Quantum Reports

11 pages, 247 KiB

Open AccessArticle

Everett’s Multiverse and the World as Wavefunction

by Tappenden Paul

Quantum Rep. 2019, 1(1), 119-129; https://doi.org/10.3390/quantum1010012 - 12 Sep 2019

Cited by 2 | Viewed by 3186

Everett suggested that there’s no such thing as wavefunction collapse. He hypothesized that for an idealized spin measurement the apparatus evolves into a superposition on the pointer basis of two apparatuses, each displaying one of the two outcomes which are standardly thought of [...] Read more.

Everett suggested that there’s no such thing as wavefunction collapse. He hypothesized that for an idealized spin measurement the apparatus evolves into a superposition on the pointer basis of two apparatuses, each displaying one of the two outcomes which are standardly thought of as alternatives. As a result, the observer ‘splits’ into two observers, each perceiving a different outcome. There have been problems. Why the pointer basis? Decoherence is generally accepted by Everettian theorists to be the key to the right answer there. Also, in what sense is probability involved, when all possible outcomes occur? Everett’s response to that problem was inadequate. A first attempt to find a different route to probability was introduce by Neil Graham in 1973 and the path from there has led to two distinct models of branching. I describe how the ideas have evolved and their relation to the concepts of uncertainty and objective probability. Then I describe the further problem of wavefunction monism, emphasized by Maudlin, and make a suggestion as to how it might be resolved. Full article

12 pages, 1897 KiB

Open AccessArticle

Complex Deep Learning with Quantum Optics

by Antonio Manzalini

Quantum Rep. 2019, 1(1), 107-118; https://doi.org/10.3390/quantum1010011 - 30 Jul 2019

Cited by 8 | Viewed by 4538

Abstract

The rapid evolution towards future telecommunications infrastructures (e.g., 5G, the fifth generation of mobile networks) and the internet is renewing a strong interest for artificial intelligence (AI) methods, systems, and networks. Processing big data to infer patterns at high speeds and with low [...] Read more.

The rapid evolution towards future telecommunications infrastructures (e.g., 5G, the fifth generation of mobile networks) and the internet is renewing a strong interest for artificial intelligence (AI) methods, systems, and networks. Processing big data to infer patterns at high speeds and with low power consumption is becoming an increasing central technological challenge. Electronics are facing physically fundamental bottlenecks, whilst nanophotonics technologies are considered promising candidates to overcome the limitations of electronics. Today, there are evidences of an emerging research field, rooted in quantum optics, where the technological trajectories of deep neural networks (DNNs) and nanophotonics are crossing each other. This paper elaborates on these topics and proposes a theoretical architecture for a Complex DNN made from programmable metasurfaces; an example is also provided showing a striking correspondence between the equivariance of convolutional neural networks (CNNs) and the invariance principle of gauge transformations. Full article

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16 pages, 768 KiB

Open AccessReview

Spin-Orbit Angular Momentum Conversion in Metamaterials and Metasurfaces

by Graciana Puentes

Quantum Rep. 2019, 1(1), 91-106; https://doi.org/10.3390/quantum1010010 - 25 Jul 2019

Cited by 9 | Viewed by 3697

Abstract

In the last decades, unprecedented progress in the manipulation of the spin angular momentum (SAM) and orbital angular momentum (OAM) of light has been achieved, enabling a number of applications, ranging from classical and quantum communication to optical microscopy and super-resolution imaging. Metasurfaces [...] Read more.

