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Quantum Trajectory Method in Quantum Optics Tarek Ahmed Mokhiemer Graduate Student King Fahd University of Petroleum and Minerals Graduate Student King Fahd University of Petroleum and Minerals
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Outline General overview QTM applied to a Two level atom interacting with a classical field A more formal approach to QTM QTM applied to micromaser References
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The beginning … J. Dalibard, Y. Castin and K. M ø lmer, Phys. Rev. Lett. 68, 580 (1992)Phys. Rev. Lett. 68, 580 (1992) R. Dum, A. S. Parkins, P. Zoller and C. W. Gardiner, Phys. Rev. A 46, 4382 (1992)Phys. Rev. A 46, 4382 (1992) H. J. Carmichael, “ An Open Systems Approach to Quantum Optics ”, Lecture Notes in Physics (Springer, Berlin, 1993)
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Quantum Trajectory Method is a numerical Monte-Carlo analysis used to solve the master equation describing the interaction between a quantum system and a Markovian reservoir. system Reservoir
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A single quantum trajectory represents the evolution of the system wavefunction conditioned to a series of quantum jumps at random times 0.050.10.150.2 0.4 0.6 0.8 1 Time
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The evolution of the system density matrix is obtained by taking the average over many quantum trajectories. 2000 Trajectories 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Time
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The quantum trajectory method is equivalent to solving the master equation
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Advantages of QTM Computationally efficient Physically Insightful !
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A single quantum trajectory Initial state Non-Unitary Evolution Quantum Jump Non-Unitary Evolution Quantum Jump
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The Master Equation (Lindblad Form)
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Two level atom interacting with a classical field
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.
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The probability of spontaneous emission of a photon at Δt is: Initial state:
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Г: spontaneous decay rate Applying Weisskopf-Wigner approximations … ( Valid for small Δt)
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Deriving the conditional evolution Hamiltonian H cond
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Two methods Compare the probability of decay each time step with a random number Integrate the Schr ö dinger's equation till the probability of decay equals a random number.
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Non-Hermetian Hamiltonian μ: Normalization Constant
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A single Quantum Trajectory time
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Average of 2000 Trajectories: Time
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Spontaneous decay in the absence of the driving field time
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Is a single trajectory physically realistic or is it just a “ clever mathematical trick ” ?
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A more formal approach … starting from the master equation
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Jump Superoperator: Applying the Dyson expansion
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Initial state Non-Unitary Evolution Quantum Jump Non-Unitary Evolution Quantum Jump
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The more general case …
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Different Unravellings A single number stateA superposition of number states
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The Micromaser “ Single atoms interacting with a highly modified vacuum inside a superconducting resonator ”
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Quantum Semiclass. Opt. 8, 73 – 104 (1996)
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Atom passing without emitting a photon Atom emits a photon while passing through the cavity The field acquires a photon from the thermal reservoir The field loses a photon to the thermal reservoir Jump superoperator
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Comparison between QTM and the analytical solution
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The power of the Quantum Trajectory Method time
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Transient Evolution of the Probability Distribution p(n) n
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Limitation of the method
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Conclusion Quantum Trajectory Method can be used efficiently to simulate transient and steady state behavior of quantum systems interacting with a markovian reservoir. They are most useful when no simple analytic solution exists or the dimensions of the density matrix are very large.
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References A quantum trajectory analysis of the one-atom micromaser, J D Cressery and S M Pickles, Quantum Semiclass. Opt. 8, 73 – 104 (1996) Wave-function approach to dissipative processes in quantum optics,Phys. Rev. Lett., 68, 580 (1992) Quantum Trajectory Method in Quantum Optics, Young-Tak Chough Measuring a single quantum trajectory, D Bouwmeester and G Nienhuis, Quantum Semiclass. Opt. 8 (1996) 277 – 282
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Questions …
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