CCPQ: Quantum Dynamics in Atomic, Molecular and Optical Physics

Lead Research Organisation: University College London
Department Name: Chemistry


The dynamics of quantum particles is the basis to describing the material world. Collisions between nuclei provides basic chemical reactivity, while the movements of electrons around nuclei provides the fine mechanistic details. To understand these motions we need to solve the time-dependent Schroedinger equation - a non-trivial problem for more than 3 particles that requires a huge computational effort.

State-of-the art experiments using attosecond or femtosecond pulses of radiation allow us to follow the motion of these particles, but without computer simulations the results are difficult to understand. This field of research is presently undergoing a huge expansion, due to the provision of new light sources such as free electron lasers (FELs), and software needs to be developed to keep up to the new capabilities. CCPQ has two community codes (R-matrix suite, MCTDH wavepacket dynamics) to treat these processes. The results give a deep inside into the fundamental reactivity of molecules, where quantum mechanical behaviour must be considered.

The interactions of anti-matter particles are also a topic of much interest, primarily due to the use of positrons in medical imaging, but also as a field of fundamental science in experiments such as the ALPHA project. Here, anti-matter particles are collided with normal matter and the different decay channels investigated. CCPQ is developing a code in collaboration with experimentalists to help understand the behaviour of these exotic sounding, but useful, particles.

Going from few bodies to many-bodies introduces some of the most fascinating phenomena in physics, such as superfluidity, superconductivity and ferroelectricity. However, to directly simulate them also introduces an exponentially scaling overhead in computation effort with the system size. While usually the preserve of condensed matter systems such strongly-correlated physics, where particles behaviour collectively, are now accessible in controlled ways with cold-atoms trapped in optical lattices. This has opened up previously inaccessible coherent dynamics in many-body systems to experimental scrutiny, such as examining what happens if the interaction and kinetic energies of particles are quenched across a quantum phase transition. The advances of this unique perspective are now reciprocating back to condensed matter problems where interaction of THz radiation on femtosecond timescales is also revealing correlated coherent electrons motion in solid-state systems. This topic of strongly-correlated many-body dynamics is the final strand of CCPQ development - embodied by the TNT project which introduces new ways of compressing many-body states to overcome the exponential barrier. It will support not only the emerging quantum technology of cold-atom quantum simulation, but also may eventually aid in designing and controlling real materials where optical pulses can switch properties such as superconductivity or ferroelectricity with great technological potential.

CCPQ supports the development of these world leading community codes by providing a forum for the exchange of ideas, by providing networking opportunities for researchers to help disseminate the codes, and by supporting training workshops for users of the codes. It also provides direct support in the form of computer experts at the Daresbury laboratory who help optimise the codes for use on large high performance computers (HPC).

Planned Impact

The profile of CCPQ is of direct benefit to UK science as a whole, helping to keep it at the forefront of research into the fundamental properties of matter. The CCPQ codes impact directly in the fields of research addressed in the Academic Beneficiaries. Outside academia, the direct beneficiaries are industry requiring data to help develop technologies. This is exemplified by the success of Quantemol Ltd., and Quantemol will remain a close project partner of CCPQ in the proposed work. Accurate data on the interaction of light and electrons with atoms and molecules is of critical importance, for example, in the modelling of large-scale plasma dynamics. These plasma dynamics can range from small-scale industrial plasmas in plasma lasers used for EUV lithography, through the modelling of plasmas throughout an entire fusion reactor (from the hot core to the divertor region to the reactor walls), including the presence of contaminants due to wall degradation, up to supernova modelling in astrophysics.

Atomic and molecular physics plays a key role in the development and advancement of new technology through the provision of diagnostics. This is of particular relevance for large-scale infrastructure projects, such as FELs. In the initial application of new technology, simple systems need to be investigated so that the performance of the facility can be established. Computational methods developed by CCPQ have been proved to provide the accuracy needed to enable facility researchers to assess performance.

In many-body physics it is the primary aim of the CCPQ's TNT library to become the backbone of the UK's computational methods for the study of strongly-correlated systems for the next 15 years and more. In addition we expect that as the TNT approach grows and crosses new scientific frontiers, it will significantly push what is achievable with the ever-advancing capabilities of HPC and will aid the strategic driver of widely spreading HPC skills. Beyond these direct and immediate impacts for research based on well-established TNT algorithms, we further anticipate that the low level tensor software routines will have far-reaching benefits. Specifically, because of its generality it can serve as the foundation for the development of novel tensor network algorithms that are now widely believed by computer scientists to provide the much sought after extension of standard linear algebra algorithms to multidimensional data analysis. Given the huge importance of complex classical systems in natural sciences, operations research and industry as yet unforeseen applications of TNT could emerge in the near future.


