Pumping a BBO crystal by a violet diode laser with a wavelength of (405 nm) output power of (24 mW) and a line width of (3nm) was employed to generate entangled photons with a wavelength of 810 nm by achieving type II phase matching conditions. The coincidence count rate obtained in this experiment was in the range of (18000) counts/s. Two BBO crystals with different thicknesses of (4 mm and 2 mm) were tested, where maximum count rates of about (18000) counts/s was obtained with a (5*5*2) mm BBO crystal where the short coherence time for the pumping source was tolerated by using shorter BBO crystals. Also, the effect of compensating crystal on the walk-off effect was studied. The coincidence count rates were increased by using these crystals when their optic axes were fixed in the opposite direction relative to the optic axis of the original BBO crystal
Pumping a BBO crystal by a violet diode laser with a wavelength of (405 nm) output power of (24 mW) and a line width of (3nm) was employed to generate entangled photons with a wavelength of 810 nm by achieving type II phase matching conditions. The coincidence count rate obtained in this experiment was in the range of (18000) counts/s. Two BBO crystals with different thicknesses of (4 mm and 2 mm) were tested, where maximum count rates of about (18000) counts/s was obtained with a (552) mm BBO crystal where the short coherence time for the pumping source was tolerated by using shorter BBO crystals. Also, the effect of compensating crystal on the walk-off effect was studied. The coincidence count rates were increased by using these crystals when their optic axes were fixed in the opposite direction relative to the optic axis of the original BBO crystal
The method allowing enhance the eficiency of entangled photon sources based on Type II spontaneous parametric down conversion (SPDC) by means of mode inversion of one of the SPDC output beams is described. Overlap between the the entire signal in idler beams can be achieved using the mode inversion thus maximizing the SPDC photon pair yields. With this method, coincidence count rates as high as 60 kHz from a single 0.5 mm long bulk BBO crystal pumped by the second-harmonic radiation of a femtosecond Ti: Sapphire laser, were obtained.
We report a bright source of polarization-entangled photon pairs using spontaneous parametric down-conversion (SPDC) in a 10 mm long type-II PPKTP crystal pumped by a broadband multi-mode diode laser with the coherence length of 330 μm. Ordinarily, the huge mismatch between the pump coherence length and the PPKTP length would degrade the polarization entanglement completely. By employing the universal Bell-state synthesizer scheme, we remove the spectral/temporal distinguishability of the biphoton amplitudes entirely to recover high-visibility and high-fidelity two-photon polarization entanglement. The pair detection rates are 7,000 pairs/mW via single-mode fibers (with 99.2% fidelity) and 90,900 pairs/mW via multi-mode fibers (with 96.8% fidelity). We also analyze the scheme theoretically to show the effect of broadband multi-mode pumping on the phase matching condition of the type-II PPKTP.
With the continuous development of optical quantum sensor technology, the importance of quantum entanglement sources is growing. As an essential component of optical quantum systems, entanglement sources have broad applications in quantum communication, imaging, computing, and other fields. However, the high-power consumption and preparation costs associated with these sources hinder their integration and expansion. To address these issues, we conducted experiments using a 40mW laser diode and a typical type-II barium metaborate (BBO) crystal to prepare a low-power and low-cost quantum entanglement source. Our results show an average count of over 15,000 entangled photons per second and over 7,500 entangled photon pairs per second, which are in good agreement with theoretical analysis. We have made significant progress towards achieving the goal of low-power and low-cost entanglement sources, which will facilitate the practical application of quantum entanglement lighting and promote the wider adoption of optical quantum systems in the future.
Nowadays, with the continuous development of optical quantum sensor technology, the importance of the quantum entanglement source is increasing day by day. As an indispensable part of optical quantum systems, the quantum entanglement source has a wide prospect of application in quantum communication, quantum imaging, quantum computing, life science and so on. However, the current power consumption and preparation cost of quantum entanglement sources are relatively huge, which impedes further integration and expansion. In view of these problems, we establish a quantum entanglement source model pumped by a low-power laser diode based on spontaneous parametric down-conversion (SPDC) theory and phase matching technology, to effectively analyze the influence of components and characteristics of each module of quantum entanglement source on its performance. Furthermore, we prepare a quantum entanglement source with a 10mW laser diode and a typical type-II barium metaborate (BBO) crystal to conduct experiment whose result is 2053 counts per second in average which is in desirable agreement with the model. To some extent, the low-power and low-cost goal of quantum entanglement source has been achieved, which has made a significant contribution to the practical application of quantum entanglement lighting, and is conducive to the popularization of optical quantum systems in the future.
A compact source of polarization-entangled photon pairs is developed using a blue single-mode laser diode (/spl lambda/ = 402 nm, P = 30 mW) as the pump source of a beta-barium-borate (BBO) nonlinear optical crystal . Using the technique to optimize the collection efficiency, the created photon pairs are coupled into single-mode optical fibers, which are directly connected to quenched silicon avalanche photodiodes (Si APDs). The entanglement of the generated photon pairs was tested with the measurement of the polarization correlations in H/V and +45/spl deg// -45/spl deg/ basis and by violating the Clauser-Horne-Shimony-Holt (CHSH)-type Bell inequality. This compact, robust and economic source can be employed in any application of quantum information and quantum communication, in particular in practicable entanglement based quantum key distribution.
Ultra-broadband frequency entangled biphotons have exceptionally short temporal duration and can achieve narrow Hong–Ou–Mandel (HOM) interference patterns, making them vital for quantum metrology applications. However, the bandwidth of previously demonstrated biphotons used for HOM interference has been limited to less than 400 nm, which is not wide enough to achieve ultra-high precision in quantum metrology. In order to push the precision to its limit, we have theoretically designed a 20-mm-long chirped periodically poled lithium niobate (CPPLN) crystal with type-II phase matching. Pumped by a 405 nm laser, the down-converted signal and idler photons can cover the wavelength range from 420 to 5200 nm, approaching the transparent upper bound of the LN crystal. In the simulated Hong–Ou–Mandel (HOM) interference, the full-width at half-maximum of the interference pattern is 965 attoseconds, with a visibility of 99.44%. Following a similar approach, we also designed a type-0 CPPLN crystal to achieve higher brightness. These ultra-broadband biphoton sources can generate ultra-narrow quantum interference patterns, which have the potential for attosecond-level high-precision quantum metrology.