Berkeley CMT

Time/Venue Wednesday, December 13 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Bob Birgeneau
Title tba
Abstract tba

Time/Venue Wednesday, November 8 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Bob Birgeneau
Title tba
Abstract tba

Time/Venue Wednesday, October 11 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Bob Birgeneau
Title tba
Abstract tba

Time/Venue Wednesday, September 27 at 2:00 PM Pacific Time in Location TBA and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host James Analytis
Title Single-Component Superconductivity in UTe2 at Ambient Pressure
Abstract The foremost question for a new superconductor is the symmetry of the superconducting order parameter. UTe2 has been inferred to have a multi-component order parameter that can lead to exotic effects like time reversal symmetry breaking. However, this proposal has been clouded by questions about sample homogeneity and a lack of direct experimental probes for multi-component superconductivity. We use pulse echo ultrasound to study samples of UTe2 with both one and two superconducting transitions, showing that both types of samples have no thermodynamic discontinuities in their shear elastic moduli—direct evidence that UTe2 has a single component superconducting order parameter. We further show that the superconductivity is highly sensitive to strains that modify the uranium-dominated Fermi surfaces, whereas strains that modify the tellurium-dominated Fermi surfaces do not couple to superconductivity. This leads us to suggest a single-component, spin-triplet, odd parity order parameter—specifically the B2u order parameter—as the most likely order parameter in UTe2 (https://doi.org/10.48550/arXiv.2307.10938).

Time/Venue Tuesday, September 26 at 11:00 AM Pacific Time in 325 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
Title Programmable adiabatic demagnetization: State preparation by simulated cooling
Abstract We propose an efficient protocol for preparing low energy states of arbitrary fermionic Hamiltonians on a noisy bosonic quantum simulator. This procedure involves performing adiabatic cooling by coupling the target system with a simulated bath. The bath is periodically monitored in order to extract entropy from the system. By fermionizing the simulated target system and the bath together, we allow individual fermionic excitations of the system to coherently hop to the bath sites. In this way, we achieve a cooling rate linearly proportional to the density of these excitations, despite the fact that they are non-local in terms of the bosonic degrees of freedom of the hardware. We study the performance of our protocol in the presence of noise via an application to the Kitaev chain model (equivalent to the 1D transverse-field Ising model) in both the trivial and the topological phases. We further discuss a generalization of the protocol to higher dimensional systems. In particular, we show that certain topological phases, such as the chiral phase of the Kitaev honeycomb model can be prepared efficiently using our protocol.

Time/Venue Friday, September 22 at 12:00 PM Pacific Time in 325 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Nonlinear bosonization of Fermi surfaces
Abstract We develop a new method for bosonizing the Fermi surface based on the formalism of the coadjoint orbits. This allows one to parametrize the Fermi surface by a bosonic field that depends on the spacetime coordinates and on the position on the Fermi surface. The Wess-Zumino-Witten term in the effective action, governing the adiabatic phase acquired when the Fermi surface changes its shape, is completely fixed. As an effective field theory the action also involves a Hamiltonian which contains, beside the kinetic energy and the Landau interaction, terms with arbitrary number of derivatives and fields. We show that the resulting local effective field theory captures both linear and nonlinear effects in Landau’s Fermi liquid theory. The approach can be extended to encompass non-Fermi liquids, which correspond to strongly interacting fixed points obtained by deforming Fermi liquids with relevant interactions.

Time/Venue Wednesday, September 20 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Entanglement Linear Response — Extracting the Quantum Hall Conductance from a Single Bulk Wavefunction and Beyond
Abstract In this talk, I will introduce the so-called entanglement linear response, i.e., response under entanglement generated unitary dynamics. As an application, I will show how it can be applied to certain anomalies in 1D CFTs. Moreover, I will apply it to extract the quantum Hall conductance from a wavefunction and how it embraces a previous work on the chiral central charge. This gives us a new connection between entanglement, anomaly and topological response.

Time/Venue Wednesday, September 6 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Multiband Euler topology and Andreev reflection
Abstract The well-known free-fermion topological phases of matter such as the Chern and QSH insulators are characterised by topological quantum numbers assigned to single isolated bands. While these phases are now very well understood, there are still interesting features to explore within topological band theory. I will explain how nodes in real Bloch Hamiltonians carry non-Abelian topological charges which arise from the geometry of the classifying space. Moreover, by braiding these nodes around each other in reciprocal space, it is possible to induce a ‘multi-band’ topological phase, where the two band subspace supporting the nodes is labelled with an integer, the Euler class. So far the experimental signatures of these unusual phases of matter have remained elusive. One way in which the properties of nodal materials may be probed is by analysing their low-energy Andreev reflection characteristics: for instance, the nodal topology in proximity-induced superconducting graphene gives rise to specular Andreev reflection, in contrast to the more usual case of retroreflection. I will demonstrate how the properties of nodes in Euler materials similarly display unusual signatures when investigated with Andreev reflection. This provides a route through which Euler materials could be identified experimentally.

Time/Venue Wednesday, August 30 at 2:00 PM Pacific Time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
Title Strange metallic transport of the strongly interacting Hubbard model and hard core bosons
Abstract tba

Time/Venue Wednesday, July 26 at 2:00 pm in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09
Meeting ID: 995 2349 9113 Passcode: 600704
Host Chris Waechtler/Joel Moore
Title Steady-state quantum Zeno effect of driven-dissipative bosons with dynamical mean-field theory
Abstract The study of the driven-dissipative quantum many-body problem has gained, in the last decade, considerable traction. Photonic systems, specifically, have emerged as particularly suited platforms thanks to the ease of introduction of driving and dissipation, and the latter has been harnessed as a convenient tool for the preparation of strongly-correlated many-body states. Despite these recent efforts, the picture on driven-dissipative many-body quantum systems is still incomplete and calls, among others, for the development of new, powerful numerical methods which are able to cope with the sheer size of the Hilbert space and, at the same time, to carefully handle the presence of correlations. In this work, we overcome these problems by employing the DMFT technique in the context of driven-dissipative bosonic lattices. As a case study for the effectiveness of our specific implementation of this technique, we demonstrate the ability to reproduce the so-called quantum Zeno effect in a Bose-Hubbard lattice of cavities with strong two-particle dissipation.
References
1. Seclì et al, New J. Phys. 23, 063056 (2021).
2. Seclì et al, Phys. Rev. A 106, 13707 (2022).