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Physical Review A

Indistinguishability of entangled photons generated with achromatic phase matching

Juan P. Torres, Morgan W. Mitchell, Martin Hendrych

Published Feb 28, 2005• 18 citations
Publisher

Abstract

We put forward a method to suppress distinguishing information contained in the frequency spectrum of entangled photon pairs generated in spontaneous parametric down-conversion. The distinguishing information is shown to be suppressed by employing achromatic phase-matching techniques to tailor the group velocities of the generated signal and idler photons, and thus tuning their spectral properties. The method can be implemented in materials and frequency bands where conventional solutions do not hold, and it can benefit from the dispersion cancellation inherent to entangled photons featuring frequency correlation or anticorrelation. The generation of polarization Bell states is discussed.

DOI
10.1103/physreva.71.022320

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We put forward a method to suppress distinguishing information contained in the frequency spectrum of entangled photon pairs generated in spontaneous parametric down-conversion. The distinguishing information is shown to be suppressed by employing achromatic phase-matching techniques to tailor the group velocities of the generated signal and idler photons, and thus tuning their spectral properties. The method can be implemented in materials and frequency bands where conventional solutions do not hold, and it can benefit from the dispersion cancellation inherent to entangled photons featuring frequency correlation or anticorrelation. The generation of polarization Bell states is discussed.
We put forward a new scheme to tailor the frequency correlations of paired photons which allows their spectral properties to be tuned from correlation to anticorrelation, including uncorrelation. The method is based on the proper tailoring of the group velocities of all interacting waves through the use of beams with angular dispersion. The method can be implemented in materials and frequency bands where conventional solutions do not hold. This technique makes possible the generation of frequency correlated photons, heralded single photons with a high degree of purity from pairs of uncorrelated photons, and the suppression of distinguishing information contained in the frequency spectrum of polarization entangled photon pairs.
The transverse momentum correlation of photon pairs generated by noncollinear spontaneous parametric down-conversion with type-I phase matching is transformed into polarization entanglement. A robust wavefront-splitting interferometer scheme is used, due to which the phase of the entangled state does not require active stabilization. Frequency-degenerate signal and idler photons are separated and coupled into single-mode optical fibers. The concept is demonstrated in a compact and modular setup. A straightforward alignment process for producing any of the Bell states is presented. The entangled source has an output photon flux of $8.33\ifmmode\pm\else\textpm\fi{}1.27$ kcps/mW normalized to pump power (150 mW), and $17\ifmmode\pm\else\textpm\fi{}3%$ heralding ratio. The measured state fidelity with respect to the negative anticorrelated Bell state is $0.951\ifmmode\pm\else\textpm\fi{}0.004$.
We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase-matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO4. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.
We present a scheme for generating polarization-entangled photons pairs with arbitrary joint spectrum. Specifically, we describe a technique for spontaneous parametric down-conversion in which both the center frequencies and the bandwidths of the down-converted photons may be controlled by appropriate manipulation of the pump pulse. The spectral control offered by this technique permits one to choose the operating wavelengths for each photon of a pair based on optimizations of other system parameters (loss in optical fiber, photon counter performance, etc.). The combination of spectral control, polarization control, and lack of group-velocity matching conditions makes this technique particularly well suited for a distributed quantum information processing architecture in which integrated optical circuits are connected by spans of optical fiber.