Quan­tum Leap: Breakth­rough for Secu­re Com­mu­ni­ca­ti­on with ‘Arti­fi­ci­al Atoms’

First QCom Tests in Lower Sax­o­ny over a 79 km long Opti­cal Fiber Con­nec­tion from Han­no­ver to Braun­schweig:

In a major sci­en­ti­fic breakth­rough, rese­ar­chers from Leib­niz Uni­ver­si­ty Han­no­ver (LUH), Phy­si­ka­lisch-Tech­ni­sche Bun­des­an­stalt (PTB) in Braun­schweig, and the Uni­ver­si­ty of Stutt­gart have imple­men­ted a new method for secu­re com­mu­ni­ca­ti­on using semi­con­duc­tor quan­tum dots. This advance­ment could revo­lu­tio­ni­ze how we pro­tect our con­fi­den­ti­al infor­ma­ti­on from cyber thre­ats.
Con­ven­tio­nal encryp­ti­on methods rely on com­plex mathe­ma­ti­cal algo­rith­ms and the limits of cur­rent com­pu­ting power. Howe­ver, with the rise of quan­tum com­pu­ters, the­se methods are beco­ming incre­asing­ly vul­nerable, neces­si­ta­ting quan­tum key dis­tri­bu­ti­on (QKD). QKD is a tech­no­lo­gy that lever­a­ges the uni­que pro­per­ties of quan­tum phy­sics to secu­re data trans­mis­si­on. By using sin­gle pho­tons as car­ri­ers of quan­tum keys, QKD ensu­res that any attempt to inter­cept the com­mu­ni­ca­ti­on is detec­ted imme­dia­te­ly, as it intro­du­ces errors in the signal. This method has been con­ti­nuous­ly opti­mi­zed over the years, but estab­li­shing lar­ge net­works has been chal­len­ging due to the limi­ta­ti­ons of exis­ting quan­tum light sources.
The team, led by Pro­fes­sors Fei Ding, Ste­fan Kück, and Peter Mich­ler, has made signi­fi­cant stri­des in this field. They used semi­con­duc­tor quan­tum dots as sin­gle-pho­ton sources, achie­ving high secu­re key trans­mis­si­on rates over a 79-kilo­me­ter distance bet­ween Han­no­ver and Braun­schweig. This is the first quan­tum com­mu­ni­ca­ti­on link in Lower Sax­o­ny.

Figu­re: Dis­tri­bu­ti­on of quan­tum bits bet­ween Leib­niz Uni­ver­si­ty of Han­no­ver (Ali­ce) and PTB Braun­schweig (Bob) over 79 km of deploy­ed fib­re with a total loss of 25.49 dB. Map data from Goog­le (©2023 Goog­le). Cre­dit: Light: Sci­ence & Appli­ca­ti­ons (2024). 

Pro­fes­sor Fei Ding explai­ned the breakth­rough: “We work with quan­tum dots, which are tiny struc­tures simi­lar to atoms but tail­o­red to our needs. For the first time, we used the­se ‘arti­fi­ci­al atoms’ in a quan­tum com­mu­ni­ca­ti­on expe­ri­ment bet­ween two dif­fe­rent cities. This set­up, known as the ‘Nie­der­sach­sen Quan­tum Link,’ con­nects Han­no­ver and Braun­schweig via opti­cal fiber.”
The need for secu­re com­mu­ni­ca­ti­on is as old as huma­ni­ty its­elf. Quan­tum com­mu­ni­ca­ti­on uses the quan­tum cha­rac­te­ristics of light to ensu­re that mes­sa­ges can­not be inter­cept­ed. “Quan­tum dot devices emit sin­gle pho­tons, which we con­trol and send to Braun­schweig for mea­su­re­ment. This pro­cess is fun­da­men­tal to quan­tum key dis­tri­bu­ti­on,” Ding explai­ned. He expres­sed his exci­te­ment about the out­co­me of this col­la­bo­ra­ti­ve effort: “Some years ago, we only dreamt of using quan­tum dots in real-world quan­tum com­mu­ni­ca­ti­on sce­na­ri­os. Today, we are thril­led to demons­tra­te their poten­ti­al for many more fasci­na­ting expe­ri­ments and appli­ca­ti­ons in the future, moving towards a ‘quan­tum inter­net’.”

Click here to see the artic­le titled “High-rate inter­ci­ty quan­tum key dis­tri­bu­ti­on with a semi­con­duc­tor sin­gle-pho­ton source” published in Light: Sci­ence & Appli­ca­ti­ons.

Figu­re: Fly­ing sin­gle pho­tons emit­ted from a quan­tum dot are cou­pled into a field-based deploy­ed fib­re in the city of Han­no­ver, Ger­ma­ny, and sent to Braun­schweig, Ger­ma­ny. Cre­dit: Light: Sci­ence & Appli­ca­ti­ons (2024).

1. Ger­man Fede­ral Minis­try of Edu­ca­ti­on and Rese­arch (BMBF) – QR.X, SQuaD and SemI­QON
2. Euro­pean Rese­arch Coun­cil Con­so­li­da­tor Grant  MiNet
3. Euro­pean Union’s Hori­zon 2020 rese­arch and inno­va­ti­on pro­gram  Quro­pe
4. EMPIR pro­gram­me co-finan­ced by the Par­ti­ci­pa­ting Sta­tes and from the Euro­pean Union’s Hori­zon 2020 rese­arch and inno­va­ti­on program­me – SEQUME
5. Ger­man Rese­arch Foun­da­ti­on (DFG)  Inter­Sync
6. Germany’s Excel­lence Stra­tegy – Quan­tum Fron­tiers
7. Fle­xi­ble Funds pro­gram­me by Leib­niz Uni­ver­si­ty Han­no­ver

Aut­hors: Jing­zhong Yang, Micha­el Zopf

Aut­hor of the illus­tra­ti­ons: © Dan Huy Chau, Jing­zhong Yang