## Physics

### Anisotropic Features of the Two-dimensional Hydrogen Atom in a Magnetic Field. (arXiv:1701.06235v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

The aim of the current work is the numerical research of the anisotropic characteristics of the two-dimensional hydrogen atom induced by a magnetic field. The ground state energy (GSE) of the two-dimensional hydrogen atom and the corresponding wave function have been numerically calculated in the Born-Oppenheimer approximation and with taking into account the finite mass of the proton. The non-linear dependence of GSE on the angle {\alpha} between the magnetic field vector and the normal to the plane of electron motion in a wide range of magnetic field strength has been found. The effect of a significant reduction of GSE (up to 1.9-fold) is observed with increasing the angle {\alpha} up to 90 degrees.

Categories: Journals, Physics

### Interferometric visibility and coherence. (arXiv:1701.05051v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

Recently, the basic concept of quantum coherence (or superposition) has gained a lot of renewed attention, after Baumgratz et al. [PRL 113:140401 (2014)], following \AA{}berg [arXiv:quant-ph/0612146], have proposed a resource theoretic approach to quantify it. This has resulted in a large number of papers and preprints exploring various coherence monotones, and debating possible forms for the resource theory. Here we take the view that the operational foundation of coherence in a state, be it quantum or otherwise wave mechanical, lies in the observation of interference effects.

Our approach here is to consider an idealised multi-path interferometer, with a suitable detector, in such a way that the visibility of the interference pattern provides a quantitative expression of the amount of coherence in a given probe state. We present a general framework of deriving coherence measures from visibility, and demonstrate it by analysing several concrete visibility parameters, recovering some known coherence measures and obtaining some new ones.

Categories: Journals, Physics

### Towards Searching for Entangled Photons in the CMB Sky. (arXiv:1701.03437v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

We explore the possibility of detecting an entangled pair of cosmic microwave background (CMB) photons from casually disconnected patches of the sky or other cosmological sources. The measurement uses the standard HBT intensity interferometer with the polarizer orientations for the two detectors chosen as in a Bell inequality experiment. However, unless the angle between the two sources is large such that entanglement is less likely, the entanglement signal is contaminated with un-entangled background which makes it hard to isolate the signal.

Categories: Journals, Physics

### cMERA for Interacting Fields. (arXiv:1612.02427v2 [hep-th] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

We upgrade cMERA to a systematic variational ansatz and develop techniques for its application to interacting quantum field theories in arbitrary spacetime dimensions. By establishing a correspondence between the first two terms in the variational expansion and the Gaussian Effective Potential, we can exactly solve for a variational approximation to the cMERA entangler. As examples, we treat scalar $\varphi^4$ theory and the Gross-Neveu model and extract non-perturbative behavior. We also comment on the connection between generalized squeezed coherent states and more generic entanglers.

Categories: Journals, Physics

### Multi-partite entanglement. (arXiv:1612.02437v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

We give an introduction to the theory of multi-partite entanglement. We begin by describing the "coordinate system" of the field: Are we dealing with pure or mixed states, with single or multiple copies, what notion of "locality" is being used, do we aim to classify states according to their "type of entanglement" or to quantify it? Building on the general theory of multi-partite entanglement - to the extent that it has been achieved - we turn to explaining important classes of multi-partite entangled states, including matrix product states, stabilizer and graph states, bosonic and fermionic Gaussian states, addressing applications in condensed matter theory. We end with a brief discussion of various applications that rely on multi-partite entangled states: quantum networks, measurement-based quantum computing, non-locality, and quantum metrology.

Categories: Journals, Physics

### Three-body problem in 3D space: ground state, (quasi)-exact-solvability. (arXiv:1611.08157v3 [math-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

We study aspects of the quantum and classical dynamics of a $3$-body system in 3D space with interaction depending only on mutual distances. The study is restricted to solutions in the space of relative motion which are functions of mutual distances only. It is shown that the ground state (and some other states) in the quantum case and the planar trajectories in the classical case are of this type. The quantum (and classical) system for which these states are eigenstates is found and its Hamiltonian is constructed. It corresponds to a three-dimensional quantum particle moving in a curved space with special metric. The kinetic energy of the system has a hidden $sl(4,R)$ Lie (Poisson) algebra structure, alternatively, the hidden algebra $h^{(3)}$ typical for the $H_3$ Calogero model. We find an exactly solvable three-body generalized harmonic oscillator-type potential as well as a quasi-exactly-solvable three-body sextic polynomial type potential; both models have an extra integral.

