Nonlinear pi phase shift for single fiber-guided photons interacting with a single atom

Understand

Realizing a strong interaction between individual optical photons is an important objective of research in quantum science and technology.

• Since photons do not interact directly, this goal requires, e.g., an optical medium in which the light experiences a phase shift that depends nonlinearly on the photon number.
• Once the additional phase shift for two photons reaches pi, such an ultra-strong nonlinearity could even enable the direct implementation of high-fidelity quantum logic operations.
• However, the nonlinear response of standard optical media is many orders of magnitude too weak for this task.