Office: 3W2.2a

Email: s.r.clark@bath.ac.uk

Tel: +44(0)1225 38 4539

# Dr Stephen Clark

## Biographical information

- Lecturer in Physics, University of Bath, September 2015 -
- Visiting Research Scientist, Max Planck Research Department for Structural Dynamics, University of Hamburg, Germany, February 2014–
- Senior Scientist, Atomic and Laser Physics Department, University of Oxford, March 2014 - September 2015
- Career Development Fellow, Keble College, University of Oxford, October 2013 - September 2015
- Senior Research Fellow, Centre for Quantum Technologies, National University of Singapore, January 2013 - March 2014
- Research Fellow and Tutor, Keble College University of Oxford, October 2009 - October 2013
- Research Fellow, Centre for Quantum Technologies, National University of Singapore, April 2009 - March 2014
- Post-Doctoral Research Associate, Atomic and Laser Physics Department, University of Oxford, October 2007 - April 2009
- PGDipLATHE (Oxford) 2011
- DPhil (Oxford) 2007
- MASt (Cambridge) 2003
- MPhys (Bristol) 2002

## Research interests

My research interests are pretty much anything with the word 'quantum' attached to it, like quantum computation, quantum materials, quantum simulation, and so on. While I have been known to flirt with foundational issues on occasion, my main focus is increasingly grounded in trying to exploit various quantum phenomena in technology.

### Tensor network theory

A major research theme of mine is understanding the nature of entanglement, correlations and quantum mutual information in ground states and thermal states of commonly encountered many-body systems with striking and deep connections to their classical simulability. This has mainly involved exploiting and further developing sophisticated tensor network theory (TNT) techniques for efficiently simulating many-body quantum systems.

Currently this most prominently includes the density matrix renormalization group (DMRG) method and its generalization to time-dependent phenomena via the time-evolving block decimation (TEBD) algorithm applicable to 1D systems. A major long-term effort to extend the success of these methods to 2D quantum lattice systems is underway. Other goals are to eventually connecting tensor network theory to other extremely successful techniques in condensed matter physics such as density functional theory (DFT) and dynamical mean-field theory (DMFT).

### Driven condensed matter systems

The second major theme of my research is the application of the above numerical methods to driven condensed matter systems. Strong periodic driving of a system has been long known to dramatically alter the behaviour of a system.

The classic example is the Kaptiza pendulum where vertically shaking the pivot point of a pendulum very fast can make the inverted position a dynamically stable configuration. Can we do the same for strongly-correlated electron systems? If we drive molecular or lattice distortions strongly can we stabilise desired forms of order in a material or even cause new phases of matter to emerge which are not possible in equilibrium? If we can then this may permit the controlled manipulation of material properties giving quantum enhanced functionality.

## Publications

Noh, C., Clark, S., Jaksch, D. and Angelakis, D. G., 2017. Out-of-equilibrium phases in driven-dissipative coupled resonator arrays. *In*: Angelakis, D. G., ed. *Quantum Simulations with Photons and Polaritons.Vol. XIII. 1 ed.* Springer International Publishing, p. 43.

Žnidarič, M., Mendoza-Arenas, J. J., Clark, S. R. and Goold, J., 2016. Dephasing enhanced spin transport in the ergodic phase of a many-body localizable system. *Annalen der Physik*

Clark, S., 2016. *Odd states of matter:how three British theorists scooped the 2016 Nobel Prize for Physics.* [Non-academic press]

Kreula, J. M., Clark, S. R. and Jaksch, D., 2016. Non-linear quantum-classical scheme to simulate non-equilibrium strongly correlated fermionic many-body dynamics. *Scientific Reports*, 6, 32940.

Kreula, J. M., García-Álvarez, L., Lamata, L., Clark, S. R., Solano, E. and Jaksch, D., 2016. Few-qubit quantum-classical simulation of strongly correlated lattice fermions. *EPJ Quantum Technology*, 3, p. 11.

