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Quantum coherence

Frederik J R Rombouts, Richard Alexander, Erna Cleiren, Alex De Groot, Michel Carpentier, Joyce Dijkmans, Katleen Fierens, Stefan Masure, Diederik Moechars, Martina Palomino-Schätzlein, Antonio Pineda-Lucena, Andrés A Trabanco, Daan Van Glabbeek, Ann Vos, Gary Tresadern
An approach to identify β-secretase 1 (BACE1) fragment binders that do not interact with the catalytic aspartate dyad is presented. A ThermoFluor (thermal shift) and a fluorescence resonance energy transfer enzymatic screen on the soluble domain of BACE1, together with a surface plasmon resonance (SPR) screen on the soluble domain of BACE1 and a mutant of one catalytic Asp (D32N), were run in parallel. Fragments that were active in at least two of these assays were further confirmed using one-dimensional NMR (WaterLOGSY) and SPR binding competition studies with peptidic inhibitor OM99-2...
February 28, 2017: ACS Omega
W Wang, L Hu, Y Xu, K Liu, Y Ma, Shi-Biao Zheng, R Vijay, Y P Song, L-M Duan, L Sun
We propose and experimentally demonstrate a new method to generate arbitrary Fock state superpositions in a superconducting quantum circuit, where a qubit is dispersively coupled to a microwave cavity mode. Here, the qubit is used to conditionally modulate the probability amplitudes of the Fock state components of a coherent state to those of the desired superposition state, instead of pumping photons one by one into the cavity as in previous schemes. Our method does not require the adjustment of the qubit frequency during the cavity state preparation and is more robust to noise and accumulation of experimental errors compared to previous ones...
June 2, 2017: Physical Review Letters
Guillem Aromi, Jorge Salinas-Uber, Marta Estrader, Jordi Garcia, Paul Lloyd-Williams, Anna Sadurní, Dominik Dengler, Joris van Slageren, Nicholas Chilton, Olivier Roubeau, Simon Teat, Jordi Ribas-Ariño
Controlling the charges and spins of molecules lyes at the heart of spintronics. We report the design of a photoswitchable molecule consisting of two independent spins separated by a photo-switchable moiety contained within a new ligand, H4L, that features a dithienylethene photochromic unit and two lateral coordinating moieties, yielding molecules with the [MM···MM] topology. Compounds [M4L2(py)6] (M = Cu, 1; Co, 2; Ni, 3; Zn, 4) have been prepared and described by single crystal X-ray diffraction (SCXRD)...
June 16, 2017: Chemistry: a European Journal
D M Villeneuve, Paul Hockett, M J J Vrakking, Hiromichi Niikura
Electrons detached from atoms or molecules by photoionization carry information about the quantum state from which they originate, as well as the continuum states into which they are released. Generally, the photoelectron momentum distribution is composed of a coherent sum of angular momentum components, each with an amplitude and phase. Here we show, by using photoionization of neon, that a train of attosecond pulses synchronized with an infrared laser field can be used to disentangle these angular momentum components...
June 16, 2017: Science
Seung Kyu Min, Federica Agostini, Ivano Tavernelli, E K U Gross
We report the first nonadiabatic molecular dynamics study based on the exact factorization of the electron-nuclear wave function. Our approach (a coupled-trajectory mixed quantum-classical, CT-MQC, scheme) is based on the quantum-classical limit derived from systematic and controlled approximations to the full quantum-mechanical problem formulated in the exact-factorization framework. Its strength is the ability to correctly capture quantum (de)coherence effects in a trajectory-based approach to excited-state dynamics...
June 19, 2017: Journal of Physical Chemistry Letters
Melissa Trepanier, Daimeng Zhang, Oleg Mukhanov, V P Koshelets, Philipp Jung, Susanne Butz, Edward Ott, Thomas M Antonsen, Alexey V Ustinov, Steven M Anlage
Through experiments and numerical simulations we explore the behavior of rf SQUID (radio frequency superconducting quantum interference device) metamaterials, which show extreme tunability and nonlinearity. The emergent electromagnetic properties of this metamaterial are sensitive to the degree of coherent response of the driven interacting SQUIDs. Coherence suffers in the presence of disorder, which is experimentally found to be mainly due to a dc flux gradient. We demonstrate methods to recover the coherence, specifically by varying the coupling between the SQUID meta-atoms and increasing the temperature or the amplitude of the applied rf flux...
