26-Oct, 10AM AEST - 25-Sep, 7PM EDT

Jennifer Cano (Stony Brook University and the Flatiron Institute) 

Engineering topological phases with a superlattice potential

Abstract: Spontaneous symmetry breaking on the surface of a topological insulator can realize exotic quantum phases such as a quantum anomalous Hall insulator or topological superconductor. However, in all known 3D topological insulators, the Coulomb interaction is too weak to open a gap. We propose a new route to manipulate topological surface states by an artificial superlattice potential. The superlattice potential creates tunable van Hove singularities, which, when combined with strong spin-orbit coupling and Coulomb repulsion give rise to a topological meron lattice spin texture. The periodicity of this designer meron lattice can be tuned by varying the periodicity of the potential. We then show that a superlattice potential applied to Bernal-stacked bilayer graphene can also create topological flat bands, similar to twisted bilayer graphene. The superlattice potential offers flexibility in both lattice size and geometry, making it a promising alternative to achieve designer flat bands without a moire heterostructure.

28-Sep, 10AM AEST - 27-Sep, 8PM EDT

Rafael Fernandes  (University of Minnisota) 

The rich landscape of intertwined electronic phases in quantum materials

Quantum materials encompass a wide family of systems that display many fascinating phenomena, from high-temperature superconductivity to topological order. They stand out not only as promising candidates for new technological applications, but also as windows into the fundamental microscopic properties of interacting electrons, whose collective behavior can be very different from the behavior of an individual electron. Macroscopically, these electronic correlations are manifested by the emergence of complex phase diagrams displaying a plethora of electronic states that are not independent, but intertwined. In this talk, I will present a theoretical framework that captures the intricate interplay between electronic states of matter that may seem unrelated at first sight. Based on the concept of vestigial orders, it generalizes to the quantum realm concepts common to the description of liquid crystals. More specifically, in this approach, thermal or quantum fluctuations cause an electronically ordered state to partially melt in multiple stages, leading to the emergence of two or more intertwined phases with comparable energy scales. This framework not only sheds new light on the known phase diagrams of various quantum materials, such as iron-based superconductors, but it also provides new insights into the experimental realization of exotic states, such as a charge-4e superconducting phase in twisted bilayer graphene.

24-Aug 10AM AEST - 23-Aug, 8PM EDT

Sergey Frolov (University of Pittsburgh) 

Superconductors and Semiconductors, Nanowires and Majorana, Research and Integrity

This talk will be on three topics, but in a way it is one. My research focus and passion is the proximity effect. It is when superconducting correlations are induced in a non-superconducting material. Because superconductivity is always tied to a spin order, proximity effects get especially rich when the non-superconductor is magnetic, or has strong spin-orbit coupling for electrons. Superconductivity induced by proximity must take into account these interactions in the new host, and can evolve into exotic phases such as triplet or topological superconductivity. This is where Majorana modes come in, they are edge states of a topological superconductor with unusual properties such as predicted non-Abelian exchange. For the past decade I was busy studying their possible manifestations in semiconductor nanowires, where superconductivity is subject to both spin-orbit and magnetic field effects at the same time. We got very excited at first when we found experimental signatures, zero-bias peaks, that behaved as expected for Majorana modes. We shortly learned that another effect, non-topological Andreev states, can exhibit all of the same signatures. Despite these dual interpretations, papers claiming new Majorana sightings kept appearing. After I and my colleague Vincent Mourik looked into extra data from those papers we found unjustified data selection that invalidated conclusions. Several papers are under investigation as a result of our work. In my talk I want to touch on the implications of this, and sketch a path forward for our topic and for the broader field of quantum and condensed matter physics.

27 July 10AM AEDT - 26 July 8PM EST

Susanne Stemmer (University of California, Santa Barbara)

Topological Insulator States in Thin Films of Cadmium Arsenide 

Over the past decade, the unique properties of topological materials have generated huge excitement in the condensed matter physics community.  Recently, high-quality thin films of cadmium arsenide (Cd3As2), a three-dimensional Dirac semimetal in its bulk version, have emerged as a promising platform for the observation of quantum transport phenomena from topological states and the realization of new topological phases.  In this talk, we will first discuss our recent progress in the growth of epitaxial thin films Cd3As2 by molecular beam epitaxy.  We will discuss the evolution of the electronic states of thin (001) Cd3As2 films as their thickness is scaled. We will discuss how different topological states in these films give rise to distinct features in magnetotransport studies. 

