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Quantum coherence

Rongchun Zhang, Nghia Tuan Duong, Yusuke Nishiyama, Ayyalusamy Ramamoorthy
Solid-state 1H NMR spectroscopy has attracted much attention in the recent years due to the remarkable spectral resolution improvement by ultrafast magic-angle-spinning (MAS) as well as due to the sensitivity enhancement rendered by proton detection. Although these developments have enabled the investigation of a variety of challenging chemical and biological solids, the proton spectral resolution is still poor for many rigid solid systems owing to the presence of conformational heterogeneity and the unsuppressed residual proton-proton dipolar couplings even with the use of the highest currently feasible sample spinning speed of ~130 kHz...
May 24, 2017: Journal of Physical Chemistry. B
Yinghong Xue, Tingyu Li, Katsuyuki Kasai, Yoshiko Okada-Shudo, Masayoshi Watanabe, Yun Zhang
We experimentally show a quantum interference in phase space by interrogating photon number probabilities (n = 2, 3, and 4) of a displaced squeezed state, which is generated by an optical parametric amplifier and whose displacement is controlled by amplitude of injected coherent light. It is found that the probabilities exhibit oscillations of interference effect depending upon the amplitude of the controlling light field. This phenomenon is attributed to quantum interference in phase space and indicates the capability of controlling quantum interference using amplitude...
May 23, 2017: Scientific Reports
Kevin Whitham, Tobias Hanrath
The formation of epitaxially connected quantum dot solids involves a complex interplay of interfacial assembly, surface chemistry, and irreversible directed attachment. We describe the basic mechanism in context of a coherent phase transition with distinct nucleation and propagation steps. The proposed mechanism explains how defects in the pre-assembled structure influence nucleation and how basic geometric relationships govern the transformation from hexagonal assemblies of isolated dots to interconnected solids with square symmetry...
May 22, 2017: Journal of Physical Chemistry Letters
Artur Branny, Santosh Kumar, Raphaël Proux, Brian D Gerardot
An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor...
May 22, 2017: Nature Communications
Di Zheng, Shunping Zhang, Qian Deng, Meng Kang, Peter Nordlander, Hongxing Xu
Strong coupling between plasmons and excitons in nanocavities can result in the formation of hybrid plexcitonic states. Understanding the dispersion relation of plexcitons is important both for fundamental quantum science and for applications including optoelectronics and nonlinear optics devices. The conventional approach, based on statistics over different nanocavities suffers from large inhomogeneities from the samples, owing to the non-uniformity of nanocavities and the lack of control over the locations and orientations of the excitons...
May 22, 2017: Nano Letters
Andrew J Pell, Kevin J Sanders, Sebastian Wegner, Guido Pintacuda, Clare P Grey
We propose two broadband pulse schemes for (14)N solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) that achieves (i) complete population inversion and (ii) efficient excitation of the double-quantum spectrum using low-power single-sideband-selective pulses. We give a comprehensive theoretical description of both schemes using a common framework that is based on the jolting-frame formalism of Caravatti et al. [J. Magn. Reson. 55, 88 (1983)]. This formalism is used to determine for the first time that we can obtain complete population inversion of (14)N under low-power conditions, which we do here using single-sideband-selective adiabatic pulses...
May 21, 2017: Journal of Chemical Physics
Rajesh Dutta, Kaushik Bagchi, Biman Bagchi
Kubo's fluctuation theory of line shape forms the backbone of our understanding of optical and vibrational line shapes, through such concepts as static heterogeneity and motional narrowing. However, the theory does not properly address the effects of quantum coherences on optical line shape, especially in extended systems where a large number of eigenstates are present. In this work, we study the line shape of an exciton in a one-dimensional lattice consisting of regularly placed and equally separated optical two level systems...
May 21, 2017: Journal of Chemical Physics
Bin Bai, Yu Zhou, Ruifeng Liu, Huaibin Zheng, Yunlong Wang, Fuli Li, Zhuo Xu
From quantum point of view, Hanbury Brown-Twiss effect is a result of constructive-destructive two-photon interference. There should be no Hanbury Brown-Twiss effect if there was no two-photon interference. In this paper, we observed Hanbury Brown- Twiss effect in a specially designed experiment, in which two-photon interference is impossible by keeping only one two-photon probability amplitude in the experimental scheme. However, our experimental results can still be interpreted by Glauber's quantum optical coherence theory...
