arXiv subjects

Marcello Bacchi

Publications and source records attributed to Marcello Bacchi.

4 recordsLinked to original sources

arXiv2026

Gigahertz-rate thin-film lithium niobate receiver for time-bin quantum communication

Time-bin encoded quantum states of light are crucial for quantum technology applications. The integration of manipulation functionalities into chip-scale devices is essential for deploying scalable, high-performance, and cost-effective quantum networks. Here we develop a fully integrated, high-throughput quantum receiver based on the thin-film lithium niobate (TFLN) platform, capable of high-speed electro-optic manipulation of time-bin encoded quantum states. The device's novel architecture enables active switching of time-bin quantum states with an electro-optic bandwidth exceeding 30 Ghz, while supporting real-time arbitrary projective measurements with a bandwidth of over 1 GHz. We showcase its versatility and performance through several applications, including the certification of entanglement with Bell's inequality violation by 38 standard deviations and with >95% visibility. We then apply it to a fiber-based quantum communication scenario, where we experimentally demonstrate an entanglement-based quantum key distribution (QKD) protocol, achieving stable finite-size secure key rates exceeding 25 kbit/s over 12 hours of continuous operation. By leveraging a high-speed active switching scheme, the system overcomes the need for temporal post-selection, eliminating a fundamental loophole that compromises the security of time-bin entanglement-based QKD protocols and relaxes the temporal resolution requirements of single-photon detectors. Moreover, it enables active selection of the projection basis, increasing the flexibility for communication parties. This approach establishes a versatile and scalable architecture for time-bin encoded quantum communication, enabling practical protocols on industry-grade photonic technology.

quant-ph↗

arXiv2025

Time-resolved certification of frequency-bin entanglement over multi-mode channels

Frequency-bin entangled photons can be efficiently produced on-chip which offers a scalable, robust and low-footprint platform for quantum communication, particularly well-suited for resource-constrained settings such as mobile or satellite-based systems. However, analyzing such entangled states typically requires active and lossy components, limiting scalability and multi-mode compatibility. We demonstrate a novel technique for processing frequency-encoded photons using linear interferometry and time-resolved detection. Our approach is fully passive and compatible with spatially multi-mode light, making it suitable for free-space and satellite to ground applications. As a proof-of-concept, we utilize frequency-bin entangled photons generated from a high-brightness multi-resonator source integrated on-chip to show the ability to perform arbitrary projective measurements over both single- and multi-mode channels. We report the first measurement of the joint temporal intensity between frequency-bin entangled photons, which allows us to certify entanglement by violating the Clauser-Horne-Shimony-Holt (CHSH) inequality, with a measured value of $|S|=2.32\pm0.05$ over multi-mode fiber. By combining time-resolved detection with energy-correlation measurements, we perform full quantum state tomography, yielding a state fidelity of up to $91\%$. We further assess our ability to produce non-classical states via a violation of time-energy entropic uncertainty relations and investigate the feasibility of a quantum key distribution protocol. Our work establishes a resource-efficient and scalable approach toward the deployment of robust frequency-bin entanglement over free-space and satellite-based links.

quant-ph↗

arXiv2025

Post-selection free time-bin entanglement on a thin-film lithium niobate photonic chip

Time-bin entanglement is the most commonly used form of entanglement for quantum communication protocols over fiber networks, due to the natural resilience of this encoding scheme to thermal phase fluctuations in optical fibers. Projective measurements on some bases in the time-bin encoding need, however, post-selection of the measured events, introducing a loophole in Bell tests and requiring high temporal resolution. In this work, we demonstrate chip-integrated receivers for time-bin entanglement certification including a high-speed optical switch to remove such post-selection loophole. The receivers are realized using thin-film lithium niobate and operate at a switching frequency of 5 GHz, enabling high secure key rates. We demonstrate a Bell inequality violation by more than 24 standard deviations without the need for time resolution at the time-bin separation level.

quant-ph↗

arXiv2024

Photon number distribution of squeezed light from a silicon nitride microresonator measured without photon number resolving detectors

The measurement of the photon number distribution (PND) allows one to extract metrics of non-classicality of fundamental and technological relevance, but in principle it requires the use of detectors with photon number resolving (PNR) capabilities.In this work we reconstruct the PND of two-mode pulsed squeezed light generated from a silicon nitride microresonator using threshold detectors and variable optical attenuations. The PNDs are characterized up to 1.2 photons/pulse, through which we extracted an on-chip squeezing level of 6.2(2) dB and a noise reduction factor of -3.8(2) dB. The PNDs are successfully reconstructed up to an Hilbert space dimension of 6x6. The analysis performed on the photon-number basis allows us to characterize the influence of a spurious thermal background field that spoils the photon number correlations. We evaluate the impact of self and cross phase modulation on the generation efficiency in case of a pulsed pump, and validate the results through numerical simulations of the master equation of the system.

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