22 June 10AM AEST - 21 June 8PM EDT

Lu Li  (University of Michigan)  

Quantum Oscillations of Electrical Resistivity in an Insulator

In metals, orbital motions of conduction electrons are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators, in which all the electrons are localized. Here we report a notable exception in an insulator — ytterbium dodecaboride (YbB12). The resistivity of YbB12, despite much larger than that of usual metals, exhibits profound quantum oscillations under intense magnetic fields. This unconventional oscillation is shown to arise from the insulating bulk instead of conducting surface states. The large effective masses indicate strong correlation effects between electrons. Our result is the first discovery of quantum oscillations in the electrical resistivity of a strongly correlated insulator and will bring crucial insight into understanding the ground state in gapped Kondo systems

25 May 10AM AEDT - 24 May  8PM EST

Ana Maria Rey   (JILA, NIST and University of Colorado )

Optical lattice clocks: From Timekeepers to Spies of the Quantum Realm

Abstract: Harnessing the behavior of complex systems is at the heart of quantum technologies. Precisely engineered ultracold gases are emerging as a powerful tool for this task. In this talk I will explain how ultracold strontium atoms trapped by light can be used to create optical lattice clocks – the most precise timekeepers ever imagined. I am going to explain why these clocks are not only fascinating, but of crucial importance since they can help us to answer cutting-edge questions about complex many-body phenomena and magnetism, to unravel big mysteries of our universe and to build the next generation of quantum technologies.

23 Mar 10AM AEDT - 22 Feb 7PM EST

Nadya Mason (University of Illinois at Urbana-Champaign)

Electronic Transport in Strain-Engineered Graphene

There is wide interest in using strain-engineering to modify the physical properties of 2D materials, for both basic science and applications. Deformations of graphene, for example, can lead to the opening of band gaps, as well as the generation of pseudo-magnetic fields and novel electronic states. We demonstrate how controllable, device-compatible strain patterns in graphene can be engineered by depositing graphene on corrugated substrates. We discuss several techniques for creating corrugated substrates, focusing on periodic spherical curvature patterns in the form of closely packed nanospheres. We show how the smaller nanospheres induce larger tensile strain in graphene, and explain the microscopic mechanism of this. We also present experimental results demonstrating how a nearly periodic array of underlying nanospheres creates a strain superlattice in graphene, which exhibits mini-band conductance dips and pseudomagnetic field effects that depend on the magnitude of induced strain. This control of the strain degree of freedom provides a novel platform both for fundamental studies of 2D electron correlations and for prospective applications in 2D electronic devices.

23 Feb 10AM AEDT - 22 Feb 6PM EST

Ehud Altman (UC Berkley)

Phase transitions and critical states of monitored quantum systems

Generic unitary evolution of a quantum state, as affected for example by non-integrable Hamiltonian dynamics or by random gates in a quantum circuit, leads to encoding of information into highly non-local degrees of freedom, where the information becomes irretrievable. Recent work on quantum circuits began to explore how this kind of non-local encoding is affected by an external observer that can perform measurement on the quantum state as it evolves. It was found that a large system undergoes a phase transition, from a state with non local encoding, evidenced by volume law entanglement, at a small enough measurement rate to an area law state above a threshold rate. I will review how such transitions in the dynamics of quantum information can be understood in terms of effective statistical mechanics models, which describe a self organized  quantum error correcting code in random circuits. I will then use these models or random circuits to predict new universal phenomena in the dynamics of quantum information in monitored systems and discuss possible tests of these predictions using quantum hardware. 

10 Nov 9AM (AEDT) - 9 Nov 5PM (EST)

Michael Fuhrer (Monash University)

Topological Materials for Low-energy Electronics

The impending end of Moore’s Law has prompted a search for a new computing technology with vastly lower energy consumed per operation than silicon CMOS. The recent discovery of topological phases of matter offers a possible solution: a “topological transistor” in which an electric field tunes a material from a conventional insulator “off” state to a topological insulator “on” state, in which topologically protected edge modes carry dissipationless current. Due to the combined effects of Rashba spin-orbit interaction and electric field control of the bandgap, the topological transistor may switch at lower voltage, overcoming “Boltzmann’s tyranny”[1].

