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APL Photonics

Optimal generation of mesoscopic twin-beam states by means of a natively femtosecond laser system

Alex Pozzoli, Marco Lamperti, Matteo Clerici, Maria Bondani, Alessia Allevi

Published Mar 1, 2025• 3 citations
Publisher

Abstract

Mesoscopic twin-beam states, which exhibit robust nonclassical correlations, hold significant potential for applications in quantum technologies, including underwater quantum communication and quantum metrology. As Ytterbium-based lasers delivering sub-picosecond pulses are becoming the cornerstone of ultrafast photonics, optimizing the generation of quantum states of light driven by such short pulses while avoiding the presence of noise sources, such as spurious light, is also becoming essential. To this end, we propose an optical scheme that delivers well-populated entangled states in the red spectral region by pumping parametric down-conversion with optically tilted pulses, addressing the limited gain caused by group velocity mismatch between the driving pump field and the generated quantum radiation. The results obtained so far encourage the exploitation of this source in further optical schemes.

DOI
10.1063/5.0254736

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Mesoscopic twin-beam states, which exhibit robust nonclassical correlations, hold significant potential for applications in quantum technologies, including underwater quantum communication and quantum metrology. As Ytterbium-based lasers delivering sub-picosecond pulses are becoming the cornerstone of ultrafast photonics, optimizing the generation of quantum states of light driven by such short pulses while avoiding the presence of noise sources, such as spurious light, is also becoming essential. To this end, we propose an optical scheme that delivers well-populated entangled states in the red spectral region by pumping parametric down-conversion with optically tilted pulses, addressing the limited gain caused by group velocity mismatch between the driving pump field and the generated quantum radiation. The results obtained so far encourage the exploitation of this source in further optical schemes.
The robustness of nonclassical correlations exhibited by mesoscopic twin-beam states of light makes them useful for applications in the context of quantum technologies, such as for underwater quantum communication. To this aim, it is crucial to optimize the production of such quantum states of light, and study their level of nonclassicality in terms of different nonclassicality criteria. In this work, we realize an efficient source of well-populated twin-beam states in the red spectral region by pumping parametric down conversion with a natively sub-picosecond laser system. The nonclassical character of such states is investigated in terms of both the noise reduction factor and high-order correlation functions. The obtained results encourage the exploitation of this source in further optical schemes for practical applications.
We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic ($\ensuremath{\sim}{10}^{3}$ detected photons) twin beam produced by picosecond-pulsed spontaneous nondegenerate parametric down-conversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25dB3.25\phantom{\rule{0.3em}{0ex}}\mathrm{dB}3.25dB. The number of temporal modes contained in the twin beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous down-conversion and thus does not suffer from limitations due to the finite gain of the parametric process. Twin beams are also used to demonstrate the conditional preparation of a nonclassical (sub-Poissonian) state.
Squeezed states of light and entangled photon source are fundamental resources for quantum science and technology, enabling advances in quantum communication, computation, and precision metrology. Here, we experimentally demonstrate the generation of ultrabright squeezed vacuum and entangled photon pairs via type-I high-gain parametric down-conversion. Using femtosecond pump pulses at 1,030 nm, we produce ultrabright squeezed vacuum with pulses energies on the order of 10 μJ at a central wavelength of 2,060 nm, corresponding to a photon number exceeding 10 14 . By implementing SU(1,1) interferometric configuration, we achieve flexible control over the mode structure, allowing the transition between multimode entangled photon pairs and nearly single-mode squeezed states. This results provide a high-intensity quantum light source that facilitates the study of nonclassical ultrafast dynamics.
Nowadays, optical Quantum Communication has reached a mature level, especially in free space and through optical fibers. Experimental implementations usually involve single-photon states or weak coherent states detected by single-photon detectors. In contrast to these standard configurations, in our work we consider mesoscopic twin-beam (TWB) states revealed by photon-number-resolving detectors. By properly acting on the natural divergence of the generated beams, we show that they remain nonclassical even at a moderate distance from the nonlinear crystal in which they are produced. We also consider the case where one of the two parties of TWB is partially transmitted through water, and show that the nonclassicality of the states is preserved. This result suggests that mesoscopic TWB states can be considered for the new and growing scenario of underwater Quantum Communication.