Nonstationary dissipative dynamics of a single qubit

Using master equation and quantum Monte Carlo wavefunction approaches, we study the circumstances surrounding the emergence and degradation of the elusive squeezing of fluctuations in two-level atom resonance fluorescence. For its measurement we suggest conditional homodyne detection (CHD) [G.T. Foster, L.A. Orozco, H.M. Castro-Beltran, H.J. Carmichael, Phys. Rev. Lett. 85, pp. 3149-3152, 2000], which is nearly independent of detector efficiencies, which have harmed previous attemps. Squeezing in resonance fluorescence requires a weak laser, so the average interval between emitted photons is much longer than the regression time to the steady state; here, the spectrum of the out-of-phase quadrature is a negative peak. In CHD, moderate fields generate a non-zero third-order correlation in the dipole fluctuations that contaminates squeezing, making the noise nonGaussian. If the probability to emit two and even three close photons is still small the additional contribution is also negative, helping to make the full spectrum a bit larger and easier to measure. Strong driving spreads the photoemission distribution, which destroys squeezing, and the third order fluctuations become responsible for the non-classicality of the fluorescence.

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“…16 The mean photon number, k , and the dispersion, Δk 2 = ( k 2 − k 2 ) 1/2 , are the most common measures. From the ergodic theorem,…”

Section: Quantum Jump Methodsmentioning

confidence: 99%

Emergence and degradation of squeezing in resonance fluorescence

2011

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“…Work on related problems has been reported in Refs. [5,7,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], Refs. [27][28][29] consider a LZ transition for two states coupled to a bath of harmonic oscillators, and Refs.…”

Section: Introductionmentioning

confidence: 99%

Landau-Zener problem with decay and dephasing

Avishai

Band

2014

Phys. Rev. A

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Two aspects of the classic two-level Landau-Zener (LZ) problem are considered. First, we address the LZ problem when one or both levels decay, i.e., εj(t) → εj(t) − iΓj /2. We find that if the system evolves from an initial time −T to a final time +T such that |ε1(±T ) − ε2(±T )| is not too large, the LZ survival probability of a state |j can increase with increasing decay rate of the other state |i = j . This surprising result occurs because the decay results in crossing of the two eigenvalues of the instantaneous non-Hermitian Hamiltonian. On the other hand, if |ε1(±T ) − ε2(±T )| → ∞ as T → ∞, the probability is independent of the decay rate. These results are based on analytic solutions of the time-dependent Schrödinger equations for two cases: (a) the energy levels depend linearly on time, and (b) the energy levels are bounded and of the form ε1,2(t) = ±ε tanh(t/T ). Second, we study LZ transitions affected by dephasing by formulating the Landau-Zener problem with noise in terms of a Schrödinger-Langevin stochastic coupled set of differential equations. The LZ survival probability then becomes a random variable whose probability distribution is shown to behave very differently for long and short dephasing times. We also discuss the combined effects of decay and dephasing on the LZ probability.

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Nonstationary dissipative dynamics of a single qubit

Cited by 2 publications

References 23 publications

Emergence and degradation of squeezing in resonance fluorescence

Emergence and degradation of squeezing in resonance fluorescence

Landau-Zener problem with decay and dephasing

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