I will discuss our work on atomically thin films of Na3Bi (a topological Dirac semimetal) as a platform for a topological transistor. We study thin films of Na3Bi grown in ultra-high vacuum by molecular beam epitaxy[2], characterized with electronic transport, scanning tunneling microscopy (STM), and angle-resolved photoemission spectroscopy[2-5]. When thinned to a few atomic layers Na3Bi is a large gap (>300 meV) 2D topological insulator with topologically protected edge modes observable in STM. Electric field applied perpendicular to the Na3Bi film, by potassium doping or by proximity of an STM tip, closes the bandgap completely and reopens it as a conventional insulator[4]. Electrical transport measurements demonstrate that the current is carried by helical topological edge modes over millimeter-scale distances[5]. The large bandgap of 2D Na3Bi, significantly greater than room temperature, and its compatibility with silicon, make it a promising platform for topological transistors.

27 Oct 10AM (AEDT) - 26 Oct 7PM (EDT)

Elaine Li  (University of Texas )

Semiconductor Moiré Superlattices: a New Material Platform for Quantum Information Science. 

When two atomically thin van der Waals (vdW) layers are vertically stacked together, the atomic alignment between the layers exhibits periodical variations, leading to a new type of in-plane superlattices known as the moiré superlattices. The twist angle controls the size of the moiré supercells and acts as a unique knob to control the material properties. In this talk, I will discuss how new excited states (excitons and phonons) emerge in highly tunable semiconductor moiré superlattices. I will speculate on new and exciting directions relevant to quantum information science based on these materials. 

13 Oct 9AM (AEDT) - 12 Oct 6PM EDT

Susan Coppersmith  (UNSW)

Quantum Stochastic Resonance of individual Fe atoms 

Stochastic resonance, where noise synchronizes a system’s response to an external drive, is a phenomenon that occurs in a wide variety of noisy systems ranging from the dynamics of neurons to the periodicity of ice ages. This talk will present theory and experiments on a quantum system that exhibits stochastic resonance — the quantum tunneling of the magnetization of a single Fe atom measured using spin-polarized scanning tunneling microscopy. Stochastic resonance is shown deep in the quantum regime, where fluctuations are driven by tunneling of the magnetization, as well as in a semi-classical crossover region where thermal excitations set in. An analytic theory with no adjustable parameters agrees quantitatively with experiment, and provides a path towards probing dynamics on time scales shorter than can be resolved experimentally. 

22 Sep 10AM  (AEST) - 21 Sep 8PM (EDT) 

Piers Coleman (The Rutgers University)

Dark-Matter Challenges of the Solid State 

At the turn of the 20th century, physicists faced an uncanny range of unsolved problems: simple questions, such as why hot objects change color, why matter is hard and why the sun keeps on shining, went unanswered. These problems heralded a new era of quantum physics. What was truly remarkable about discovery in this heroic era, was the intertwined nature of research in the lab and in the cosmos: solving superconductivity really did help answer why the sun keeps on shining, while looking at the stars provided clues as to why matter is hard.

The challenges facing us today, epitomized by our failure to quantize gravity and the mysteries of dark matter and energy, challenge physics to its core. But equally, physics in the lab and cosmos remain just as intertwined as they were a hundred years ago.  I will discuss the less well-known dark matter challenges of the solid state, epitomized by the strange metals with linear resistivity that accompany high temperature superconductivity, the discovery of insulators with Fermi surfaces and the phenomenon of Quantum criticality. I will argue that these laboratory-scale problems challenge our fundamental understanding of emergent quantum matter in ways that are no less intertwined with their cosmological counterparts than they were a hundred years ago.

9 Sep 9AM (AEST) - 8 Sep 7PM (EDT)

Elena Ostrovskaya (Australian National University)

Exploring non-Hermitian physics with exciton polariton 

Exciton polaritons are hybrid light-matter bosons formed by excitons in semiconductors strongly coupled to microcavity photons. Sufficiently strong optical pumping can drive exciton polaritons to a macroscopically occupied coherent state similar to a Bose-Einstein condensate. The same optical pump that injects polaritons into the system and drives them to condensation can also be used to induce effective trapping potentials for exciton polaritons. In this talk, I will discuss how the optically induced confinement enables us to explore the non-Hermitian physics of the exciton-polariton systems experimentally. I will also talk about the opportunities that this platform provides for probing non-Hermitian topology. 

