Realistic implementations of quantum communication (QC) protocols suffer from imperfections of our currently available setups, limiting the information transmission range. The most recent laboratory tests show that the properties of existing optical fibers, sources of single photons and their detectors limit the range of secure quantum communication for the distances up to 260 km. Due to a very good quality of the emitted light, huge flexibility in terms of its wavelength and relatively low cost, the most popular realistic single-photon sources are based on the spontaneous parametric down- conversion (SPDC) process. This kind of devices produce entangled pairs of photons, out of which one photon (called idler) can be sent to a heralding detector in the QC implementations and the other one (signal) can be used to distribute the secure key. Photons belonging to a given pair can be correlated in many degrees of freedom. Typically, they exhibit so-called spectral anticorrelations, which means that a little deviation of the frequency of signal photon from its central value corresponds to a similar deviation of the frequency of idler photon, but in the opposite direction. However, it is possible to generate two-photon states with positive spectral correlations [Opt. Lett., 39, 1481 (2014), Phys. Rev. A 94 , 013838 (2016)]. In this situation, the frequencies of signal and idler photons are always shifted in the same direction. Such a feature of a pair of photons can be used to reduce unwanted noise when transmitting information over long distances in fibers [Optica, 4, 84 (2017), Sci. Rep., 9, 3111 (2019)].
A simple, room-temperature, cavity- and vacuum-free interface for an efficient photon-matter interaction is implemented. In the experiment a heralded single photon generated by the process of spontaneous parametric down-conversion is absorbed by a single atom-like system, specifically a nitrogen-vacancy color center in diamond. Here phonon-assisted absorption solves the mismatch problem of a narrow absorption bandwidth in a typical atomic medium and broadband spectrum of quantum light. The source is tunable in the spectral range 452-575 nm, which overlaps well with the absorption spectrum of nitrogen-vacancy centers. This can also be considered as a useful technique paving the way for development of novel quantum information processing and sensing applications.arXiv:1909.05843
We theoretically investigate the problem of finding optimal characteristics of photon pairs, produced in the spontaneous parametric down-conversion (SPDC) process, for fiber-based quantum communication (QC) protocols. By using the accessible setup parameters, the pump pulse duration and the extended phase-matching function width, we minimize the temporal width of SPDC photons within the general scenario. This allows one to perform more effectively the temporal filtering procedure, which aims at reducing the noise acquired by the measurement devices. Moreover, we compare the obtained results with the achievable parameter values for SPDC sources based on β-Barium Borate (BBO) crystal. We also investigate the influence of non-zero detection timing jitter. Finally, we apply our optimization strategy to a simple quantum key distribution scheme to show that the full optimization of an SPDC source can potentially extend the maximal security distance by several tens of kilometres, which is around 50\% more as compared to previous approaches.arXiv:1908.00989
Quantum communication and clock synchronization protocols can be significantly enhanced by the careful preparation of the wavepackets of the produced photons. Following the theoretical proposal published in [Optica, 4, 84 (2017)], we experimentally demonstrate the effect of a remote temporal wavepacket narrowing of a heralded single photon. It is performed by utilizing the time-resolved measurement on the heralding photon which is frequency entangled with the heralded one. We also investigate optimal photon pair source characteristics that minimize the heralded wavepacket width.Sci. Rep., 9 , 3111 (2019)
We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range 457 nm - 2300 nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric down conversion, where one of photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as 40000 in our detection setting. A photon detection efficiency as high as 64 % at 1550 nm and 15 % at 2300 nm was observed.Opt. Lett., 43, 6085 (2018)
Proper characterization of nonlinear crystals is essential for designing single photon sources. We show a technique for dispersion characterization of a nonlinear material by making use of phase matching in the process of parametric down conversion. Our method is demonstrated on an exemplary periodically poled potassium titanyl phosphate (PPKTP) crystal phase-matched for 396 nm to 532 nm and 1550 nm. We show a procedure to characterize the dispersion in the range of 390 to 1800 nm by means of only one spectrometer for the UV-visible range.J. Phys. Commun. 2 065014 (2018)
However, optimization of the properties of these photons for specific applications is an open problem. We theoretically demonstrate the possibility of extending the maximal distance of secure quantum communication when a photon pair source and standard fibers are used in a scenario where Alice and Bob do not share a global time reference. It is done by manipulating the spectral correlation within a photon pair and by optimizing chromatic dispersion in transmission links. Contrary to typical expectations, we show that in some situations the secure communication distance can be increased by introducing some extra dispersion.Phys. Rev. A 98, 062310 (2018)
Chromatic dispersion is one of the main limitations to the security of quantum communication protocols that rely on the transmission of single photons in single-mode fibers. This phenomenon forces the trusted parties to define longer detection windows to avoid losing signal photons and increases the amount of detection noise that is being registered. In this work, we analyze the effects of chromatic dispersion on a photon pair generated via spontaneous parametric down-conversion and propagating in standard telecommunication fibers. We also present the possibility of reducing the detection noise by manipulating the spectral correlation of the pair. As an example, we show that our results can be used to increase the maximal security distance of a discrete-variable quantum key distribution scheme in which the photon source is located between the legitimate participants of the protocol.Optica 4, 84 (2017)
Correlated photon pairs produced by a spontaneous parametric down conversion (SPDC) process can be used for secure quantum communication over long distances including free space transmission over a link through turbulent atmosphere. We experimentally investigate the possibility to utilize the intrinsic strong correlation between the pump and output photon spatial modes to mitigate the negative targeting effects of atmospheric beam wander. Our approach is based on a demonstration observing the deflection of the beam on a spatially resolved array of single photon avalanche diodes (SPAD-array).Opt. Express 24 , 20947 (2016)
Sources of photon pairs based on the spontaneous parametric down conversion process are commonly used for long distance quantum communication. The key feature for improving the range of transmission is engineering their spectral properties. Following two experimental papers [Opt. Lett., 38, 697 (2013)] and [Opt. Lett., 39, 1481 (2014)] we analytically and numerically analyze the characteristics of a source. It is based on a β-barium borate (BBO) crystal cut for type II phase matching at the degenerated frequencies 755 nm → 1550 nm + 1550 nm. Our analysis shows a way for full control of spectral correlation within a fiber-coupled photon pair simultaneously with optimal brightness.Phys. Rev. A 94 , 013838 (2016)
September, 2018 - April, 2019
January - August, 2018
PhD Student, Brasil
June - August, 2017
The research project aims at developing: 1) single-photon sources and single photon characterization techniques, and their 2) applications in a selection of problems, which have a high potential to be solved using carefully prepared states of photons. Those problems are quantum communication with single-mode fibers and free space link using satellite receiver, efficient entangled two-photon absorption and quantum interference with nanostructures.
The Faculty of Physics, Astronomy and Informatics of the Nicolaus Copernicus University in Toruń, Poland, organizes Torun Astrophysics Physics Summer program. Students interested in experimental and/or theoretical quantum optics related to single photon are welcome to apply. It can be done:
1) when the current program edition is active via TAPS website directly or
2) all year long at firstname.lastname@example.org by sending CV (max. 4 pages) and motivation letter (max. 1 page).