1. Quantum Control in the Presence of Relaxation
Benjamin Recht
MIT Media Lab, 2002
Collaborators:
Yael Maguire
Seth Lloyd
Isaac Chuang
Neil Gershenfeld

2. Decoherence and Relaxation
Quantum
Classical
Order
Disorder

3. Correcting relaxation in NMR
Red: 90 pulse
Green: Spins Relax
Orange: Control Pulse
Push the spins back into the plane
Induced signal with and without correction pulses

4. Recht Angle vs Ernst Angle
A new interpretation of an old result on steady-state NMR
In the limit where T1=T2 our schemes produce larger NMR signals and use smaller RF pulses

5. Waveform Shaping Spins Ringing Control Pulses
We can write arbitrary envelopes on the spins using control pulses
Zooming in, the spins process at their natural rate and we push them around

6. Preserving Entangled States
We have numerically demonstrated the preservation of quantum information using only unitary operations
Even under restrictive assumptions, we can store one third of an “ebit”