Boundary effects on radiative processes of two entangled atoms

We analyze radiative processes of a quantum system composed by two identical two-level atoms interacting with a massless scalar field prepared in the vacuum state in the presence of perfect reflecting flat mirrors. We consider that the atoms are prepared in a stationary maximally entangled state. We investigate the spontaneous transitions rates from the entangled states to the collective ground state induced by vacuum fluctuations. In the empty-space case, the spontaneous decay rates can be enhanced or inhibited depending on the specific entangled state and changes with the distance between the atoms. Next, we consider the presence of perfect mirrors and impose Dirichlet boundary conditions on such surfaces. In the presence of a single mirror the transition rate for the symmetric state undergoes a slight reduction, whereas for the antisymmetric state our results indicate a slightly enhancement. Finally, we investigate the effect of multiple reflections by two perfect mirrors on the transition rates.Comment: submitted version to the journa

Fulling-Davies-Unruh effect for accelerated two-level single and entangled atomic systems

We investigate the transition rates of uniformly accelerated two-level single and entangled atomic systems in empty space as well as inside a cavity. We take into account the interaction between the systems and a massless scalar field from the viewpoint of an instantaneously inertial observer and a coaccelerated observer, respectively. The upward transition occurs only due to the acceleration of the atom. For the two-atom system, we consider that the system is initially prepared in a generic pure entangled state. In the presence of a cavity, we observe that for both the single and the two-atom cases, the upward and downward transitions are occurred due to the acceleration of the atomic systems. The transition rate manifests subtle features depending upon the cavity and system parameters, as well as the initial entanglement. It is shown that no transition occurs for a maximally entangled super-radiant initial state, signifying that such entanglement in the accelerated two-atom system can be preserved for quantum information procesing applications. Our analysis comprehensively validates the equivalence between the effect of uniform acceleration for an inertial observer and the effect of a thermal bath for a coaccelerated observer, in free space as well as inside a cavity, if the temperature of the thermal bath is equal to the Unruh temperature.Comment: 42 pages LaTeX, Comments are welcom

Are multiple reflecting boundaries capable of enhancing entanglement harvesting?

Quantum entanglement harvesting in the relativistic setup attracted a lot of attention in recent times. Acquiring more entanglement within two qubits may be very desirable to establish fruitful communication between them. On the other hand use of reflecting boundaries in a spacetime has close resemblance to the cavity quantum optomechanical systems. Here, in presence of two reflecting boundaries, we study the generation of entanglement between two uniformly accelerated Unruh-DeWitt detectors which are interacting with the background scalar fields. Like no boundary and single boundary situations, entanglement harvesting is possible for their motions in opposite Rindler wedges. We observe that the reflecting boundaries can play double roles. In some parameter space it causes suppression, while in other parameter space we can have enhancement of entanglement compared to no boundary and single boundary cases. Thus increase of boundaries has significant impact in this phenomena and a suitable choices of parameters provides desirable increment of it.Comment: Minor corrections done, published in Phys. Rev.

Atom-field dynamics in curved spacetime

Some aspects of atom-field interactions in curved spacetime are reviewed. Of great interest are radiative processes arising out of Rindler and black hole spacetimes, which involve the role of Hawking-Unruh effect. The conventional understandings of atomic radiative transitions and energy level shifts are reassessed in curved spacetime. On one hand, the study of the role played by spacetime curvature in quantum radiative phenomena has implications for fundamental physics, notably the gravity-quantum interface. In particular, one examines the viability of Equivalence Principle, which is at the heart of Einstein's general theory of relativity. On the other hand, it can be instructive for manipulating quantum information and light propagation in arbitrary geometries. Some issues related to nonthermal effects of acceleration are also discussed.Comment: 31 pages, 5 figure

Strong Interactions of Single Atoms and Photons near a Dielectric Boundary

Modern research in optical physics has achieved quantum control of strong interactions between a single atom and one photon within the setting of cavity quantum electrodynamics (cQED). However, to move beyond current proof-of-principle experiments involving one or two conventional optical cavities to more complex scalable systems that employ N >> 1 microscopic resonators requires the localization of individual atoms on distance scales < 100 nm from a resonator's surface. In this regime an atom can be strongly coupled to a single intracavity photon while at the same time experiencing significant radiative interactions with the dielectric boundaries of the resonator. Here, we report an initial step into this new regime of cQED by way of real-time detection and high-bandwidth feedback to select and monitor single Cesium atoms localized ~100 nm from the surface of a micro-toroidal optical resonator. We employ strong radiative interactions of atom and cavity field to probe atomic motion through the evanescent field of the resonator. Direct temporal and spectral measurements reveal both the significant role of Casimir-Polder attraction and the manifestly quantum nature of the atom-cavity dynamics. Our work sets the stage for trapping atoms near micro- and nano-scopic optical resonators for applications in quantum information science, including the creation of scalable quantum networks composed of many atom-cavity systems that coherently interact via coherent exchanges of single photons.Comment: 8 pages, 5 figures, Supplemental Information included as ancillary fil

Resonance interaction of two entangled atoms accelerating between two mirrors

We study the resonance interaction between two entangled identical atoms coupled to a quantized scalar field vacuum, and accelerating between two mirrors. We show how radiative processes of the two-atom entangled state can be manipulated by the atomic configuration undergoing noninertial motion. Incorporating the Heisenberg picture with symmetric operator ordering, the vacuum fluctuation and the self-reaction contributions are distinguished. We evaluate the resonance energy shift and the relaxation rate of energy of the two atom system from the self-reaction contribution in the Heisenberg equation of motion. We investigate the variation of these two quantities with relevant parameters such as atomic acceleration, interatomic distance and position with respect to the boundaries. We show that both the energy level shift and the relaxation rate can be controlled by tuning the above parameters

New Trends in Quantum Electrodynamics

Quantum electrodynamics is one of the most successful physical theories, and its predictions agree with experimental results with exceptional accuracy. Nowadays, after several decades since its introduction, quantum electrodynamics is still a very active research field from both the theoretical and experimental points of view. The aim of this Special Issue is to present recent relevant advances in quantum electrodynamics, both theoretical and experimental, and related aspects in quantum field theory and quantum optics