News › Fraun­ho­fer IOF · First suc­cessful exch­ange of quan­tum keys bet­ween Erfurt and Jena via opti­cal fiber

The Thu­rin­gian Minis­try of Sci­ence has fun­ded the deve­lo­p­ment of an infra­struc­ture for quan­tum com­mu­ni­ca­tion net­works in the Free State with ele­ven mil­lion euros. This includes a fiber-based test route bet­ween Jena and Erfurt. Now, part­ners from the Fraun­ho­fer Insti­tute for Applied Optics and Pre­cis­ion Engi­nee­ring IOF have suc­cessfully exch­an­ged quan­tum keys on the 75-km route for the first time.

It is a mile­stone for rese­arch into high-secu­rity quan­tum com­mu­ni­ca­tion in Thu­rin­gia and Ger­many: for the first time, quan­tum keys have been suc­cessfully exch­an­ged over a distance of 75 km via opti­cal fiber on a test route bet­ween Jena and Erfurt. More than 300,000 quan­tum keys were sent bet­ween the Thu­rin­gian cities over a test period of ten days.

The test route, fun­ded by the state, had alre­ady been com­ple­ted in the spring of this year. It con­nects the Fraun­ho­fer IOF in Jena with the Fraun­ho­fer Cen­ter for Microelec­tro­nic and Opti­cal Sys­tems for Bio­me­di­cine (MEOS) in Erfurt. It has now been suc­cessfully put into ope­ra­tion with the latest test runs.

Thu­rin­gia to become a quan­tum hub

Thuringia’s Minis­ter of Eco­no­mics, Wolf­gang Tie­fen­see, is deligh­ted with the com­mis­sio­ning: »Thu­rin­gia is one of the lea­ding loca­ti­ons in the field of quan­tum com­mu­ni­ca­tion. As a state, we have been inves­t­ing spe­ci­fi­cally in the expan­sion of these com­pe­ten­cies for years. The test track is ano­ther important and very con­crete step in this direc­tion. It will become the start­ing point for a secure quan­tum com­mu­ni­ca­ti­ons infra­struc­ture throug­hout Ger­many. Thu­rin­gia, with its rese­arch insti­tu­ti­ons and com­pa­nies, will form a cen­tral hub in this.«

The spe­cial added value of the test track is that it takes highly com­plex quan­tum key dis­tri­bu­tion (QKD) tech­no­lo­gies out of the labo­ra­tory and embeds them in a real, ever­y­day infra­struc­ture. Accor­din­gly, the test track uses con­ven­tio­nal opti­cal fiber, for exam­ple, as is alre­ady used today in IT networks.
and could thus form the basis for the wide­spread imple­men­ta­tion of quan­tum sys­tems in the future. Also, about 6 km of the test rou­tes run above ground, allo­wing sce­na­rios of alre­ady exis­ting net­works to be mimicked.

»For quan­tum net­works of the future, it is important to test novel sys­tems in real infra­struc­tures,« explains Prof. Dr. Andreas Tün­ner­mann, direc­tor of Fraun­ho­fer IOF. »In this con­text, our test track should expli­citly be acces­si­ble to part­ners from indus­try and com­merce. As Fraun­ho­fer IOF, we want to be an ›enabler‹ that enables entre­pre­neurs to test and opti­mize their own sys­tems for quan­tum com­mu­ni­ca­tion in prac­ti­cal ever­y­day scenarios.«
Visua­liza­tion of the quan­tum fiber test track bet­ween Erfurt and Jena.

First suc­cessful quan­tum key exchange

The first com­pany that has now suc­cessfully exch­an­ged quan­tum keys on the fiber test track with the sup­port of Fraun­ho­fer IOF is Quan­tum Optics Jena GmbH. In 2020, the young start-up had spun off from the Fraun­ho­fer Insti­tute and has since been deve­lo­ping plug-in solu­ti­ons for quan­tum com­mu­ni­ca­tion. »We are hugely exci­ted about the suc­cessful test run,« says Dr. Kevin Füch­sel, CEO of Quan­tum Optics Jena. »But we are also gra­teful to Fraun­ho­fer IOF for the oppor­tu­nity to test our sys­tem under ever­y­day con­di­ti­ons. In this way, we jointly pro­mote a trans­fer of sci­ence into indus­try and the prac­ti­cal ever­y­day life of users.«

For the col­le­agues from Quan­tum Optics Jena, the first test on the test track imme­dia­tely yiel­ded exci­ting results: »We see that the sys­tem works dif­fer­ently in the real field than in the labo­ra­tory,« Füch­sel con­ti­nues. »In the lab, we trans­mit at about 300 bits per second with com­pa­ra­ble los­ses. That gives us one encryp­tion key per second. In the field, we’re at about 200 bits, so a little less. A key is 256 bits long and can the­r­e­fore be rene­wed almost every second for cryp­to­gra­phic pro­tec­tion, i.e. encryp­tion and decryp­tion, of the trans­mit­ted infor­ma­tion. It is pre­cis­ely this fast, tap-proof and auto­ma­ted key rene­wal that distin­gu­is­hes quan­tum key dis­tri­bu­tion from estab­lished methods.«

Quan­tum Optics Jena is plan­ning a second test run in the near future to fur­ther deepen the results obtai­ned from the first test run and to fur­ther deve­lop its solutions.
Quan­tum Optics Jena GmbH during quan­tum key exchange.

Expan­sion of the route toward Sax­ony and Bava­ria planned

»So far, our test track offers a two-node con­nec­tion bet­ween Erfurt and Jena,« insti­tute direc­tor Tün­ner­mann dis­cus­ses the cur­rent loca­ti­ons. But there are alre­ady plans for the future: »We hope to expand our test track even fur­ther and estab­lish a net­work in the direc­tion of Sax­ony and Bavaria.«

The fiber track was crea­ted as part of the Thu­rin­gian Minis­try of Science’s fun­ding for quan­tum appli­ca­tion labo­ra­to­ries. In addi­tion to the test track, state-of-the-art labo­ra­to­ries for the gene­ra­tion as well as ana­ly­sis of quan­tum sta­tes and their appli­ca­tion in high-secu­rity com­mu­ni­ca­ti­ons were estab­lished in Erfurt and Jena. The fun­ding from the state of Thu­rin­gia is clo­sely coor­di­na­ted with fede­ral initia­ti­ves. It is also part of the digi­ta­liza­tion pro­ject of the Thu­rin­gian Minis­try of Eco­nomy, Sci­ence and Digi­tal Society.

Quan­tum key exch­ange over ever grea­ter distances

Light par­tic­les known as quanta are expec­ted to make our com­mu­ni­ca­ti­ons highly secure in the future. For this to suc­ceed, sys­tems must be crea­ted that enable the relia­ble exch­ange of so-cal­led quan­tum keys over various distances.

The Fraun­ho­fer IOF has been rese­ar­ching various pos­si­bi­li­ties for trans­mit­ting highly secure quan­tum keys for quite some time. As part of the QuNET initia­tive, a pilot pro­ject of the Ger­man Fede­ral Minis­try of Edu­ca­tion and Rese­arch, a free-beam link was set up bet­ween the Jena public uti­lity com­pany and the Fraun­ho­fer IOF on the Beu­ten­berg Cam­pus in Jena. Here, quan­tum keys are exch­an­ged over 1.7 km by means of free beams.

The exch­ange of quan­tum keys via fibers is now the next step to rea­lize even grea­ter distances. In order to be able to encrypt glo­bal com­mu­ni­ca­tion net­works in a quan­tum-safe man­ner, an exch­ange via satel­li­tes is also envi­sa­ged in the future.