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Quantum coherence

Lothar Wondraczek, Esa Tyystjärvi, Jorge Méndez-Ramos, Frank A Müller, Qinyuan Zhang
Solar energy harvesting is largely limited by the spectral sensitivity of the employed energy conversion system, where usually large parts of the solar spectrum do not contribute to the harvesting scheme, and where, of the contributing fraction, the full potential of each photon is not efficiently used in the generation of electrical or chemical energy. Extrinsic sensitization through photoluminescent spectral conversion has been proposed as a route to at least partially overcome this problem. Here, we discuss this approach in the emerging context of photochemical energy harvesting and storage through natural or artificial photosynthesis...
December 2015: Advanced Science (Weinheim, Baden-Wurttemberg, Germany)
Abou El-Hamd H Mohamed, Naglaa S Mohamed, Ahmed R Hamed, Mohamed-Elamir F Hegazy
In continuation of our chemical investigation on some medicinal plants of the genus Achillea, chromatographic investigation of the methylene chloride/methanol (1:1) extract of the air-dried aerial part of Achillea biebersteinii Afan. (family Asteraceae) afforded a new natural monoterpene (2), in addition to two known sesquiterpenes (3 and 4). Compound 1 was isolated as light needle crystals. Structures were established on the basis of MS and NMR spectroscopic (1H, 13C, 1H-1H correlation spectroscopy, heteronuclear multiple-quantum coherence and heteronuclear multiple-bond correlation) data and in case of compound 1 were confirmed by X-ray analysis...
October 24, 2016: Zeitschrift Für Naturforschung. C, A Journal of Biosciences
Takeshi Suzuki, Rohan Singh, Manfred Bayer, Arne Ludwig, Andreas D Wieck, Steven T Cundiff
Coherent control of a strongly inhomogeneously broadened system, namely, InAs self-assembled quantum dots, is demonstrated. To circumvent the deleterious effects of the inhomogeneous broadening, which usually masks the results of coherent manipulation, we use prepulse two-dimensional coherent spectroscopy to provide a size-selective readout of the ground, exciton, and biexciton states. The dependence on the timing of the prepulse is due to the dynamics of the coherently generated populations. To further validate the results, we performed prepulse polarization dependent measurements and confirmed the behavior expected from selection rules...
October 7, 2016: Physical Review Letters
M Garg, M Zhan, T T Luu, H Lakhotia, T Klostermann, A Guggenmos, E Goulielmakis
The frequency of electric currents associated with charge carriers moving in the electronic bands of solids determines the speed limit of electronics and thereby that of information and signal processing. The use of light fields to drive electrons promises access to vastly higher frequencies than conventionally used, as electric currents can be induced and manipulated on timescales faster than that of the quantum dephasing of charge carriers in solids. This forms the basis of terahertz (10(12) hertz) electronics in artificial superlattices, and has enabled light-based switches and sampling of currents extending in frequency up to a few hundred terahertz...
October 19, 2016: Nature
Qin Wang, Xing-Yu Zhou, Guang-Can Guo
In this paper, we put forward a new approach towards realizing measurement-device-independent quantum key distribution with passive heralded single-photon sources. In this approach, both Alice and Bob prepare the parametric down-conversion source, where the heralding photons are labeled according to different types of clicks from the local detectors, and the heralded ones can correspondingly be marked with different tags at the receiver's side. Then one can obtain four sets of data through using only one-intensity of pump light by observing different kinds of clicks of local detectors...
October 19, 2016: Scientific Reports
R McIntosh, S J Henley, S R P Silva, S Bhattacharyya
Whilst resonant transmission is well understood and can be fully harnessed for crystalline superlattices, a complete picture has not yet emerged for disordered superlattices. It has proven difficult to tune resonant transmission in disordered diamond-like carbon (DLC) superlattices as conventional models are not equipped to incorporate significant structural disorder. In this work, we present concurrent experimental and theoretical analysis which addresses resonant transmission in DLC superlattices. Devices were fabricated by growing alternate layers of DLC with different percentages of sp(3) hybridized carbon...