Categories: Journals, Physics

### Null weak values and the past of a quantum particle. (arXiv:1611.02780v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

Non-destructive weak measurements (WM) made on a quantum particle allow to extract information as the particle evolves from a prepared state to a finally detected state. The physical meaning of this information has been open to debate, particularly in view of the apparent discontinuous trajectories of the particle recorded by WM. In this work we investigate the properties of vanishing weak values for projection operators as well as general observables. We then analyze the implications when inferring the past of a quantum particle. We provide a novel (non-optical) example for which apparent discontinuous trajectories are obtained by WM. Our approach is compared to previous results.

Categories: Journals, Physics

### Necessary Adiabatic Run Times in Quantum Optimization. (arXiv:1611.02585v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

Quantum annealing is guaranteed to find the ground state of optimization problems in the adiabatic limit. Recent work [Phys. Rev. X 6, 031010 (2016)] has found that for some barrier tunneling problems, quantum annealing can be run much faster than is adiabatically required. Specifically, an $n$-qubit optimization problem was presented for which a non-adiabatic, or diabatic, annealing algorithm requires only constant runtime, while an adiabatic annealing algorithm requires a runtime polynomial in $n$.

Here we show that this non-adiabatic speed-up is a direct result of a specific symmetry in the studied problems. In the more general case, no such non-adiabatic speed-up occurs. We furthermore show why the special case achieves this speed-up compared to the general case. We conclude with the observation that the adiabatic annealing algorithm has a necessary and sufficient runtime that is quadratically better than the standard quantum adiabatic condition suggests.

Categories: Journals, Physics

### The role of phases in detecting three qubit entanglement. (arXiv:1610.06645v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Tue, 2017-02-07 05:45

We propose separability criteria for three qubit states in terms of diagonal and anti-diagonal entries to detect entanglement with positive partial transposes. We report that the phases, that is, the angular parts of anti-diagonal entries play a crucial role to determine if a given three qubit state is separable or entangled, and they must obey even an identity for separability in some cases. These criteria are strong enough to detect PPT entanglement with nonzero volume. In several cases when all the entries are zero except for diagonal and anti-diagonal entries, we characterize separability using phases. These include the cases when anti-diagonal entries of such states share a common magnitude, and when ranks are less than or equal to six. We also compute the lengths of rank six cases, and find three qubit separable states with lengths 8 whose maximum ranks of partial transposes are 7.

Categories: Journals, Physics

### Entropic uncertainty relations and their applications

Reviews of Modern Physics - Mon, 2017-02-06 17:00

Author(s): Patrick J. Coles, Mario Berta, Marco Tomamichel, and Stephanie Wehner

The Heisenberg uncertainty principle has a more precise formulation in terms of inequalities involving quantum entropies. Currently known entropic uncertainty relations are presented; they capture and extend Heisenberg’s idea of the unpredictability of the outcomes of incompatible measurements. Distinct results are obtained for finite- and infinite-dimensional Hilbert spaces. Applications are surveyed, including the formulation of entanglement witnesses, current ideas about wave-particle duality, and the analysis of quantum cryptography.

[Rev. Mod. Phys. 89, 015002] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Biphoton states in correlated turbulence

Author(s): Filippus S. Roux

The effect of turbulence on a pair of photons propagating together through the same medium is analyzed. The behavior is compared to the case where these photons propagate separately through different turbulent media. The analysis is done with a multiple phase screen approach, by deriving and solving…

[Phys. Rev. A 95, 023809] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Control of Fano resonances and slow light using Bose-Einstein condensates in a nanocavity

Author(s): M. Javed Akram, Fazal Ghafoor, M. Miskeen Khan, and Farhan Saif

In this study, a standing wave in an optical nanocavity with Bose-Einstein condensate (BEC) constitutes a one-dimensional optical lattice potential in the presence of a finite two bodies atomic interaction. We report that the interaction of a BEC with a standing field in an optical cavity coherently…