May 2017: Physical Review. E
Ganesh P Subedi, Daniel J Falconer, Adam W Barb
Asparagine-linked carbohydrates (N-glycans) are a common modification of eukaryotic proteins that confer multiple properties including the essential stabilization of therapeutic monoclonal antibodies. Here we present a rapid and efficient strategy to identify N-glycans that contact polypeptide residues and apply the method to profile the five N-glycans attached to the human antibody receptor CD16A (Fc gamma receptor IIIA). Human embryonic kidney 293S cells expressed CD16A with [13CU]-labeled N-glycans using standard protein expression techniques and medium supplemented with 3 g/L [13CU]-glucose...
June 14, 2017: Biochemistry
Y Tsaturyan, A Barg, E S Polzik, A Schliesser
The small mass and high coherence of nanomechanical resonators render them the ultimate mechanical probe, with applications that range from protein mass spectrometry and magnetic resonance force microscopy to quantum optomechanics. A notorious challenge in these experiments is the thermomechanical noise related to the dissipation through internal or external loss channels. Here we introduce a novel approach to define the nanomechanical modes, which simultaneously provides a strong spatial confinement, full isolation from the substrate and dilution of the resonator material's intrinsic dissipation by five orders of magnitude...
June 12, 2017: Nature Nanotechnology
Ji-Yin Wang, Shaoyun Huang, Guang-Yao Huang, Dong Pan, Jianhua Zhao, H Q Xu
A highly tunable linear triple quantum dot (TQD) device is realized in a single-crystalline pure-phase InAs nanowire using a local finger gate technique. The electrical measurements show that the charge stability diagram of the TQD can be represented by three kinds of current lines of different slopes and a simulation performed based on a capacitance matrix model confirms the experiment. We show that each current line observable in the charge stability diagram is associated with a case where a QD is on resonance with the Fermi level of the source and drain reservoirs...
June 16, 2017: Nano Letters
F F Krause, A Rosenauer, J Barthel, J Mayer, K Urban, R E Dunin-Borkowski, H G Brown, B D Forbes, L J Allen
This paper addresses a novel approach to atomic resolution elemental mapping, demonstrating a method that produces elemental maps with a similar resolution to the established method of electron energy-loss spectroscopy in scanning transmission electron microscopy. Dubbed energy-filtered imaging scanning transmission electron microscopy (EFISTEM) this mode of imaging is, by the quantum mechanical principle of reciprocity, equivalent to tilting the probe in energy-filtered transmission electron microscopy (EFTEM) through a cone and incoherently averaging the results...
June 2, 2017: Ultramicroscopy
Chengxian Zhang, Robert E Throckmorton, Xu-Chen Yang, Xin Wang, Edwin Barnes, S Das Sarma
Decoherence due to charge noise is one of the central challenges in using spin qubits in semiconductor quantum dots as a platform for quantum information processing. Recently, it has been experimentally demonstrated in both Si and GaAs singlet-triplet qubits that the effects of charge noise can be suppressed if qubit operations are implemented using symmetric barrier control instead of the standard tilt control. Here, we investigate the key issue of whether the benefits of barrier control persist over the entire set of single-qubit gates by performing randomized benchmarking simulations...
May 26, 2017: Physical Review Letters
A Abdelrahman, O Khosravani, M Gessner, A Buchleitner, H-P Breuer, D Gorman, R Masuda, T Pruttivarasin, M Ramm, P Schindler, H Häffner
The detailed characterization of non-trivial coherence properties of composite quantum systems of increasing size is an indispensable prerequisite for scalable quantum computation, as well as for understanding non-equilibrium many-body physics. Here, we show how autocorrelation functions in an interacting system of phonons as well as the quantum discord between distinct degrees of freedoms can be extracted from a small controllable part of the system. As a benchmark, we show this in chains of up to 42 trapped ions, by tracing a single phonon excitation through interferometric measurements of only a single ion in the chain...
June 9, 2017: Nature Communications
Arnab Kar, Ignacio Franco
Practical measures of electronic decoherence, called distilled purities, that are applicable to many-body systems are introduced. While usual measures of electronic decoherence such as the purity employ the full N-particle density matrix which is generally unavailable, the distilled purities are based on the r-body reduced density matrices (r-RDMs) which are more accessible quantities. The r-body distilled purities are derivative quantities of the previously introduced r-body reduced purities [I. Franco and H...