Cantaluppi, A., Mitrano, M., Nicoletti, D., Kaiser, S., Perucchi, A., Lupi, S., Di Pietro, P., Pontiroli, D., Riccò, M., Clark, S. R., Jaksch, D. and Cavalleri, A., 2016. Light-induced superconductivity in metallic K3C60. *In*: *International Conference on Ultrafast Phenomena, UP 2016*, 2016-07-17 - 2016-07-22. OSA - The Optical Society, UTu3A.3.

Rajasekaran, S., Casandruc, E., Laplace, Y., Nicoletti, D., Gu, G. D., Clark, S. R., Jaksch, D. and Cavalleri, A., 2016. Parametric Amplification of a Terahertz Quantum Plasma Wave. *Nature Physics*, 12, pp. 1012-1016.

Johnson, T. H., Yuan, Y., Bao, W., Clark, S. R., Foot, C. and Jaksch, D., 2016. Hubbard model for atomic impurities bound by the vortex lattice of a rotating BEC. *Physical Review Letters*, 116, 240402.

Johnson, T. H., Cosco, F., Mitchison, M. T., Jaksch, D. and Clark, S. R., 2016. Thermometry of ultracold atoms via non-equilibrium work distributions. *Physical Review A: Atomic, Molecular, and Optical Physics*, 93 (5).

Mitrano, M., Cantaluppi, A., Nicoletti, D., Kaiser, S., Perucchi, A., Lupi, S., Di Pietro, P., Pontiroli, D., Riccò, M., Clark, S. R., Jaksch, D. and Cavalleri, A., 2016. Possible light-induced superconductivity in K3 C60 at high temperature. *Nature*, 530 (7591), pp. 461-464.

Mendoza-Arenas, J. J., Clark, S. R., Felicetti, S., Romero, G., Solano, E., Angelakis, D. G. and Jaksch, D., 2016. Beyond mean-field bistability in driven-dissipative lattices:bunching-antibunching transition and quantum simulation. *Physical Review A: Atomic, Molecular, and Optical Physics*, 93 (2), 023821.

Clark, S., 2016. *Could laser-powered superconductors spark a technological revolution?* [Non-academic press]

Goold, J., Gogolin, C., Clark, S. R., Eisert, J., Scardicchio, A. and Silva, A., 2015. Total correlations of the diagonal ensemble herald the many-body localization transition. *Physical Review B : Condensed Matter and Materials Physics*, 92 (18), 180202(R).

Singla, R., Cotugno, G., Kaiser, S., Först, M., Mitrano, M., Liu, H. Y., Cartella, A., Manzoni, C., Okamoto, H., Hasegawa, T., Clark, S. R., Jaksch, D. and Cavalleri, A., 2015. THz-frequency modulation of the Hubbard U in an organic Mott insulator. *Physical Review Letters*, 115 (18), 187401.

Clark, S., 2015. Viewpoint: Emerging Quantum Order in an Expanding Gas. *Physics*, 8 (99).

Först, M., Caviglia, A. D., Scherwitzl, R., Mankowsky, R., Zubko, P., Khanna, V., Bromberger, H., Wilkins, S. B., Chuang, Y. -D., Lee, W. S., Schlotter, W. F., Turner, J. J., Dakovski, G. L., Minitti, M. P., Robinson, J., Clark, S. R., Jaksch, D., Triscone, J. -M., Hill, J. P., Dhesi, S. S. and Cavalleri, A., 2015. Spatially resolved ultrafast magnetic dynamics launched at a complex-oxide hetero-interface. *Nature Materials*, 14, 883.

Mendoza-Arenas, J. J., Clark, S. R. and Jaksch, D., 2015. Coexistence of energy diffusion and local thermalization in nonequilibrium XXZ spin chains with integrability breaking. *Physical Review E*, 91 (4), 042129.

