W e descri be a new scheme for perf ormin g quan tum key distributi on .W e present tw o physica l implementations for the quantum key distribu tio n system.T he Ùrst implementation uses a typ e-I I optical-parametri c ampliÙer to generate the optical pulses w hich contain the key inf ormation.T he second implementation uses correlated semicondu ctor emitters to generate the optical pulses.PAC S numb ers: 03.67.Dd , 03. 67.H k, 42.50.D v, 42.50.Lc 1 .I n t r o d u ct i on : qu an t u m st at es p r o vi d e secu r i t y Let us consider the fol l owing scenari o: one p erson (Al i ce) wa nts to send a secret m essage to a second p erson ( Bo b).At the sam e ti me, an eavesdropp er (Eve) i s attem pti ng to obta i n the secret m essage.Al i ce and Bo b can use a One-Ti me Pa d crypto gra phi c pro to col in order to securely tra nsm i t thei r secret m essage.Thi s pro to col consists of Al i ce and Bo b ha vi ng a shared secret key pri or to the sending of the secret m essage.The key wi ll consi st of a stri ng of ra ndo m bi nary da ta .The key i s used to encode the secret m essage by a sim pl e bi nary addi ti on of the secret m essage wi th the key .The encoded secret message can then b e tra nsm i tted over a publ i c channel (i .e. a channel whi ch can b e seen by any one i ncl udi ng Eve).As l ong as the key data i s shared by onl y Al i ce and Bo b and the key i s onl y used once, i t i s pro vabl y i m p ossibl e for Eve to decode the encoded m essage.Thi s wo ul d app ear to b e a very p owerful techni que for sending secret messages.The catch i s tha t i t i s ha rd to create and di stri bute a key tha t i s shared by Al i ce and Bo b but al so rem ai ns secret after the di stri buti on pro cedure.Presum -Ê corr esp on din g au t h o r; e-m ail : ray me r@ore gon .uor ego n. edu (4 37)
W e descri be a new scheme for perf ormin g quan tum key distributi on .W e present tw o physica l implementations for the quantum key distribu tio n system.T he Ùrst implementation uses a typ e-I I optical-parametri c ampliÙer to generate the optical pulses w hich contain the key inf ormation.T he second implementation uses correlated semicondu ctor emitters to generate the optical pulses.PAC S numb ers: 03.67.Dd , 03. 67.H k, 42.50.D v, 42.50.Lc 1 .I n t r o d u ct i on : qu an t u m st at es p r o vi d e secu r i t y Let us consider the fol l owing scenari o: one p erson (Al i ce) wa nts to send a secret m essage to a second p erson ( Bo b).At the sam e ti me, an eavesdropp er (Eve) i s attem pti ng to obta i n the secret m essage.Al i ce and Bo b can use a One-Ti me Pa d crypto gra phi c pro to col in order to securely tra nsm i t thei r secret m essage.Thi s pro to col consists of Al i ce and Bo b ha vi ng a shared secret key pri or to the sending of the secret m essage.The key wi ll consi st of a stri ng of ra ndo m bi nary da ta .The key i s used to encode the secret m essage by a sim pl e bi nary addi ti on of the secret m essage wi th the key .The encoded secret message can then b e tra nsm i tted over a publ i c channel (i .e. a channel whi ch can b e seen by any one i ncl udi ng Eve).As l ong as the key data i s shared by onl y Al i ce and Bo b and the key i s onl y used once, i t i s pro vabl y i m p ossibl e for Eve to decode the encoded m essage.Thi s wo ul d app ear to b e a very p owerful techni que for sending secret messages.The catch i s tha t i t i s ha rd to create and di stri bute a key tha t i s shared by Al i ce and Bo b but al so rem ai ns secret after the di stri buti on pro cedure.Presum -Ê corr esp on din g au t h o r; e-m ail : ray me r@ore gon .uor ego n. edu (4 37)