25 Aug 10AM (AEST) - 24-Aug, 8PM EDT

Jelena Vuckovic (Stanford University)

Inverse Designed Integrated Photonics 

Photonics with superior properties can be implemented in a variety of old (silicon, silicon nitride) and new (silicon carbide, diamond) photonic materials by combining state of the art photonics optimization techniques (photonics inverse design) with new fabrication approaches. In addition to making  photonics more robust (e.g., to errors in fabrication and variation in temperature), more compact, and more efficient, this approach can also enable new functionalities.  While in our early work we focused on inverse design and demonstration of individual photonic devices, our more recent work focused on scaling it to photonic integrated circuits fabricated in a commercial semiconductor foundry. We illustrate this with several examples, including optical interconnects based on a combination of mode and wavelength division multiplexing, diamond and silicon carbide photonic circuits. 

28 Jul 10AM (AEST) - 27 Jul 8PM (EDT)

Tami Pereg-Barnea (McGill University)

Domain and Skyrmion bound states on the surface of magnetic topological insulators 

A 3D topological insulator (TI) hosts an odd number of Dirac cones as its 2D surface states spectrum. The states are exponentially localized to the surface and their (pseudo)spin is locked to the surface momentum direction due to spin-orbit interaction. If the TI is also magnetic there are fixed magnetic moments on the surface, co-existing with the itinerant Dirac electrons. The magnetic moments interact with each other both directly (exchange) and indirectly (RKKY) and may form a ferromagnetic state. The magnetic state couples to the Dirac electrons and serves as a Dirac mass which, when uniform, opens a gap in the spectrum. When the ordering of the magnetic moments is modified by excitation such as skyrmions and domain walls, the Dirac electrons see a landscape of spatially dependent mass. This leads to localized low energy states around domain walls and skyrmions. In this talk we will see how the bound states can be detected by a surface conductivity measurement; how the skyrmion-skyrmion interaction is altered due to the presence of Dirac electrons and encounter emergent topological bands in the presence of a skyrmion solid.  *No prior knowledge of the subject is assumed* 

23 Jun  10AM (AEST) - 22 Jun 8PM (EDT) 

Jeanie Lau (The Ohio State University)

Tunable Helical Edge States in van der Waals Materials 

Helical conductors, systems that have no bulk conduction but support dissipationless conducting states at their edges, may be engineered to realize Majorana statistics for quantum computation. Underlying these remarkable systems are the non-trivial topology of electronic structure in the bulk, arising band inversion in the bulk and crossing of conductance and valence bands at the system boundary. Here we show that helical edge states are achievable and tunable in few-layer van der Waals materials. In Bernal-stacked trilayer and tetralayer graphene, we observe helical edge states at moderate and strong magnetic fields, respectively, arising from the competing effects of inter-layer coherence, electrostatic polarization and exchange interaction. As the interlayer potential and magnetic field varies, we observe a series of quantum transitions among the phases that host 2, 1 and 0 helical edge states on each edge. Our work highlights the complex competing symmetries in few-layer graphene and the rich quantum phases in this seemingly simple system. Lastly, in thin exfoliated Bi4I4 samples, which is a quasi-1D topological insulator and candidate for higher order topological states, we observe gate tunable magneto-transport and Josephson current. Our combined transport, photoemission, and theoretical results indicate that the gate-tunable channels consist of novel gapped side surface states, a 2D TI in the bottommost layer, and helical hinge states of the upper layers.

26 May 10AM (AEST) and 25-May 8PM (EDT)

Brian LeRoy (University of Arizona)

Quantum simulators: from the Fermi Hubbard model to quantum assisted NMR inference 

Topological phases have been dominating the limelight in the past 10 years. They may provide a pathway to protected topological quantum computing, as well as reduced dissipation electronics. Their potential for new quantum devices, however, has been so far untapped. In my talk I will review the principles behind topological insulators, and then show how these ideas take a new life when applied to systems where light and matter interact. As I will show, the combination of photonics and topology gives rise to topological-polaritons, new paradigms for infra-red detectors and energy harvesting, and new methods for conversion and amplification of low frequency EM radiation.

