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Department of Physics

The Cavendish Laboratory
 

This series of colloquia in the Cavendish Laboratory aims to cover all aspects of modern quantum many-body physics. It is broadly aligned with our research themes on Theoretical Condensed Matter PhysicsFundamental Physics of Quantum MatterApplied Quantum Physics and DevicesSynthetic Quantum SystemsQuantum Information and Control, and Energy Materials

As such, it features talks on both fundamental many-body physics as well as their exploitation in devices, covering all aspects of quantum phenomena in condensed matter and synthetic many-body systems, and their theoretical description.

The aim for these colloquia is to be accessible to a wider audience compared to a typical group seminar, and everyone is most welcome to attend them!

Click below to see details of the upcoming and previous talks. Please check this page regularly to keep informed as speakers are confirmed and details of their talks are added to the list.


Upcoming talks:

17 January 2024 @16:00: Prof Ian Walmsley FRS (Imperial College London)

Prof Ian Walmsley FRS (Imperial College London): Lighting the Quantum Future

Venue: Small Lecture Theatre

Light has a central role in emerging quantum technologies because of its ability to control matter and its unique capacity for displaying quantum features in ambient condition. Non-error corrected optical quantum machines performing specialised tasks have already demonstrated a quantum advantage over the best algorithms running on conventional computers, and practical applications for such machines are being explored. Meanwhile, designs for error-corrected fault-tolerant quantum computers based on light are reducing the performance requirements for individual components and systems, although the engineering challenges are severe. I will outline some recent progress toward scaling photonic quantum simulation and new modes of harnessing light in quantum computing.
See also: Optica Quantum, Vol. 1, Issue 1, pp. 35-40, (2023)

 

31 January 2024 @16:00: Prof Werner Krauth (Ecole Normale Supérieure de Paris, University of Oxford)

Prof Werner Krauth (Ecole Normale Supérieure de Paris, University of Oxford): Mixing, stopping, coupling, lifting, and other keys to the second Monte Carlo revolution

Venue: Small Lecture Theatre

The Monte Carlo method is at the origin of the revolution in physics that has brought the electronic computer into our research laboratories and class rooms. Since its beginning, in 1953, the method has relied on the detailed-balance condition to map general computational problems onto equilibrium-statistical-physics systems. Such reversible Markov chains are generally characterized by diffusive transport. In the last two decades, a second revolution has taken place, where the detailed balance is broken and thus, also, the analogy with equilibrium statistical physics. The steady state of non-reversible Markov chains agrees with that of the equilibrium approach, but it is often approached ballistically, rather than diffusively
In this talk, I will introduce to this interdisciplinary field of research about non-equilibrium in equilibrium, starting with the keywords of modern Markov-chain Monte Carlo. In particular, I will discuss applications from Bethe-ansatz solvable particle models to new Monte Carlo algorithms in statistical and chemical physics.

 

13 Feb 2024 @16:00: Prof Paolo Radaelli (University of Oxford)

Prof Paolo Radaelli (University of Oxford): Merons, bimerons and skyrmions in α-Fe2O3: from cosmology to spintronics

Venue: Small Lecture Theatre

 

The field of quantum matter/quantum materials draws inspiration from a variety of theories, seeking materials in which they can be embodied and verified.  In some cases, the materials in question end up being rather useful, though not necessarily in a way that is closely related to the original research motivation.  A celebrated example [1] is the analogy, proposed by Wojciech H. Zurek, between cosmological strings [2] and vortex lines in the superfluid, which suggested cryogenic experiments to test cosmological string formation in 4He.  The work I will describe in this talk started off as an attempt to seek the analogue of cosmological strings in easy-axis antiferromagnets with low in-plane anisotropy, leading to an approximate U(1) symmetry.

A well-known example of such materials is hematite (a-Fe2O3), which orders at a high Néel temperature (TN ~ 960 K).  At room temperature and above, the spins are aligned perpendicular to the high-symmetry trigonal axis and are also slightly canted due to the Dzyaloshinskii-Moriya interaction, giving rise to a ‘weak’ but measurable net ferromagnetism.  Below the Morin transition temperature (TM ~ 260 K), the spins flip out of plane and lose their canting, leading to perfect antiferromagnetism and the loss of the net magnetic signal.  We reasoned that the above-Morin phase should be topologically rich and could in principle support vortices, while the easily accessible low-temperature phase would be topologically ‘trivial’.  I will discuss our recent work [3,4], in which we demonstrated that, indeed, hematite supports a rich variety of topological textures (merons, antimerons, bimerons), which can be tuned in and out of existence simply by cycling temperature over a narrow range through TM or by application of biaxial/uniaxial strain [5].  Remarkably, these magnetic textures can be imaged in real space by X-ray spectral microscopy (X-PEEM, transmission X-ray microscopy and holography [6]).  I will also discuss the recent collaboration with Cambridge colleagues, in which we imaged by N-V centre microscopy [7] the ‘emergent’ multipolar charges associated with topological textures.  My final question is: can topological textures in hematite be at all useful?  I will argue that the answer may be yes, particularly in the blooming field of antiferromagnetic spintronics/skyrmionics.