R em ar k s on En tan gle m en t , its Sou r ces an d A p p lic ation s M .`uk ow sk i I n st yt ut F izy ki T eorety cznej i Astro Ùzyki , Uni wersytet G da¥ski W i ta Stw osza 57, 80-952 G da ¥sk, Po l and and Insti tut f ur Ex peri m enta l physi k, Uni versi t at Inns bruck, 6020 Innsbruck, Austri a W e shall discuss the cent ral r ole pla yed in the quantu m information theory by entan glement .A generali zed version of Bell ' s theorem w ill be presented , as well as metho ds in multiphoton interf erometry to obtain correlations violatin g the Bell inequali tie s.Finally , w e shall present some quantum inf ormationa l applicati on s of entanglement.PAC S numb ers: 03.65.U d, 03.67.{a, 42.50.A r 1.I n t r o d u ct io n Current adv ances i n the op erati ona l contro l of qua ntum pheno m ena enabl e us to use the para do xi cal aspects of the qua ntum wo rl d as sources of pra cti cal appl i cati ons.The mai n areas i n whi ch qua ntum pheno m ena can b e harnessed to p erform ta sks im p ossibl e for classical theo ry of i nf orm ati on are qua ntum crypto gra phy (a l ready a rel i abl e techno l ogy), qua ntum com muni cati on (a t the sta ge of bi rth, e.g. the tel eporta ti on exp eri ments) and qua ntum com puta ti on (stunni ng theo reti cal resul ts, brea ki ng the l i m its of the T uri ng -t yp e machines, but sti l l far away fro m op erati onal real i zati ons).The basic no ti on i n the qua ntum i nform a ti on theo ry i s tha t of the qua ntum bi t or the qubi t.Cl a ssical bi ts can ta ke one of the two p ossibl e values 0 or 1 ( \ on " or \ o˜" , etc.).The qubi ts (the simpl est quantum system s wi th pure sta tes descri bed by a two -dim ensional Hi l b ert space, e.g.spins 1/ 2), since they are qua ntum enti ti es, they can b e in an arbi tra ry sup erp ositi on of two ba sis states j 0 i and j 1 i : j q u bi t i = ˜j 0 i + Ù j 1 i :(1 ) (2 1)
Facul t y of P hy si cs, A da m Mi cki ewi cz Uni versi ty Um ultowsk a 85, 61-61 4 Po zna¥, Pol and ( Recei ved A ugust 18, 2 003) A proto col for t elep ort i ng t w o qudit s simult aneousl y in opposite directions using a single pair of ma ximall y entangled qudits is presented .T his pro cedure w or ks pro vided that the pro duct of dimensi ons d 1 and d 2 of the tw o qudits to be telep orted do es not exceed the dimension d of the indiv id ual qudits in the maximall y entangled pair.PAC S numb ers: 03.67.{a
of Col or ado and Na ti onal Insti t ute of Standa rds and T echno lo gy Bo ul der, Col ora do 80 309-0440, U. S.A. and M. Chi of al o Scuol a No r mal e Superi ore, Pi azza dei Caval i eri 7, 56126 Pi sa, Ita l y W e consi der t he sup erÛuid ph ase transition that arises when a F eshbach resonance pairin g occurs in a dilute F ermi gas.T his is related to the phenomenon of sup ercondu cti v it y describ ed by the seminal Bardeen { Coop er{ Schrie ˜er theory .In supercondu ctivi ty , the phase transition is caused by a couplin g betw een pairs of electrons w ithin the medium.T his coupli ng is perturbative and leads to a critical temp erature T c w hich is small compared to the Fermi temp erature T F .Even high-T c sup erconductors typically ha ve a critical temp erature which is two orders of magnitude below T F .H ere w e describ e a resonance pairing mechanism in a quantum degenerate gas of potassium ( 4 0 K ) atoms w hich leads to sup erÛui di ty in a no vel regime | a regime that promises the unique opp ortunity to exp erimentally study the cross-over from the Bardeen À C oop er{Schrie˜er phase of w eakly-coupled fermions to the Bose{Einstei n condensate of strongly-boun d comp osite bosons.W e Ùnd that the transitio n to a superÛuid phase is possible at the high critical temp erature of about 0 :5 T F .I t should b e straightf orw ard to verif y this prediction, since these temp eratures can already be achieved exp erimentally .
Quantum Cryptography A. Ekert Quantum Communications with Optical Fibers N. Gisin, S. Iblisdir, W. Tittel, and H. Zbinden Advanced Quantum Communications Experiments with Entangled Photons M. Aspelmeyer, H. R. B.. ohm, A. Fedrizzi, S. Gasparoni, M. Lindenthal, G. Molina-Terriza, A. Poppe, K. Resch, R. Ursin, P. Walther, A. Zeilinger, and T. Jennewein The DARPA Quantum Network C. Elliott Experimental Cryptography Using Continuous Polarization States S. Lorenz, N. Lutkenhaus, G. Leuchs, and N. Korolkova Quantum Logic Using Linear Optics J.D. Franson, B.C. Jacobs, and T.B. Pittman Practical Quantum Cryptography: Secrecy Capacity and Privacy Amplification G. Gilbert, M. Hamrick, and F.J. Thayer Quantum State Sharing T. Symul, A.M. Lance, W.P. Bowen, P.K. Lam, B.C. Sanders, and T.C. Ralph Free-Space Quantum Cryptography C. Kurtsiefer, M. Halder, H. Weinfurter, P. Zarda, P.R. Tapster, P.M. Gorman, and J.G. Rarity Noise-Immune Quantum Key Distribution Z.D. Walton, A.V. Sergienko, B.E.A. Saleh, and M.C. Teich Index