arXiv subjects

L. Horvath

Publications and source records attributed to L. Horvath.

9 recordsLinked to original sources

arXiv2017

Large time-asymmetric quantum fluctuations in amplitude-intensity correlation measurements of a V-type three-level atom resonance fluorescence

In this paper we show that the scattered field of a bichromatically driven V-type three-level atom exhibit asymmetry and large violation of classical bounds in amplitude-intensity correlations. These features result from the noncommutativity of amplitude and intensity field operators, and the strong non-Gaussian fluctuations in this system. The amplitude-intensity correlations of resonance fluorescence, with its large third-order fluctuations, describe the nonclassical features of the emitted field more accurately than the second-order measure related to squeezing. Spectra and variances of these correlations, along intensity-intensity correlations, provide a wealth of supporting information.

quant-ph↗

arXiv2016

Experimental investigation of the radial structure of energetic particle driven modes

Alfvén eigenmodes (AEs) and energetic particle modes (EPMs) are often excited by energetic particles (EPs) in tokamak plasmas. One of the main open questions concerning EP driven instabilities is the non-linear evolution of the mode structure. The aim of the present paper is to investigate the properties of beta-induced AEs (BAEs) and EP driven geodesic acoustic modes (EGAMs) observed in the ramp-up phase of off-axis NBI heated ASDEX Upgrade (AUG) discharges. This paper focuses on the changes in the mode structure of BAEs/EGAMs during the non-linear chirping phase. Our investigation has shown that in case of the observed down-chirping BAEs the changes in the radial structure are smaller than the uncertainty of our measurement. This behaviour is most probably the consequence of that BAEs are normal modes, thus their radial structure strongly depends on the background plasma parameters rather than on the EP distribution. In the case of rapidly upward chirping EGAMs the analysis consistently shows shrinkage of the mode structure. The proposed explanation is that the resonance in the velocity space moves towards more passing particles which have narrower orbit widths.

physics.plasm-ph↗

arXiv2007

Quantum Stochastic Heating of a Trapped Ion

The resonant heating of a harmonically trapped ion by a standing-wave light field is described as a quantum stochastic process combining a coherent Schroedinger evolution with Bohr-Einstein quantum jumps. Quantum and semi-quantum treatments are compared.

quant-ph↗

arXiv2007

Effect of atomic beam alignment on photon correlation measurements in cavity QED

Quantum trajectory simulations of a cavity QED system comprising an atomic beam traversing a standing-wave cavity are carried out. The delayed photon coincident rate for forwards scattering is computed and compared with the measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that a moderate atomic beam misalignment can account for the degradation of the predicted correlation. Fits to the experimental data are made in the weak-field limit with a single adjustable parameter--the atomic beam tilt from perpendicular to the cavity axis. Departures of the measurement conditions from the weak-field limit are discussed.

quant-ph↗

arXiv2003

Photon coincidence spectroscopy for two-atom cavity quantum electrodynamics

We show that photon coincidence spectroscopy can provide an unambiguous signature of two atoms simultaneously interacting with a quantised cavity field mode. We also show that the single-atom Jaynes-Cummings model can be probed effectively via photon coincidence spectroscopy, even with deleterious contributions to the signal from two-atom events. In addition, we have explicitly solved the eigenvectors and eigenvalues of two two-level atoms coupled to a quantised cavity mode for differing coupling strengths.

quant-ph↗

arXiv2003

Competition-induced shifts of spectral peaks in photon coincidence spectroscopy

We show that shifts in locations of two-photon coincidence spectral peaks, for a bichromatically-driven two-level atom passing through a single-mode cavity, are due to competition between excitation pathways for a Jaynes-Cummings system. We also discuss an analogous shift of (single-photon) spectral peaks for a driven three-level V-system, which demonstrates that competition between excitation pathways is also important in this simple system.

quant-ph↗

arXiv2001

Perturbative corrections to photon coincidence spectroscopy

Photon coincidence spectroscopy is a promising technique for probing the nonlinear regime of cavity quantum electrodynamics in the optical domain, however its accuracy is mitigated by two factors: higher-order photon correlations, which contribute to an enhanced pair count rate, and non-simultaneity of emitted photon pairs from the optical cavity. We show that the technique of photon coincidence spectroscopy is effective in the presence of these effects if the quantitative predictions are adjusted to include non-simultaneity and higher-order correlations.

quant-ph↗

arXiv2001

Multiphoton Coincidence Spectroscopy

We extend the analysis of photon coincidence spectroscopy beyond bichromatic excitation and two-photon coincidence detection to include multichromatic excitation and multiphoton coincidence detection. Trichromatic excitation and three-photon coincidence spectroscopy are studied in detail, and we identify an observable signature of a triple resonance in an atom-cavity system.

quant-ph↗

arXiv1999

Non-simultaneity in two-photon coincidence spectroscopy

Photon coincidence spectroscopy relies on detecting multiphoton emissions from the combined atom-cavity system in atomic beam cavity quantum electrodynamics experiments. These multiphoton emissions from the cavity are nearly simultaneous approximately on the cavity lifetime scale. We determine the optimal time for the detection window of photon pairs in two-photon coincidence spectroscopy. If the window time is too short, some photon pairs will not be detected; if the window time is too long, too many nearly coincident independent single photons will be falsely interpreted as being a photon pair. The paper has been submitted to The European Physical Journal D.

quant-ph↗