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Experimental entanglement swapping through single-photon χ(2) nonlinearity.

Yoshiaki Tsujimoto1, Kentaro Wakui2, Tadashi Kishimoto2

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Area of Science:

  • Quantum Information Science
  • Nonlinear Optics
  • Photonics

Background:

  • Photonic quantum information processing relies on nonlinear photon-photon interactions for essential operations like two-qubit gates and entanglement swapping.
  • The weak interaction between single photons has historically hindered the all-photonic realization of these crucial quantum operations.

Purpose of the Study:

  • To demonstrate entanglement swapping using sum-frequency generation (SFG) in a nonlinear optical waveguide.
  • To address the stringent signal-to-noise ratio (SNR) requirements for entanglement swapping protocols.

Main Methods:

  • Utilized sum-frequency generation (SFG) in a χ(2)-nonlinear optical waveguide for single-photon interactions.
  • Employed an ultralow-dark-count superconducting single-photon detector for a high-SNR entanglement heralder.
  • Leveraged ultrafast telecom entangled photon-pair sources operating in the GHz range to enhance system clock speed.

Main Results:

  • Achieved a high signal-to-noise ratio (SNR) for the entanglement heralder, meeting the protocol's demands.
  • Confirmed a lower bound of 0.770(76) for the fidelity of the swapped entangled state, exceeding the classical limit of 0.5.
  • Demonstrated the feasibility of entanglement swapping using all-single-photonic nonlinear interactions.

Conclusions:

  • The developed SFG-based entanglement heralder and detection system satisfy the high SNR requirements for photonic entanglement swapping.
  • The successful demonstration of entanglement swapping with high fidelity highlights the potential of nonlinear optical waveguides.
  • These findings pave the way for advancements in long-distance quantum communication and scalable photonic quantum computation.