251 results found
Lim J, Paleček D, Caycedo-Soler F, et al., 2015, Vibronic origin of long-lived coherence in an artificial molecular light harvester., Nature Communications, Vol: 6, ISSN: 2041-1723
Natural and artificial light-harvesting processes have recently gained new interest. Signatures of long-lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization-controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.
Tamascelli D, Rosenbach R, Plenio MB, 2015, Improved scaling of time-evolving block-decimation algorithm through reduced-rank randomized singular value decomposition, PHYSICAL REVIEW E, Vol: 91, ISSN: 1539-3755
Kost M, Cai J, Plenio MB, 2015, Resolving single molecule structures with Nitrogen-vacancy centers in diamond., Scientific Reports, Vol: 5, ISSN: 2045-2322
We present theoretical proposals for two-dimensional nuclear magnetic resonance spectroscopy protocols based on Nitrogen-vacancy (NV) centers in diamond that are strongly coupled to the target nuclei. Continuous microwave and radio-frequency driving fields together with magnetic field gradients achieve Hartmann-Hahn resonances between NV spin sensor and selected nuclei for control of nuclear spins and subsequent measurement of their polarization dynamics. The strong coupling between the NV sensor and the nuclei facilitates coherence control of nuclear spins and relaxes the requirement of nuclear spin polarization to achieve strong signals and therefore reduced measurement times. Additionally, we employ a singular value thresholding matrix completion algorithm to further reduce the amount of data required to permit the identification of key features in the spectra of strongly sub-sampled data. We illustrate the potential of this combined approach by applying the protocol to a shallowly implanted NV center addressing a small amino acid, alanine, to target specific hydrogen nuclei and to identify the corresponding peaks in their spectra.
Mikelsons G, Cohen I, Retzker A, et al., 2015, Universal set of gates for microwave dressed-state quantum computing, New Journal of Physics, Vol: 17, ISSN: 1367-2630
We propose a set of techniques that enable universal quantum computing to be carried out using dressed states. This applies in particular to the effort of realizing quantum computation in trapped ions using long-wavelength radiation, where coupling enhancement is achieved by means of static magnetic-field gradient. We show how the presence of dressing fields enables the construction of robust single and multi-qubit gates despite the unavoidable presence of magnetic noise, an approach that can be generalized to provide shielding in any analogous quantum system that relies on the coupling of electronic degrees of freedom via bosonic modes.
Lemmer A, Cormick C, Schmiegelow CT, et al., 2015, Two-dimensional spectroscopy for the study of ion coulomb crystals., Physical Review Letters, Vol: 114, ISSN: 1079-7114
Ion Coulomb crystals are currently establishing themselves as a highly controllable test bed for mesoscopic systems of statistical mechanics. The detailed experimental interrogation of the dynamics of these crystals, however, remains an experimental challenge. In this work, we show how to extend the concepts of multidimensional nonlinear spectroscopy to the study of the dynamics of ion Coulomb crystals. The scheme we present can be realized with state-of-the-art technology and gives direct access to the dynamics, revealing nonlinear couplings even in the presence of thermal excitations. We illustrate the advantages of our proposal showing how two-dimensional spectroscopy can be used to detect signatures of a structural phase transition of the ion crystal, as well as resonant energy exchange between modes. Furthermore, we demonstrate in these examples how different decoherence mechanisms can be identified.
Jeske J, Ing DJ, Plenio MB, et al., 2015, Bloch-Redfield equations for modeling light-harvesting complexes, Journal of Chemical Physics, Vol: 142, ISSN: 1089-7690
We challenge the misconception that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from an indiscriminate use of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally, we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson complex in regards to spatial correlation length of the noise, noise strength, temperature, and their connection to the transfer time and transfer probability.
Hangleiter D, Mitchison MT, Johnson TH, et al., 2015, Nondestructive selective probing of phononic excitations in a cold Bose gas using impurities, Physical review A: General physics, Vol: 91, ISSN: 0556-2791
We introduce a detector that selectively probes the phononic excitations of a cold Bose gas. The detector is composed of a single impurity atom confined by a double-well potential, where the two lowest eigenstates of the impurity form an effective probe qubit that is coupled to the phonons via density-density interactions with the bosons. The system is analogous to a two-level atom coupled to photons of the radiation field. We demonstrate that tracking the evolution of the qubit populations allows probing both thermal and coherent excitations in targeted phonon modes. The targeted modes are selected in both energy and momentum by adjusting the impurity's potential. We show how to use the detector to observe coherent density waves and to measure temperatures of the Bose gas down to the nanokelvin regime. We analyze how our scheme could be realized experimentally, including the possibility of using an array of multiple impurities to achieve greater precision from a single experimental run.
Baumgratz T, Cramer M, Plenio MB, 2014, Quantifying coherence, Physical Review Letters, Vol: 113, ISSN: 1079-7114
We introduce a rigorous framework for the quantification of coherence and identify intuitive and easily computable measures of coherence. We achieve this by adopting the viewpoint of coherence as a physical resource. By determining defining conditions for measures of coherence we identify classes of functionals that satisfy these conditions and other, at first glance natural quantities, that do not qualify as coherence measures. We conclude with an outline of the questions that remain to be answered to complete the theory of coherence as a resource.