In the last decades, unprecedented progress in the manipulation of the spin angular momentum (SAM) and orbital angular momentum (OAM) of light has been achieved, enabling a number of applications, ranging from classical and quantum communication to optical microscopy and super-resolution imaging. Metasurfaces are artificially engineered 2D metamaterials with designed subwavelength-size building blocks, which allow the precise control of optical fields with unparalleled flexibility and performance. The reduced dimensionality of optical metasurfaces enables new physics and leads to functionalities and applications that are remarkably different from those achievable with bulk materials. In this review, we present an overview of the progress in optical metasurfaces for the manipultation of SAM and OAM of light, for applications in integrated spin-orbit conversion (SOC) devices. Full article

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9 pages, 270 KiB

Open AccessArticle

Solution to the Time-Dependent Coupled Harmonic Oscillators Hamiltonian with Arbitrary Interactions

by Alejandro R. Urzúa, Irán Ramos-Prieto, Manuel Fernández-Guasti and Héctor M. Moya-Cessa

Quantum Rep. 2019, 1(1), 82-90; https://doi.org/10.3390/quantum1010009 - 22 Jul 2019

Cited by 26 | Viewed by 4543

Abstract

We show that by using the quantum orthogonal functions invariant, we found a solution to coupled time-dependent harmonic oscillators where all the time-dependent frequencies are arbitrary. This system may be found in many applications such as nonlinear and quantum physics, biophysics, molecular chemistry, [...] Read more.

We show that by using the quantum orthogonal functions invariant, we found a solution to coupled time-dependent harmonic oscillators where all the time-dependent frequencies are arbitrary. This system may be found in many applications such as nonlinear and quantum physics, biophysics, molecular chemistry, and cosmology. We solve the time-dependent coupled harmonic oscillators by transforming the Hamiltonian of the interaction using a set of unitary operators. In passing, we show that N time-dependent and coupled oscillators have a generalized orthogonal functions invariant from which we can write a Ermakov–Lewis invariant. Full article

11 pages, 279 KiB

Open AccessArticle

Moyal Bracket and Ehrenfest’s Theorem in Born–Jordan Quantization

by Maurice de Gosson and Franz Luef

Quantum Rep. 2019, 1(1), 71-81; https://doi.org/10.3390/quantum1010008 - 15 Jul 2019

Viewed by 2915

Abstract

The usual Poisson bracket

{A, B}

can be identified with the so-called Moyal bracket

{A, B}_{M}

for larger classes of symbols than was previously thought, provided that one uses the Born–Jordan quantization rule instead of the [...] Read more.

The usual Poisson bracket

{A, B}

can be identified with the so-called Moyal bracket

{A, B}_{M}

for larger classes of symbols than was previously thought, provided that one uses the Born–Jordan quantization rule instead of the better known Weyl correspondence. We apply our results to a generalized version of Ehrenfest’s theorem on the time evolution of averages of operators. Full article

8 pages, 639 KiB

Open AccessArticle

Selective Engineering for Preparing Entangled Steady States in Cavity QED Setup

by Emilio H. S. Sousa and J. A. Roversi

Quantum Rep. 2019, 1(1), 63-70; https://doi.org/10.3390/quantum1010007 - 08 Jul 2019

Cited by 3 | Viewed by 2587

Abstract

We propose a dissipative scheme to prepare maximally entangled steady states in cavity QED setup, consisting of two two-level atoms interacting with the two counter-propagating whispering-gallery modes (WGMs) of a microtoroidal resonator. Using spontaneous emission and cavity decay as the dissipative quantum dynamical [...] Read more.

We propose a dissipative scheme to prepare maximally entangled steady states in cavity QED setup, consisting of two two-level atoms interacting with the two counter-propagating whispering-gallery modes (WGMs) of a microtoroidal resonator. Using spontaneous emission and cavity decay as the dissipative quantum dynamical source, we show that the steady state of this system can be steered into a two-atom single state as well as into a two-mode single state. We probed the compound system with weak field coupled to the system via a tapered fiber waveguide, finding it is possible to determine whether the two atoms or two modes are driven to a maximally entangled state. Through the transmission and reflection measurements, without disturbing the atomic state, when the cavity modes are being driven, or without disturbing the cavity field state, when a single atom being driven, one can get the information about the maximal entanglement. We also investigated for both subsystem, two-atom and two-mode states, the entanglement generation and under what conditions one can transfer entanglement from one subsystem to the other. Our scheme can be selectively used to prepare both maximally entangled atomic state as well as maximally entangled cavity-modes state, providing an efficient method for quantum information processing. Full article

