Coupled atom-cavity system

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Coupled atom-cavity system

• Rabi oscillation 2-level atom in oscillating
  electromagnetic field
• i) stimulated emission e, ngt ? G, n1gt
• ii) absorption G, n1gt ? e, ngt
• coupling energy ?g DE0 , 2g frequency of
  Rabi cycle

Energy dissipation rates sources of decoherence
? cavity decay rate (leaking energy) ?
free-space atomic dipole decay rate (spontaneous
emission)
Excited State
T
T(t) 2gt
Ground State
Credit Caltech Quantum Optics
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Strong-coupling regime
g gtgt ?, ?

• Coherent time-evolution dominates over the
  incoherent (damping)
• Time domain coherent exchanges of a photon

One central conflict in achieving strong
coupling i) Minimize Vmode lengtharea ?
wavelength ii) Minimize ? 1/(finesselength)
sharper resonance peak gt higher finesse
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Another source of Decoherence

• Motional Effects
• coupling (g) depends on position of atom
• Motional degrees of freedom
• trapped ions could be useful in CQED
• however, hard to fit ion trap in tiny
  optical-size cavity

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Universal Set of Quantum GatesConditional
Quantum Phase Gate

• Circular Rydberg states highly excited atom
• (g0, ?, ?)/2p (25, 1, 0.03) kHz

egt natom 51
Cavity-coupled
ggt natom 50
atomic qubit 0a, 1a are igt, ggt cavity qubit
0c, 1c are n 0 or 1 photons
i gt natom 49
g, 1gt e, 0gt -g, 1gt
Full Rabi cycle
i, 0gt i, 1gt g, 0gt
No phase Change
A. Rauschenbeutel et al. 1999
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Conditional Quantum Phase Gatefor entanglement
(average nphoton 0.18)
Atomic qubit
Field qubit
Phase gate interaction
gt
What good is entanglement in CQED?
A. Rauschenbeutel et al. 1999