| 1. |
- Nyberg, Markus, et al.
(författare)
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A simple method to calculate first-passage time densities with arbitrary initial conditions
- 2016
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18:6
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Tidskriftsartikel (refereegranskat)abstract
- Numerous applications all the way from biology and physics to economics depend on the density of first crossings over a boundary. Motivated by the lack of general purpose analytical tools for computing first-passage time densities (FPTDs) for complex problems, we propose a new simple method based on the independent interval approximation (IIA). We generalise previous formulations of the IIA to include arbitrary initial conditions as well as to deal with discrete time and non-smooth continuous time processes. We derive a closed form expression for the FPTD in z and Laplace-transform space to a boundary in one dimension. Two classes of problems are analysed in detail: discrete time symmetric random walks (Markovian) and continuous time Gaussian stationary processes (Markovian and non-Markovian). Our results are in good agreement with Langevin dynamics simulations.
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| 2. |
- Higgins, Gerard, 1989, et al.
(författare)
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Micromotion minimization using Ramsey interferometry
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:12
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Tidskriftsartikel (refereegranskat)abstract
- We minimize the stray electric field in a linear Paul trap quickly and accurately, by applying interferometry pulse sequences to a trapped ion optical qubit. The interferometry sequences are sensitive to the change of ion equilibrium position when the trap stiffness is changed, and we use this to determine the stray electric field. The simplest pulse sequence is a two-pulse Ramsey sequence, and longer sequences with multiple pulses offer a higher precision. The methods allow the stray field strength to be minimized beyond state-of-the-art levels. Using a sequence of nine pulses we reduce the 2D stray field strength to (10.5 +/- 0.8) mV m(-1) in 11 s measurement time. The pulse sequences are easy to implement and automate, and they are robust against laser detuning and pulse area errors. We use interferometry sequences with different lengths and precisions to measure the stray field with an uncertainty below the standard quantum limit. This marks a real-world case in which quantum metrology offers a significant enhancement. Also, we minimize micromotion in 2D using a single probe laser, by using an interferometry method together with the resolved sideband method; this is useful for experiments with restricted optical access. Furthermore, a technique presented in this work is related to quantum protocols for synchronizing clocks; we demonstrate these protocols here.
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| 3. |
- Nicolai, L., et al.
(författare)
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Bi ultra-thin crystalline films on InAs(111)A and B substrates: a combined core-level and valence-band angle-resolved and dichroic photoemission study
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Bi on both the In-terminated (A) face and the As-terminated (B) face of InAs(111) has been investigated by low-energy electron diffraction, scanning tunnelling microscopy, and photoelectron spectroscopy using synchrotron radiation. The changes upon Bi deposition of the In 4d and Bi 5d(5/2) photoelectron signals allow to get a comprehensive picture of the Bi/InAs(111) interface. From the early stage the Bi growth on the A face is epitaxial, contrary to that on the B face that proceeds via the formation of islands. Angle-resolved photoelectron spectra show that the electronic structure of a Bi deposit of approximate to 10 bi-layers on the A face is identical to that of bulk Bi, while more than approximate to 30 bi-layers are needed for the B face. Both bulk and surface electronic states observed are well accounted for by fully relativistic ab initio calculations performed using the one-step model of photoemission. These calculations are used to analyse the dichroic photoemission data recorded in the vicinity of the Fermi level around the (Gamma) over bar point of the Brillouin zone.
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| 4. |
- Zhu, Jingyuan, et al.
(författare)
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Physical requirements for scaling up network-based biocomputation
- 2021
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Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 23:10
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Tidskriftsartikel (refereegranskat)abstract
- The high energy consumption of electronic data processors, together with physical challenges limiting their further improvement, has triggered intensive interest in alternative computation paradigms. Here we focus on network-based biocomputation (NBC), a massively parallel approach where computational problems are encoded in planar networks implemented with nanoscale channels. These networks are explored by biological agents, such as biological molecular motor systems and bacteria, benefitting from their energy efficiency and availability in large numbers. We analyse and define the fundamental requirements that need to be fulfilled to scale up NBC computers to become a viable technology that can solve large NP-complete problem instances faster or with less energy consumption than electronic computers. Our work can serve as a guide for further efforts to contribute to elements of future NBC devices, and as the theoretical basis for a detailed NBC roadmap.
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| 5. |
- Baird, C. D., et al.
(författare)
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Realising single-shot measurements of quantum radiation reaction in high-intensity lasers
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- Modern laser technology is now sufficiently advanced that collisions between high-intensity laser pulses and laser-wakefield-accelerated (LWFA) electron beams can reach the strong-field regime, so that it is possible to measure the transition between the classical and quantum regimes of light-matter interactions. However, the energy spectrum of LWFA electron beams can fluctuate significantly from shot to shot, making it difficult to clearly discern quantum effects in radiation reaction (RR), for example. Here we show how this can be accomplished in only a single laser shot. A millimetre-scale pre-collision drift allows the electron beam to expand to a size larger than the laser focal spot and develop a correlation between transverse position and angular divergence. In contrast to previous studies, this means that a measurement of the beam's energy-divergence spectrum automatically distinguishes components of the beam that hit or miss the laser focal spot and therefore do and do not experience RR.
