Entangled Colors

• Post by: admin
• December 17, 2009
• No Comment

Our paper Discrete, tunable color entanglement has been published in Physical Review Letters.

Two photons can be entangled in many different degrees of freedom, such as their polarization (the all-time favorite in the community). Photon pairs created in spontaneous parametric downconversion are intrinsically entangled in energy (and thus in frequency) and momentum. The frequency entanglement however is continuous, i.e. the spectral components of each photon are entangled with each other. To verify this entanglement one can single out a pair of frequencies within the photon spectrum, which in earlier experiments was usually done after an actual measurement via interference filters or apertures.

In our experiment in contrast, only the two colors which show up in the final entangled state are present in the initial state. Hence the title ‘discrete’ color entanglement. The frequency bins in our experiment are well separated and we can even tune the frequency difference between them. In other words, each photon can be seen as a frequency qubit with a tunable energy gap. In addition, we were able to reconstruct a density matrix for the entangled states and calculate properties such as their tangle and purity.

Physics Today has highlighted our work here.