October 19, 2016: Scientific Reports
Yuantao Xie, Clément Le Priol, Jean J Heremans
Low-temperature quantum phase coherence lengths were experimentally measured in mesoscopic circular arenas fabricated on InGaAs quantum wells. The arenas are connected to wide sample regions by short side-wires, to investigate the effects of geometry in comparison to intrinsic materials properties on quantum decoherence. Universal conductance fluctuations were used to quantify the phase coherence lengths as a function of temperature and geometry. The experimental data show a dependence of phase coherence lengths on side-wire length and width-to-length ratio, which is accounted for by the competing effects of decoherence by coupling to the classical environment and Nyquist decoherence in ergodic wires...
October 18, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
F Alpeggiani, S D'Agostino, D Sanvitto, D Gerace
We report theoretical evidence that bulk nonlinear materials weakly interacting with highly localized plasmonic modes in ultra-sub-wavelength metallic nanostructures can lead to nonlinear effects at the single plasmon level in the visible range. In particular, the two-plasmon interaction energy in such systems is numerically estimated to be comparable with the typical plasmon linewidths. Localized surface plasmons are thus predicted to exhibit a purely nonclassical behavior, which can be clearly identified by a sub-Poissonian second-order correlation in the signal scattered from the quantized plasmonic field under coherent electromagnetic excitation...
October 18, 2016: Scientific Reports
Guohua Tao
Accurately describing nuclear motion is crucial in electronically nonadiabatic dynamics simulations. In this work, a coherence-controlled (CC) approach is proposed based on the mapping between the classical state space and the full electronic matrix and that between the decomposed state space and different nuclear dynamics that allows nuclear motion to properly follow either Ehrenfest dynamics in the coherence domain or Born-Oppenheimer-like dynamics in the single-state domain in a consistent manner. This new method is applied to several benchmark models involving nonadiabatic transitions in two-state or three-state systems, and the obtained results are in excellent agreement with exact quantum calculations...
October 17, 2016: Journal of Physical Chemistry Letters
Arne Laucht, Rachpon Kalra, Stephanie Simmons, Juan P Dehollain, Juha T Muhonen, Fahd A Mohiyaddin, Solomon Freer, Fay E Hudson, Kohei M Itoh, David N Jamieson, Jeffrey C McCallum, Andrew S Dzurak, A Morello
Coherent dressing of a quantum two-level system provides access to a new quantum system with improved properties-a different and easily tunable level splitting, faster control and longer coherence times. In our work we investigate the properties of the dressed, donor-bound electron spin in silicon, and assess its potential as a quantum bit in scalable architectures. The two dressed spin-polariton levels constitute a quantum bit that can be coherently driven with an oscillating magnetic field, an oscillating electric field, frequency modulation of the driving field or a simple detuning pulse...
October 17, 2016: Nature Nanotechnology
Félix Beaudoin, Dany Lachance-Quirion, W A Coish, Michel Pioro-Ladrière
Microwave-frequency superconducting resonators are ideally suited to perform dispersive qubit readout, to mediate two-qubit gates, and to shuttle states between distant quantum systems. A prerequisite for these applications is a strong qubit-resonator coupling. Strong coupling between an electron-spin qubit and a microwave resonator can be achieved by correlating spin- and orbital degrees of freedom. This correlation can be achieved through the Zeeman coupling of a single electron in a double quantum dot to a spatially inhomogeneous magnetic field generated by a nearby nanomagnet...
October 17, 2016: Nanotechnology
George F Reiter, Aniruddha Deb, Yoshiharu Sakurai, Masayoshi Itou, Alexander I Kolesnikov
X-ray Compton scattering measurements of the electron momentum distribution in water confined in both single walled and double walled carbon nanotubes (SWNT and DWNT), as a function of temperature and confinement size, presented here, together with earlier measurements of the proton momentum distribution in the same systems, using neutron Compton scattering, provide a coherent picture of an anomalous state of water that exists because of nano-confinement. This state cannot be described by the weakly interacting molecule picture...
October 17, 2016: Journal of Physical Chemistry Letters
Kai Song, Shuming Bai, Qiang Shi
Recent experimental and theoretical studies have revealed that quantum coherence plays an important role in the excitation energy transfer in photosynthetic light harvesting complexes. Inspired by the recent single molecule two-color double-pump experiment, we investigate theoretically the effect of pulse shaping on observing coherent energy transfer in the single bacterial light harvesting 2 (LH2) complex. It is found that, quantum coherent energy transfer can be observed when the time delay and phase difference between the two laser pulses are controlled independently...
