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Chinese Physics B

Engineering the spectra of photon triplets generated from micro/nanofiber

Chuan Qu, Dongqin 东琴 Guo 郭, Xiaoxiao 笑笑 Li 李, Zhenqi 振旗 Liu 刘, Yi 义 Zhao 赵, Shenghai 胜海 Zhang 张, Zhengtong 正统 Wei 卫

Published Jan 9, 2024• 1 citation
Publisher

Abstract

Quantum light sources are the core resources for photonics-based quantum information processing. We investigate the spectral engineering of photon triplets generated by third-order spontaneous parametric down-conversion in micro/nanofiber. The phase mismatching at one–third pump frequency gives rise to non-degenerate photon triplets, the joint spectral intensity of which has an elliptical locus with a fixed eccentricity of 6 / 3 . Therefore, we propose a frequency-division scheme to separate non-degenerate photon triplets into three channels with high heralding efficiency for the first time. Choosing an appropriate pump wavelength can compensate for the fabrication errors of micro/nanofiber and also generate narrowband, non-degenerate photon triplet sources with a high signal-to-noise ratio. Furthermore, the long-period micro/nanofiber grating introduces a new controllable degree of freedom to tailor phase matching, resulting from the periodic oscillation of dispersion. In this scheme, the wavelength of photon triplets can be flexibly tuned using quasi-phase matching. We study the generation of photon triplets from this novel perspective of spectrum engineering, and we believe that this work will accelerate the practical implementation of photon triplets in quantum information processing.

