From EIT photon correlations to Raman anti-correlations in coherently prepared Rb vapor

We have experimentally observed switching between photon-photon correlations (bunching) and anti-correlations (anti-bunching) between two orthogonally polarized laser beams in an EIT configuration in Rb vapor. The bunching and anti-bunching sswitching occurs at a specific magnetic field strength.Comment: 4 pages and 3 figure

Quantum limit of optical magnetometry in the presence of ac-Stark shifts

We analyze systematic (classical) and fundamental (quantum) limitations of the sensitivity of optical magnetometers resulting from ac-Stark shifts. We show that in contrast to absorption-based techniques, the signal reduction associated with classical broadening can be compensated in magnetometers based on phase measurements using electromagnetically induced transparency (EIT). However due to ac-Stark associated quantum noise the signal-to-noise ratio of EIT-based magnetometers attains a maximum value at a certain laser intensity. This value is independent on the quantum statistics of the light and defines a standard quantum limit of sensitivity. We demonstrate that an EIT-based optical magnetometer in Faraday configuration is the best candidate to achieve the highest sensitivity of magnetic field detection and give a detailed analysis of such a device.Comment: 11 pages, 4 figure

Radiation trapping in coherent media

We show that the effective decay rate of Zeeman coherence, generated in a Rb87 vapor by linearly polarized laser light, increases significantly with the atomic density. We explain this phenomenon as the result of radiation trapping. Our study shows that radiation trapping must be taken into account to fully understand many electromagnetically induced transparency experiments with optically thick media

Dynamics of a two-level system coupled with a quantum oscillator in the very strong coupling limit

The time-dependent behavior of a two-level system interacting with a quantum oscillator system is analyzed in the case of a coupling larger than both the energy separation between the two levels and the energy of quantum oscillator ($\Omega < \omega < \lambda$, where $\Omega$ is the frequency of the transition between the two levels, $\omega$ is the frequency of the oscillator, and $\lambda$ is the coupling between the two-level system and the oscillator). Our calculations show that the amplitude of the expectation value of the oscillator coordinate decreases as the two-level system undergoes the transition from one level to the other, while the transfer probability between the levels is staircase-like. This behavior is explained by the interplay between the adiabatic and the non-adiabatic regimes encountered during the dynamics with the system acting as a quantum counterpart of the Landau-Zener model. The transition between the two levels occurs as long as the expectation value of the oscillator coordinate is driven close to zero. On the contrary, if the initial conditions are set such that the expectation values of the oscillator coordinate are far from zero, the system will remain locked on one level.Comment: 4 pages, 4 figures, to be published in Physical Review

Coherence properties of the microcavity polariton condensate

A theoretical model is presented which explains the dominant decoherence process in a microcavity polariton condensate. The mechanism which is invoked is the effect of self-phase modulation, whereby interactions transform polariton number fluctuations into random energy variations. The model shows that the phase coherence decay, g1(t), has a Kubo form, which can be Gaussian or exponential, depending on whether the number fluctuations are slow or fast. This fluctuation rate also determines the decay time of the intensity correlation function, g2(t), so it can be directly determined experimentally. The model explains recent experimental measurements of a relatively fast Gaussian decay for g1(t), but also predicts a regime, further above threshold, where the decay is much slower.Comment: 5 pages, 1 figur

Witnessing Entanglement with Second-Order Interference

Second-order interference and Hanbury-Brown and Twiss type experiments can provide an operational framework for the construction of witness operators that can test classical and nonclassical properties of a Gaussian squeezed state (GSS), and provide entanglement witness operators to study the separability properties of correlated Gaussian squeezed sates.Comment: 10 pages, 12 figure

Zeno and Anti Zeno effect for a two level system in a squeezed bath

We discuss the appearance of Zeno (QZE) or anti-Zeno (QAE) effect in an exponentially decaying system. We consider the quantum dynamics of a continuously monitored two level system interacting with a squeezed bath. We find that the behavior of the system depends critically on the way in which the squeezed bath is prepared. For specific choices of the squeezing phase the system shows Zeno or anti-Zeno effect in conditions for which it would decay exponentially if no measurements were done. This result allows for a clear interpretation in terms of the equivalent spin system interacting with a fictitious magnetic field.Comment: 18 pages, 7 figures;added references for section 4;changes in the nomenclatur