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| 6. |
- Ahlberg, Sebastian, et al.
(författare)
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Many-body effects on tracer particle diffusion with applications for single-protein dynamics on DNA
- 2015
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- 30% of the DNA in E. coli bacteria is covered by proteins. Such a high degree of crowding affects the dynamics of generic biological processes (e.g. gene regulation, DNA repair, protein diffusion etc) in ways that are not yet fully understood. In this paper, we theoretically address the diffusion constant of a tracer particle in a one-dimensional system surrounded by impenetrable crowder particles. While the tracer particle always stays on the lattice, crowder particles may unbind to a surrounding bulk and rebind at another, or the same, location. In this scenario we determine how the long time diffusion constant D (after many unbinding events) depends on (i) the unbinding rate of crowder particles k(off), and (ii) crowder particle line density rho, from simulations (using the Gillespie algorithm) and analytical calculations. For small k(off), we find D similar to k(off)/rho(2) when crowder particles do not diffuse on the line, and D similar to root Dk(off)/rho when they are diffusing; D is the free particle diffusion constant. For large k(off), we find agreement with mean-field results which do not depend on k(off). From literature values of k(off) and D, we show that the small k(off) -limit is relevant for in vivo protein diffusion on crowded DNA. Our results apply to single-molecule tracking experiments.
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| 7. |
- Kanski, Janusz, 1946, et al.
(författare)
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Electronic structure of (Ga,Mn)As revisited
- 2017
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Ingår i: New Journal of Physics. - : Institute of Physics (IOP). - 1367-2630. ; 19:2, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The detailed nature of electronic states mediating ferromagnetic coupling in dilute magnetic semiconductors, specifically (Ga,Mn)As, has been an issue of long debate. Two confronting models have been discussed emphasizing host band vs. impurity band carriers. Using angle resolved photoemission we show that the electronic structure of the (Ga,Mn)As system is significantly modified from that of GaAs throughout the valence band. Close to the Fermi energy, the presence of Mn induces a strong mixing of the bulk bands of GaAs, which results in the appearance of a highly dispersive band in the gap region of GaAs.For Mn concentrations above 1% the band reaches the Fermi level, and can thus host the delocalized holes needed for ferromagnetic coupling. Overall, our data provide a firm evidence of delocalized carriers belonging to the modified host valence band.
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| 8. |
- Konopik, Michael, et al.
(författare)
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Solving the subset sum problem with a nonideal biological computer
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:9
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Tidskriftsartikel (refereegranskat)abstract
- We consider the solution of the subset sum problem based on a parallel computer consisting of self-propelled biological agents moving in a nanostructured network that encodes the computing task in its geometry. We develop an approximate analytical method to analyze the effects of small errors in the nonideal junctions composing the computing network by using a Gaussian confidence interval approximation of the multinomial distribution. We concretely evaluate the probability distribution for error-induced paths and determine the minimal number of agents required to obtain a proper solution. We finally validate our theoretical results with exact numerical simulations of the subset sum problem for different set sizes and error probabilities, and discuss the scalability of the nonideal problem using realistic experimental error probabilities.
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| 9. |
- Blackburn, Thomas, 1989, et al.
(författare)
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Reaching supercritical field strengths with intense lasers
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- It is conjectured that all perturbative approaches to quantum electrodynamics (QED) break down in the collision of a high-energy electron beam with an intense laser, when the laser fields are boosted to supercritical strengths far greater than the critical field of QED. As field strengths increase toward this regime, cascades of photon emission and electron-positron pair creation are expected, as well as the onset of substantial radiative corrections. Here we identify the important role played by the collision angle in mitigating energy losses to photon emission that would otherwise prevent the electrons reaching the supercritical regime. Weshow that a collision between an electron beam with energy in the tens of GeV and a laser pulse of intensity 10 W cm 24 2 - at oblique, or even normal, incidence is a viable platform for studying the breakdown of perturbative strong-field QED. Our results have implications for the design of near-term experiments as they predict that certain quantum effects are enhanced at oblique incidence. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
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| 10. |
- Liu, Ji-Cai, et al.
(författare)
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High-resolution x-ray spectra of carbon monoxide reveal ultrafast dynamics induced by long UV pulse
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- In theoretical simulations of a UV + x-ray pump-probe (UVX-PP) setup, we show that frequency detuning of the pump UV pulse acts as a camera shutter by regulating the duration of the UVX-PP process. This two-photon absorption with long overlapping UV and x-ray pulses, allowing for high spectral resolution, thereby provides information about ultrafast dynamics of the nuclear wave packet without the requirement of ultrashort pulses and controlled delay times. In a case study of carbon monoxide, the calculated UVX-PP spectra of the O1s (-1)2 pi (1) and C1s (-1)2 pi (1) core-excited states show different vibrational profiles. The interference of intermediate vibrational states reveals details of nuclear dynamics in the UVX-PP process related to a variable duration time controlled by the UV detuning. Both O1s (-1)2 pi (1) and C1s (-1)2 pi (1) pump-probe channels display a splitting of the spectral profile, which however is associated with different physical mechanisms. At the O1s (-1)2 pi (1) resonance, the observed dispersive and non-dispersive spectral bands intersect and result in destructive interference.
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