EIT and Slow and Stored Light

Photons are the fastest and simplest carriers of quantum information, but their main strength is also their weakness: they are difficult to localize and store. A solution to this problem may be to store and process quantum information in matter - which would thus form the nodes of a quantum network - and to communicate between these nodes using photons. The hyperfine states of atoms, for example, represent reliable and long-lived storage and processing units.

Together with Mikhail Lukin and his group at the Harvard Physics Department, we developed a technique to transfer quantum states between light fields and matter. This "stored light" technique uses a dynamic form of electromagnetically induced transparency (EIT) to map quantum states of photons into coherently driven atomic media by adiabatically reducing the group velocity of propagating pulses to zero, resulting in a coherently controlled absorption process.

In conventional EIT, an external optical field (the "control field") is used to make an otherwise opaque medium transparent near an atomic resonance. A second, weak optical field (the "signal field"), at an appropriate frequency and polarization, can then propagate without dissipation and loss but with a substantially reduced group velocity ("slow light").

The stored light technique employs a dynamic control field, which allows the information in an input signal pulse to be linearly, coherently, and reversibly mapped with high efficiency into a collective atomic state without suffering the signal pulse bandwidth limitations imposed in conventional EIT by a static control field.

Our collaboration also demonstrated a general technique that optimizes light pulse storage and retrieval; slow and stored light with integrated gain and large pulse delay; and slow and stored light in coated vapor cells.