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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Domain-engineered PPLN for entangled photon generation and other quantum information applications

Paulina S. Kuo, Jason S. Pelc, Oliver Slattery, Lijun Ma, Xiao Hong Tang

Published May 1, 2014• 6 citations
Publisher

Abstract

We describe the design and application of domain-engineered, periodically poled lithium niobate (PPLN) for use to produce entangled photons and for other tools in quantum information and communications. By specially designing and controlling the PPLN poling pattern, multiple nonlinear optical processes can be simultaneously phasematched. This capability can be used to generate polarization-entangled photon pairs through type-II spontaneous parametric downconversion. The single PPLN crystal is designed to produce both the |HV〉 and |VH〉 states where the downconverted photons are distinguishable by wavelengths, which enables generation of post-selection-free, polarization-entangled twin photons. We describe the design and fabrication of the PPLN crystal, and initial experimental results for downconversion of a 775 nm pump to 1532 nm and 1567 nm orthogonally polarized photons. We also discuss other applications of engineered optical frequency conversion for quantum information including the use of dual-wavelength upconversion as a beamsplitter to route or analyze photons.

DOI
10.1117/12.2058567

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We describe the design and application of domain-engineered, periodically poled lithium niobate (PPLN) for use to produce entangled photons and for other tools in quantum information and communications. By specially designing and controlling the PPLN poling pattern, multiple nonlinear optical processes can be simultaneously phasematched. This capability can be used to generate polarization-entangled photon pairs through type-II spontaneous parametric downconversion. The single PPLN crystal is designed to produce both the |HV〉 and |VH〉 states where the downconverted photons are distinguishable by wavelengths, which enables generation of post-selection-free, polarization-entangled twin photons. We describe the design and fabrication of the PPLN crystal, and initial experimental results for downconversion of a 775 nm pump to 1532 nm and 1567 nm orthogonally polarized photons. We also discuss other applications of engineered optical frequency conversion for quantum information including the use of dual-wavelength upconversion as a beamsplitter to route or analyze photons.
We develop and demonstrate a source of polarization-entangled photon pairs using spontaneous parametric down-conversion (SPDC) in domain-engineered, periodically poled lithium niobate (PPLN) at telecom wavelengths. Pumped at 775 nm, this domain-engineered type-II SPDC source produces non-degenerate signal and idler pairs at 1530 nm and 1569 nm. Because of birefringence, the photon pair with horizontally polarized signal and vertically polarized idler has a different phasematching condition than the pair with vertically polarized signal and horizontally polarized idler. Using phase-modulation of the domain structure, we produced a crystal that can simultaneously generate both states in a distributed fashion throughout a single crystal. Performing SPDC using this aperiodically poled crystal, we observed polarization entanglement visibility above 93%. We compare the phase-modulated crystal to other aperiodic structures, including dual-periodically-poled and interlaced biperiodic structures.
We characterize spontaneous parametric downconversion in a domain-engineered, type-II periodically poled lithium niobate (PPLN) crystal using seeded emission and single-photon techniques. Using continuous-wave (CW) pumping at 775 nm wavelength, the signal and idler are at 1532.5 nm and 1567.5 nm, respectively. The domain-engineered crystal simultaneously phasematches signal and idler pairs: [H(1532.5 nm), V(1567.5 nm)] and [V(1532.5 nm), H(1567.5 nm)]. We observe the tuning curves of these processes through difference-frequency generation and through CW fiber-assisted, single-photon spectroscopy. These measurements indicate good matching in amplitude and bandwidth of the two processes and that the crystal can in principle be used effectively to generate polarization-entangled photon pairs.
A periodically poled lithium niobate (PPLN) crystal has been used as an efficient source of non-collinearly generated polarization-entangled photon pairs at 810 and 1550 nm. The PPLN crystal was endowed with a specially designed poling pattern and the entangled photons were generated via the nonlinear optical process of spontaneous parametric down conversion (SPDC). A novel design based on overlapping two concurrent type-I quasi-phase-matching structures in a single PPLN crystals produced correlated pairs of alternatively polarized photons in largely separated spectral regions. The phase of the resulting two-photon state is directly linked to parameters of the nonlinear grating. Continuous tunability of the generated Bell state, from Phi(+) to Phi(-), has been demonstrated by translating a slightly wedged crystal perpendicular to the pump beam.
We propose to integrate the electro-optic tuning function into polarization-entangled photon pair generation process in a periodically poled lithium niobate (PPLN). Due to the versatility of PPLN, both the spontaneously parametric down conversion and electro-optic polarization rotation effects could be realized simultaneously. Orthogonally-polarized and parallel-polarized photon pairs thus are instantly switchable by tuning the applied field. The characteristics of the source are investigated showing adjustable bandwidths and high entanglement degrees. Moreover, other kinds of reconfigurable entanglement are also achievable based on suitable domain-design. We believe the domain engineering is a very promising solution for next generation function-integrated quantum circuits.
A method is presented for the first time to our knowledge for generating multiple-channel polarization-entangled photon pairs simultaneously based on type II quasi-phase-matched spontaneous parametric downconversion pumped by monochromatic light in a single periodically poled lithium niobate (PPLN) crystal. The expression for the count of the polarization-entangled photon pairs is analytically obtained. It is predicted that one-, two-, and even three-channel polarization-entangled photon pairs can be simultaneously generated just by suitably choosing the PPLN grating period and the pump frequency.
Abstract Polarisation-entangled photon pairs generated through nonlinear optical processes are crucial ingredients for a range of quantum information processing applications, such as quantum sensing and communication. In this work, we report an optimised design of a lithium niobate on insulator waveguide that is capable of directly generating polarisation-entangled photon pairs enabled through two different spontaneous parametric down-conversion processes simultaneously in the telecommunication wavelength band with a single poling period, based on Type II phase matching. The generated photon pairs cover wavelengths in telecom O (1310 nm) and telecom C (1550 nm) bands with the computed spectral brightness of ≈ 2 × 10 9 pairs sec − 1 mW − 1 . We also study the effect of temporal delay on the quality of entanglement, which is minimised by selecting an appropriate length of the waveguide and pump bandwidth. The optimised integrated quantum light source, presented here, eliminates the need for complex domain engineering or intermodal dispersion and will serve as a valuable resource for various quantum-optical experiments.