Quantum Entanglement and Interferometry

Bethany Little

Kishore T. Kapale

David S. Simon, Gregg S. Jaeger, Alexander V. Sergienko

James F. Smith

Mathematical analysis is presented related to novel quantum entangled states useful for interferometry. For interferometry applications, the approach based on entanglement presented here, even in the presence of loss offers a quadratic reduction in the number of photons required while maximizing phase sensitivity and visibility. Reducing the number of photons decreases the effects of certain mechanisms that degrade results. The new interferometer is an improvement on a previous interferometer based on linear combination of M&N states (LCMNS). LCMNS have been shown to be much more robust in the presence of environmental effects than plain M&N states or N00N states. Adaptive optics techniques are used to adjust the coefficients of the LCMNS. Closed form expressions for the minimum phase error, visibility, and coefficients are derived. Environmental effects are included using open systems theory. Numerical results are provided.

Ana Laura Gramajo, Daniel Domı́nguez, María José Sánchez

We study the manipulation of quantum entanglement by periodic external fields in the Landau-Zener-Stuckelberg interferometry of coupled flux qubits. As an entanglement measure we compute numerically the concurrence of two coupled flux qubits, both driven by a dc+ac magnetic flux. We show that it is possible to create or destroy entanglement in a controlled way by tuning the system at or near multiphoton resonances.