Abstract
A crystal superlattice structure featuring nonlinear layers with alternating orthogonal optic axes interleaved with orthogonal poling directions, is shown to generate high-quality hyperentangled photon pairs via orthogonal quasi-phase-matched spontaneous parametric downconversion. We demonstrate that orthogonal quasi-phase matching (QPM) processes in a single nonlinear domain structure correct phase and group-velocity mismatches concurrently. Compared with the conventional two-orthogonal-crystals source and the double-nonlinearity single-crystal source, the orthogonal QPM superlattice is shown to suppress the spatial and temporal distinguishability of the generated photon pairs by several orders of magnitude, depending on the number of layers. This enhanced all-over-the-cone indistinguishability enables the generation of higher fluxes of photon-pairs by means of the combined use of (a) long nonlinear crystal in noncollinear geometry, (b) low coherence-time pumping and ultra-wide-band spectral detection, and (c) focused pumping and over-the-cone detection. While each of these three features is challenging by itself, it is remarkable that the orthogonal QPM superlattice meets all of these challenges without the need for separate spatial or temporal compensation.
Highlights
Hyperentanglement, the simultaneous entanglement in multiple degrees of freedom of a quantum system, has been widely used to circumvent limitations of linear optics1 in realizing various quantum operations like Bell-state analysis2–7, beating the channel capacity limit8, superdense teleportation9, deterministic entanglement purification10, 11, and teleportation of multiple degrees of freedom12
The simplest source of hyperentangled photon pairs is based on spontaneous parametric downconversion (SPDC) in a single type-II nonlinear crystal22
The bandwidth of spectral entanglement is limited by the phase matching condition, which can often be aided by use of periodically poled crystals that introduce quasi-phase matching (QPM)
Summary
Hyperentanglement, the simultaneous entanglement in multiple degrees of freedom of a quantum system, has been widely used to circumvent limitations of linear optics in realizing various quantum operations like Bell-state analysis, beating the channel capacity limit, superdense teleportation, deterministic entanglement purification , and teleportation of multiple degrees of freedom. A perfect source of hyperentangled photon pairs (biphotons) allows multiple possibilities for biphoton emissions that are indistinguishable in all degrees of freedom — spatial, spectral, and polarization — over its entire emission cone. The simplest source of hyperentangled photon pairs is based on spontaneous parametric downconversion (SPDC) in a single type-II nonlinear crystal. Entanglement is enabled by the multiple possibilities of satisfying energy and momentum conservation for the orthogonal polarization. The type-II process exhibits polarization and spectral entanglement within small solid angles centered about two specific noncollinear directions defined by the intersection of two emission cones with offset axes. A more efficient source of hyperentangled biphotons uses two abutted thin nonlinear crystals with orthogonal optic axes, each generating type-I SPDC with the same pump . A principal limitation of this cascaded-crystals (CC) source is that the nonlinear crystals must be rather thin
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
