Theory of quantum systems

We have a range of exciting potential DPhil projects connected to our wider research topics (see "Our Research" on the menu link), and to research in other groups at Oxford, around the UK, and internationally. For up to date information on how to apply for a DPhil in Atomic and Laser Physics, please see the official Department Website .

Our specific available projects (with relevant background references) include:

Exploration of dynamics in systems with long-range interactions:

Several experimental platforms allow for the generation of long-range interactions (atoms in optical cavities, arrays of trapped ions, and moving atoms in tweezer arrays). Recently, we have begun to explore how this gives rise to fast scrambling of quantum information, a phenomenon that was originally discussed in the context of quantum information in black holes. This opens interesting connections to many-body physics in black holes, while providing a route in experiments to rapid generation of entanglement, and potentially resource states for quantum computing. We recently identified a dynamical phase transition that occurs as a function of the range of the coupling distance, between regimes of slow and fast scrambling. We plan to explore the many-body physics of this further, including looking at ground-state phase transitions as a function of the coupling strength, which could be explored in a series of ongoing experiments.

• Nicolò Defenu, Tobias Donner, Tommaso Macrì, Guido Pagano, Stefano Ruffo, and Andrea Trombettoni Rev. Mod. Phys. 95, 035002 (2023)
• Tomohiro Hashizume, Gregory S. Bentsen, Sebastian Weber, Andrew J. Daley, Deterministic Fast Scrambling with Neutral Atom Arrays, Phys. Rev. Lett. 126, 200603 (2021). 
• Gregory Bentsen, Tomohiro Hashizume, Anton S. Buyskikh, Emily J. Davis, Andrew J. Daley, Steven S. Gubser, and Monika Schleier-Smith, Treelike interactions and fast scrambling with cold atoms, Phys. Rev. Lett. 123, 130601 (2019).
• Sridevi Kuriyattil, Tomohiro Hashizume, Gregory Bentsen, and Andrew J. Daley, Onset of scrambling as a dynamical transition in tunable-range quantum circuits, PRX Quantum 4, 030325 (2023) 

Theory of quantum computing and simulation with neutral atoms 

Neutral atom arrays have rapidly emerged as a leading candidate for implementation of general purpose quantum computing, and continue to be a leading candidate in analogue quantum simulation. We will explore the new opportunities provided by (1) the ability to move atoms in the array during the dynamics, especially creating hypercube architectures for quantum computing, (2) new ways to verify quantum advantage in analogue quantum simulation. We will also explore more deeply how decoherence that is present in experiments, and which we can model on a microscopic level, changes our ability to compute the dynamics using classical numerical techniques, shifting the criteria for achieving a quantum advantage. 

• D. Bluvstein et al., Nature 604, 451 (2022)
• Andrew J. Daley, Immanuel Bloch, Christian Kokail, Stuart Flannigan, Natalie Pearson, Matthias Troyer, and Peter Zoller, Practical quantum advantage in quantum simulation, Nature 607, 667 (2022).
• S. Flannigan, N. Pearson, G. H. Low, A. Buyskikh, I. Bloch, P. Zoller, M. Troyer, A. J. Daley, Propagation of errors and quantitative quantum simulation with quantum advantage, Quantum Science and Technology, 7, 045025 (2022).
• Gerard Pelegrí, Andrew J. Daley, Jonathan D. Pritchard, High-fidelity multiqubit Rydberg gates via two-photon adiabatic rapid passage, Quantum Science and Technology, 7, 045020 (2022).

Many-body quantum optics and open quantum systems

Control over individual quantum particles was originally pioneered from the point of view of quantum optics (resulting in the Nobel prize for Serge Haroche and Dave Wineland in 2012). There has been a long tradition of exploring continuous measurement techniques, and understanding how they can be used to control a many-particle quantum system. We recently developed new methods that allow us to compute the state of many-particle quantum systems undergoing non-markovian dissipative processes, as arises, e.g., with atomic ensembles in an optical cavity. We will explore generalisations of these ideas,  both to understand (1) how measurement and feedback in multi-mode optical cavities can be used to engineer chosen many-body states with applications to generating resource states for quantum metrology and quantum computing, and (2) how quantum optics techniques can be generalised to provide descriptions of modern quantum transport systems.

• Valentin Link, Kai Müller, Rosaria G. Lena, Kimmo Luoma, François Damanet, Walter T. Strunz, and Andrew J. Daley, Non-Markovian Quantum Dynamics in Strongly Coupled Multimode Cavities Conditioned on Continuous Measurement, PRX Quantum, PRX Quantum 3, 020348 (2022).
• Stuart Flanningan, François Damanet, and Andrew J. Daley, Many-body quantum state diffusion for non-Markovian dynamics in strongly interacting systems, Phys. Rev. Lett. 128, 063601 (2022).
•  A. J. Daley, Quantum trajectories and open many-body quantum systems, Adv. Phys. 63, 77 (2014). (arXiv:1405.6694)
• Inés de Vega and  Daniel Alonso, Rev. Mod. Phys. 89, 15001 (2017)