Denny, S. J., Clark, S. R., Laplace, Y., Cavalleri, A. and Jaksch, D., 2015. Proposed parametric cooling of bilayer cuprate superconductors by terahertz excitation. *Physical Review Letters*, 114 (13), 137001.

Johnson, T. H., Elliott, T. J., Clark, S. R. and Jaksch, D., 2015. Capturing exponential variance using polynomial resources:applying tensor networks to non-equilibrium stochastic processes. *Physical Review Letters*, 114 (9), 090602.

Johnson, T. H., Clark, S. R. and Jaksch, D., 2014. What is a quantum simulator? *EPJ Quantum Technology*, 1 (10), 10.

Mendoza-Arenas, J. J., Mitchison, M. T., Clark, S. R., Prior, J., Jaksch, D. and Plenio, M. B., 2014. Transport enhancement from incoherent coupling between one-dimensional quantum conductors. *New Journal of Physics*, 16, 053016.

Mitrano, M., Cotugno, G., Clark, S. R., Singla, R., Kaiser, S., Staehler, J., Beyer, R., Dressel, M., Baldassarre, L., Nicoletti, D., Perucchi, A., Hasegawa, T., Okamoto, H., Jaksch, D. and Cavalleri, A., 2014. Pressure dependent relaxation in the photo-excited Mott insulator ETF2TCNQ:Influence of hopping and correlations on quasiparticle recombination rates. *Physical Review Letters*, 112 (11), 117801.

Kaiser, S., Clark, S. R., Nicoletti, D., Cotugno, G., Tobey, R. I., Dean, N., Lupi, S., Okamoto, H., Hasegawa, T., Jaksch, D. and Cavalleri, A., 2014. Deconstructing the Hubbard Hamiltonian by Ultrafast Quantum Modulation Spectroscopy in Solid-state Mott Insulators. *Scientific Reports*, 4, 3823.

Schetakis, N., Grujic, T., Clark, S. R., Jaksch, D. and Angelakis, D. G., 2013. Frozen photons in Jaynes Cummings arrays. *Journal of Physics B: Atomic Molecular and Optical Physics*, 46 (22), 224025.

Mendoza-Arenas, J. J., Al-Assam, S., Clark, S. R. and Jaksch, D., 2013. Heat transport in the XXZ spin chain:from ballistic to diffusive regimes and dephasing enhancement. *Journal of Statistical Physics*

Dorner, R., Clark, S. R., Heaney, L., Fazio, R., Goold, J. and Vedral, V., 2013. Extracting quantum work statistics and fluctuation theorems by single qubit interferometry. *Physical Review Letters*, 110 (23), 230601.

Grujic, T., Clark, S. R., Jaksch, D. and Angelakis, D. G., 2013. Repulsively induced photon super-bunching in driven resonator arrays. *Physical Review A: Atomic, Molecular, and Optical Physics*, 87 (5), 053846.

Walters, R., Cotugno, G., Johnson, T. H., Clark, S. R. and Jaksch, D., 2013. Ab initio derivation of Hubbard models for cold atoms in optical lattices. *Physical Review A: Atomic, Molecular, and Optical Physics*, 87 (4), 043613.

Meznaric, S., Clark, S. R. and Datta, A., 2013. Quantifying the Nonclassicality of Operations. *Physical Review Letters*, 110 (7), 070502.

Pino, M., Prior, J. and Clark, S. R., 2013. Capturing the re-entrant behaviour of one-dimensional Bose-Hubbard model. *Physica Status Solidi (C)*, 250 (1), pp. 51-58.

Mendoza-Arenas, J. J., Grujic, T., Jaksch, D. and Clark, S. R., 2013. Dephasing enhanced transport in nonequilibrium strongly correlated quantum systems. *Physical Review B : Condensed Matter and Materials Physics*, 87, 235130.