Rivas Á, Huelga SF, Plenio MB, 2014, Quantum non-Markovianity: characterization, quantification and detection., Reports on Progress in Physics, Vol: 77, ISSN: 1361-6633
We present a comprehensive and up-to-date review of the concept of quantum non-Markovianity, a central theme in the theory of open quantum systems. We introduce the concept of a quantum Markovian process as a generalization of the classical definition of Markovianity via the so-called divisibility property and relate this notion to the intuitive idea that links non-Markovianity with the persistence of memory effects. A detailed comparison with other definitions presented in the literature is provided. We then discuss several existing proposals to quantify the degree of non-Markovianity of quantum dynamics and to witness non-Markovian behavior, the latter providing sufficient conditions to detect deviations from strict Markovianity. Finally, we conclude by enumerating some timely open problems in the field and provide an outlook on possible research directions.
Mueller C, Kong X, Cai J-M, et al., 2014, Nuclear magnetic resonance spectroscopy with single spin sensitivity, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Cai J, Jelezko F, Plenio MB, 2014, Hybrid sensors based on colour centres in diamond and piezoactive layers, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Mendoza-Arenas JJ, Mitchison MT, Clark SR, et al., 2014, Transport enhancement from incoherent coupling between one-dimensional quantum conductors, NEW JOURNAL OF PHYSICS, Vol: 16, ISSN: 1367-2630
Killoran N, Cramer M, Plenio MB, 2014, Extracting Entanglement from Identical Particles, PHYSICAL REVIEW LETTERS, Vol: 112, ISSN: 0031-9007
Woods MP, Groux R, Chin AW, et al., 2014, Mappings of open quantum systems onto chain representations and Markovian embeddings, JOURNAL OF MATHEMATICAL PHYSICS, Vol: 55, ISSN: 0022-2488
Plenio MB, Almeida J, Huelga SF, 2013, Origin of long-lived oscillations in 2D-spectra of a quantum vibronic model: Electronic versus vibrational coherence, JOURNAL OF CHEMICAL PHYSICS, Vol: 139, ISSN: 0021-9606
Prior J, Castro E, Chin AW, et al., 2013, Wavelet analysis of molecular dynamics: Efficient extraction of time-frequency information in ultrafast optical processes, JOURNAL OF CHEMICAL PHYSICS, Vol: 139, ISSN: 0021-9606
Cai J, Plenio MB, 2013, Chemical Compass Model for Avian Magnetoreception as a Quantum Coherent Device, PHYSICAL REVIEW LETTERS, Vol: 111, ISSN: 0031-9007
Partner HL, Nigmatullin R, Burgermeister T, et al., 2013, Dynamics of topological defects in ion Coulomb crystals, NEW JOURNAL OF PHYSICS, Vol: 15, ISSN: 1367-2630
London P, Scheuer J, Cai J-M, et al., 2013, Detecting and Polarizing Nuclear Spins with Double Resonance on a Single Electron Spin, PHYSICAL REVIEW LETTERS, Vol: 111, ISSN: 0031-9007
Pyka K, Keller J, Partner HL, et al., 2013, Topological defect formation and spontaneous symmetry breaking in ion Coulomb crystals, NATURE COMMUNICATIONS, Vol: 4, ISSN: 2041-1723
Ulm S, Rossnagel J, Jacob G, et al., 2013, Observation of the Kibble-Zurek scaling law for defect formation in ion crystals, NATURE COMMUNICATIONS, Vol: 4, ISSN: 2041-1723
Frenzel MF, Plenio MB, 2013, Matrix product state representation without explicit local Hilbert space truncation with applications to the sub-ohmic spin-boson model, NEW JOURNAL OF PHYSICS, Vol: 15, ISSN: 1367-2630
Bermudez A, Bruderer M, Plenio MB, 2013, Controlling and Measuring Quantum Transport of Heat in Trapped-Ion Crystals, PHYSICAL REVIEW LETTERS, Vol: 111, ISSN: 0031-9007
Cramer M, Bernard A, Fabbri N, et al., 2013, Spatial entanglement of bosons in optical lattices, NATURE COMMUNICATIONS, Vol: 4, ISSN: 2041-1723
Ermakova A, Pramanik G, Cai J-M, et al., 2013, Detection of a Few Metallo-Protein Molecules Using Color Centers in Nanodiamonds, NANO LETTERS, Vol: 13, Pages: 3305-3309, ISSN: 1530-6984
Bermudez A, Schaetz T, Plenio MB, 2013, Dissipation-Assisted Quantum Information Processing with Trapped Ions, PHYSICAL REVIEW LETTERS, Vol: 110, ISSN: 0031-9007
Kaufmann H, Ulm S, Jacob G, et al., 2012, Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal, PHYSICAL REVIEW LETTERS, Vol: 109, ISSN: 0031-9007
Chin AW, Huelga SF, Plenio MB, 2012, Quantum Metrology in Non-Markovian Environments, PHYSICAL REVIEW LETTERS, Vol: 109, ISSN: 0031-9007
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