5 May 9AM (AEST) and 4 May 7PM (EDT)   

Dimi Culcer (UNSW) 

Generating an anomalous Hall effect in a non-magnetic conductor: an in-plane magnetic field as a probe of the Berry curvature 

28 April 5PM (AEDT) and 28 April 3AM (EDT)   

Eugene Demler (Harvard University) 

Quantum simulators: from the Fermi Hubbard model to quantum assisted NMR inference 

Topological phases have been dominating the limelight in the past 10 years. They may provide a pathway to protected topological quantum computing, as well as reduced dissipation electronics. Their potential for new quantum devices, however, has been so far untapped. In my talk I will review the principles behind topological insulators, and then show how these ideas take a new life when applied to systems where light and matter interact. As I will show, the combination of photonics and topology gives rise to topological-polaritons, new paradigms for infra-red detectors and energy harvesting, and new methods for conversion and amplification of low frequency EM radiation.

24 March 10:00 (AEDT) and 23 March 18:00 (EDT)

Gil Refael (California Institute of Technology)

Topological Physics at the Light-Matter Interface 

Topological phases have been dominating the limelight in the past 10 years. They may provide a pathway to protected topological quantum computing, as well as reduced dissipation electronics. Their potential for new quantum devices, however, has been so far untapped. In my talk I will review the principles behind topological insulators, and then show how these ideas take a new life when applied to systems where light and matter interact. As I will show, the combination of photonics and topology gives rise to topological-polaritons, new paradigms for infra-red detectors and energy harvesting, and new methods for conversion and amplification of low frequency EM radiation.

24 February 10:00 (AEDT) and 23 February 18:00 (USA Eastern Time)

Dimitri Basov (Columbia University)

Live form New York: Programmable Quantum Materials

Experimentally realizing quantum phases of matter and controlling their properties is a central goal of the physical sciences. Novel quantum phases with controllable properties are essential for new electronic, photonic, and energy management technologies. Quantum materials offer particularly appealing opportunities for the implementation of on-demand quantum phases.  This class of materials host interacting many-body electronic systems featuring an intricate interplay of topology, reduced dimensionality, and strong correlations that leads to the emergence of “quantum matter’’ exhibiting macroscopically observable quantum effects over a vast range of length and energy scales. Central to the nano-optical exploration of quantum materials is the notion of polaritons: hybrid light-matter modes that are omnipresent in polarizable media. Infrared nano-optics allows one to directly image polaritonic waves yielding rich insights into the electronic phenomena of the host material supporting polaritons. We utilized this novel general approach to investigate the physics of on-demand hyperbolic exciton-polaritons in a prototypical atomically layered van der Waals semiconductor WSe2 in which polaritons are prompted by femto-second photo-excitation. 

25 November 10AM (AEDT)  - and  24 November 6PM (USA EST)

Eva Andrei (Rutgers University)

The magic of atomically thin materials 

The realization of two dimensional (2D) atomically thin layers has made it possible to tune the properties of a material without changing its chemical composition, for example by introducing strain1, plucking out atoms2, or intentionally stacking the layers in various ways3. In particular, by tuning the twist between two superposed graphene crystals to certain magic angles, one can create nearly flat electronic bands where the enhanced Coulomb interactions favor the emergence of correlated states that alternate between superconducting, ferromagnetic or nematic4 phases at the turn of a knob. More recently, the discovery of flat bands in graphene membranes that underwent a buckling transition5, points the way to new strategies for inducing correlated phases without the exquisitely fine tuning required in twisted bilayers. In this talk I will cover highlights of this rapidly evolving field from its serendipitous discovery3 to recent developments.

11 November  9:00 (AEDT) and 17:00 (USA Eastern Time)

Meera Parish (Monash University)

The fate of quantum impurities in a Fermi sea

The scenario of a mobile impurity immersed in a Fermi gas appears in a wide variety of systems ranging from neutron stars to cold atomic gases to the absorption spectra in doped semiconductors. In this case, the impurity attractively interacts with the surrounding fermions and becomes "dressed" by excitations of the Fermi gas to form a quasiparticle, a particle-like object with a different mass from the bare impurity. In this talk, I will discuss how cold atoms can provide fundamental insight into the nature of these quasiparticles, particularly how they can break down in a manner not previously explored in Fermi systems. 

