Microcomb-driven large-scale fully connected quantum network

TL;DR

The paper addresses the scalability of fully connected quantum networks under untrusted network providers by implementing a measurement-device-independent QKD framework based on two-photon Hong-Ou-Mandel interference. It introduces integrated soliton microcomb sources and silicon-photonic transmitter chips to generate and lock hundreds of parallel frequency channels, enabling massively parallel MDI-QKD. The authors demonstrate a 200-user fully connected network over 200 km with per-channel secure key rates on the order of tens of bits per second, with high HOM visibilities and robust, locally locked frequency channels. They discuss implications for metropolitan-to-intercity deployment and note potential extensions to quantum repeater-based architectures, highlighting practical, scalable, secure quantum networking with reduced infrastructure costs.

Abstract

Fully connected quantum networks enable simultaneously connecting every user to every other user and are the most versatile and robust networking architecture. However, the scalability of such networks remains great challenge for practical applications. Here we construct a large-scale fully connected quantum network founded on two-photon Hong-Ou-Mandel (HOM) interference, where user-to-user security is guaranteed even with untrusted network provider. Using integrated soliton microcomb (SMC) and photonic encoding chips, we realize precise massive parallel frequency generation and locking, high-visibility HOM interferences and measurement-device-independent (MDI) quantum key distribution. The proposed architecture enables a 200-user fully connected quantum network over 200 kilometers with strict information-theoretic security via untrusted network provider. The implemented networking architecture paves the way for realizing large-scale fully connected MDI quantum networks across metropolitan and intercity regions.

Figures (4)

• Figure 1: Fully connected quantum network with untrusted network provider.a, Schematic fully connected MDI-QKD network (four users as an example), in which all terminal users could connected to each other simultaneously without trusting the network provider and each user requires only a frequency-locked seed laser source. b, The typical frequency-locking laser arrays for massively parallel MDI-QKD network, which is a formidable technical challenge. c, Experimental setup of the sub-system of the massively parallel fully connected MDI-QKD network using SMC and QKD transmitter chips over 200 km.
• Figure 2: Locally fully stabilized SMC chips.a, Schematic diagram of SMC local frequency locking setup. The seed laser is locked to a local Rubidium cell. The repetition rate of the SMC chip is locked to a 49-GHz local radio frequency (RF) reference via an intensity modulator (IM). b, Optical frequency spectra of two independently locked SMC chips. c-d, The concurrent repetition rate fluctuations in realtime and statistics of two independent SMCs within 3-hour running. e, The real-time beat frequencies of three pairs of comb teeth within the concurrent time span and f their corresponding statistical distributions. g-h, The monitored real-time operation temperature fluctuation and corresponding statistical distributions of the independent repetition rate locked SMC chips.
• Figure 3: Transmitter chip characterization.a, Schematic of the polarization-encoded transmitter chip (4 MZIs + VOA). b, The images of the optoelectronic packaged transmitter chip. c, Voltage-dependent transmittance of the MZIs of both transmitter chips. d, The normalized temporal intensity profiles of the pulsed comb teeth modulated by the on-chip MZI, which includes the time jitter of the SNSPD. Arrival time drifts of photon pulses e, with and f, without time-drift compensation after transmission over a 100-km fiber channel. g, HOM interference fringe of the 90-ps tooth pair H28&H28. h, HOM visibilities of tooth pairs from H50&H50 to C12&C12 (corresponding to CH-60&CH-60 to CH+19&CH+19 of the comb teeth).
• Figure 4: Secure key rates and QBERs of integrated parallel MDI-QKD system over 200 km fiber.a, QBERs and b, secure key rates of different tooth pairs spanning H50&H50 to C14&C14. c-d, Real-time secure key rates and QBERs of H28&H28 over 3 hours' running, where secure keys is extracted every 1000 s. The blue and red colors denote the equivalent loss and 200-km fiber channels, respectively. e, Secure key rates per channel as distance. ${}^*$: Ref. yinhl2016_404km_mdi used ultralow loss (ULL, 0.16 dB/km) fiber and Ref. wengerowsky2018_entanglement_fully_network simulated the channel with attenuators.