Measurement-device-independent quantum key distribution: from idea towards application

Abstract

We assess the overall performance of our quantum key distribution (QKD) system implementing the measurement-device-independent (MDI) protocol using components with varying capabilities such as different single-photon detectors and qubit preparation hardware. We experimentally show that superconducting nanowire single-photon detectors allow QKD over a channel featuring 60 dB loss, and QKD with more than 600 bits of secret key per second (not considering finite key effects) over a 16 dB loss channel. This corresponds to 300 and 80 km of standard telecommunication fiber, respectively. We also demonstrate that the integration of our QKD system into FPGAbased hardware (instead of state-of-the-art arbitrary waveform generators) does not impact on its performance. Our investigation allows us to acquire an improved understanding of the trade-offs between complexity, cost and system performance, which is required for future customization of MDI-QKD. Given that our system can be operated outside the laboratory over deployed fiber, we conclude that MDI-QKD is a promising approach to information-theoretic secure key distribution.

Quantum key distribution without detector vulnerabilities using optically seeded lasers

“…If Charlie violates the protocol and measures the pulses separately, he can learn the absolute values of the bits, but not their correlation. Therefore he cannot announce the correct correlation to the users, who will then unveil his attempt through public discussion.Irrespective of Charlie's choice, the users' apparatuses no longer need a detector and the detection vulnerability of Quantum Cryptography is removed.This striking feature of MDI-QKD has fostered intense experimental work and various demonstrations have been provided so far [13][14][15][16][17][18]. However, to achieve high-visibility interference at Charlie's beam splitter, the light source in previous experiments was set to emit long pulses at modest clock rates, thus restricting the key rate to less than a hundred bit/s (see Table I).…”

“…Recently it was shown that two-photon interference [11] from independent light sources can be exploited to avoid the use of detectors at the two ends of the communication channel [12,13]. This new form of detection-safe quantum cryptography, called Measurement-Device-Independent Quantum Key Distribution (MDI-QKD), has been experimentally demonstrated [13][14][15][16][17][18], but with modest delivered key rates.Here we introduce a novel pulsed laser seeding technique to obtain high-visibility interference from gain-switched lasers and thereby perform quantum cryptography without detector vulnerabilities with unprecedented bit rates, in excess of 1 Mb/s. This represents a 2 to 6 orders of magnitude improvement over existing implementations and for the first time promotes the new scheme as a practical resource for quantum secure communications.…”

“…Recently it was shown that two-photon interference [11] from independent light sources can be exploited to avoid the use of detectors at the two ends of the communication channel [12,13]. This new form of detection-safe quantum cryptography, called Measurement-Device-Independent Quantum Key Distribution (MDI-QKD), has been experimentally demonstrated [13][14][15][16][17][18], but with modest delivered key rates.…”

“…1(b). The lasing action of the slave laser is then initiated by stimulated emission from the light of the master laser rather than by its own spontaneous emission, thus reducing the uncertainty in its emission 4 [14][15][16][17], respectively. Low source clock rate (2nd column) and large pulse width (3rd column) have been used in previous experiments to achieve high-visibility two-photon interference.…”

“…They should emit indistinguishable pulses, to enable high-visibility two-photon interference [11], and at the same time each pulse should display a random optical phase, to meet a fundamental security condition [22]. In most demonstrations so far [13,[15][16][17], light pulses have been carved from a continuous-wave laser. However, the pulses generated this way have a constant or slowly varying optical phase thus violating the random phase condition.…”