 

References

[1]    Zurek, W. H. Cosmological experiments in superfluid helium? Nature 317, 505–508 (1985).

[2]    Kibble, T. W. B. “Topology of cosmic domains and strings.” J. Phys. A: Math. Gen. 9, 1387–1398 (1976);

[3]    F. P. Chmiel, N. Waterfield Price, R. D. Johnson, A. D. Lamirand, J. Schad, G. Van Der Laan, D. T. Harris, J. Irwin, M. S. Rzchowski, C. B. Eom, and P. G. Radaelli, Nat. Mater. 17, 581 (2018).

[4]    H. Jani, J. C. Lin, J. Chen, J. Harrison, F. Maccherozzi, J. Schad, S. Prakash, C. B. Eom, A. Ariando, T. Venkatesan, and P. G. Radaelli, Nature 590, 74 (2021).

[5]    H. Jani, J. Harrison, S. Hooda, S. Prakash, P. Nandi, J. Hu, Z. Zeng, J.-C. Lin, G. ji Omar, J. Raabe, S. Finizio, A. V.-Y. Thean, A. Ariando, and P. G. Radaelli, Nat. Mater https://doi.org/10.1038/s41563-024-01806-2 (2024 in press) arXiv:2303.03217 [cond-mat.mtrl-sci]

[6]    J. Harrison, H. k. Jani, J. Hu, M. Lal, J-C Lin, H. Popescu, J. Brown, N. Jaouen, A. Ariando, and P. G. Radaelli, Optics Express 32, pp. 5885-5897 (2024) , https://doi.org/10.1364/OE.508005

[7]    A. K. C. Tan, H. Jani, M. Högen, L. Stefan, C. Castelnovo, D. Braund, A. Geim, M. S. G. Feuer, H. S. Knowles, A. Ariando, P. G. Radaelli, and M. Atatüre, Nat. Mater 23, 205-212 (2023), https://doi.org/10.1038/s41563-023-01737-4

28 February 2024 @16:00: Prof Bilge Yildiz (MIT)

Prof Bilge Yildiz (MIT): Protonic Electrochemical Synapses for Energy-Efficient Brain-Inspired Computing

Venue: Small Lecture Theatre

In this talk, I will share our work on the ionic electrochemical synapses, whose electronic conductivity we control deterministically by electrochemical insertion/extraction of dopant ions into/out of the channel layer. This work is motivated by the need to enable significant reductions in the energy consumption of computing, and is inspired by the ionic processes in the brain. Proton as the working ion in our research presents with very low energy consumption, on par with biological synapses in the brain. Our modeling results indicate the desirable material properties, including as ion conductivity and interface charge transfer kinetics, that we must achieve for fast, low energy and low voltage performance of these devices. Importantly, the conductance change in these electrochemical devices depends non-linearly on the gate voltage, due to field-enhanced ion migration in the electrolyte, and charge transfer kinetics at the electrolyte-channel interface. We are leveraging these intrinsic nonlinearities to emulate bio-realistic learning rules deduced from neuroscience studies, such as spike timing dependence of plasticity and Hebbian learning rules. Our findings indicate that protonic electrochemical synapses can serve as energy-efficient and reliable building blocks for brain-inspired computing hardware.

 

13 March 2024 @16:00: Prof Maciej Lewenstein (ICFO – The Institute of Photonic Sciences)

Prof Maciej Lewenstein (ICFO – The Institute of Photonic Sciences): Attoscience, Nobel 2023, and Quantum Simulators

Venue: Small Lecture Theatre

I will start my talk with an introduction to "super-intense laser-matter physics".

I will then focus on the phenomenon of High Harmonics Generation (HHG) and its physical nature. I will explain how this phenomenon may lead to generations of attosecond pulse trains or isolated attosecond pulses in XUV range. In the second part, I will focus on recent developments in the field that allow to study QED aspects of attophysics. The third part will be devoted to the discussion of quantum simulators of atto-physics with ultracold atoms. I will end with my personal story of Nobel 2023. 

1 May 2024 @16:00: Prof Claudia Felser (Max Planck Institute for Chemical Physics of Solids)

Prof Claudia Felser (Max Planck Institute for Chemical Physics of Solids)

Venue: Small Lecture Theatre

Title and abstract coming soon.

15 May 2024 @16:00: Prof Jean Dalibard (Collège de France, Kaster Brossel Laboratory)

Prof Jean Dalibard (Collège de France, Kaster Brossel Laboratory)

Venue: Small Lecture Theatre

Title and abstract coming soon. 

 

22 May 2024 @16:00: Prof Monika Schleier-Smith (Stanford University)

Prof Monika Schleier-Smith (Stanford University)

Venue: Small Lecture Theatre

Title and abstract coming soon.