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Strong-Coupling Regime in Coupled Atom-Cavity System

This article discusses the strong-coupling regime in a coupled atom-cavity system, focusing on Rabi oscillations, energy dissipation rates, sources of decoherence, and achieving universal quantum gates. Motional effects and the potential of trapped ions in cavity quantum electrodynamics (CQED) are also explored.

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Strong-Coupling Regime in Coupled Atom-Cavity System

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  1. Coupled atom-cavity system • Rabi oscillation: 2-level atom in oscillating electromagnetic field • i) stimulated emission |e, n>  |G, n+1> • ii) absorption |G, n+1>  |e, n> • coupling energy: ћg = |Ď•Ē0| , 2g = frequency of Rabi cycle Energy dissipation rates: sources of decoherence κ = cavity decay rate (“leaking” energy) γ = free-space atomic dipole decay rate (spontaneous emission) Excited State Θ Θ(t) = 2gt Ground State Credit: Caltech Quantum Optics

  2. Strong-coupling regime g >> κ, γ • 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 = length*area  ~ wavelength ii) Minimize: κ ~ 1/(finesse*length) sharper resonance peak => higher finesse

  3. 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

  4. Universal Set of Quantum Gates:Conditional Quantum Phase Gate • Circular Rydberg states: highly excited atom • (g0, κ, γ)/2π ~ (25, 1, 0.03) kHz |e>: natom= 51 Cavity-coupled |g>: natom= 50 atomic qubit: 0a, 1a are |i>, |g> cavity qubit: 0c, 1c are n = 0 or 1 photons | i >: natom= 49 |g, 1> |e, 0> -|g, 1> Full Rabi cycle |i, 0> |i, 1> |g, 0> No phase Change A. Rauschenbeutel et al. 1999

  5. Conditional Quantum Phase Gatefor entanglement (average nphoton ~ 0.18) Atomic qubit: Field qubit: Phase gate interaction => What good is entanglement in CQED? A. Rauschenbeutel et al. 1999

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