October 17, 2016: Journal of Physical Chemistry. B
Belén Sotillo, Vibhav Bharadwaj, J P Hadden, Masaaki Sakakura, Andrea Chiappini, Toney Teddy Fernandez, Stefano Longhi, Ottavia Jedrkiewicz, Yasuhiko Shimotsuma, Luigino Criante, Roberto Osellame, Gianluca Galzerano, Maurizio Ferrari, Kiyotaka Miura, Roberta Ramponi, Paul E Barclay, Shane Michael Eaton
Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV's states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically...
October 17, 2016: Scientific Reports
M Bitter, V Milner
The periodically kicked rotor is a paradigm system for studying quantum effects on classically chaotic dynamics. The wave function of the quantum rotor localizes in angular momentum space, similarly to Anderson localization of the electronic wave function in disordered solids. Here, we observe dynamical localization in a system of true quantum rotors by subjecting nitrogen molecules to periodic sequences of femtosecond pulses. Exponential distribution of the molecular angular momentum-the hallmark of dynamical localization-is measured directly by means of coherent Raman scattering...
September 30, 2016: Physical Review Letters
T P Harty, M A Sepiol, D T C Allcock, C J Ballance, J E Tarlton, D M Lucas
We demonstrate a two-qubit logic gate driven by near-field microwaves in a room-temperature microfabricated surface ion trap. We introduce a dynamically decoupled gate method, which stabilizes the qubits against fluctuating energy shifts and avoids the need to null the microwave field. We use the gate to produce a Bell state with fidelity 99.7(1)%, after accounting for state preparation and measurement errors. The gate is applied directly to ^{43}Ca^{+} hyperfine "atomic clock" qubits (coherence time T_{2}^{*}≈50  s) using the oscillating magnetic field gradient produced by an integrated microwave electrode...
September 30, 2016: Physical Review Letters
Sungguen Ryu, M Kataoka, H-S Sim
Generating and detecting a prescribed single-electron state is an important step towards solid-state fermion optics. We propose how to generate an electron in a Gaussian state, using a quantum-dot pump with gigahertz operation and realistic parameters. With the help of a strong magnetic field, the electron occupies a coherent state in the pump, insensitive to the details of nonadiabatic evolution. The state changes during the emission from the pump, governed by competition between the Landauer-Buttiker traversal time and the passage time...
September 30, 2016: Physical Review Letters
C Wan, M Scala, G W Morley, Atm A Rahman, H Ulbricht, J Bateman, P F Barker, S Bose, M S Kim
We propose an interferometric scheme based on an untrapped nano-object subjected to gravity. The motion of the center of mass (c.m.) of the free object is coupled to its internal spin system magnetically, and a free flight scheme is developed based on coherent spin control. The wave packet of the test object, under a spin-dependent force, may then be delocalized to a macroscopic scale. A gravity induced dynamical phase (accrued solely on the spin state, and measured through a Ramsey scheme) is used to reveal the above spatially delocalized superposition of the spin-nano-object composite system that arises during our scheme...
September 30, 2016: Physical Review Letters
Lucas Kocia, Anna Klales
The time-dependent WKB approximation for a coherent state is expanded to third order around a guiding real trajectory, allowing for the novel treatment of nonlinearity in its semiclassical dynamics, which is generally present in all physical systems far from the classical regime. The result is a closed-form solution consisting of a linear combination of Airy functions and their derivatives multiplied by an exponential. The expression's ability to capture nonlinearity is demonstrated by examining the autocorrelation of initial coherent states in anharmonic systems with few to many contributing periodic orbits...
September 2016: Physical Review. E
Haleh Hashemi Haeri, Philipp Spindler, Jörn Plackmeyer, Thomas Prisner
Carbon-centered radicals are interesting alternatives to otherwise commonly used nitroxide spin labels for dipolar spectroscopy techniques because of their narrow ESR linewidth. Herein, we present a novel BDPA biradical, where two BDPA (α,α,γ,γ-bisdiphenylene-β-phenylallyl) radicals are covalently tethered by a saturated biphenyl acetylene linker. The inter-spin distance between the two spin carrier fragments was measured using double quantum coherence (DQC) ESR methodology. The DQC experiment revealed a mean distance of only 1...
October 12, 2016: Physical Chemistry Chemical Physics: PCCP
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