[Phys. Rev. A 95, 023810] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Control of adiabatic light transfer in coupled waveguides with longitudinally varying detuning

Author(s): Hassan Oukraou, Laura Vittadello, Virginie Coda, Charles Ciret, Massimo Alonzo, Andon A. Rangelov, Nikolay V. Vitanov, and Germano Montemezzani

We study adiabatic light transfer in systems of two coupled waveguides with spatially varying detuning of the propagation constants, providing an analogy to the quantum phenomena of rapid adiabatic passage (RAP) and two-state stimulated Raman adiabatic passage (two-state STIRAP). Experimental demons…

[Phys. Rev. A 95, 023811] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Symmetry-protected zero-mode laser with a tunable spatial profile

Author(s): Li Ge

We propose to utilize symmetry-protected zero modes of a photonic lattice to realize a single-mode, fixed-frequency, and spatially tunable laser. These properties are the consequence of the underlying non-Hermitian particle-hole symmetry, with which the energy spectrum satisfies ɛm=−ɛn*. Unlike in t…

[Phys. Rev. A 95, 023812] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Motion-induced enhancement of Rabi coupling between atomic ensembles in cavity optomechanics

Author(s): Anil Kumar Chauhan and Asoka Biswas

We propose a scheme of enhancement of Rabi coupling between two identical atomic ensembles trapped inside an optical cavity in a membrane-in-the-middle setup. The cavity modes dispersively interact with the ensembles and the effective interaction between the ensembles is governed by the tunneling ra…

[Phys. Rev. A 95, 023813] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Viewpoint: Reservoir Computing Speeds Up

APS Physics - Mon, 2017-02-06 17:00

Author(s): Miguel C. Soriano

A brain-inspired computer made with optoelectronic parts runs faster thanks to a hardware redesign, recognizing simple speech at the rate of 1 million words per second.

[Physics 10, 12] Published Mon Feb 06, 2017

Categories: Physics

### Feature: Arts & Culture: Becoming One of the Team

APS Physics - Mon, 2017-02-06 17:00

Artist Ekaterina Smirnova is being embraced by scientists after a chance encounter with an astrophysicist turned science writer.

[Physics 10, 14] Published Mon Feb 06, 2017

Categories: Physics

### Switchable particle statistics with an embedding quantum simulator

PRA: Quantum information - Mon, 2017-02-06 17:00

Author(s): Xiao-Hang Cheng, Iñigo Arrazola, Julen S. Pedernales, Lucas Lamata, Xi Chen, and Enrique Solano

We propose the implementation of a switch of particle statistics with an embedding quantum simulator. By encoding both Bose-Einstein and Fermi-Dirac statistics into an enlarged Hilbert space, the statistics of the simulated quantum particles may be changed in situ during the time evolution, from bos…

[Phys. Rev. A 95, 022305] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Proposal for detecting a single electron spin in a microwave resonator

PRA: Quantum information - Mon, 2017-02-06 17:00

Author(s): P. Haikka, Y. Kubo, A. Bienfait, P. Bertet, and K. Mølmer

We propose a method for detecting the presence of a single spin in a crystal by coupling it to a high-quality factor superconducting planar resonator. By confining the microwave field in the vicinity of a constriction of nanometric dimensions, the coupling constant can be as high as 5–10 kHz. This c…

[Phys. Rev. A 95, 022306] Published Mon Feb 06, 2017

Categories: Journals, Physics

### Quantum coherence in the dynamical Casimir effect

PRA: Quantum information - Mon, 2017-02-06 17:00

Author(s): D. N. Samos-Sáenz de Buruaga and Carlos Sabín

We propose to use quantum coherence as the ultimate proof of the quantum nature of the radiation that appears by means of the dynamical Casimir effect in experiments with superconducting microwave waveguides. We show that, unlike previously considered measurements such as entanglement and discord, q…

[Phys. Rev. A 95, 022307] Published Mon Feb 06, 2017

Categories: Journals, Physics