Atoms

1060 KiB

Open AccessArticle

Cavity Quantum Electrodynamics of Continuously Monitored Bose-Condensed Atoms

by Mark D. Lee and Janne Ruostekoski

Atoms 2015, 3(3), 450-473; https://doi.org/10.3390/atoms3030450 - 23 Sep 2015

Cited by 2 | Viewed by 4789

We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of [...] Read more.

We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of the atom cloud and this symmetry can be restored by considering ensemble averages over many realizations. We show that the cavity optomechanical excitations of the condensate can be engineered to target specific collective modes. This is achieved by exploiting the spatial structure and symmetries of the collective modes and light fields. The cavity fields can be utilized both for strong driving of the collective modes and for their measurement. In the weak excitation limit the condensate–cavity system may be employed as a sensitive phonon detector which operates by counting photons outside the cavity that have been selectively scattered by desired phonons. Full article

(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)

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1022 KiB

Open AccessArticle

A Realization of a Quasi-Random Walk for Atoms in Time-Dependent Optical Potentials

by Torsten Hinkel, Helmut Ritsch and Claudiu Genes

Atoms 2015, 3(3), 433-449; https://doi.org/10.3390/atoms3030433 - 23 Sep 2015

Cited by 3 | Viewed by 5103

Abstract

We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential [...] Read more.

We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential that forces the atom into a non-trivial motion, strongly resembling a discrete random walk behavior between lattice sites. We provide both numerical and analytical analysis of such a quasi-random walk behavior. Full article

(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)

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389 KiB

Open AccessArticle

Quantum Entanglement and Shannon Information Entropy for the Doubly Excited Resonance State in Positronium Negative Ion

by Chien-Hao Lin and Yew Kam Ho

Atoms 2015, 3(3), 422-432; https://doi.org/10.3390/atoms3030422 - 21 Sep 2015

Cited by 9 | Viewed by 4572

Abstract

In the present work, we report an investigation on quantum entanglement in the doubly excited 2s² ¹S^e resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance [...] Read more.

In the present work, we report an investigation on quantum entanglement in the doubly excited 2s² ¹S^e resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance states with the stabilization method. Once the resonance wave function is obtained, the spatial (electron-electron orbital) entanglement entropies (von Neumann and linear) can be quantified using the Schmidt decomposition method. Furthermore, Shannon entropy in position space, a measure for localization (or delocalization) for such a doubly excited state, is also calculated. Full article

(This article belongs to the Special Issue Positron Scattering and Annihilation with Atoms and Molecules including Emerging New Resonances and their Applications in other Systems)

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939 KiB

Open AccessArticle

Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics

by Joel Clementson, Thomas Lennartsson and Peter Beiersdorfer

Atoms 2015, 3(3), 407-421; https://doi.org/10.3390/atoms3030407 - 09 Sep 2015

Cited by 28 | Viewed by 5001

Abstract

The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy [...] Read more.

The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer. Full article

(This article belongs to the Special Issue Perspectives of Atomic Physics with Trapped Highly Charged Ions)

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1111 KiB

Open AccessArticle

Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light

by Thomas J. Elliott, Gabriel Mazzucchi, Wojciech Kozlowski, Santiago F. Caballero-Benitez and Igor B. Mekhov

Atoms 2015, 3(3), 392-406; https://doi.org/10.3390/atoms3030392 - 02 Sep 2015

Cited by 17 | Viewed by 5208

Abstract

We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the [...] Read more.

We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyse the entanglement between light and matter and show how it can be exploited for realising multimode macroscopic quantum superpositions, such as Schrödinger cat states, for both bosons and fermions. We provide examples utilising different measurement schemes and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases and significantly altering the phase diagram of the atomic system. Full article

(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)

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1721 KiB

Open AccessArticle

Experiments with Highly-Ionized Atoms in Unitary Penning Traps

by Shannon Fogwell Hoogerheide, Aung S. Naing, Joan M. Dreiling, Samuel M. Brewer, Nicholas D. Guise and Joseph N. Tan

Atoms 2015, 3(3), 367-391; https://doi.org/10.3390/atoms3030367 - 14 Aug 2015

Cited by 6 | Viewed by 9320

Abstract

Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 10¹⁹ level of precision, quantum information processing and tests of fundamental theory. The proposed atomic [...] Read more.

Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 10¹⁹ level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr¹⁷⁺), as well as for studying electron capture processes. Full article

(This article belongs to the Special Issue Perspectives of Atomic Physics with Trapped Highly Charged Ions)

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1926 KiB

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Cavity-Assisted Generation of Sustainable Macroscopic Entanglement of Ultracold Gases

by Chaitanya Joshi and Jonas Larson

Atoms 2015, 3(3), 348-366; https://doi.org/10.3390/atoms3030348 - 04 Aug 2015

Cited by 7 | Viewed by 4185

Abstract

Prospects for reaching persistent entanglement between two spatially-separated atomic Bose–Einstein condensates are outlined. The system setup comprises two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that [...] Read more.

