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4 pages, 176 KiB

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Special Issue on Quantum Optics for Fundamental Quantum Mechanics

by Marco Genovese and Marco Gramegna

Appl. Sci. 2020, 10(10), 3655; https://doi.org/10.3390/app10103655 - 25 May 2020

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Abstract

With the last turn of the century, physics has experienced the transition from the first to the second quantum revolution [...] Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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25 pages, 351 KiB

Open AccessArticle

Bohmian-Based Approach to Gauss-Maxwell Beams

by Ángel S. Sanz, Milena D. Davidović and Mirjana Božić

Appl. Sci. 2020, 10(5), 1808; https://doi.org/10.3390/app10051808 - 6 Mar 2020

Cited by 6 | Viewed by 2020

Abstract

Usual Gaussian beams are particular scalar solutions to the paraxial Helmholtz equation, which neglect the vector nature of light. In order to overcome this inconvenience, Simon et al. (J. Opt. Soc. Am. A 1986, 3, 536–540) found a paraxial solution [...] Read more.

Usual Gaussian beams are particular scalar solutions to the paraxial Helmholtz equation, which neglect the vector nature of light. In order to overcome this inconvenience, Simon et al. (J. Opt. Soc. Am. A 1986, 3, 536–540) found a paraxial solution to Maxwell’s equation in vacuum, which includes polarization in a natural way, though still preserving the spatial Gaussianity of the beams. In this regard, it seems that these solutions, known as Gauss-Maxwell beams, are particularly appropriate and a natural tool in optical problems dealing with Gaussian beams acted or manipulated by polarizers. In this work, inspired in the Bohmian picture of quantum mechanics, a hydrodynamic-type extension of such a formulation is provided and discussed, complementing the notion of electromagnetic field with that of (electromagnetic) flow or streamline. In this regard, the method proposed has the advantage that the rays obtained from it render a bona fide description of the spatial distribution of electromagnetic energy, since they are in compliance with the local space changes undergone by the time-averaged Poynting vector. This feature confers the approach a potential interest in the analysis and description of single-photon experiments, because of the direct connection between these rays and the average flow exhibited by swarms of identical photons (regardless of the particular motion, if any, that these entities might have), at least in the case of Gaussian input beams. In order to illustrate the approach, here it is applied to two common scenarios, namely the diffraction undergone by a single Gauss-Maxwell beam and the interference produced by a coherent superposition of two of such beams. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

13 pages, 771 KiB

Open AccessArticle

Double Slit with an Einstein–Podolsky–Rosen Pair

by Bar Y. Peled, Amit Te’eni, Danko Georgiev, Eliahu Cohen and Avishy Carmi

Appl. Sci. 2020, 10(3), 792; https://doi.org/10.3390/app10030792 - 22 Jan 2020

Cited by 12 | Viewed by 3561

Abstract

In this somewhat pedagogical paper we revisit complementarity relations in bipartite quantum systems. Focusing on continuous-variable systems, we examine the influential class of EPR-like states through a generalization to Gaussian states and present some new quantitative relations between entanglement and local interference within [...] Read more.

In this somewhat pedagogical paper we revisit complementarity relations in bipartite quantum systems. Focusing on continuous-variable systems, we examine the influential class of EPR-like states through a generalization to Gaussian states and present some new quantitative relations between entanglement and local interference within symmetric and asymmetric double-double-slit scenarios. This approach is then related to ancilla-based quantum measurements, and weak measurements in particular. Finally, we tie up the notions of distinguishability, predictability, coherence and visibility while drawing some specific connections between them. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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9 pages, 289 KiB

Open AccessArticle

A Perturbative View from the Master Equation: Electromagnetically Induced Transparency Revisited

by Xin Wang

Appl. Sci. 2019, 9(21), 4512; https://doi.org/10.3390/app9214512 - 24 Oct 2019

Cited by 1 | Viewed by 2089

Abstract

We show that by treating the weak probe field as a perturbation to the strong coupling fields in the atomic system and using the perturbative method in a master equation, the features of linear response of phenomena of electromagnetically induced transparency (EIT) can [...] Read more.

We show that by treating the weak probe field as a perturbation to the strong coupling fields in the atomic system and using the perturbative method in a master equation, the features of linear response of phenomena of electromagnetically induced transparency (EIT) can be uniformly demonstrated, regardless of the details of atomic energy level configuration. We compare our estimation with both typical and atypical EIT-observed configurations and find that our model indeed provides a description of the sharp transmission window in central area of typical EIT curve. It can also be inferred hereby that for various systems other than atomic gas, as long as the description of the system’s dynamics comes down to the simplified form of master equation, the corresponding EIT analogs and EIT-like phenomena can also be explained in this way. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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15 pages, 359 KiB

Open AccessArticle

Optimal Estimation of Parameters Encoded in Quantum Coherent State Quadratures

by Matthieu Arnhem, Evgueni Karpov and Nicolas J. Cerf

Appl. Sci. 2019, 9(20), 4264; https://doi.org/10.3390/app9204264 - 11 Oct 2019

Cited by 4 | Viewed by 2888

Abstract

In the context of multiparameter quantum estimation theory, we investigate the construction of linear schemes in order to infer two classical parameters that are encoded in the quadratures of two quantum coherent states. The optimality of the scheme built on two phase-conjugate coherent [...] Read more.

