We study the nonlocality dynamics for two models of atoms in cavity quantum electrodynamics (QED); the first model contains atoms in a single cavity undergoing nearest-neighbor interactions with no initial correlation, and the second contains atoms confined in n different and noninteracting cavities, all of which were initially prepared in a maximally correlated state of n qubits corresponding to the atomic degrees of freedom. The nonlocality evolution of the states in the second model shows that the corresponding maximal violation of a multipartite Bell inequality exhibits revivals at precise times, defining, nonlocality sudden deaths and nonlocality sudden rebirths, in analogy with entanglement. These quantum correlations are provided analytically for the second model to make the study more thorough. Differences in the first model regarding whether the array of atoms inside the cavity is arranged in a periodic or open fashion are crucial to the generation or redistribution of quantum correlations. This contribution paves the way to using the nonlocality multipartite correlation measure for describing the collective complex behavior displayed by slightly interacting cavity QED arrays.
The next-higher-lying doublet contains two quanta of energy and lacks a classical explanation12,21,22. The corresponding dressed states have been observed (together with a few higher-order states) in microwave cavity QED13,14,15 and even ion trapping, where phonons play the role of photons23. At optical frequencies, evidence for these states has indirectly been obtained in two-photon correlation experiments where the conditional response of the system on detection of an emitted photon is monitored16,24,25,26. These optical experiments observe the quantum fluctuations in dissipative cavity QED systems but operate away from a resonance to a higher-lying state. Direct spectroscopy using a two-colour technique to excite the second doublet step-wise has been attempted in a pioneering experiment with atomic beams22. An unambiguous signature of these states remained elusive owing to large fluctuations in the number of atoms traversing the cavity.
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Using single trapped atoms, we exploit the anharmonicity of the energy-level spectrum to drive a multiphoton transition directly from the vacuum state to a specific higher-lying state. We observe the quantum character of our cavity QED field by measuring a photon flux, not a photon correlation. To explain our technique, we note that a two-state atom coupled to a single-mode light field has a discrete spectrum consisting of a ladder of dressed states, , with frequencies
Single-photon source in micro- or nanoscale is the basic building block of on-chip quantum information and scalable quantum network. Enhanced spontaneous emission based on cavity quantum electrodynamics (CQED) is one of the key principles of realizing single-photon sources fabricated by micro- or nanophotonic cavities. Here we mainly review the spontaneous emission of single emitters in micro- or nanostructures, such as whispering gallery microcavities, photonic crystals, plasmon nanostructures, metamaterials, and their hybrids. The researches have enriched light-matter interaction as well as made great influence in single-photon source, photonic circuit, and on-chip quantum information.
Single-photon source in micro- or nanoscale is the basic building block of on-chip quantum information and scalable quantum network. Enhancement of spontaneous emission (SE) in the frame of cavity quantum electrodynamics (CQED), i.e. Purcell effect controlling the spontaneous emission rate through cavity modes, is one of the key principles of realizing single-photon sources [1]. With the trend of on-chip optical quantum devices, realizing single photon emission in the micro- or nanoscale is increasingly important for quantum information process. Local field enhancement or small optical mode volume in micro- or nanostructures brings huge advantages in CQED, quantum information, and light-matter interaction. So far, the enhancement of SE in the micro- or nanoscale has reached great achievements in the areas of whispering gallery microcavities, photonic crystals (PCs), surface plasmon polaritons (SPPs), metamaterials, and so on, which provides abundant choices and methods of controlling and collecting single photons. In this Review, we will mainly focus on the theories, experiments, and up-to-date applications of SE in above areas. These researches demonstrate that Purcell effect has great influence in single-photon source, photonic circuit, and on-chip quantum information.
Schematic diagram of CQED systems. a A typical CQED system consisting of a single quantum emitter (here is two level) and a cavity with coupling coefficient g, cavity loss κ, and spontaneous emission rate γ [7]. b The probability of excited-state with time evolution and c transmission spectrum for weak (red curve) and strong (blue curve) coupling regimes [5]. d Schematic diagram of Purcell enhancement at weak coupling regime [3]. e Vacuum Rabi oscillation with period energy exchange at strong coupling regime [3]. f Schematic of Rabi splitting energy by dressed state theory [7]
SE based on WGM structures. a The microdisk structure containing a single InAs quantum dot [84]. b Enhancement of spontaneous emission when WGM and exciton are on resonance [10]. c A glass microsphere doped with CdSe nanocrystals in a thin surface shell [89]. d The radiative lifetime of CdSe quantum dots with and without WGM structure [89]. e A high Q/V toroid microcavity on a chip [11]. f Measured Q/V ratio of toroid microcavities by varying principal diameter D [11]
Single photon source is one of the most important applications of the Purcell effect in microcavities [98]. The pioneering work of single photon source was done in 2000 by A. Kiraz et al. [84]. By using WGM cavity with the zero-phonon line of nitrogen-vacancy (NV) center, Purcell factor of 12 could be reached, with 25% zero-phonon line emission of diamond [88]. Therefore, by enhancing spontaneous emission and collecting single photons, WGM microcavities can realize an efficient integrable single photon source. Besides single photon sources, spontaneous emission of WGMs has also been applied in single-photon transport [99], quantum many-body simulation [100], and quantum gate [101].
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