPLACE THIS LINE W ITH YOUR P APER IDENTIFICAT ION NUMBER (DOUB LE -CLICK HERE T O EDIT) < 6 Indeed, this paper may benefit modern ap plications of quantum mechanics to en gineering i n co mmunication a nd sensing. Namel y, quantum co mmunications thro ugh entangled states [2 0], that are solutio ns o f the Sc hrödinger eq uation we derived, f rom a new clas s of co mplex stochastic processes, and quantu m radars [21] that can b enefit fro m quantum illumination [22] -[23] . Entangled states are particular solution of the Schrödinger equation w ith two or more particles li ke photons. Represent ing them through stochast ic process es could m ake eas ier their use in designing devices that employ such states. Stochastic proce sses l ike the ones that are disc ussed here can be easily si mulated digitally or through so me analogic device using discrete components. I n this vie w, filtering can witness new avenues of applicatio ns. In general, there co uld be a lot of possible new applic ations wherever a new class o f stochastic processes is uncovered. This, in view, is our hope for the future for this exciting mathematical achieve ment we have got from a world so distant from our common sense. R EFERENCES [1] A. Farina, S. Giompapa, A. Graziano, A . Liburdi, M. Ravanelli, F. Zirilli, “Tartaglia and Pascal triangle: a historical perspective with ap plications; fro m probability to modern physics, signal pro cessing, a nd finance”, S ignal, Image an d Video Processing, vol. 7 , Issue 1, pp. 173- 188 , 2013. [2] A. Farina, M. Frasca & M. Sedehi, “ Solving Schrödinger equation via Tartaglia/Pascal triangle: a possible link between stochastic pro cessing and quantum mechanics”, Signal, Imag e and Video Processing, vol. 8 , pp. 27 - 37, 201 4. [3] G. C. W ick, "P roperties of B ethe-Salpeter Wave Functions", P hysical Review, vol. 96, pp. 11 24 – 1134, 1954 . [4] A. Einstein, "Über die von der molekularkinetischen Theorie d er Wärme geford erte B ewegung von in ruhenden Flüssigkeiten suspendierte n Teilchen", Annalen der Ph ysik (in Ger man), vol. 3 22, pp. 549 – 560, 1905. [5] S.W . Hawking, G.F.R. Elli s, “The la rge scale structu re of the univers e”, Cambridge University P ress,1975 . [6] M. Frasca, “Two -di mensional Ricci flow a s a sto chastic process”, arXiv:0901.4703 [ math - ph ], 2009 , unpublished. [7] A. H. Chamseddine, A. Connes and V. Mu khanov, “Quanta of Geo metry: noncommutative aspects”, Physical Review Letter s, vol. 1 14, 091302 , 2015. [8] A. H. Chamseddine, A. Connes and V. Mukhanov, “Geometry and the quantum: basics”, J. High Energ. Phys. 2014: 9 8, 2014. [9] A. Connes, “Noncommu tative geo metry”, Acade mic Press, 1994 . [10] M. Frasca, A. Far ina, “Numer ical proof of existe nce of fractional powers of Wie ner processes”, Sign al, Image and Video Proce ssing, vol. 1 1, pp. 1365-137 0, 2017. [11] A. H. Ch amsedd ine, “Quanta of geo metry a nd unification”, Mo d. Phys. Lett. A, vol. 31, 1630046 , 2016 . [12] W.R. Ha milton, Phil. T rans. R. Soc. Lond. , vol. 124, 247 - 308 , 1834; ib. vol. 125, 95- 144 , 1835 . [13] W. Heisenberg, “ Über quantentheoretische U mdeutung kinematischer und mechanisc her B eziehungen ”, Zeitschrift für Physik, vol. 33, 87 9-893, 1925 . [14] M. Born, W. Heisenberg, P. Z. Jordan, “Zur Quantenmechanik.II.”, Zeitschrift für Physik, vol. 35, 557 -615 (1926). [15] S. W einberg, “Lectu res on Quan tum Mechanics”, Cambridge University P ress, 2015 . [16] S. Weinber g, “ The Qu antum Theo ry of Field s ”, Vol.I, Cambridge University P ress, 1995. [17] P.A.M. Dirac, “The quantum theory of t he electron”, Proc. R. S oc. Lond. A 1928 117 610-624; DOI: 10.1098/rspa.19 28.0023. [18] W. Pauli, “Zur Quanten mechanik des magnetischen Elektrons”, Zeitschri ft für Physik 4 3, 601 (1927). [19] M. Frasca, “Nonco mmutative geometry and stoc hastic processes” in F. Nielsen and F.Barb aresco (eds), Geometric Science o f I nformation. GSI 2017 . Lect ure Notes in Co mputer Science, vo l 10589. Springer Cham. [20] C.Q. Choi, “Unhackable qu antum networks take to space”, IEEE Sp ectrum 54, Issue 8, 12 (2017). [21] M. Lanzagorta, “Quantum Radar (Synthesis Lectures on Quantu m Computi ng)”, Morgan & Cla ypool Publishers, 2011. [22] S. L loyd, “ Enhanced Sensitiv ity of P hotodetection via Quantum Illumination ”, Science 321, 1463 (2008). [23] Si -Hui T an, B. I. Erk men, V. Giovannetti, S. Guha, S. Lloyd, L. Maccone, S. P irandola, and J . H. Sh apiro, “Quantum Ill umination with Gaussian Sta tes”, Phys. Rev. Le tt. 10 1, 253601 (2008). Marco Frasca is curr ently e mployed at MBDA Italia S.p.A. working on signal p rocessing and se nsing. He is a lso a theoretical p hysicist with more than 80 publicatio ns on refereed jo urnals. Alfonso Fa rina in 1974, h e j oined Selenia, then Selex ES, where he beca me Director of the Analysis of I ntegrated Systems Unit a nd subseq uently Director of Engineeri ng of t he Large B usiness S ystems Division. In 2 012, he was Senior VP and Chief T echnology O fficer o f the Compan y, reporting di rectly to the Pr esident. He retired in October 2014. From 1979 to 1985, he was also professor o f “Radar T echniques” at the University o f Naple s (I T). Today, He is a Visiting Professor at University College Lon don (UCL), De pt. Electronic and Electrical Engineering. He is a Disti nguished Lecturer of IEEE AESS and I EEE SPS Distinguished Indu stry Speaker. He is a consultant to Leonard o S.p.A. “Land & Naval Defence Electronics Division” ( Rome). He is a Me mber of the Editorial Bo ard of IEEE SP Magazine.

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