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Physical Review A

Monitoring for time ordering and time asymmetry of spectral correlations in filtered resonance fluorescence generated from a Λ -type atomic system

Ze-an Peng, Guoqing Yang, Qing-Lin Wu, Gao‐xiang Li

Published Oct 15, 2018• 2 citations
Publisher

Abstract

Frequency-resolved correlation (FRC) is investigated in fluorescent emission radiated from a $\mathrm{\ensuremath{\Lambda}}$-type atomic system by employing weak coupling regime between quantum emitter and cavities, in which each cavity substituting a Lorentzian filter is assumed to pass through only one fluorescent photon at a time so that the analytical discussions for time orderings can be carried out in a truncated Hilbert space with single-excitation state for each cavity mode. In the limit of bad cavity (large passband width of filter) and short delay, the conditional time ordering amplitudes are introduced with the help of conditioned dressed atom-photon states prepared by preselection to probe into the effect of preferential screening for time orderings of filter-detector systems. Meanwhile, the past quantum state formalism is also applied in FRC to further excavate their collective monitoring effect. Based on the obtained two-mode correlation signals, it is found that, in nonresonant two-photon cascaded processes, bunching and antibunching can appear in two opposite detection orderings, respectively, and can be switched. The physical origin is explored that the two different transition amplitudes of emitted photons from a common spectral band of resonance fluorescence are responsible for opposite time orderings, thus, the imbalance between two complementary time orderings can be enhanced, which is impossible to achieve in resonance fluorescence of two-level atoms. This mechanism is embodied in the conditional time ordering amplitudes produced by this detection theory of cavity modes.

