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Details of Grant 

EPSRC Reference: EP/W005743/1
Title: New paradigms of quantum many-body dynamics
Principal Investigator: Turner, Dr C J
Other Investigators:
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Department: Physics and Astronomy
Organisation: UCL
Scheme: EPSRC Fellowship
Starts: 01 October 2021 Ends: 30 September 2025 Value (£): 463,724
EPSRC Research Topic Classifications:
Quantum Optics & Information
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
27 Jul 2021 Stephen Hawking Fellowship - R2 Interviews Announced
26 Jul 2021 Stephen Hawking Fellowship - R2 Interviews- Panel 2 Announced
Summary on Grant Application Form
In recent years there has been lots of progress in our ability to control things at the quantum scale, led by the high-profile efforts of IBM and Google to create a working quantum computer. With these new tools, we hope to solve some hard computation problems that are not practical using classical computers and to simulate models for challenging quantum systems, such as the fractional quantum Hall effect and high-Tc superconductivity.

The novel features of these devices is the level of control over individual elements or qubits which interact strongly with one another. However, understanding these devices is difficult because of the profound effect of interactions in generating chaos and complexity. Their dramatic effect can be seen in a classic example: a pendulum presents a simple and familiar periodic motion. Simply coupling two pendulums together, however, generates chaotic motion which is much more complex and difficult to predict. Similarly, interacting quantum systems typically thermalise rapidly, scrambling any information stored inside and rendering it irrecoverable. This makes chaotic systems difficult to control and so understanding how to prevent thermalisation is key to the operation of quantum devices.

A landmark experiment on a prototype quantum device [H. Bernien et al., Nature 551, 579 (2017)] found something incredibly surprising. When prepared in a particular initial configuration, the device would periodically return to that state, whereas from many other starting states the device would quickly thermalise and never return. I proposed the first theoretical explanation of this finding and gave it the name ``many-body quantum scars'' after a similar phenomenon in the case of single-particle systems where there are no interactions. The significance of this finding was highlighted widely in the press and prompted viewpoint articles in Nature Physics and Quanta magazine.

The underlying causes for the effect remains a mystery, despite the large amount of research activity it has generated.

This fellowship will pursue a research programme that brings together computational techniques and analytical insight towards answering some of the fundamental questions around the different forms of ergodicity breaking -- namely, quantum scars and many-body localisation (MBL). This includes the search for a mathematical structure or guiding principle which underlies and stabilises the many-body scar and whether many-body localisation can survive when extended beyond one spatial dimension.

The practical benefits to this work include novel computation techniques for simulating non-ergodic many-body systems which could see wider application. Furthermore, improved understanding of the mechanisms of ergodicity breaking could lead to new ways to control and manipulate the quantum coherences which are central to quantum technology, and in the face of a noisy and chaotic environment which tends to destroy them.
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