Invited: DIQKD Talk Series (Chair: Feihu Xu)

Tue, 30 Aug , 15:00 - 16:30

    Invited Talk 1: Experimental d evice independent quantum key distribution based on photonic system

    Speaker: Wen-Zhuo Liu (University of Science and Technology of China)

    It is well known that QKD enables information-theoretic secure communication between two distant users. However, its security typically relies on the well-characterized devices operated by legitimate users. In practical scenarios, the imperfect characteristics of devices provide potential attackers with side-channels and back doors In contrast, the device independent QKD protocol - an entanglement - based protocol - provides a scheme for secret key generation without any knowledge of the underlying quantum devices. Given a minimal set of fundamental assumptions, its security can be verified by the violation of Bell inequality. Despite its beauty in theory, device independent QKD is difficult to achieve experimentally. Especially in photonic systems, an efficiency of no less than 90% is normally required, which is far beyond the state of the art. Here, I would like to present some recent progress we have made on photonic device-independent QKD . Combining theoretical and experimental improvements, we accomplished a proof-of-principle experiment of device-independent QKD based on polarization entangled photons in the scenario of asymptotic limit. The results present an important step towards a full demonstration of photonic device independent QKD.

    Invited Talk 2: Device-independent quantum key distribution between distant users

    Speaker: Harald Weinfurter (University of Munich)

    Abstract: Here we present an experimental system that enables for device independent quantum key distribution (DIQKD) between two distant users. The experiment is based on the entanglement between two single rubidium atoms. They are trapped by two fully independent set-ups and separated by 400 meter line of sight. Each atom emits a photon whose polarisation is entangled with the spin state of the atom. The photons are sent to a Bell-state measurement whereby event ready entanglement between the atomic states is obtained with a fidelity of ℱ ≥0.892(23) based on entanglement swapping.

    Implementing a DIQKD protocol with random key basis, we observe a significant violation of a Bell inequality of S = 2.578(75) — well above the classical limit of 2 — and a quantum bit error ratio of only 0.078(9). In the asymptotic limit, this results in a secret key rate of 0.07 bits per entangled pair (compared to a maximum 0.025 bit/pair for the protocol used) and thus demonstrates the system’s capability to generate secret keys.

    In the future, quantum networks will provide high efficiency detection of states shared by the network nodes. Our results show how shared entanglement can be utilized for secure key exchange even with potentially untrusted devices, and that DIQKD indeed will become the standard service for key exchange.

    Invited Talk 3: Experimental quantum key distribution certified by Bell’s theorem

    Speaker: Nicolas Sangouard (Universit´e Paris-Saclay, CEA, CNRS)

    Abstract: Quantum key distribution protocols provide information-theoretic security, a strong form of security unreachable by classical means. However, quantum protocols realised so far are subject to a class of attacks exploiting implementation defects in the quantum devices involved. Following the pioneering work of Ekert proposing the use of entanglement to bound an adversary’s information from Bell’s theorem, we present here the experimental realisation of a complete quantum key distribution protocol immune to these vulnerabilities. We achieve this by combining theoretical developments on finite-statistics analysis, error correction, and privacy amplification, with an event-ready scheme enabling the rapid generation of high-fidelity entanglement between two trapped-ion qubits connected by an optical fibre link. The secrecy of our key is guaranteed device-independently: it is based on the validity of quantum theory, and certified by measurement statistics observed during the experiment. Our result paves the way for further quantum information applications based on the device-independence principle.