New Paper on time-bin-encoded Quan­tum Key Dis­tri­bu­ti­on published

Quan­tum Key Dis­tri­bu­ti­on (QKD) stands as the most matu­re branch of quan­tum cryp­to­gra­phy, offe­ring tru­ly unbre­aka­ble secu­ri­ty for the forth­co­ming quan­tum inter­net. Solid-sta­te quan­tum light sources, such as semi­con­duc­tor quan­tum dots (SQDs), have attrac­ted strong inte­rest becau­se they emit high-qua­li­ty non-clas­si­cal pho­tons for quan­tum com­mu­ni­ca­ti­ons, pro­mi­sing hig­her secu­re key rates and enab­ling quan­tum repea­ters. Enco­ding infor­ma­ti­on in the tem­po­ral degree of free­dom of pho­to­nic qubits — time‑bin enco­ding — shows strong poten­ti­al for long‑haul quan­tum com­mu­ni­ca­ti­ons in prac­ti­cal sce­na­ri­os. Time‑bin qubits are intrin­si­cal­ly robust against envi­ron­men­tal insta­bi­li­ties that affect deploy­ed fib­re links.

Sin­gle pho­tons emit­ted by a quan­tum dot embedded in a pho­to­nic device are cou­pled into a fib­re and encoded by ‘Ali­ce’ into three distinct time-bin qubits. After ‘Bob’ per­forms the decryp­ti­on, a sequence of quan­tum keys is shared bet­ween the users. Cre­dit: Cre­dit: Light: Sci­ence & Appli­ca­ti­ons (2026). DOI: 10.1038/s41377-026–02205‑9.

In a new cover artic­le in Light: Sci­ence & Appli­ca­ti­ons, an inter­na­tio­nal team from seve­ral Ger­man and Chi­ne­se uni­ver­si­ties reports the first genui­ne time‑bin QKD demons­tra­ti­on dri­ven by an on‑demand telecom‑band semi­con­duc­tor QD device. In this work, three distinct time-bin qubit sta­tes are pre­pared deter­mi­ni­sti­cal­ly and ran­dom­ly by a self-sta­bi­li­sed time-bin enco­der that con­verts pola­ri­zed sin­gle pho­tons emit­ted from a tele­com C‑band QD. At the recei­ver, the encoded pho­to­nic qubits are decoded using an actively sta­bi­li­zed inter­fe­ro­me­ter equip­ped with a pha­se shif­ter, enab­ling long-term ope­ra­ti­on wit­hout manu­al tuning. The sys­tem achie­ves a trans­mis­si­on distance more than120 km over an opti­cal fib­re link bet­ween enco­der and deco­der, while main­tai­ning an excep­tio­nal sta­bi­li­ty for more than 6 hours of con­ti­nuous ope­ra­ti­on.

The pro­of-of-con­cept expe­ri­ment results in the hig­hest secu­re key rate among the time-bin QKDs based on a high-per­for­mance QD device. The device deli­vers bright, high-puri­ty sin­gle pho­tons at an ope­ra­ti­on rate around 76 MHz. The sys­tem main­ta­ins avera­ge quan­tum bit error rates below 11% at 120 km of stan­dard opti­cal fib­re. In a prac­ti­cal fini­te key regime, an avera­ge secu­re key rate of ~15 bits/s remain sta­ble that is fea­si­ble for real-world text mes­sa­ge encryp­ti­on appli­ca­ti­ons.

Achie­ved secu­re key rates over distance. Quan­tum-bit error rate and achie­va­ble key rates over fib­re distance. The results show a maxi­mum achie­va­ble trans­mis­si­on distance of 127km.

“Most exis­ting QD-based QKD sys­tems are vul­nerable to chan­ges in the prac­ti­cal quan­tum chan­nel cau­sed by envi­ron­men­tal fac­tors, such as tur­bu­lence, tem­pe­ra­tu­re and vibra­ti­ons. This neces­si­ta­tes acti­ve com­pen­sa­ti­on. In con­trast, time-bin enco­ding, whe­re qubits are encoded in the tem­po­ral posi­ti­on of sin­gle pho­tons, offers intrin­sic sta­bi­li­ty against such chan­nel fluc­tua­tions even wit­hout any com­plex com­pen­sa­ti­on pro­to­cols”, sum­ma­ri­ses Dr. Jing­zhong Yang from the Insti­tu­te for Solid Sta­te Phy­sics at Leib­niz Uni­ver­si­ty of Han­no­ver (LUH). “Our results unders­core the fea­si­bi­li­ty of inte­gra­ting QD sin­gle-pho­ton sources into sta­ble and field-deploya­ble time-bin QKD sys­tems, mar­king an important step toward sca­lable, quan­tum-secu­re com­mu­ni­ca­ti­on net­works based on solid-sta­te sin­gle-pho­ton emit­ters.” Click here to see the artic­le.

Fun­ding:
- Bun­des­mi­nis­te­ri­um für For­schung, Tech­no­lo­gie und Raum­fahrt (BMFTR): Quantenrepeater.Net (QR.N), Schirm­pro­jekt Quan­ten­kom­mu­ni­ka­ti­on
  Deutsch­land (SQuaD) und Semi­con­duc­tor Inte­gra­ted Quan­tum Opti­cal Net­work (SemI­QON)
- Euro­pean Rese­arch Coun­cil Con­so­li­da­tor Grant (ERC): Lar­ge-sca­le mul­ti­par­ti­te ent­an­gle­ment on a quan­tum metro­lo­gy net­work (MiNet)
- Quan­tERA II (Hori­zont Euro­pa 2020): Enhan­ced Quan­tum Dot Sources and Opti­cal Ato­mic Memo­ries for Tele­com­mu­ni­ca­ti­on Inter­Con­nec­ti­vi­ty
  (EQSOTIC)
- Deut­sche For­schungs­ge­mein­schaft (DFG): Time and Fre­quen­cy Syn­chro­ni­zed Inter­ci­ty Quan­tum Com­mu­ni­ca­ti­on (Inter­Sync)
- Exzel­lenz­stra­te­gie des Bun­des und der Län­der: Quan­tum Fron­tiers

Aut­hor of the text: © Leib­niz Uni­ver­si­tät Han­no­ver (LUH)