Demonstration of spectral correlation control in a source of polarization-entangled photon pairs at telecom wavelength

Abstract

Spectrally correlated photon pairs can be used to improve performance of long range fiber based quantum communication protocols. We present a source based on spontaneous parametric down-conversion producing polarization entangled photons without spectral filtering. In addition, the spectral correlation within the photon pair can be controlled by changing the pump pulse duration or coupled spatial modes characteristics. The spectral and polarization correlations were characterized. The generated photon pairs feature both positive spectral correlations, no correlations, or negative correlations and polarization entanglement with the fidelity as high as 0.97 (no background subtraction) with the expected Bell state. © 2018 Optical Society of America OCIS codes: 190.4410,300.6190,270.4180,270.5565 Controlling the spectral correlations of a polarization entangled photon pair produced via spontaneous parametric down-conversion (SPDC) could have important benefits to applications in optical quantum information. Photonic quantum gates require pure states, which can be created by heralded sources producing pairs of spectrally decorrelated photons [1][2][3][4][5][6][7][8][9][10][11]. On the other hand, long distance fiber based quantum communication and quantum metrology [12,13] suffers from chromatic dispersion, which could potentially be improved [14] with positive spectral correlations [15][16][17]. Here we experimentally demonstrate the effective control of spectral correlations in a photon pair source, based on a β−barium borate (BBO) crystal which we characterized previously in Ref. [18]. It produces polarization entangled pairs in the telecom band and can be tuned to create negative, none or positive spectral correlations. In addition to that we show high quality polarization entanglement without using spectral filtering or compensation crystals by adopting the compensation scheme shown in Ref. [19].In the SPDC process, one photon of the pump converts into a photon pair. Energy and momentum conservation relations, jointly described as phase matching, and the properties of the pump photons, govern the characteristics of the generated photons. The probability amplitude for a photon pair emission in a given direction and at a given frequency can be described by the product of the pump spatio-temporal amplitude and the phase matching function [5,19]. The phase matching depending on the properties of the nonlinear media specifies the allowed emissions. Typically, the output photons are coupled into optical fibers. This corresponds to collecting photons from a specific range of directions, defined by the fiber and the optics. From this point of view, coupling can be understood as an additional condition to phase matching. Therefore, one can introduce an effective phase matching function (EPMF) [5,18], which fully describes the joint effect of the crystal and coupling into fibers. We approximate the EPMF using a Gaussian function with the characteristic width σ. The spectral part of the pump can also be approximated by...

Spectrally Pure States at Telecommunications Wavelengths from Periodically PoledMTiOXO4(M=Jin1, Zhao2, Deng3 et al. 2016Phys. Rev. Applied210150View full textAdd to dashboardCite

“…Such a quantum state engineering method can be realized by considering the group-velocity-matched (GVM) condition in specific crystals at certain wavelengths [4][5][6]. Previous work in the field has shown that the GVM condition can be realized in several crystals, e.g., KDP crystal at 830 nm [1,2,7], periodically poled KTP crystal (PPKTP) at 1584 nm [5,8] and BBO crystal at 1514 nm [4,9,10].…”

Pulsed source of spectrally uncorrelated and indistinguishable photons at telecom wavelengths

“…Another solution is to adapt the pump laser spectrum and the dispersion properties of the non-linear material. This approach has been implemented in various media such as bulk crystals [12][13][14], waveguides [15,16], or fibers [17]. Quantum communication requires narrowband sources and recent focus has shifted to using periodically poled potassium titanyl phosphate (PPKTP) nonlinear crystals with ps pulsed lasers [18][19][20][21][22][23] to address these demands of quantum communication.…”

Spectral correlation control in down-converted photon pairs

“…Optical elements are dispersive and cause unwanted modification of the photons' temporal characteristics. The deteriorating dispersion effects can be reduced by using photon pairs that are spectrally narrow and feature appropriate spectral correlations [16][17][18].The spectra of SMF coupled photon pairs generated in SPDC process can be negatively [19,20], positively [16][17][18][21][22][23] or not correlated at all [24][25][26]. The effect of negative correlation originates from the energy conservation relation and is a consequence of pumping by a continuous wave (CW) laser.…”

“…Uncorrelated spectra can be achieved in a nonlinear crystal by using a pulsed laser pump with careful setup parameter choice or by using narrow spectral filters. However, for positive correlation, an additional requirement of group velocity matching needs to be fulfilled [21].Here we perform numerical analysis of the SPDC photon pair source experimentally analyzed in Refs [17,18], which is schematically depicted in Fig. 1.…”