Quantum Control in the Presence of Relaxation

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Quantum Control in the Presence of Relaxation
Benjamin Recht MIT Media Lab, 2002
Collaborators Yael Maguire Seth Lloyd Isaac
Chuang Neil Gershenfeld
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Decoherence and Relaxation
Quantum
Classical
Order
Disorder
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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
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Recht Angle vs Ernst Angle

• A new interpretation of an old result on
  steady-state NMR

• In the limit where T1T2 our schemes produce
  larger NMR signals and use smaller RF pulses

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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
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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