Southwest Quantum Information and Technology

Constraints on photon loss for continuous-variable entanglement swapping using Gaussian resources

Presenting Author: Alex Kwiatkowski, University of Colorado Boulder, NIST
Contributing Author(s): Ezad Shojaee, Scott Glancy, Emanuel Knill

In many procedures for entanglement swapping in the continuous variable domain the entangling measurement is quadrature measurement of two modes combined on a beamsplitter, where the two modes are sent by the two parties that wish to swap entanglement. In the presence of sufficient photon loss however, we show that such measurements cannot be used to swap entanglement. We show analytically that if the modes sent by the two parties suffer losses that average between them to 50% or more, then any linear optical circuit followed by quadrature measurement has a separable POVM on those modes and therefore cannot be used to perform entanglement swapping. We also show that the result holds even if the measurement circuit includes ancillas prepared in arbitrary Gaussian states, and conclude that the average loss threshold of 50% must be met in order to perform entanglement swapping with Gaussian resources alone.

(Session 5 : Saturday from 5:00pm - 7:00pm)