Piotr Kolenderski

Toward a downconversion source of positively spectrally correlated and decorrelated telecom photon pairs

Summary form only given. The frequency correlation (or decorrelation) of photon pairs is of great importance in long-range quantum communications and photonic quantum computing. We experimentally characterize a spontaneous parametric down conversion (SPDC) source, based on a β-Barium Borate (BBO) crystal cut for type-II phase matching at 1550 nm which has the capability to emit photons with positive or no spectral correlations. Our system, depicted in Fig. 1a), employs a carefully designed detection method exploiting two InGaAs detectors.In the process of SPDC the joint effect of the nonlinear crystal and the collection optics can be described using an effective phase matching function [2,3]. Its diagonal slices can be accessed by measuring the joint spectral amplitudes for a range of CW pump laser settings. For that we measured the relative detection time statistics of photons traveling through two long fibers and exploit the dispersion experienced in single mode fiber [1]. The measurement results are depicted in Fig. 1b) and agree well with the theoretical model presented in Ref. [2]. The EPMF in this configuration suitable for generating positively-correlated or uncorrelated photon pairs without using spectral filtering when pumped using broadband pulses. This measurement was only possible because of the improved sensitivity of our fiber spectrometer, which was achieved by using a combination of free-running and gated InGaAs detectors.

Time and spectrum-resolving multiphoton correlator for 300–900 nm

We demonstrate a single-photon sensitive spectrometer in the visible range, which allows us to perform time-resolved and multi-photon spectral correlation measurements at room temperature. It is based on a monochromator composed of two gratings, collimation optics, and an array of single photon avalanche diodes. The time resolution can reach 110 ps and the spectral resolution is 2u2009nm/pixel, limited by the design of the monochromator. This technique can easily be combined with commercial monochromators and can be useful for joint spectrum measurements of two photons emitted in the process of parametric down conversion, as well as time-resolved spectrum measurements in optical coherence tomography or medical physics applications.

Implementing the Aharon-Vaidman quantum game with a Young type photonic qutrit

The Aharon-Vaidman (AV) game exemplifies the advantage of using simple quantum systems to outperform classical strategies. We present an experimental test of this quantum advantage by using a three-state quantum system (qutrit) encoded in a spatial mode of a single photon passing through a system of three slits. The preparation of a particular state is controlled as the photon propagates through the slits by varying the number of open slits and their respective phases. The measurements are achieved by placing detectors in the specific positions in the near and far-field after the slits. This set of tools allowed us to perform tomographic reconstructions of generalized qutrit states, and implement the quantum version of the AV game with compelling evidence of the quantum advantage.

Spectral correlation control in down-converted photon pairs

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.

Towards correcting atmospheric beam wander via pump beam control in a down conversion process.

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).

Dispersion measurement method with down conversion process

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. We use our procedure to improve the Sellmeier coefficients measured by another methods. Our method is demonstrated on an exemplary periodically poled potassium titanyl phosphate KTiOPO4 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.

Reducing detection noise of a photon pair in a dispersive medium by controlling its spectral entanglement

We analyze the effect of the chromatic dispersion on the characteristics of the state of a photon pair generated in the spontaneous parametric down-conversion process and propagated through standard telecommunication fibers. We investigate the possibility for reduction of the detection noise during the measurement by manipulating the spectral correlation within the pair. We show that our results can be applied to increase the maximal security distance of a discrete-variable quantum key distribution scheme with the source of photons located in the middle between the legitimate participants of a protocol.

On photonic spectral entanglement improving quantum communication (Conference Presentation)

Let us consider the experimental setup where SPDC source generates photon pairs which are subsequently coupled to single-mode fibers (SMFs). We assume that there are three parties involved: 1) Alice, possessing the photon pair source, detection system and the fiber connecting them, 2) Bob, who monitors the output of the second, long-distance fiber and 3) Eve, who can perform the most general collective attacks in order to acquire information which Alice and Bob wish to transfer. Typically, in fiber-based communication the chromatic dispersion is considered to be an obstacle, limiting the maximal distance at which information carrier can be securely transmitted. 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. nnWe consider standard BB84 quantum key distribution protocol, based on the SPDC source located in between Alice and Bob. The parameters of standard realistic telecommunication fibers (SMF28e+) are take into account. The source emits photon which apart of being entangled in polarization degree of freedom are entangled in spectral domain. This is the key feature which allows one to reduce detection noise by manipulating the spectral correlation between the produced photons. In this way the maximal security distance can be increased by around 10%.

Playing a quantum game with a qutrit

The Aharon Vaidman (AV) quantum game [1] demonstrates the advantage of using simple quantum systems to outperform classical strategies. We present an experimental test of this quantum advantage by using a three-state quantum system (qutrit) encoded in a spatial mode of a single photon passing through a system of three slits [2,3]. We prepare its states by controlling the photon propagation and the number of open and closed slits. We perform POVM measurements by placing detectors in the positions corresponding to near and far field. These tools allow us to perform tomographic reconstructions of qutrit states and play the AV game with compelling evidence of the quantum advantage.

Experimental state estimation for spatial qubits

We experimentally demonstrate a quantum state estimation and tomography for qubits encoded in a single photons spatial degree of freedom. The experimental setup depicted in Fig. 1 consists of: 1) polarization entangled photon pairs source; 2) spatial encoder allowing to map a polarization state into spatial state; 3) polarization analyzer and 4) spatial state analyzer. The 28 element spatial quantum state measurement set was implemented using imaging optics and a linear array of 28 single photon avalanche diodes (SPAD). The timing information from all the detectors was acquired using custom made FPGA electronics.