In the Quantum Atom Optics group, we use cold, dense, clouds of atoms to store, retrieve, and manipulate pulses of light encoding quantum information.
For my PhD, I extend the storage of light into the creation of stationary light. Stationary light may be contrasted with stored light: When light is stored, the information in the light is mapped onto a long-lived excitation of the atoms. This excitation may later be converted back to a pulse of light. To create stationary light, the excitation is continually mapped back to light in such a way that the light and the excitation remain trapped within the memory. The stationary light field may then be used to produce further, nonlinear interactions.
In the Gradient Echo Memory (GEM), the information pulse (probe) is mapped onto the atomic excitation (spinwave) by a coherent 2-photon interaction with a driving laser field (control). A gradient in the atomic detuning causes the memory to map different frequency components of the probe to different spatial components of the memory, creating a spinwave that is the approximate Fourier transform of the probe pulse. Reversing the gradient rephases the spinwave, and sending the control field recalls the pulse in a time-reversal of the storage process. Adding a counter-propagating control field creates another probe field travelling along with the second control field.
I find a novel solution for stationary light that is suited to the Gradient Echo Memory scheme. By carefully choosing the detunings and angles of the control fields, the equations of motion of the probes and spinwave are massively simplified. A spinwave can be written that, when the counter-propagating control fields are sent, creates a pair of counter-propagating probe fields that are equal and opposite throughout the memory: they do not cause any evolution of the spinwave, and do not escape the memory.
I present this theory of stationary light with supporting experimental evidence and discussion about possible applications.
Followed by light refreshments in the DQS Tea Room