(This article belongs to the Special Issue Selected Papers from the 16th International Conference on Squeezed States and Uncertainty Relations (ICSSUR 2019))

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13 pages, 1117 KiB

Open AccessArticle

Experimentally Accessible Witnesses of Many-Body Localization

by Marcel Goihl, Mathis Friesdorf, Albert H. Werner, Winton Brown and Jens Eisert

Quantum Rep. 2019, 1(1), 50-62; https://doi.org/10.3390/quantum1010006 - 17 Jun 2019

Cited by 5 | Viewed by 3360

Abstract

The phenomenon of many-body localized (MBL) systems has attracted significant interest in recent years, for its intriguing implications from a perspective of both condensed-matter and statistical physics: they are insulators even at non-zero temperature and fail to thermalize, violating expectations from quantum statistical [...] Read more.

The phenomenon of many-body localized (MBL) systems has attracted significant interest in recent years, for its intriguing implications from a perspective of both condensed-matter and statistical physics: they are insulators even at non-zero temperature and fail to thermalize, violating expectations from quantum statistical mechanics. What is more, recent seminal experimental developments with ultra-cold atoms in optical lattices constituting analog quantum simulators have pushed many-body localized systems into the realm of physical systems that can be measured with high accuracy. In this work, we introduce experimentally accessible witnesses that directly probe distinct features of MBL, distinguishing it from its Anderson counterpart. We insist on building our toolbox from techniques available in the laboratory, including on-site addressing, super-lattices, and time-of-flight measurements, identifying witnesses based on fluctuations, density–density correlators, densities, and entanglement. We build upon the theory of out of equilibrium quantum systems, in conjunction with tensor network and exact simulations, showing the effectiveness of the tools for realistic models. Full article

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13 pages, 352 KiB

Open AccessArticle

Informational Work Storage in Quantum Thermodynamics

by Shang-Yung Wang

Quantum Rep. 2019, 1(1), 37-49; https://doi.org/10.3390/quantum1010005 - 04 Jun 2019

Viewed by 2510

Abstract

We present a critical examination of the difficulties with the quantum versions of a lifted weight that are widely used as work storage systems in quantum thermodynamics. To overcome those difficulties, we turn to the strong connections between information and thermodynamics illuminated by [...] Read more.

We present a critical examination of the difficulties with the quantum versions of a lifted weight that are widely used as work storage systems in quantum thermodynamics. To overcome those difficulties, we turn to the strong connections between information and thermodynamics illuminated by Szilard’s engine and Landauer’s principle, and consider the concept of informational work storage. This concept is in sharp contrast with the usual one of mechanical work storage underlying the idealization of a quantum weight. An informational work storage system based on maximally mixed qubits that does not act as an entropy sink and is capable of truly distinguishing work from heat is studied. Applying it to the problem of single-shot work extraction in various extraction schemes, we show that for a given system state the maximum extractable work is independent of extraction scheme, in accordance with the second law of thermodynamics. Full article

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14 pages, 1160 KiB

Open AccessArticle

Entanglement Dynamics of Three and Four Level Atomic System under Stark Effect and Kerr-Like Medium

by S. Jamal Anwar, M. Ramzan, M. Usman and M. Khalid Khan

Quantum Rep. 2019, 1(1), 23-36; https://doi.org/10.3390/quantum1010004 - 28 May 2019

Cited by 12 | Viewed by 2778

Abstract

We investigated numerically the dynamics of quantum Fisher information (QFI) and entanglement for three- and four-level atomic systems interacting with a coherent field under the effect of Stark shift and Kerr medium. It was observed that the Stark shift and Kerr-like medium play [...] Read more.