May 19, 2017: Scientific Reports
Yao Zhang, Qiu-Shi Meng, Li Zhang, Yang Luo, Yun-Jie Yu, Ben Yang, Yang Zhang, Ruben Esteban, Javier Aizpurua, Yi Luo, Jin-Long Yang, Zhen-Chao Dong, J G Hou
The coherent interaction between quantum emitters and photonic modes in cavities underlies many of the current strategies aiming at generating and controlling photonic quantum states. A plasmonic nanocavity provides a powerful solution for reducing the effective mode volumes down to nanometre scale, but spatial control at the atomic scale of the coupling with a single molecular emitter is challenging. Here we demonstrate sub-nanometre spatial control over the coherent coupling between a single molecule and a plasmonic nanocavity in close proximity by monitoring the evolution of Fano lineshapes and photonic Lamb shifts in tunnelling electron-induced luminescence spectra...
May 19, 2017: Nature Communications
Clément Hainaut, Isam Manai, Radu Chicireanu, Jean-François Clément, Samir Zemmouri, Jean Claude Garreau, Pascal Szriftgiser, Gabriel Lemarié, Nicolas Cherroret, Dominique Delande
We report on the observation of the coherent enhancement of the return probability ["enhanced return to the origin" (ERO)] in a periodically kicked cold-atom gas. By submitting an atomic wave packet to a pulsed, periodically shifted, laser standing wave, we induce an oscillation of ERO in time that is explained in terms of a periodic, reversible dephasing in the weak-localization interference sequences responsible for ERO. Monitoring the temporal decay of ERO, we exploit its quantum-coherent nature to quantify the decoherence rate of the atomic system...
May 5, 2017: Physical Review Letters
Naotaka Yoshikawa, Tomohiro Tamaya, Koichiro Tanaka
The electronic properties of graphene can give rise to a range of nonlinear optical responses. One of the most desirable nonlinear optical processes is high-harmonic generation (HHG) originating from coherent electron motion induced by an intense light field. Here, we report on the observation of up to ninth-order harmonics in graphene excited by mid-infrared laser pulses at room temperature. The HHG in graphene is enhanced by an elliptically polarized laser excitation, and the resultant harmonic radiation has a particular polarization...
May 19, 2017: Science
Sarangam Majumdar, Sukla Pal
Bacteria are far more intelligent than we can think of. They adopt different survival strategies to make their life comfortable. Researches on bacterial communication to date suggest that bacteria can communicate with each other using chemical signaling molecules as well as using ion channel mediated electrical signaling. Though in past few decades the scopes of chemical signaling have been investigated extensively, those of electrical signaling have received less attention. In this article, we present a novel perspective on time-sharing behavior, which maintains the biofilm growth under reduced nutrient supply between two distant biofilms through electrical signaling based on the experimental evidence reported by Liu et al...
May 17, 2017: Journal of Cell Communication and Signaling
Felipe Fávaro de Oliveira, Denis Antonov, Ya Wang, Philipp Neumann, Seyed Ali Momenzadeh, Timo Häußermann, Alberto Pasquarelli, Andrej Denisenko, Jörg Wrachtrup
Atomic-size spin defects in solids are unique quantum systems. Most applications require nanometre positioning accuracy, which is typically achieved by low-energy ion implantation. A drawback of this technique is the significant residual lattice damage, which degrades the performance of spins in quantum applications. Here we show that the charge state of implantation-induced defects drastically influences the formation of lattice defects during thermal annealing. Charging of vacancies at, for example, nitrogen implantation sites suppresses the formation of vacancy complexes, resulting in tenfold-improved spin coherence times and twofold-improved formation yield of nitrogen-vacancy centres in diamond...
May 17, 2017: Nature Communications
A R Dixon, J F Dynes, M Lucamarini, B Fröhlich, A W Sharpe, A Plews, W Tam, Z L Yuan, Y Tanizawa, H Sato, S Kawamura, M Fujiwara, M Sasaki, A J Shields
Quantum key distribution's (QKD's) central and unique claim is information theoretic security. However there is an increasing understanding that the security of a QKD system relies not only on theoretical security proofs, but also on how closely the physical system matches the theoretical models and prevents attacks due to discrepancies. These side channel or hacking attacks exploit physical devices which do not necessarily behave precisely as the theory expects. As such there is a need for QKD systems to be demonstrated to provide security both in the theoretical and physical implementation...