DOI
10.1103/physreva.98.043828

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Frequency-resolved correlation (FRC) is investigated in fluorescent emission radiated from a \ensuremathΛ\mathrm{\ensuremath{\Lambda}}\ensuremathΛ-type atomic system by employing weak coupling regime between quantum emitter and cavities, in which each cavity substituting a Lorentzian filter is assumed to pass through only one fluorescent photon at a time so that the analytical discussions for time orderings can be carried out in a truncated Hilbert space with single-excitation state for each cavity mode. In the limit of bad cavity (large passband width of filter) and short delay, the conditional time ordering amplitudes are introduced with the help of conditioned dressed atom-photon states prepared by preselection to probe into the effect of preferential screening for time orderings of filter-detector systems. Meanwhile, the past quantum state formalism is also applied in FRC to further excavate their collective monitoring effect. Based on the obtained two-mode correlation signals, it is found that, in nonresonant two-photon cascaded processes, bunching and antibunching can appear in two opposite detection orderings, respectively, and can be switched. The physical origin is explored that the two different transition amplitudes of emitted photons from a common spectral band of resonance fluorescence are responsible for opposite time orderings, thus, the imbalance between two complementary time orderings can be enhanced, which is impossible to achieve in resonance fluorescence of two-level atoms. This mechanism is embodied in the conditional time ordering amplitudes produced by this detection theory of cavity modes.
Frequency-resolved quantum correlation of resonance fluorescence is investigated in a two-atom radiating system. In this quantum radiating system, only one atom is driven by a laser field, and the spontaneous transition of the undriven atom resonates with one of the Rabi sidebands of the driven atom. A single-mode empty cavity is applied to serve as a Lorentzian filter to output the superbunched fluorescent photon pairs when its frequency is tuned to halfway between the central peak and one of the side peaks. In the case of large filter width, two-photon correlation signal and its physical correspondence can be bridged analytically in our approach. It reveals that this superbunching effect turns out to be the constructive quantum interference between a pair of coupled two-photon cascaded transitions. Ulteriorly, it is the consequence of the modulations of the unfiltered dressed-state transition amplitudes by the filter. Our analytical formalism also shows that, although the dipole-dipole interaction is usually weak, the interatomic coherence caused by this weak perturbation can also play a crucial role in breaking through the superbunching limit obtained from a single two-level atom in the same parameter regime. In addition to being a treasurable quantum pump to probe into the target quantum system, it is also found in our investigation that this superbunched fluorescence can serve as a promising quantum response in detecting this weak perturbation in the interior of the quantum source. A general case is also considered when the two-atom radiating system is monitored by two filter-detector monitoring systems. It is found that this filtered strong quantum correlation can be maintained even though the two photons are spatially separated.
Abstract Frequency-resolved photon statistics of resonance fluorescence generated from a two-level system driven by a strong laser field and a weak laser field with equal frequencies are studied. The frequency resolution of fluorescent radiation is described by quantum filtering dynamics, which is simulated theoretically by two single-mode quantum optical cavities with tunable frequencies to scan the incident fluorescent radiation. By calculating the two-photon intensity–intensity correlation functions in terms of the cavity modes, we demonstrate that two-color strong correlations of resonance fluorescence can be generated not only between the opposite sidebands, but also between the central band and one of the sidebands: although both sidebands are broadened due to the perturbation of the weak laser field on the strong-field dressed atom. We emphasize that these properties are in contrast to the conventional case of the standard single-atom Mollow triplet. Moreover, if the resonance frequencies of the two filtering cavities are tuned appropriately, broadband two-color strong correlations are predicted, and the physical origin is revealed from the perspective of quantum interference of photon emission dynamics. This can be considered as a feasible scheme for the design of broadband non-classical light sources, and may be beneficial to the quantum precise detection of atomic and molecular dynamics via quantum optical spectroscopy.
The space-time connection between the Mollow cascaded transitions with time orderings and the spatially directional correlated emissions of Mollow photons is analyzed theoretically in a strong laser-dressed subwavelength two-atom antenna, which supports only two-level electric dipole transitions. It can be regarded as the most prototypical collective quantum radiator to exploit the space-time quantum characteristics of the Mollow physics of resonance fluorescence. By constructing the photon filtering dynamics from the dressed two-atom antenna to a pair of quantum sensors, the frequency-resolved spatial two-point two-time correlations of different Mollow spectral lines are examined analytically in terms of the quantum sensor modes. It is shown that a rich significance of spatial directionality lies in the time orderings of cascaded emissions between different Mollow spectral lines. This feature enables the time orderings of different Mollow spectral lines to be tailored geometrically and thus prepared deterministically to produce highly directional temporal bunching effects of the Mollow photons with giant nonclassicality only for a specific two-photon detection order. The dressed two-atom system is therefore able to operate as a highly directional atomic antenna that may provide versatile applications in the fields of atom-photon-based quantum precise measurement physics and Mollow spectroscopy.
We focus on the influence of multiphoton effect on the fluorescence spectrum and photon statistics of the bichromatically driven two-level atomic system. The influence of the multiphoton effect of the weaker driving field on the system and spontaneous emission are revealed by Schrieffer-Wolff perturbation theory, respectively. The physical origin of the multiphoton process affecting the fluorescence spectral asymmetry characteristics is fully investigated by studying the population distribution and the dressed atomic transition weight. Further, the suppression condition of the central peak of the central band is investigated. The photon statistical properties of the system are revealed by studying the frequency-resolved correlations between different sidepeaks and the central peak and sidepeak, respectively. In particular, the physical picture of the asymmetry of the two-photon correlation signal that is affected by the multiphoton process of the weaker driving field affecting the timing detection is fully revealed by the two methods of correlation moment and conditional quantum state, respectively. These results of ours provide a theoretical approach for studying multiphoton processes in multichromatically driven quantum systems, as well as for developing quantum simulation techniques such as spin locking.
Frequency-filtered photon correlations have been proven to be extremely useful in grasping how the detection process alters photon statistics. Harnessing the spectral correlations also permits refinement of the emission and unraveling of previously hidden strong correlations in a plethora of quantum-optical systems under continuous-wave excitation. In this work, we investigate such correlations for time-dependent excitation and develop a methodology to compute efficiently time-integrated correlations, which are at the heart of the photon-counting theory, and subsequently apply it to analyze the photon emission of pulsed systems. By combining this formalism with the —which facilitates frequency-resolved correlations—we demonstrate how spectral filtering enhances single-photon purity and suppresses multiphoton noise in time-bin-encoded quantum states. Specifically, filtering the central spectral peak of a dynamically driven two-level system boosts temporal coherence and improves the fidelity of time-bin entanglement preparation, even under conditions favoring multiphoton emission. These results establish spectral filtering as a critical tool for tailoring photon statistics in pulsed quantum light sources.
Frequency-resolved photon emission is central to applications from quantum information encoding to high-resolution spectroscopy, and then studying their correlations is therefore essential for revealing the underlying emission pathways and multiphoton statistics. Here, we investigate frequency-resolved N-photon correlations in an ultrastrongly coupled cavity QED system where a qubit interacts with a single-mode cavity. Owing to counter-rotating interactions, the eigenstates and energy spectrum are strongly modified, giving rise to rich spectral and statistical properties in the emitted frequency-resolved photons. Through frequency-selective detection, we reveal pronounced multiphoton antibunching, as well as multiphoton bunching originating from cascade transitions among dressed eigenstates. In particular, we show that parity symmetry plays a decisive role in shaping these correlations. The symmetry-breaking opens additional transition channels and dramatically enhances the generation of correlated photon pairs and even photon triplets of different frequencies. Our work extends frequency-resolved correlations to the ultra-strong coupling regime and demonstrates their potential as a sensitive probe of symmetry in light-matter interaction systems.