How the COW happened

Jan C. A. Boeyens

R. Colella, A. W. Overhauser

In the course of a casual conversation during a social gathering, in the spring of 1974, we were discussing some recent developments in the area of diffraction from perfect crystals, namely, interferometry in the Angstrom region. I (R.C.) was asked by Al Overhauser whether or not I knew anything about the subject. "Not much" was my answer, "but I can read some papers". Al then proceeded to describe a possible experiment, namely, the effect of gravity on the quantum mechanical phase of the neutron, in essence, what later was called the COW experiment (Colella, Overhauser, Werner).

Claus Kiefer

F. Rezazadeh, A. Mani, M. Khodabandeh +2 more

We present a rigorous mathematical framework for verifying effective entanglement in a Coherent One-Way (COW) quantum key distribution setup. In particular, we introduce a two-parameter family of entanglement witnesses, identify the parameter ranges where they constitute valid witnesses, and demonstrate their ability to reveal effective entanglement in the COW protocol. Additionally, we analyze previously obtained experimental data from a COW implementation and report clear signatures of effective entanglement.

Hannah Clear, Daniel Evan, George McGilvray +1 more

In this paper, we explore the de Broglie wavelength of an average cow, and investigate if it is possible for a cow to also act as a wave. It is perfectly viable to calculate the de Broglie wavelength of a macroscopic object, such as in this case a cow, if we consider each atom of the cow to be coherent. The de Broglie wavelength of an average cow was found to be 1.3 × 10^−37 m.