June 7, 2017: Journal of Chemical Physics
Shruti Puri, Christian Kraglund Andersen, Arne L Grimsmo, Alexandre Blais
Quantum annealing aims at solving combinatorial optimization problems mapped to Ising interactions between quantum spins. Here, with the objective of developing a noise-resilient annealer, we propose a paradigm for quantum annealing with a scalable network of two-photon-driven Kerr-nonlinear resonators. Each resonator encodes an Ising spin in a robust degenerate subspace formed by two coherent states of opposite phases. A fully connected optimization problem is mapped to local fields driving the resonators, which are connected with only local four-body interactions...
June 8, 2017: Nature Communications
Elisabet Romero, Javier Prior, Alex W Chin, Sarah E Morgan, Vladimir I Novoderezhkin, Martin B Plenio, Rienk van Grondelle
Experimental/theoretical evidence for sustained vibration-assisted electronic (vibronic) coherence in the Photosystem II Reaction Center (PSII RC) indicates that photosynthetic solar-energy conversion might be optimized through the interplay of electronic and vibrational quantum dynamics. This evidence has been obtained by investigating the primary charge separation process in the PSII RC by two-dimensional electronic spectroscopy (2DES) and Redfield modeling of the experimental data. However, while conventional Fourier transform analysis of the 2DES data allows oscillatory signatures of vibronic coherence to be identified in the frequency domain in the form of static 2D frequency maps, the real-time evolution of the coherences is lost...
June 6, 2017: Scientific Reports
Hao Chen, Shuhui Cai, Zhong Chen
The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields...
May 24, 2017: Journal of Magnetic Resonance
Quntao Zhuang, Elton Yechao Zhu, Peter W Shor
We give a capacity formula for the classical information transmission over a noisy quantum channel, with separable encoding by the sender and limited resources provided by the receiver's preshared ancilla. Instead of a pure state, we consider the signal-ancilla pair in a mixed state, purified by a "witness." Thus, the signal-witness correlation limits the resource available from the signal-ancilla correlation. Our formula characterizes the utility of different forms of resources, including noisy or limited entanglement assistance, for classical communication...
May 19, 2017: Physical Review Letters
Jian Lu, Xian Li, Harold Y Hwang, Benjamin K Ofori-Okai, Takayuki Kurihara, Tohru Suemoto, Keith A Nelson
We report a demonstration of two-dimensional (2D) terahertz (THz) magnetic resonance spectroscopy using the magnetic fields of two time-delayed THz pulses. We apply the methodology to directly reveal the nonlinear responses of collective spin waves (magnons) in a canted antiferromagnetic crystal. The 2D THz spectra show all of the third-order nonlinear magnon signals including magnon spin echoes, and 2-quantum signals that reveal pairwise correlations between magnons at the Brillouin zone center. We also observe second-order nonlinear magnon signals showing resonance-enhanced second-harmonic and difference-frequency generation...
May 19, 2017: Physical Review Letters
Benjamin Shepperson, Anders A Søndergaard, Lars Christiansen, Jan Kaczmarczyk, Robert E Zillich, Mikhail Lemeshko, Henrik Stapelfeldt
Rotation of molecules embedded in helium nanodroplets is explored by a combination of fs laser-induced alignment experiments and angulon quasiparticle theory. We demonstrate that at low fluence of the fs alignment pulse, the molecule and its solvation shell can be set into coherent collective rotation lasting long enough to form revivals. With increasing fluence, however, the revivals disappear-instead, rotational dynamics as rapid as for an isolated molecule is observed during the first few picoseconds. Classical calculations trace this phenomenon to transient decoupling of the molecule from its helium shell...
May 19, 2017: Physical Review Letters
Anthony Leverrier
Establishing the security of continuous-variable quantum key distribution against general attacks in a realistic finite-size regime is an outstanding open problem in the field of theoretical quantum cryptography if we restrict our attention to protocols that rely on the exchange of coherent states. Indeed, techniques based on the uncertainty principle are not known to work for such protocols, and the usual tools based on de Finetti reductions only provide security for unrealistically large block lengths. We address this problem here by considering a new type of Gaussian de Finetti reduction, that exploits the invariance of some continuous-variable protocols under the action of the unitary group U(n) (instead of the symmetric group S_{n} as in usual de Finetti theorems), and by introducing generalized SU(2,2) coherent states...
May 19, 2017: Physical Review Letters
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