Abstract
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.
Highlights
Photons are a key resource for optical quantum-enhanced technologies, such as quantum computing, quantum communication, and quantum metrology [1]
Tailoring spectral properties of photon pairs produced by spontaneous parametric downconversion (SPDC) and spontaneous four-wave mixing (FWM) is of great importance, since many applications require specific spectral states, in particular, with different degree of spectral entanglement; for example, strong frequency entanglement [2, 3] is required for high-resolution quantum measurements [4] and frequency-encoded quantum information processing [5], while unentangled or indistinguishable photons [6,7,8] are needed for multiplexed single-photon generation [9, 10] and quantum information processing based on multi-photon quantum interference [11, 12]
We show how the phase-matching spectrum obtained via the highprecision sumfrequency generation (SFG) measurements is useful for efficient and precise optimization of a spectral indistinguishability of SPDC photons, a key metric for optical quantum applications based on multi-photon interference
Summary
Photons are a key resource for optical quantum-enhanced technologies, such as quantum computing, quantum communication, and quantum metrology [1]. Sources, since a seed light used for stimulated emissions becomes a source of noise photons due to its high spatial and spectral overlap with the amplified signal lights While such previous demonstrated techniques have been used for reconstructing JSI arising from the product of a pump spectral distribution and a phase-matching spectrum of a nonlinear device, an independent characterization of the two contributions would be preferable for precise diagnosis and engineering of photon pair sources. We demonstrate another classical method to characterize SPDC sources, utilizing frequency-resolved sum-frequency generation (SFG), the reverse process of SPDC. We show how the phase-matching spectrum obtained via the highprecision SFG measurements is useful for efficient and precise optimization of a spectral indistinguishability of SPDC photons, a key metric for optical quantum applications based on multi-photon interference
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