Generation of photon triplets via three-photon parametric down-conversion

• Applicants: Professorin Maria Chekhova, Ph.D.; Professor Dr. Nicolas Joly
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 311185701

Final Report Abstract

The main goal of the project was first-time realization of third-order parametric down conversion (TOPDC), a new nonlinear process where a single pump photon splits in three photons with lower energies. This effect is very important for quantum optics, being the lowest-order nonlinear effect that directly produces a non-Gaussian state, and many groups are trying to implement it. Here we considered two platforms for TOPDC: optical fibers and nonlinear crystals. The former provide a large interaction length, together with adjustable dispersion landscape, necessary to satisfy the phase-matching by using different spatial modes. The latter offer an efficient way to satisfy the phase-matching through optical birefringence and, often, a high nonlinearity. TOPDC can be viewed as the “quantum reciprocal” of the classical third harmonic generation (THG): both processes have the same phase-matching conditions and their efficiencies depend on the same second-order optical nonlinearity; therefore demonstration of THG is usually the first step towards TOPDC. However, TOPDC has a much lower efficiency. In the ‘fiber’ part of the project, we achieved tunable phase-matching in hollow-core fibers filled with noble gas and demonstrated THG in a Xe-filled single-ring fiber. However, because of the weak nonlinearity of the gas, as well as the poor overlap between the spatial modes of the pump and the triplets, one cannot expect a measurable generation rate. To circumvent intra-modal phase-matching, we designed and fabricated a totally new hybrid microstructrured fiber, and demonstrated phase-matched THG between two single-lobed spatial modes for the first time. The drawback is that phase-matching is hardly tunable in this case. Finally, we used tapered fibers with the dispersion adjusted through the waist diameter. The latter is however very critical and impossible to reproduce with the current fabrication technique. We mitigated this problem by embedding the taper inside a gas cell so as to allow the tuning of the phase-matching, and demonstrated tunable THG. We predict a reasonable rate of triplet production in such a system, which should be a privileged platform for TOPDC. In the ‘crystal’ part of the project, we investigated phase-matched TOPDC in calcite. According to the theoretical calculations, unseeded TOPDC is too weak to detect with the existing equipment. Therefore, we implemented seeded TOPDC under e->eoo phase-matching and observed single photons emitted at a rate of 15 Hz, which, however, was too low to register two-photon coincidences. The reason for the low generation rate being the low nonlinearity of calcite, we turned to another possibility, namely to use a material with very high nonlinearity (silicon). Due to the high nonlinearity, the material can be very thin, which eliminates the need for phase-matching. We tested this idea by implementing non-phase-matched SPDC in a microscale layer of lithium niobate using its strongest nonlinearity component, not available under phase-matching. With an effective length of 1.4 micrometers, this was the thinnest source of SPDC to-date, resulting in an ultrabroad frequency and angular spectrum and giant entanglement. With TOPDC in silicon, the same technique gave so far poor results because of the fluorescence, but we expect a measurable rate of triplets by passing to a different pumping wavelength. Although the main goal of the project, namely realization of unseeded TOPDC, has not been achieved, new promising ways towards it were discovered in the course of work: (i) the use of tapered or suspendedcore fibers with the phase-matching tunable through surrounding-gas pressure and (ii) the use of ultrathin layers of strongly nonlinear materials like silicon of chalcogenide glass. Further work along these lines is required to implement TOPDC.

Publications

• Hybrid photonic-crystal fiber for single-mode phase matched generation of third harmonic and photon triplets. Optica, 3(9), 952.
  Cavanna, Andrea; Just, Felix; Jiang, Xin; Leuchs, Gerd; Chekhova, Maria V.; St.J., Russell Philip & Joly, Nicolas Y.
  
• Tunable optical parametric generator based on the pump spatial walk-off. Optics Letters, 41(3), 646.
  Cavanna, Andrea; Just, Felix; Sharapova, Polina R.; Taheri, Michael; Leuchs, Gerd & Chekhova, Maria V.
  
• Dispersion tuning in sub-micron tapers for third-harmonic and photon triplet generation. Optics Letters, 43(10), 2320.
  Hammer, Jonas; Cavanna, Andrea; Pennetta, Riccardo; Chekhova, Maria V.; Russell, Philip St.J. & Joly, Nicolas Y.
  
• Microscale Generation of Entangled Photons without Momentum Conservation. Physical Review Letters, 123(26).
  Okoth, C.; Cavanna, A.; Santiago-Cruz, T. & Chekhova, M. V.
  
• Seeded and unseeded high-order parametric down-conversion. Physical Review A, 99(4).
  Okoth, Cameron; Cavanna, Andrea; Joly, Nicolas Y. & Chekhova, Maria V.
  
• Broadly tunable photon-pair generation in a suspended-core fiber. Physical Review Research, 2(1).
  Hammer, Jonas; Chekhova, Maria V.; Häupl, Daniel R.; Pennetta, Riccardo & Joly, Nicolas Y.
  
• Idealized Einstein-Podolsky-Rosen states from non–phase-matched parametric down-conversion. Physical Review A, 101(1).
  Okoth, C.; Kovlakov, E.; Bönsel, F.; Cavanna, A.; Straupe, S.; Kulik, S. P. & Chekhova, M. V.
  
• Progress toward third-order parametric down-conversion in optical fibers. Physical Review A, 101(3).
  Cavanna, Andrea; Hammer, Jonas; Okoth, Cameron; Ortiz-Ricardo, Erasto; Cruz-Ramirez, Hector; Garay-Palmett, Karina; U.'Ren, Alfred B.; Frosz, Michael H.; Jiang, Xin; Joly, Nicolas Y. & Chekhova, Maria V.