We report on the generation of indistinguishable photon pairs at telecom wavelengths based on a type-II parametric down conversion process in a periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase matching, pump laser characteristics and coupling geometry are optimised to obtain spectrally uncorrelated photons with high coupling efficiencies. Four photons are generated by a counter-propagating pump in the same crystal and anlysed via two photon interference experiments between photons from each pair source as well as joint spectral and g((2)) measurements. We obtain a spectral purity of 0.91 and coupling efficiencies around 90% for all four photons without any filtering. These pure indistinguishable photon sources at telecom wavelengths are perfectly adapted for quantum network demonstrations and other multi-photon protocols.
We report on the generation of indistinguishable photon pairs at telecom wavelengths based on a type-II parametric down conversion process in a periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase matching, pump laser characteristics and coupling geometry are optimised to obtain spectrally uncorrelated photons with high coupling efficiencies. Four photons are generated by a counter-propagating pump in the same crystal and anlysed via two photon interference experiments between photons from each pair source as well as joint spectral and g((2)) measurements. We obtain a spectral purity of 0.91 and coupling efficiencies around 90% for all four photons without any filtering. These pure indistinguishable photon sources at telecom wavelengths are perfectly adapted for quantum network demonstrations and other multi-photon protocols.
We report on the generation of indistinguishable photon pairs at telecom wavelengths based on a type-II parametric down conversion process in a periodically poled potassium titanyl phosphate (PPKTP) crystal. The phase matching, pump laser characteristics and coupling geometry are optimised to obtain spectrally uncorrelated photons with high coupling efficiencies. Four photons are generated by a counter-propagating pump in the same crystal and anlysed via two photon interference experiments between photons from each pair source as well as joint spectral and g((2)) measurements. We obtain a spectral purity of 0.91 and coupling efficiencies around 90% for all four photons without any filtering. These pure indistinguishable photon sources at telecom wavelengths are perfectly adapted for quantum network demonstrations and other multi-photon protocols.
We report on the generation of an indistinguishable heralded single-photon state, using highly nondegenerate spontaneous parametric downconversion (SPDC). Spectrally factorable photon pairs can be generated by incorporating a broadband pump pulse and a group-velocity matching (GVM) condition in a periodically-poled potassium titanyl phosphate (PPKTP) crystal. The heralding photon is in the near IR, close to the peak detection efficiency of off-the-shelf Si single-photon detectors; meanwhile, the heralded photon is in the telecom L-band where fiber losses are at a minimum. We observe spectral factorability of the SPDC source and consequently high purity (90%) of the produced heralded single photons by several different techniques. Because this source can also realize a high heralding efficiency (> 90%), it would be suitable for time-multiplexing techniques, enabling a pseudo-deterministic single-photon source, a critical resource for optical quantum information and communication technology.
Time-frequency domain is a promising platform for optical quantum technologies due to large Hilbert space available for quantum information encoding. Moreover, photons appear as perfect candidates for interface between different quantum systems as they can be transmitted over large distances in a low-loss manner. Obviously mostly desired would be such link at telecommunication wavelengths, because it can be integrated with classical communication schemes. We report on a tunable telecom-wavelength photon pair source based on bulk periodically poled potassium titanyl phosphate (PPKTP) pumped by femtosecond laser pulses. The pairs are produced via type-II spontaneous parametric down conversion (SPDC). The spectra of photons, which lies in telecommunication range, in our source can be affected via both changing the spectrum of pumping laser and changing the phase matching by using crystals of different lengths. By appropriate choice of these parameters either the pair of photons occupy single-mode in frequency and is in a separable state or is multimode and entangled [1]. Here we report on experimental active modification the photon pairs’ spectral properties. We employ fast electro-optic temporal phase modulation to induce a deterministic change of photons’ joint spectral intensity (JSI). Central wavelength of one photon is shifted by up to 0.2 nm. The measurement of the spectrum of single photons is based upon frequency to time mapping, implemented by large group delay dispersion (GDD) in chirped fiber Bragg grating (CFBG) [2]. An unprecedented sub-10 pm resolution of correlated single-photon spectral measurements has been achieved. Further work will be done to modify not only the position, but also the shape of JSI by using techniques based on the time-lens principle [3]. References: [1] P. G. Evans, R. S. Bennink, W. P. Grice, T. S. Humble, Phys. Rev. Lett. 105, 253601 (2010) [2] A. O. C. Davis, P. M. Saulnier, M. Karpinski, B. J. Smith, arXiv:1610.03040 (2016) [3] M. Karpiński, M. Jachura, L. J. Wright, B. J. Smith, Nature Photonics 11, 53–57 (2017)
We theoretically investigated spectrally uncorrelated biphotons generated in a counter-propagating spontaneous parametric downconversion (CP-SPDC) from periodically poled M T i O X O 4 ( M = K , Rb, Cs; X = P , As) crystals. By numerical calculation, it was found that the five crystals from the KTP family can be used to generate heralded single photons with high spectral purity and wide tunability. Under the type-0 phase-matching condition, the purity at 1550 nm was between 0.91 and 0.92, and the purity can be maintained over 0.90 from 1500 nm to 2000 nm wavelength. Under the type-II phase-matching condition, the purity at 1550 nm was 0.96, 0.97, 0.97, 0.98, and 0.98 for PPKTP, PPRTP, PPKTA, PPRTA, and PPCTA, respectively; furthermore, the purity can be kept over 0.96 for more than 600 nm wavelength range. We also simulated the Hong–Ou–Mandel interference between independent photon sources for PPRTP crystals at 1550 nm, and interference visibility was 92% (97%) under the type-0 (type-II) phase-matching condition. This study may provide spectrally pure narrowband single-photon sources for quantum memories and quantum networks at telecom wavelengths.
We report on the generation of a bright photon source at telecom wavelengths using spontaneous parametric down-conversion in a type II periodically poled potassium titanyl phosphate crystal. Simultaneous resonances of the pump and the two down-converted fields are achieved with a properly designed optical cavity. This triple-resonance optical parametric oscillator operates far below threshold, generating photon pairs at 1560 nm wavelength with a bandwidth of 8 MHz. Time correlation measurements produce an estimate of 27.7 ns for the coherence time, and production rate of 134±25 s−1 MHz−1 mW−1 for photon pairs. As photon pairs in the telecom regime are suitable for long-distance transmission, this source may find application in quantum communications.
The ideal photon-pair source for building up multi-qubit states needs to produce indistinguishable photons with high efficiency. Indistinguishability is crucial for minimising errors in two-photon interference, central to building larger states, while high heralding rates will be needed to overcome unfavourable loss scaling. Domain engineering in parametric down-conversion sources negates the need for lossy spectral filtering allowing one to satisfy these conditions inherently within the source design. Here, we present a telecom-wavelength parametric down-conversion photon source that operates on the achievable limit of domain engineering. We generate photons from independent sources which achieve two-photon interference visibilities of up to 98.6 ± 1.1% without narrow-band filtering. As a consequence, we reach net heralding efficiencies of up to 67.5%, which corresponds to collection efficiencies exceeding 90%.