May 16, 2017: Scientific Reports
Lorenzo De Santis, Carlos Antón, Bogdan Reznychenko, Niccolo Somaschi, Guillaume Coppola, Jean Senellart, Carmen Gómez, Aristide Lemaître, Isabelle Sagnes, Andrew G White, Loïc Lanco, Alexia Auffèves, Pascale Senellart
A strong limitation of linear optical quantum computing is the probabilistic operation of two-quantum-bit gates based on the coalescence of indistinguishable photons. A route to deterministic operation is to exploit the single-photon nonlinearity of an atomic transition. Through engineering of the atom-photon interaction, phase shifters, photon filters and photon-photon gates have been demonstrated with natural atoms. Proofs of concept have been reported with semiconductor quantum dots, yet limited by inefficient atom-photon interfaces and dephasing...
May 15, 2017: Nature Nanotechnology
Rok Žitko, Michele Fabrizio
We study how the non-Fermi-liquid nature of the overscreened multi-channel Kondo impurity model affects the response to a BCS pairing term that, in the absence of the impurity, opens a gap Δ. We find that the low-energy spectrum in the limit Δ → 0 actually does not correspond to the spectrum strictly at Δ = 0. In particular, in the two-channel Kondo model the Δ → 0 ground state is an orbitally degenerate spin-singlet, while it is an orbital singlet with a residual spin degeneracy at Δ = 0. In addition, there are fractionalized spin-1/2 sub-gap excitations whose energy in units of Δ tends towards a finite and universal value when Δ → 0; as if the universality of the anomalous power-law exponents that characterise the overscreened Kondo effect turned into universal energy ratios when the scale invariance is broken by Δ ≠ 0...
February 16, 2017: Physical Review. B
T Pei, A Pályi, M Mergenthaler, N Ares, A Mavalankar, J H Warner, G A D Briggs, E A Laird
The decay of spin-valley states is studied in a suspended carbon nanotube double quantum dot via the leakage current in Pauli blockade and via dephasing and decoherence of a qubit. From the magnetic field dependence of the leakage current, hyperfine and spin-orbit contributions to relaxation from blocked to unblocked states are identified and explained quantitatively by means of a simple model. The observed qubit dephasing rate is consistent with the hyperfine coupling strength extracted from this model and inconsistent with dephasing from charge noise...
April 28, 2017: Physical Review Letters
Sumit Sarkar, Sanku Paul, Chetan Vishwakarma, Sunil Kumar, Gunjan Verma, M Sainath, Umakant D Rapol, M S Santhanam
Quantum systems lose coherence upon interaction with the environment and tend towards classical states. Quantum coherence is known to exponentially decay in time so that macroscopic quantum superpositions are generally unsustainable. In this work, slower than exponential decay of coherences is experimentally realized in an atom-optics kicked rotor system subjected to nonstationary Lévy noise in the applied kick sequence. The slower coherence decay manifests in the form of quantum subdiffusion that can be controlled through the Lévy exponent...
April 28, 2017: Physical Review Letters
Vytautas Butkus, Jan Alster, Eglė Bašinskaitė, Ramu Nas Augulis, Patrik Neuhaus, Leonas Valkunas, Harry L Anderson, Darius Abramavicius, Donatas Zigmantas
The role of quantum coherence in photochemical functions of molecular systems such as photosynthetic complexes is a broadly debated topic. Coexistence and intermixing of electronic and vibrational coherences has been proposed to be responsible for the observed long-lived coherences and high energy transfer efficiency. However, clear experimental evidence of coherences with different origins operating at the same time has been elusive. In this work, multidimensional spectra obtained from a six-porphyrin nanoring system are analyzed in detail with support from theoretical modeling...
May 11, 2017: Journal of Physical Chemistry Letters
Chin-Wen Chou, Christoph Kurz, David B Hume, Philipp N Plessow, David R Leibrandt, Dietrich Leibfried
Laser cooling and trapping of atoms and atomic ions has led to advances including the observation of exotic phases of matter, the development of precision sensors and state-of-the-art atomic clocks. The same level of control in molecules could also lead to important developments such as controlled chemical reactions and sensitive probes of fundamental theories, but the vibrational and rotational degrees of freedom in molecules pose a challenge for controlling their quantum mechanical states. Here we use quantum-logic spectroscopy, which maps quantum information between two ion species, to prepare and non-destructively detect quantum mechanical states in molecular ions...
May 10, 2017: Nature
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