Johnson, T. H., Biamonte, J. D., Clark, S. R. and Jaksch, D., 2013. Solving search problems by strongly simulating quantum circuits. *Scientific Reports*, 3, 1235.

Grujic, T., Clark, S. R., Jaksch, D. and Angelakis, D. G., 2012. Non-equilibrium many-body effects in driven nonlinear resonator arrays. *New Journal of Physics*, 14, 103025.

Pino, M., Prior, J., Somoza, A. M., Jaksch, D. and Clark, S. R., 2012. Re-entrance and entanglement in the one-dimensional Bose-Hubbard model. *Physical Review A: Atomic, Molecular, and Optical Physics*, 86 (2), 023631.

Johnson, T. H., Bruderer, M., Cai, Y., Clark, S. R., Bao, W. and Jaksch, D., 2012. Breathing oscillations of a trapped impurity in a Bose gas. *EPL (Europhysics Letters)*, 98 (2), 26001.

Denny, S. J., Biamonte, J. D., Jaksch, D. and Clark, S. R., 2011. Algebraically contractible topological tensor network states. *Journal of Physics A: Mathematical and Theoretical*, 45 (1), 015309.

Al-Assam, S., Clark, S. R., Foot, C. J. and Jaksch, D., 2011. Capturing long range correlations in two-dimensional quantum lattice systems using correlator product states. *Physical Review B : Condensed Matter and Materials Physics*, 84 (20), 205108.

Johnson, T. H., Clark, S. R., Bruderer, M. and Jaksch, D., 2011. Impurity transport through a strongly interacting bosonic quantum gas. *Physical Review A: Atomic, Molecular, and Optical Physics*, 84 (2), 023617.

Wall, S., Brida, D., Clark, S. R., Ehrke, H. P., Jaksch, D., Ardavan, A., Bonora, S., Uemura, H., Takahashi, Y., Hasegawa, T., Okamoto, H., Cerullo, G. and Cavalleri, A., 2011. Quantum interference between charge excitation paths in a solid state Mott insulator. *Nature Physics*, 7, pp. 114-118.

Biamonte, J. D., Clark, S. R. and Jaksch, D., 2010. Categorical Tensor Network States. *AIP Advances*, 1, 042172.

Bruderer, M., Johnson, T. H., Clark, S. R., Jaksch, D., Posazhennikova, A. and Belzig, W., 2010. Phonon resonances in atomic currents through Bose-Fermi mixtures in optical lattices. *Physical Review A: Atomic, Molecular, and Optical Physics*, 82, 043617.

Clark, S. R., Connor, A. J., Jaksch, D. and Popescu, S., 2010. Entanglement consumption of instantaneous nonlocal quantum measurements. *New Journal of Physics*, 12, 083034.

Clark, S. R., Prior, J., Hartmann, M. J., Jaksch, D. and Plenio, M. B., 2010. Exact matrix product solutions in the Heisenberg picture of an open quantum spin chain. *New Journal of Physics*, 12, 025005.

Walters, R., Clark, S. R. and Jaksch, D., 2010. Decoherence of a quantum memory coupled to a collective spin bath. *International Journal of Quantum Information*, 8, 271.

Johnson, T. H., Clark, S. R. and Jaksch, D., 2010. Dynamical simulations of classical stochastic systems using matrix product states. *Physical Review E*, 82, 036702.

Hartmann, M. J., Prior, J., Clark, S. R. and Plenio, M. B., 2009. Density Matrix Renormalization Group in the Heisenberg Picture. *Physical Review Letters*, 102, 057202.

Rodriguez, M., Clark, S. R. and Jaksch, D., 2008. Adiabatic melting of two-component Mott-insulator states. *Physical Review A: Atomic, Molecular, and Optical Physics*, 77 (4), 043613.

Bruderer, M., Klein, A., Clark, S. R. and Jaksch, D., 2008. Transport of strong-coupling polarons in optical lattices. *New Journal of Physics*, 10, 033015.