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AIP Advances

Spectral characterization of an SPDC source with a fast broadband spectrometer

Brianna Farella, Gregory Medwig, Raphael A. Abrahão, ANDREI NOMEROTSKI

Published Apr 1, 2024• 9 citations
Publisher

Abstract

Knowing the properties of single photons produced in a Spontaneous Parametric Down-Conversion (SPDC) source can be crucial for specific applications and uses. In particular, the spectral properties are of key relevance. Here, we investigate a commercial SPDC source using our fast broadband spectrometer. Our analysis is a valid method for other SPDC sources, as well as other single-photon generation techniques, thus providing a good example of how to use this spectrometer design. We calibrate the spectrometer using known lines of the argon emission spectrum. We show that the two down-converted photons from the SPDC source have different spectral properties depending on the pump power, and under which condition we measured spectrally similar down-converted photons. Finally, we were able to reconstruct and investigate the spectral information for the pump photon.

DOI
10.1063/5.0168423

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The European Physical Journal Special Topics•Apr 26, 2021•6 citations
Knowing the properties of single photons produced in a Spontaneous Parametric Down-Conversion (SPDC) source can be crucial for specific applications and uses. In particular, the spectral properties are of key relevance. Here, we investigate a commercial SPDC source using our fast broadband spectrometer. Our analysis is a valid method for other SPDC sources, as well as other single-photon generation techniques, thus providing a good example of how to use this spectrometer design. We calibrate the spectrometer using known lines of the argon emission spectrum. We show that the two down-converted photons from the SPDC source have different spectral properties depending on the pump power, and under which condition we measured spectrally similar down-converted photons. Finally, we were able to reconstruct and investigate the spectral information for the pump photon.
Knowing the properties of the single photons produced in a Spontaneous Parametric Down-Conversion (SPDC) source can be crucial for specific applications and uses. In particular, the spectral properties are of key relevance. Here, we investigate a commercial SPDC source using our fast broadband spectrometer. Our analysis is a valid method for other SPDC sources, as well as other single-photon generation techniques, thus providing a good example of how to use this spectrometer design. We calibrate the spectrometer using known lines of the argon emission spectrum. We show that the two down-converted photons from the SPDC source have different spectral properties depending on the pump power, and in which condition we measured spectrally similar down-converted photons. Lastly, we were able to reconstruct and investigate the spectral information for the pump photon.
Abstract The photon statistics of spontaneous parametric down-conversion (SPDC) exhibit dependencies on wavelength, pump power, and coincidence time. Notably, the average photon numbers were found to asymmetrically increase with increasing pump power around the degenerate wavelength of emission. We employ a four-detector Hanbury Brown and Twiss interferometer to study the photon statistics of the signal beam. Coupling the detection scheme to a spectrometer enabled the dynamic probing of different bandwidths within the broadband emission. Spectrally resolving the photon statistics revealed that shorter wavelengths increased nonlinearly with pump power, while longer wavelengths showed more linear behavior, indicating a wavelength-dependent efficiency in the generation of the SPDC. The detection and characterization of complex light sources has wide ranging applications in the fields of quantum metrology, quantum communications, and quantum computing, more specifically, a system that is sensitive to wavelength and photon number distribution.
The spectral distribution of photon pairs produced by spontaneous parametric downconversion (SPDC) is one of the most exploited degrees of freedom in multiphoton experiments. Consequently, the characterization of such correlations is, without a doubt, a task of utmost importance. Common methods for measuring the joint spectral intensity (JSI) of correlated photon pairs often exhibit several drawbacks, such as the requirement for a bright source to offset high losses or the need for two-dimensional measurements, which can lead to prolonged acquisition times. In this work, we experimentally demonstrate a technique that allows for the reconstruction of the JSI from a single interferometric measurement, thus reducing the dimensionality of the problem. The reconstructed JSIs show good agreement with those obtained directly through a fiber spectrometer, confirming the effectiveness of our approach. This technique significantly enhances the efficiency of JSI characterization, offering a resource-efficient method for quantum state characterization in SPDC-based experiments.
The ability to determine the joint spectral properties of photon pairs produced by the processes of spontaneous parametric downconversion (SPDC) and spontaneous four-wave mixing (SFWM) is crucial for guaranteeing the usability of heralded single photons and polarization-entangled pairs for multi-photon protocols. In this paper, we compare six different techniques that yield either a characterization of the joint spectral intensity or of the closely related purity of heralded single photons. These six techniques include: (i) scanning monochromator measurements, (ii) a variant of Fourier transform spectroscopy designed to extract the desired information exploiting a resource-optimized technique, (iii) dispersive fibre spectroscopy, (iv) stimulated-emission-based measurement, (v) measurement of the second-order correlation function g(2) for one of the two photons, and (vi) two-source Hong–Ou–Mandel interferometry. We discuss the relative performance of these techniques for the specific cases of a SPDC source designed to be factorable and SFWM sources of varying purity, and compare the techniques’ relative advantages and disadvantages.
Tailoring spectral properties of photon pairs is of great importance for optical quantum information and measurement applications. High-resolution spectral measurement is a key technique for engineering spectral properties of photons, making them ideal for various quantum applications. Here we demonstrate spectral measurements and optimization of frequency-entangled photon pairs produced via spontaneous parametric downconversion (SPDC), utilizing frequency-resolved sum-frequency generation (SFG), the reverse process of SPDC. A joint phase-matching spectrum of a nonlinear crystal around 1580 nm is captured with a 40 pm resolution and a > 40 dB signal-to-noise ratio, which is significantly improved compared to traditional frequency-resolved coincidence measurements. Moreover, our scheme is applicable to collinear degenerate sources whose characterization is difficult with previously demonstrated stimulated difference frequency generation (DFG). We also illustrate that the observed phase-matching function is useful for finding an optimal pump spectrum to maximize the spectral indistinguishability of SPDC photons. We expect that our precise spectral characterization technique will be useful tool for characterizing and tailoring SPDC sources for a wide range of optical quantum applications.
Abstract In our laboratory, we employ two biphoton sources for quantum key distribution. The first is based on cw parametric down-conversion of photons at 404 nm in PPKTP waveguide chips, while the second is based on the pulsed parametric down-conversion of 775 nm photons in PPLN waveguides. The spectral characterization is important for the determination of certain side-channel attacks. A Hong-Ou-Mandel experiment employing the first photon source revealed a complex structure of the common Hong-Ou-Mandel dip. By measuring the spectra of the single photons at 808 nm, we were able to associate these structures to the superposition of different transverse modes of the pump photons in our waveguide chips. The pulsed source was characterized by means of single-photon spectra measured by a sensitive spectrum analyzer as well as dispersion-based measurements. Finally, we also describe Hong-Ou-Mandel experiments using the photons from the second source.