DOI
10.1088/1674-1056/ad1c5d

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Quantum light sources are the core resources for photonics-based quantum information processing. We investigate the spectral engineering of photon triplets generated by third-order spontaneous parametric down-conversion in micro/nanofiber. The phase mismatching at one–third pump frequency gives rise to non-degenerate photon triplets, the joint spectral intensity of which has an elliptical locus with a fixed eccentricity of 6 / 3 . Therefore, we propose a frequency-division scheme to separate non-degenerate photon triplets into three channels with high heralding efficiency for the first time. Choosing an appropriate pump wavelength can compensate for the fabrication errors of micro/nanofiber and also generate narrowband, non-degenerate photon triplet sources with a high signal-to-noise ratio. Furthermore, the long-period micro/nanofiber grating introduces a new controllable degree of freedom to tailor phase matching, resulting from the periodic oscillation of dispersion. In this scheme, the wavelength of photon triplets can be flexibly tuned using quasi-phase matching. We study the generation of photon triplets from this novel perspective of spectrum engineering, and we believe that this work will accelerate the practical implementation of photon triplets in quantum information processing.
Spectrally uncorrelated biphotons are the essential resources for achieving various quantum information processing protocols. We theoretically investigate the generation of spectrally uncorrelated biphotons emitted by spontaneous four-wave mixing from a fiber nonlinear interferometer which consists of an N-stage nonlinear gain fiber and an (N-1)-stage dispersion modulation fiber. The output biphoton states of nonlinear interference are the coherent superposition of various biphoton states born in each nonlinear fiber, and thus the interference fringe will reshape the biphoton joint spectra. As a result, resorting to Taylor expansion to first order for phase mismatching, we theoretically verify that the orientation of phase matching contours will rotate in a specific way with only varying the length of dispersion modulation fiber. The rotation in orientation of phase matching contours may result in spectrally uncorrelated biphotons and even arbitrary correlation biphotons. Further, we choose micro/nanofiber as the nonlinear gain fiber and single-mode communication fiber as dispersion modulation fiber to numerically simulate the generation of spectrally uncorrelated biphotons from spontaneous fourwave mixing. Here, due to significant frequency detuning (hundreds of THz), Raman background noise can be considerably suppressed, even at room temperature, and photons with largely tunable wavelengths can be achieved, indicating a practicability in many quantum fields. A photon mode purity of 97.2% will be theoretically attained without weakening the heralding nature of biphoton sources. We think that this fiber nonlinear interference with the flexibly engineered quantum state can be an excellent practical source for quantum information processing.
Pure-state single photons and large-bandwidth-correlation biphotons are fundamental resources for quantum information processing. The dispersion properties of micro/nanofiber (MNF) can be tailored by carefully choosing its diameter, resulting in a flexibly tailored biphoton spectrum. We theoretically investigate pure-state single photons and large-bandwidth-correlation biphotons produced by degenerate spontaneous four-wave mixing in MNF. In our simulation, a single-photon state with a purity of 99% will be theoretically attained by choosing the appropriate pump bandwidth and center wavelength with respect to the diameter and length of the MNF. Further, when an appropriate diameter with a negligible curvature at the zero dispersion wavelength is chosen, even a narrow pump bandwidth is capable of motivating remarkably broadband correlation biphotons, e.g., for a MNF diameter of 0.7 μm, the theoretical full width at half maximum is 473 nm. In practice, the application of a MNF-based quantum light source is dependent on the technologies that precisely control and measure the diameter. Our theoretical investigation will guide the experimental realization of high-quality quantum light sources based on MNF.
Abstract Photon triplet sources exhibit non-Gaussian features, a key property for applications in quantum computing and quantum information. However, spectral correlations can limit the performance and detection efficiency of these systems. Motivated by this observation, we present a theoretical analysis of the spectral properties of photon triplets generated through spontaneous third-order parametric down-conversion in photonic devices, and discuss strategies to quantify and minimize such correlations. We propose two approaches: dispersion engineering in waveguides and pump engineering in resonators. We apply these strategies in two realistic source designs, namely a high-index-contrast optical fiber and a silicon nitride microring resonator. Finally, we discuss detection strategies for probing non-Gaussian features of the triplet state. We find that it is feasible to achieve few-mode generation of photon triplets using state-of-the-art experimental systems, a crucial step toward practical applications of photon triplet sources in quantum technologies.
The spontaneous decay of a pump photon into a tripartite entangled photon state (photon triplets) has been extensively studied in theory. Observation of these photon triplets at optical frequencies is of interest for fundamental science and future applications of quantum optics, such as quantum computing and quantum cryptography. This decay is known as spontaneous third-order parametric down-conversion (TOPDC). Experimentally, TOPDC has not been demonstrated in the optical frequency domain. TOPDC is enabled by the third-order nonlinearity of the material in which the interaction takes place. In optical fibres, the effective nonlinearity of the glass is increased manifold. The reason for this is the long light-matter interaction length and the tight confinement of light in the waveguide. Optical fibres are therefore the ideal platform for the observation of TOPDC, provided that phase matching can be achieved. In this thesis, the use of submicrometre fibre tapers is studied in the context of TOPDC, both in experiment and theory. Comparing different fibre-based TOPDC sources, fibre tapers rank among the highest in terms of expected triplet generation rate. At the same time, the background noise generated in these fibres is very low, which leads to a high expected three-photon coincidence-to-accidental ratio (CAR) on the order of 7000. In the experiments related to TOPDC, the precision of manufacturing fibre tapers is studied. A novel gas-based mechanism for dispersion tuning is demonstrated. Without this mechanism the manufacturing precision of the fibre tapers would not suffice to observe TOPDC in an experiment. The tuning mechanism is demonstrated using third-harmonic generation, which is the inverse process of TOPDC. The resonant third-harmonic radiation generated around 460nm can be tuned at a rate of −0.118nm/bar. This is achieved by introducing pressurised argon in the taper environment. The background noise from fibre tapers is characterised. The effect of the tuning mechanism on the three-photon-state and the signal-to-noise ratio is studied in theory. In another part of the thesis, gas-filled suspended-core fibres (SCFs) are used as a spectrally tunable source of entangled photon pairs (biphotons). Generation of biphotons via spontaneous four-wave mixing (FWM) in fibres offers great advantages over the generation in bulk crystals, which is the commonly employed technique. The most important advantages are the excellent control of the spatial mode structure, the extra degrees of freedom for dispersion design and the possibility to integrate the fibres into existing networks. Yet, fibre biphoton sources lack the convenient spectral tunability of crystal-based sources. Introducing pressurised gas into the hollow channels of the SCF is demonstrated to be a convenient and broadband spectral tuning mechanism. The FWM-sidebands can be continuously tuned at a rate of −0.3 THz/bar, in the quantum and in the seeded scenario. A high two-photon-CAR exceeding 10000 is measured for the biphoton state, and the frequency entangled joint-spectral intensity is measured. Finally, seeded FWM is used to characterise the core size of high-NA submicrometre fibres to a nanometre precision. If ultrafast pulses are used instead of nanosecond pulses, this will present a non-destructive and high precision characterisation technique for such fibres. The results of this work present an important step towards realising TOPDC at optical frequencies in the near future. The experimental realisation of a broadly tunable biphoton source combines the convenient tuning mechanism found in crystal-based sources with the advantages of fibre-based biphoton generation. Such tunable fibre biphoton sources can therefore be competitive with crystal-based systems for quantum optics applications.
We study the third-order spontaneous parametric down-conversion (TOSPDC) process, as a means to generate entangled photon triplets. Specifically, we consider thin optical fibers as the nonlinear medium to be used as the basis for TOSPDC in configurations where phase matching is attained through the use of more than one fiber transverse modes. Our analysis in this paper, which follows from our earlier paper [Opt. Lett. 36, 190--192 (2011)], aims to supply experimentalists with the details required in order to design a TOSPDC photon-triplet source. Specifically, our analysis focuses on the photon triplet state, on the rate of emission, and on the TOSPDC phase-matching characteristics for the cases of frequency-degenerate and frequency nondegenerate TOSPDC.