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Quantum coherence

Sonia Conesa-Boj, Ang Li, Sebastian Koelling, Matthias Brauns, Joost Ridderbos, Ton T Nguyen, Marcel A Verheijen, Paul M Koenraad, Floris Arnoud Zwanenburg, Erik P A M Bakkers
The ability of core-shell nanowires to overcome existing limitations of heterostructures is one of the key ingredients for the design of next generation devices. This requires a detailed understanding of the mechanism for strain relaxation in these systems, in order to eliminate strain-induced defect formation and thus to boost important electronic properties such as carrier mobility. Here we demonstrate how the hole mobility of [110]-oriented Ge-Si core-shell nanowires can be substantially enhanced thanks to the realization of large band offset and coherent strain in the system, reaching values as high as 4200 cm(2)/(Vs) at 4K and 1600 cm(2)/(Vs) at room temperature for high hole densities of 1019 cm(-3)...
February 23, 2017: Nano Letters
N Rawat, Y Shin, I Balasingham, N Rawat, Y Shin, I Balasingham, I Balasingham, N Rawat, Y Shin
An electroencephalogram (EEG) based image encryption combined with Quantum walks (QW) is encoded in Fresnel domain. The computational version of EEG randomizes the original plaintext whereas QW can serve as an excellent key generator due to its inherent nonlinear chaotic dynamic behavior. First, a spatially coherent monochromatic laser beam passes through an SLM, which introduces an arbitrary EEG phase-only mask. The modified beam is collected by a CCD. Further, the intensity is multiply with the QW digitally...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
Igor Altfeder, Andrey A Voevodin, Michael H Check, Sarah M Eichfeld, Joshua A Robinson, Alexander V Balatsky
Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance...
February 22, 2017: Scientific Reports
Wojciech Kozlowski, Santiago F Caballero-Benitez, Igor B Mekhov
A many-body atomic system coupled to quantized light is subject to weak measurement. Instead of coupling light to the on-site density, we consider the quantum backaction due to the measurement of matter-phase-related variables such as global phase coherence. We show how this unconventional approach opens up new opportunities to affect system evolution. We demonstrate how this can lead to a new class of final states different from those possible with dissipative state preparation or conventional projective measurements...
February 22, 2017: Scientific Reports
Ali Hatef, Naser Zamani, William Johnston
We systematically investigate the optical response of a semiconductor quantum dot (QD) hybridized with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) region. The VO2NP features a semiconductor to metal phase change characteristic below and above a critical temperature that leads to an abrupt change in the particle's optical properties. This feature means that the QD-VO2NP hybrid system can support the coherent coupling of exciton-polaritons and exciton-plasmon polaritons in the semiconductor and metal phases of the VO2NP, respectively...
February 21, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Lili Wang, Graham B Griffin, Alice Zhang, Feng Zhai, Nicholas E Williams, Richard F Jordan, Gregory S Engel
In multidimensional spectroscopy, dynamics of coherences between excited states report on the interactions between electronic states and their environment. The prolonged coherence lifetimes revealed through beating signals in the spectra of some systems may result from vibronic coupling between nearly degenerate excited states, and recent observations confirm the existence of such coupling in both model systems and photosynthetic complexes. Understanding the origin of beating signals in the spectra of photosynthetic complexes has been given considerable attention; however, strategies to generate them in artificial systems that would allow us to test the hypotheses in detail are still lacking...
February 21, 2017: Nature Chemistry
Yu Zhou, Abdullah Rasmita, Ke Li, Qihua Xiong, Igor Aharonovich, Wei-Bo Gao
The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid-state emitters have emerged as promising candidates with their prospects for on-chip integration as quantum nodes and sources of coherent photons connecting these nodes. Under a strongly driving resonant laser field, such quantum emitters can exhibit quantum behaviour such as Autler-Townes splitting and the Mollow triplet spectrum. Here we demonstrate coherent control of a strongly driven optical transition in silicon vacancy centre in diamond...
February 20, 2017: Nature Communications
Atul Mantri, Tommaso F Demarie, Joseph F Fitzsimons
Measurement-based quantum computing (MBQC) is a model of quantum computation where quantum information is coherently processed by means of projective measurements on highly entangled states. Following the introduction of MBQC, cluster states have been studied extensively both from the theoretical and experimental point of view. Indeed, the study of MBQC was catalysed by the realisation that cluster states are universal for MBQC with (X, Y)-plane and Z measurements. Here we examine the question of whether the requirement for Z measurements can be dropped while maintaining universality...
February 20, 2017: Scientific Reports
T Konishi, E Clarke, C W Burrows, J J Bomphrey, R Murray, G R Bell
The lateral ordering of arrays of self-assembled InAs-GaAs quantum dots (QDs) has been quantified as a function of growth rate, using the Hopkins-Skellam index (HSI). Coherent QD arrays have a spatial distribution which is neither random nor ordered, but intermediate. The lateral ordering improves as the growth rate is increased and can be explained by more spatially regular nucleation as the QD density increases. By contrast, large and irregular 3D islands are distributed randomly on the surface. This is consistent with a random selection of the mature QDs relaxing by dislocation nucleation at a later stage in the growth, independently of each QD's surroundings...
February 13, 2017: Scientific Reports
Y F Chen, J C Tung, P H Tuan, Y T Yu, H C Liang, K F Huang
A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators...
January 2017: Physical Review. E
David B Lingerfelt, Patrick J Lestrange, Joseph J Radler, Samantha E Brown-Xu, Pyosang Kim, Felix N Castellano, Lin X Chen, Xiaosong Li
Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a bi-nuclear platinum complex, where a persistent periodic beating in the transient absorption signal's anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of bi-nuclear platinum complexes exhibiting a range of inter-platinum distances...
