Abstract
A proposal is made for the generation of polarization-entangled photon pairs from a periodically poled crystal allowing for high collection efficiency, high entanglement, and stable operation. The theory is formulated for colinear propagation for application to waveguides. The key feature of the theory is the use of type II phase matching using both the +1 and -1 diffraction orders of the poling structure. Although these conditions are fairly restrictive in terms of operating parameters, practical operating conditions can be found. For example, we find that a HeNe pump laser may be used for a periodically poled rubidium-doped potassium titanyl phosphate (Rb:KTP) waveguide to yield single mode polarization-entangled pairs. Fidelities of 0.98 are possible under practical conditions.
Highlights
Photonic entanglement is essential to the study of fundamental physics and quantum information science
We propose a new source scheme for polarization-entangled photon pairs, one which builds on the two-source theme of Kwiat and co-workers [5, 6] and Kim et al [9] by effectively creating two sources within a single crystal and using only a single pass of the pump laser beam through that crystal
The waveguide is formed by the diffusion of rubidium-doped potassium titanyl phosphate (Rb) [10] into KTP which displaces some of the K ions in the lattice, forming and an alloy of Rubidium Titanyl Phosphate (RTP) and KTP varying from pure RTP at the surface to pure KTP at a depth of tens of micrometers. (We denote this system as an Rb:KTP waveguide.) The complexity of the alignment is much reduced compared to previous sources, leading to superior stability and high fidelity
Summary
Photonic entanglement is essential to the study of fundamental physics and quantum information science. The basic design has been to effectively create two pair sources with orthogonal polarization and place them so that one cannot determine which source generated the pair other than through the emitted polarization yielding entangled pairs The first such source used type-II phase-matched SPDC in which the down-converted photons were emitted into two non-concentric cones, one with ordinary polarization and the other with extraordinary polarization. In 1999, Kwiat and his colleagues demonstrated a new source scheme using type-I SPDC where an extraordinary polarized pump produces two photons that have matching ordinary polarizations [6] They stacked together two such identical thin nonlinear crystals but rotated one crystal 90◦ about the pump direction. The waveguide is formed by the diffusion of Rb [10] into KTP which displaces some of the K ions in the lattice, forming and an alloy of Rubidium Titanyl Phosphate (RTP) and KTP varying from pure RTP at the surface to pure KTP at a depth of tens of micrometers. (We denote this system as an Rb:KTP waveguide.) The complexity of the alignment is much reduced compared to previous sources, leading to superior stability and high fidelity
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