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Related Projects

Project Reference Relationship Related To Start End Award Value
EP/M022544/1 13/08/2015 30/06/2016 £101,608
EP/M022544/2 Transfer EP/M022544/1 01/07/2016 18/08/2020 £89,023
Description CCPQ is a network supporting the development of software for specialist calculations requiring details of molecular dynamics at the quantum mechanical level. Three codes in particular are supported able to calculate properties of (i) the many-body quantum effects that must be understood to make use of the emerging "quantum technologies". (ii) the description of electrons interacting with molecules, important in industrial processes based on plasma etching, and the development of short laser pulses using what is termed high-harmonic generation. (iii) the study of photo-excited molecules, important in solar energy capture and other light based technologies. The collaboration uses the resources available at the EPSRC funded central laboratories (The Daresbury and Rutherford Labs) to improve the standard of code development.
Exploitation Route The codes are all open source and available to other researchers.
Sectors Other

Description CCPQ has a related spin-out company, Quantemol, that provides software to industry developed as part of the collaboration. A workshop was held in Sept. 2017 to help train industry based workers in using the software.
First Year Of Impact 2017
Sector Electronics,Manufacturing, including Industrial Biotechology
Description Software Infrastructure
Amount £433,575 (GBP)
Funding ID EP/P022146/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 09/2017 
End 08/2019
Description Standard REsearch
Amount £376,329 (GBP)
Funding ID EP/P013953/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 05/2017 
End 04/2020
Title Quantics 
Description A package for quantum dynamics simulations of molecular systems, solving the time-dependent Schroedinger equation using a variety of methods but based on the powerful MCTDH algorithm. 
Type Of Technology Software 
Year Produced 2017 
Open Source License? Yes  
Impact Quantics is a general purpose molecular quantum dynamics package able to calculate spectra, reaction cross-sections, etc. Recent work has been to improve the Gaussian wavepacket based vMCG algorithm and its direct dynamics method that calculates the potential surfaces on-the-fly. A novel diabatisation algorithm makes the method almost black-box in character for excited-state simulations. 
Title R-matrix with time-dependence (RMT) suite 
Description The RMT suite is a computational approach to solve the time-dependent Schrödinger equation for multi-electron atoms and molecules in strong laser fields. The codes can be used to extract experimental observables (e.g. photoelectron, high harmonic or transient absorption spectra) or to provide direct access to more detailed atomic/molecular information (e.g. electron emission channel resolved populations, full multi-electron wavefunction data). The code supports the description of dynamics in laser fields in the XUV to mid-IR wavelength range. Currently the codes are restricted to linearly polarised light pulses, and single ionisation phenomena, but development branches exist building capability for arbitrary polarisation, double ionisation and relativistic (spin-orbit) effects. 
Type Of Technology Software 
Year Produced 2017 
Impact The atomic codes have been used in support of cutting edge ultrafast metrology techniques, for example attosecond transient absorption spectroscopy [Opt. Lett. 41 79 (2016)] and XUV initiated high-harmonic generation [Phys. Rev. Lett. 117 093201 (2016)] 
Title Tensor Network Theory library 
Description Tensor Network Theory (TNT) provides efficient and accurate methods for simulating strongly correlated quantum systems. It does this by encoding, as a network of tensors, the many-body wave function representing the system and the operators that act on it. TNT algorithms can then be broken down into a series of tensor operations. The TNT library contains highly optimised routines for manipulating tensors in the network. These routines are used to build the most common TNT algorithms, such as Density Matrix Renormalisation Group (DMRG) and time-evolving block decimation (TEBD) for 1D quantum lattice systems. Development of codes for Projected Entangled Pair States (PEPS) suitable for 2D lattice systems are underway. 
Type Of Technology Software 
Year Produced 2017 
Impact We have pioneered the combination of TNT with non-equilibrium dynamical mean field theory (NE-DMFT). This was outlined in the paper: Ultra-fast control of magnetic relaxation in a periodically driven Hubbard model Juan Jose Mendoza-Arenas, Fernando Javier Gomez-Ruiz, Martin Eckstein, Dieter Jaksch, Stephen R. Clark Ann. Phys. (Berlin) 2017, 529, 1700024 Linking to experiments which drive systems strongly with THz radiation we have used TNT to examine a strongly driven quantum system and analysed the emergence of pairing. This resulted in this paper: Enhancement of super-exchange pairing in the periodically-driven Hubbard model J. Coulthard, S. R. Clark, S. Al-Assam, A. Cavalleri, D. Jaksch Phys. Rev. B 96, 085104 (2017) We have continued to use TNT for boundary driven open quantum spin-chains and in particular focused on disordered systems exhibiting many-body localisation. A recent paper looked into how dephasing effects spin transport: Dephasing enhanced spin transport in the ergodic phase of a many-body localizable system Marko Žnidaric, Juan Jose Mendoza-Arenas, Stephen R. Clark, John Goold Annalen Der Physik 529, 1600298 (2017) 
Title UKRmol+ 
Description Software suite to determine correlated multielectronic bound and continuum wave functions for molecular systems. Allows for the calculation of electron scattering cross sections, the characterization of transient negative ions (resonances) and transition moments for use in photoionization and related studies. 
Type Of Technology Software 
Year Produced 2017 
Impact The code can deal with larger R-matrix calculations in terms of number of electrons in the target. Results have been published in e.g. a) Sieradzka A and Gorfinkiel J D J. Chem. Phys. 147 034303 (2017) Darby-Lewis D, Mašín Z and Tennyson J, J. Phys. B,50, 175201 (2017) c) Bruner et al Faraday Discuss., 194, 369 (2016)