In the context of multiparameter quantum estimation theory, we investigate the construction of linear schemes in order to infer two classical parameters that are encoded in the quadratures of two quantum coherent states. The optimality of the scheme built on two phase-conjugate coherent states is proven with the saturation of the quantum Cramér–Rao bound under some global energy constraint. In a more general setting, we consider and analyze a variety of n-mode schemes that can be used to encode n classical parameters into n quantum coherent states and then estimate all parameters optimally and simultaneously. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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12 pages, 2796 KiB

Open AccessArticle

Quantum-Key-Distribution (QKD) Networks Enabled by Software-Defined Networks (SDN)

by Hua Wang, Yongli Zhao and Avishek Nag

Appl. Sci. 2019, 9(10), 2081; https://doi.org/10.3390/app9102081 - 21 May 2019

Cited by 19 | Viewed by 6028

Abstract

As an important support for quantum communication, quantum key distribution (QKD) networks have achieved a relatively mature level of development, and they face higher requirements for multi-user end-to-end networking capabilities. Thus, QKD networks need an effective management plane to control and coordinate with [...] Read more.

As an important support for quantum communication, quantum key distribution (QKD) networks have achieved a relatively mature level of development, and they face higher requirements for multi-user end-to-end networking capabilities. Thus, QKD networks need an effective management plane to control and coordinate with the QKD resources. As a promising technology, software defined networking (SDN) can separate the control and management of QKD networks from the actual forwarding of the quantum keys. This paper systematically introduces QKD networks enabled by SDN, by elaborating on its overall architecture, related interfaces, and protocols. Then, three-use cases are provided as important paradigms with their corresponding schemes and simulation performances. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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14 pages, 306 KiB

Open AccessArticle

High-Frequency Electromagnetic Emission from Non-Local Wavefunctions

by Giovanni Modanese

Appl. Sci. 2019, 9(10), 1982; https://doi.org/10.3390/app9101982 - 15 May 2019

Cited by 6 | Viewed by 2175

Abstract

In systems with non-local potentials or other kinds of non-locality, the Landauer-Büttiker formula of quantum transport leads to replacing the usual gauge-invariant current density

J

with a current

J^{e x t}

which has a non-local part and coincides with the current of [...] Read more.

In systems with non-local potentials or other kinds of non-locality, the Landauer-Büttiker formula of quantum transport leads to replacing the usual gauge-invariant current density

J

with a current

J^{e x t}

which has a non-local part and coincides with the current of the extended Aharonov-Bohm electrodynamics. It follows that the electromagnetic field generated by this current can have some peculiar properties and in particular the electric field of an oscillating dipole can have a long-range longitudinal component. The calculation is complex because it requires the evaluation of double-retarded integrals. We report the outcome of some numerical integrations with specific parameters for the source: dipole length ∼10⁻⁷ cm, frequency 10 GHz. The resulting longitudinal field

E_{L}

turns out to be of the order of

10^{2}

to

10^{3}

times larger than the transverse component (only for the non-local part of the current). Possible applications concern the radiation field generated by Josephson tunnelling in thick superconductor-normal-superconductor (SNS) junctions in yttrium barium oxide (YBCO) and by current flow in molecular nanodevices. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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14 pages, 745 KiB

Open AccessFeature PaperArticle

Second Harmonic Revisited: An Analytic Quantum Approach

by Giovanni Chesi, Matteo M. Wauters, Nadir Fasola, Alessia Allevi and Maria Bondani

Appl. Sci. 2019, 9(8), 1690; https://doi.org/10.3390/app9081690 - 24 Apr 2019

Cited by 5 | Viewed by 2300

Abstract

We address the second-harmonic generation process in a quantum frame. Starting with a perturbative approach, we show that it is possible to achieve a number of analytic results, ranging from the up-conversion probability to the statistical properties of the generated light. In particular, [...] Read more.

We address the second-harmonic generation process in a quantum frame. Starting with a perturbative approach, we show that it is possible to achieve a number of analytic results, ranging from the up-conversion probability to the statistical properties of the generated light. In particular, the moments and the correlations of the photon-number distribution of the second-harmonic light generated by any initial state are retrieved. When possible, a comparison with the results achieved with the classical regime is successfully provided. The nonclassicality of some benchmark states is investigated by inspecting the corresponding autocorrelation function. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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13 pages, 2858 KiB

Open AccessArticle

A Photon Blockade in a Coupled Cavity System Mediated by an Atom

by Ming-Cui Li and Ai-Xi Chen

Appl. Sci. 2019, 9(5), 980; https://doi.org/10.3390/app9050980 - 8 Mar 2019

Cited by 10 | Viewed by 4150

Abstract

We investigate theoretically the photon statistics in a coupled cavity system mediated by a two-level atom. The system consists of a linear cavity weakly driven by a continuous laser, and a nonlinear cavity containing an atom inside. We find that there exists a [...] Read more.