Prospects for reaching persistent entanglement between two spatially-separated atomic Bose–Einstein condensates are outlined. The system setup comprises two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that illuminates the atoms, such that photons can scatter into the cavity. In the superradiant phase, a cavity field is established, and we show that the emerging cavity-mediated interactions between the two condensates is capable of entangling them despite photon losses. This macroscopic atomic entanglement is sustained throughout the time-evolution apart from occasions of sudden deaths/births. Using an auxiliary photon mode and coupling it to a collective quadrature of the two condensates, we demonstrate that the auxiliary mode’s squeezing is proportional to the atomic entanglement, and as such, it can serve as a probe field of the macroscopic entanglement. Full article

(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)

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321 KiB

Open AccessArticle

Influence of Virtual Photon Process on the Generation of Squeezed Light from Atoms in an Optical Cavity

by Aranya B. Bhattacherjee

Atoms 2015, 3(3), 339-347; https://doi.org/10.3390/atoms3030339 - 24 Jul 2015

Cited by 3 | Viewed by 3912

Abstract

We show that a collection of two-level atoms in an optical cavity beyond the rotating wave approximation and in the dispersive-adiabatic and non-dispersive adiabatic regime constitutes a nonlinear medium and is capable of generating squeezed state of light. It is found that squeezing [...] Read more.

We show that a collection of two-level atoms in an optical cavity beyond the rotating wave approximation and in the dispersive-adiabatic and non-dispersive adiabatic regime constitutes a nonlinear medium and is capable of generating squeezed state of light. It is found that squeezing produced in the non-dispersive adiabatic regime is significantly high compared to that produced in the dispersive-adiabatic limit. On the other hand, we also show that it could be possible to observe the Dicke superradiant quantum phase transition in the dispersive-adiabatic regime where the Ã2 term is negligible. Such a system can be an essential component of a larger quantum-communication system. Full article

(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)

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986 KiB

Open AccessArticle

On the Classical Coupling between Gravity and Electromagnetism

by Maria Becker, Adam Caprez and Herman Batelaan

Atoms 2015, 3(3), 320-338; https://doi.org/10.3390/atoms3030320 - 30 Jun 2015

Cited by 7 | Viewed by 5366

Abstract

Coupling between electromagnetism and gravity, manifested as the distorted Coulomb field of a charge distribution in a gravitational field, has never been observed. A physical system consisting of an electron in a charged shell provides a coupling that is orders of magnitude stronger [...] Read more.

Coupling between electromagnetism and gravity, manifested as the distorted Coulomb field of a charge distribution in a gravitational field, has never been observed. A physical system consisting of an electron in a charged shell provides a coupling that is orders of magnitude stronger than for any previously-considered system. A shell voltage of one megavolt is required to establish a gravitationally-induced electromagnetic force equal in magnitude to the force of gravity on an electron. The experimental feasibility of detecting these forces on an electron is discussed. The effect establishes a relation between Einstein’s energy-mass equivalence and the coupling between electromagnetism and gravity. Full article

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894 KiB

Open AccessArticle

Detailed Analysis of Configuration Interaction and Calculation of Radiative Transition Rates in Seven Times Ionized Tungsten (W VIII)

by Jérôme Deprince and Pascal Quinet

Atoms 2015, 3(3), 299-319; https://doi.org/10.3390/atoms3030299 - 30 Jun 2015

Cited by 7 | Viewed by 4156

Abstract

A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of [...] Read more.

A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f¹⁴5s²5p⁵, 4f¹⁴5s²5p⁴nl, 4f¹⁴5s5p⁶, 4f¹³5s²5p⁶, 4f¹³5s²5p⁵nl and 4f¹²5s²5p⁶nl (nl = 5d, 6s). Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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1981 KiB

Open AccessArticle

Spectra of W VIII and W IX in the EUV Region

by Alexander Ryabtsev, Edward Kononov, Rimma Kildiyarova, Wan-Ü Lydia Tchang-Brillet, Jean-Francois Wyart, Norbert Champion and Christophe Blaess

Atoms 2015, 3(3), 273-298; https://doi.org/10.3390/atoms3030273 - 30 Jun 2015

Cited by 17 | Viewed by 4943

Abstract

The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total [...] Read more.

The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented. Full article

(This article belongs to the Special Issue Atomic Data for Tungsten)

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Atoms, Volume 3, Issue 3 (September 2015) – 11 articles , Pages 273-473

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