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arXiv:2407.10517 · International Convention on Information and Communication Technology, Electronics and Microelectronics

Monolithically Integrated Ultra-Low Noise Balanced Receiver for CV-QKD

Dinka Milovančev, Nemanja Vokić

Published May 20, 2024• 1 citation
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Abstract

In this work we explore monolithic optoelectronic integration platform for significant down-scaling of input-referred noise in custom designed low-noise analog front-end used for balanced photodetection. The performance of such monolithically integrated approach is compared to heterogeneously integrated solution designed in the same technology which requires wire-bonding to the balanced photodetectors. The designed circuits are targeting bandwidth above 1GHz. The improved noise performance is leveraged against increased secure key rates and achievable reach in continuous-variable quantum key distribution (CVQKD).

DOI
10.1109/mipro60963.2024.10569398

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In this work we explore monolithic optoelectronic integration platform for significant down-scaling of input-referred noise in custom designed low-noise analog front-end used for balanced photodetection. The performance of such monolithically integrated approach is compared to heterogeneously integrated solution designed in the same technology which requires wire-bonding to the balanced photodetectors. The designed circuits are targeting bandwidth above 1GHz. The improved noise performance is leveraged against increased secure key rates and achievable reach in continuous-variable quantum key distribution (CVQKD).
In this work we propose a switchable dual bandwidth optical receiver that can be used for both classical and continuous variable quantum key distribution (CV-QKD) on a monolithic platform for opto-electronic integration. Switchable transimpedance amplifier is designed for dual bandwidth that can be switched between high bandwidth (10 GHz) for classical and low bandwidth (>1.5GHz) for quantum communication. Monolithic approach allows integration of photonics on the same chip which allows for low-noise operation as well as reconfigurable configuration between a simple link for on-off keying used for classical and optical heterodyne coherent reception used for quantum communication. The receiver performance for both classical and quantum application is simulated showing very high sensitivity as well as high secure key rates over moderate distances.
Continuous-variable quantum key distribution (CVQKD) is a promising technology for enabling quantum-secure networks, valued for its compatibility with conventional telecommunication hardware and maturing security proofs. Although the need for quantum-safe infrastructure is driven by the threat of advancing quantum computing, the widespread deployment of QKD remains elusive because current discrete-component solutions suffer from high cost, high energy consumption, and lack of conformity with the existing telecom network infrastructure. In this work, we demonstrate a compact CV-QKD system based on a custom-designed, monolithically integrated silicon photonic dualpolarization transceiver, operated with an off-chip seed laser. Taking into account the block length of 2 × 107 and employing 64-quadrature amplitude modulation (QAM) shaped probabilistically, our system achieves a secret key rate of 1.9 Mbit/s in 25km of standard single-mode fiber. This work highlights the significant potential of electronic-photonic integration to advance the practical deployment of QKD networks.
We present a design of balanced homodyne receivers suitable for ultra-low noise quantum applications such as continuous-variable quantum key distribution and quantum random number generation. For best noise and bandwidth performance a die-level low-parasitic photodiode together with a low-noise high-speed transimpedance amplifier are explored together with a planar lightwave circuit splitter chip serving as a photomixer. Bandwidths of 750 MHz and 2.6 GHz were accomplished while maintaining optimum noise performance, as evidenced by very high quantum-to-classical noise ratios of 26.8 and 18.6 dB, respectively. A common-mode rejection ratio of at least 40 dB was achieved for a frequency range of up to 1 GHz. Its application for continuous-variable quantum key distribution was evaluated by means of estimations under a strict untrusted receiver assumption, showing its potential for generating up to 43 Mbit/s secure-key rate over a reach of 10 km, whereas up to 100 Mbit/s could be supported at shorter reaches. Moreover, the high quantum-to-classical clearance values can enable high quality quantum random number generation at Gb/s rates. The multi-purpose operation of the designed balanced receivers for classical communications was examined showing reception sensitivities of −55.8 and −52.6 dBm at 500 Mbit/s and 1 Gbit/s quadrature phase shift keying transmission, respectively, using the 750 MHz receiver. The faster 2.6 GHz receiver enabled 10 Gbit/s duobinary transmission at −14.8 dBm sensitivity.
Quantum key distribution (QKD) is a prominent application in the field of quantum cryptography, providing information-theoretic security for secret key exchange. The implementation of QKD systems on photonic integrated circuits (PICs) can reduce the size and cost of such systems and facilitate their deployment in practical infrastructures. To this end, continuous-variable (CV) QKD systems are particularly well-suited as they do not require single-photon detectors, whose integration is presently challenging. Here we present a CV-QKD receiver based on a silicon PIC capable of performing balanced detection. We characterize its performance in a laboratory QKD setup using a frequency multiplexed pilot scheme with specifically designed data processing allowing high modulation and secret key rates. The obtained excess noise values are compatible with asymptotic secret key rates of 2.4 Mbit/s and 220 kbit/s at an emulated distance of 10 km and 23 km, respectively. These results demonstrate the potential of this technology toward fully integrated devices suitable for high-speed, metropolitan-distance secure communication.
Quantum key distribution (QKD) is a quantum communication technology that offers absolute security. Among its various implementations, continuous-variable (CV) QKD has garnered significant attention due to its high secret key generation rates and compatibility with conventional optical telecommunication infrastructure, which operates under ambient conditions. However, chip-based integration is crucial for realizing practical and scalable CV-QKD networks, and photonic integrated circuit technology is a potential solution, leveraging the on-chip integration of essential optical components onto silicon photonic circuits. Therefore, this work presents a compact, stable, and cost-effective quantum photonic CV-QKD system on a chip. Our architecture combines time- and polarization-multiplexing with high-extinction-ratio pulse generation to mitigate excess noise. At the same time, a real-time feedback control mechanism compensates for polarization drift, ensuring robust system performance. Fiber-based evaluations reveal secret key generation rates of 2.55 Mbps over 25 km and 0.737 Mbps over 50 km with 12 h stable operation, establishing, to our knowledge, a new benchmark for integrated photonic CV-QKD systems with both the transmitter and receiver on-chip. These results mark a significant milestone in on-chip quantum communication, paving the way for widespread adoption of photonic integrated circuits in future metropolitan quantum-secure networks.