We investigate theoretically the photon statistics in a coupled cavity system mediated by a two-level atom. The system consists of a linear cavity weakly driven by a continuous laser, and a nonlinear cavity containing an atom inside. We find that there exists a photon blockade in the linear cavity for both parameter regimes where the coupling strength between the atom and the nonlinear cavity is greater (or less) than the dissipation rate of the linear cavity. We also extend our model by pumping the two cavities simultaneously and find that the conventional photon blockade is apparent in the linear cavity, whereas the unconventional photon blockade appears in the nonlinear cavity. These results show that our work has potential applications for a single photon source in a weakly nonlinear system. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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Review

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19 pages, 15059 KiB

Open AccessReview

Measurements of Entropic Uncertainty Relations in Neutron Optics

by Bülent Demirel, Stephan Sponar and Yuji Hasegawa

Appl. Sci. 2020, 10(3), 1087; https://doi.org/10.3390/app10031087 - 6 Feb 2020

Cited by 4 | Viewed by 2601

Abstract

The emergence of the uncertainty principle has celebrated its 90th anniversary recently. For this occasion, the latest experimental results of uncertainty relations quantified in terms of Shannon entropies are presented, concentrating only on outcomes in neutron optics. The focus is on the type [...] Read more.

The emergence of the uncertainty principle has celebrated its 90th anniversary recently. For this occasion, the latest experimental results of uncertainty relations quantified in terms of Shannon entropies are presented, concentrating only on outcomes in neutron optics. The focus is on the type of measurement uncertainties that describe the inability to obtain the respective individual results from joint measurement statistics. For this purpose, the neutron spin of two non-commuting directions is analyzed. Two sub-categories of measurement uncertainty relations are considered: noise–noise and noise–disturbance uncertainty relations. In the first case, it will be shown that the lowest boundary can be obtained and the uncertainty relations be saturated by implementing a simple positive operator-valued measure (POVM). For the second category, an analysis for projective measurements is made and error correction procedures are presented. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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14 pages, 337 KiB

Open AccessReview

Quantum Correlations and Quantum Non-Locality: A Review and a Few New Ideas

by Marco Genovese and Marco Gramegna

Appl. Sci. 2019, 9(24), 5406; https://doi.org/10.3390/app9245406 - 10 Dec 2019

Cited by 21 | Viewed by 4075

Abstract

In this paper we make an extensive description of quantum non-locality, one of the most intriguing and fascinating facets of quantum mechanics. After a general presentation of several studies on this subject dealing with different but connected facets of quantum non-locality, we consider [...] Read more.

In this paper we make an extensive description of quantum non-locality, one of the most intriguing and fascinating facets of quantum mechanics. After a general presentation of several studies on this subject dealing with different but connected facets of quantum non-locality, we consider if this, and the friction it carries with special relativity, can eventually find a “solution” by considering higher dimensional spaces. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

21 pages, 416 KiB

Open AccessFeature PaperReview

Superfluids, Fluctuations and Disorder

by Alberto Cappellaro and Luca Salasnich

Appl. Sci. 2019, 9(7), 1498; https://doi.org/10.3390/app9071498 - 10 Apr 2019

Cited by 4 | Viewed by 2815

Abstract

We present a field-theory description of ultracold bosonic atoms in the presence of a disordered external potential. By means of functional integration techniques, we aim to investigate and review the interplay between disordered energy landscapes and fluctuations, both thermal and quantum ones. Within [...] Read more.

We present a field-theory description of ultracold bosonic atoms in the presence of a disordered external potential. By means of functional integration techniques, we aim to investigate and review the interplay between disordered energy landscapes and fluctuations, both thermal and quantum ones. Within the broken-symmetry phase, up to the Gaussian level of approximation, the disorder contribution crucially modifies both the condensate depletion and the superfluid response. Remarkably, it is found that the ordered (i.e., superfluid) phase can be destroyed also in regimes where the random external potential is suitable for a perturbative analysis. We analyze the simplest case of quenched disorder and then we move to present the implementation of the replica trick for ultracold bosonic systems. In both cases, we discuss strengths and limitations of the reviewed approach, paying specific attention to possible extensions and the most recent experimental outputs. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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15 pages, 2404 KiB

Open AccessReview

Topological Qubits as Carriers of Quantum Information in Optics

by Gregg Jaeger, David S. Simon and Alexander V. Sergienko

Appl. Sci. 2019, 9(3), 575; https://doi.org/10.3390/app9030575 - 10 Feb 2019

Cited by 6 | Viewed by 4207

Abstract

Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear [...] Read more.

Winding number is a topologically significant quantity that has found valuable applications in various areas of mathematical physics. Here, topological qubits are shown capable of formation from winding number superpositions and so of being used in the communication of quantum information in linear optical systems, the most common realm for quantum communication. In particular, it is shown that winding number qubits appear in several aspects of such systems, including quantum electromagnetic states of spin, momentum, orbital angular momentum, polarization of beams of particles propagating in free-space, optical fiber, beam splitters, and optical multiports. Full article

(This article belongs to the Special Issue Quantum Optics for Fundamental Quantum Mechanics)

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