We investigated numerically the dynamics of quantum Fisher information (QFI) and entanglement for three- and four-level atomic systems interacting with a coherent field under the effect of Stark shift and Kerr medium. It was observed that the Stark shift and Kerr-like medium play a prominent role during the time evolution of the quantum systems. The non-linear Kerr medium has a stronger effect on the dynamics of QFI as compared to the quantum entanglement (QE). QFI is heavily suppressed by increasing the value of Kerr parameter. This behavior was found comparable in the cases of three- and four-level atomic systems coupled with a non-linear Kerr medium. However, QFI and quantum entanglement (QE) maintain their periodic nature under atomic motion. On the other hand, the local maximum value of QFI and von Neumann entropy (VNE) decrease gradually under the Stark effect. Moreover, no prominent difference in the behavior of QFI and QE was observed for three- and four-level atoms while increasing the value of Stark parameter. However, three- and four-level atomic systems were found equally prone to the non-linear Kerr medium and Stark effect. Furthermore, three- and four-level atomic systems were found fully prone to the Kerr-like medium and Stark effect. Full article

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11 pages, 1006 KiB

Open AccessArticle

Quantum Computing, Seifert Surfaces, and Singular Fibers

by Michel Planat, Raymond Aschheim, Marcelo M. Amaral and Klee Irwin

Quantum Rep. 2019, 1(1), 12-22; https://doi.org/10.3390/quantum1010003 - 24 Apr 2019

Cited by 7 | Viewed by 4020

Abstract

The fundamental group

π_{1} (L)

of a knot or link L may be used to generate magic states appropriate for performing universal quantum computation and simultaneously for retrieving complete information about the processed quantum states. In this paper, one defines [...] Read more.

The fundamental group

π_{1} (L)

of a knot or link L may be used to generate magic states appropriate for performing universal quantum computation and simultaneously for retrieving complete information about the processed quantum states. In this paper, one defines braids whose closure is the L of such a quantum computer model and computes their braid-induced Seifert surfaces and the corresponding Alexander polynomial. In particular, some d-fold coverings of the trefoil knot, with

d = 3

, 4, 6, or 12, define appropriate links L, and the latter two cases connect to the Dynkin diagrams of

E_{6}

and

D_{4}

, respectively. In this new context, one finds that this correspondence continues with Kodaira’s classification of elliptic singular fibers. The Seifert fibered toroidal manifold

Σ^{'}

, at the boundary of the singular fiber

\tilde{E_{8}}

, allows possible models of quantum computing. Full article

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9 pages, 295 KiB

Open AccessArticle

Quantum Blockchain Using Entanglement in Time

by Del Rajan and Matt Visser

Quantum Rep. 2019, 1(1), 3-11; https://doi.org/10.3390/quantum1010002 - 17 Apr 2019

Cited by 61 | Viewed by 10458

Abstract

We propose a conceptual design for a quantum blockchain. Our method involves encoding the blockchain into a temporal GHZ (Greenberger–Horne–Zeilinger) state of photons that do not simultaneously coexist. It is shown that the entanglement in time, as opposed to an entanglement in space, [...] Read more.

We propose a conceptual design for a quantum blockchain. Our method involves encoding the blockchain into a temporal GHZ (Greenberger–Horne–Zeilinger) state of photons that do not simultaneously coexist. It is shown that the entanglement in time, as opposed to an entanglement in space, provides the crucial quantum advantage. All the subcomponents of this system have already been shown to be experimentally realized. Furthermore, our encoding procedure can be interpreted as nonclassically influencing the past. Full article

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Graphical abstract

2 pages, 177 KiB

Open AccessEditorial

Quantum Reports: A New Journal for a Broad Audience

by Lev Vaidman

Quantum Rep. 2019, 1(1), 1-2; https://doi.org/10.3390/quantum1010001 - 04 Jul 2018

Viewed by 2960

Abstract

A new MDPI journal Quantum Reports is launched as a scientific journal to provide an advanced forum for the growing community of researchers of quantum science [...] Full article

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Quantum Rep., Volume 1, Issue 1 (September 2019) – 12 articles

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