February 16, 2017: Journal of Physical Chemistry. A
I P Mercer, T Witting, T Driver, R J Cogdell, J P Marangos, J W G Tisch
We demonstrate angle-resolved coherent (ARC) wave mixing using 4 fs light pulses derived from a laser source that spans 550-1000 nm. We believe this to be the shortest pulse duration used to date in coherent multi-dimensional spectroscopy. The marriage of this ultra-broad band, few-cycle coherent source with the ARC technique will permit new investigations of the interplay between energy transfers and quantum superposition states spanning 8200  cm<sup>-1</sup>. We applied this configuration to measurements on the photosynthetic low light (LL) complex from Rhodopseudomonas palustris in solution at ambient temperature...
February 15, 2017: Optics Letters
Ashok Ajoy, Yi-Xiang Liu, Kasturi Saha, Luca Marseglia, Jean-Christophe Jaskula, Ulf Bissbort, Paola Cappellaro
Recent advances in engineering and control of nanoscale quantum sensors have opened new paradigms in precision metrology. Unfortunately, hardware restrictions often limit the sensor performance. In nanoscale magnetic resonance probes, for instance, finite sampling times greatly limit the achievable sensitivity and spectral resolution. Here we introduce a technique for coherent quantum interpolation that can overcome these problems. Using a quantum sensor associated with the nitrogen vacancy center in diamond, we experimentally demonstrate that quantum interpolation can achieve spectroscopy of classical magnetic fields and individual quantum spins with orders of magnitude finer frequency resolution than conventionally possible...
February 14, 2017: Proceedings of the National Academy of Sciences of the United States of America
Kerem Bingol, Da-Wei Li, Bo Zhang, Rafael Brüschweiler
Identification of metabolites in complex mixtures represents a key step in metabolomics. A new strategy is introduced, which is implemented in a new public web server, COLMARm, that permits the coanalysis of up to three two-dimensional (2D) NMR spectra, namely, (13)C-(1)H HSQC (heteronuclear single quantum coherence spectroscopy), (1)H-(1)H TOCSY (total correlation spectroscopy), and (13)C-(1)H HSQC-TOCSY, for the comprehensive, accurate, and efficient performance of this task. The highly versatile and interactive nature of COLMARm permits its application to a wide range of metabolomics samples independent of the magnetic field...
December 20, 2016: Analytical Chemistry
Salvador Miret-Artes, Eli Pollak
The quantum reflection measured previously by Zhao et al (Phys. Rev. A, {\bf 2008},{\it 78}, 010902(R)) for the scattering of He atoms off a microstructured grating is described and analyzed theoretically. Using the close-coupling formalism with a complex absorbing potential and describing the long range interaction in terms of the Casimir-van der Waals potential, we find probabilities and diffraction patterns which are in fairly good agreement with the experimental results. The central outcomes of this study are two fold...
February 10, 2017: Journal of Physical Chemistry Letters
Quntao Zhuang, Zheshen Zhang, Jeffrey H Shapiro
Quantum metrology utilizes nonclassical resources, such as entanglement or squeezed light, to realize sensors whose performance exceeds that afforded by classical-state systems. Environmental loss and noise, however, easily destroy nonclassical resources and, thus, nullify the performance advantages of most quantum-enhanced sensors. Quantum illumination (QI) is different. It is a robust entanglement-enhanced sensing scheme whose 6 dB performance advantage over a coherent-state sensor of the same average transmitted photon number survives the initial entanglement's eradication by loss and noise...
January 27, 2017: Physical Review Letters
Th K Mavrogordatos, G Tancredi, M Elliott, M J Peterer, A Patterson, J Rahamim, P J Leek, E Ginossar, M H Szymańska
We explore the joint activated dynamics exhibited by two quantum degrees of freedom: a cavity mode oscillator which is strongly coupled to a superconducting qubit in the strongly coherently driven dispersive regime. Dynamical simulations and complementary measurements show a range of parameters where both the cavity and the qubit exhibit sudden simultaneous switching between two metastable states. This manifests in ensemble averaged amplitudes of both the cavity and qubit exhibiting a partial coherent cancellation...
January 27, 2017: Physical Review Letters
Z R Gong, W Z Luo, Z F Jiang, H C Fu
We theoretically investigate the chiral topological excitons emerging in the monolayer transition metal dichalcogenides, where a bulk energy gap of valley excitons is opened up by a position dependent external magnetic field. We find two emerging chiral topological nontrivial excitons states, which exactly connects to the bulk topological properties, i.e., Chern number = 2. The dependence of the spectrum of the chiral topological excitons on the width of the magnetic field domain wall as well as the magnetic filed strength is numerically revealed...
February 10, 2017: Scientific Reports
Liron Stern, Boris Desiatov, Noa Mazurski, Uriel Levy
In recent years, there has been marked increase in research aimed to introduce alkali vapours into guided-wave configurations. Owing to the significant reduction in device dimensions, the increase in density of states, the interaction with surfaces and primarily the high intensities carried along the structure, a plethora of light-vapour interactions can be studied. Moreover, such platform may exhibit new functionalities such as low-power nonlinear light-matter interactions. One immense challenge is to study the effects of quantum coherence and shifts in nanoscale waveguides, characterized by ultra-small mode areas and fast dynamics...
February 9, 2017: Nature Communications
Shihong Huang, Tao Zhu, Min Liu, Wei Huang
Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods like delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately. This is because a broadening of the Gaussian spectrum, which hides the laser's intrinsic Lorentzian linewidth, cannot be avoided. Here, we introduce a new method using the strong coherent envelope to characterize the laser's intrinsic linewidth through self-coherent detection...
February 9, 2017: Scientific Reports
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