28 October 10:00  (AEDT) -  27 October 7:00 (USA  EDT)

Anton Burkov -  University of the Waterloo

Topological Metals

One of the major themes of the modern condensed matter physics is the study of materials with nontrivial electronic structure topology. Particularly significant progress in this field has happened within the last decade, due to the discovery of topologically nontrivial states of matter, that have a gap in their energy spectrum, namely Topological Insulators and Topological Superconductors. In this talk I will describe the most recent work, partly my own, extending the notions of the nontrivial electronic structure topology to gapless states of matter as well, namely to semimetals and even metals. I will discuss both the theoretical concepts, and the recent experimental work, realizing these novel states of condensed matter.

14 October 8AM (AEDT)  - 13 October 5PM (EDT)

Alex Hamiltonian (UNSW)

Interactions between spin and orbital momentum: The hole story

The electrical current in a semiconductor can be carried by negatively charged electrons or positively charged holes. Half of all the transistors in your iphone use holes, rather than electrons, to operate. In undergraduate physics, we are tell students that holes in the valence band are just an absence of an electron. But they aren’t. Valence band holes are spin-3/2 particles, and this gives them very different properties to spin-1/2 electrons. In recent years there has been growing interest in the possibility of using holes in semiconductor nanostructures for applications ranging from ultra-low energy electronics through to quantum information and communication. 

The differences between electron and holes are most striking when they are quantum confined, due to the interaction between orbital and spin angular momentum. Understanding and controlling this spin-orbit interaction is key to proposals for creating artificial topological insulators, and spin-quantum bits. Here I present new results for detecting spin-orbit interactions of holes in gallium arsenide quantum confined systems, and discuss their implications for other materials systems:

(i) A new method for detecting spin accumulation: The ability to generate and detect spin accumulation via spin-orbit interaction in non-magnetic devices is an important asset in semiconductor spintronics. We have developed a new method for detecting spin accumulation based on the concept of a spin filter, exploiting the non-linear interactions between spin accumulation and charge. Since our non-linear method does not need a magnetic field nor a long spin diffusion length, it promises new possibilities for fast detection of spin accumulation in strongly spin-orbit coupled materials with short spin diffusion lengths, such as TMDCs and topological materials [1]. 

(ii) A new signature of spin-gaps in 1D systems: One dimensional semiconductor systems with strong spin-orbit interaction are attracting great attention due to potential applications to topological quantum computing. Applying a magnetic field can open a spin gap, a pre-requisite for Majorana zero modes. The characteristic signature of this spin gap is dip in conductance when a magnetic field is applied. However, disorder and interaction effects make identifying spin gap signatures challenging. We demonstrate an alternative signature for probing spin gaps, which is insensitive to disorder, and extract a spin-orbit gap ~500 μeV for holes in gallium arsenide quantum point contacts. This approach could enable one-dimensional hole systems to be developed as a scalable and reproducible platform for topological quantum applications [2]. 

[1] A non-linear spin lter for non-magnetic materials at zero magnetic field, E. Marcellina, A. Srinivasan, F. Nichele, P. Stano, D.A. Ritchie, I. Farrer, D. Culcer, and A. R. Hamilton, PRB (in press), https://arxiv.org/abs/1907.01312

[2] New signatures of the spin gap in quantum point contacts, K. L. Hudson, A. Srinivasan, O. Goulko, J. Adam, Q. Wang, L.A. Yeoh, O. Klochan, I. Farrer, D. A. Ritchie, A. Ludwig, A.D. Wieck, J. von Delft and A. R. Hamilton, Nature Comms (in press).

23 Sep 10AM (AEST) and 8PM (EST) 

Vedika Khemani (Stanford University)

Many-body physics in the NISQ era: quantum programming a discrete time crystal

Given recent progress in the realm of noisy, intermediate scale quantum (NISQ) devices, we explore their implications for quantum many-body physics in a practical sense: we ask which physical phenomena in the realm of quantum statistical mechanics can these devices realize better than any other experimental platform. As a target, we identify discrete time crystals (DTCs),  novel out-of-equilibrium phases of matter that break time translation symmetry, and are realized in the intrinsically nonequilibrium setting of periodically driven quantum systems stabilized by disorder and many-body localization. While precursors of time-crystals have been observed across a variety of experimental platforms - ranging from trapped ions to nitrogen vacancy centers - each of these lacks one or more of the necessary ingredients for realizing a true incarnation of this phase, and detecting the long-range spatiotemporal order that is its defining feature. We show that a new generation of quantum simulators, such as Google's Sycamore processor, can be programmed to realize the DTC phase and to experimentally verify its dynamical properties using a wide range of observables and initial states.  We also discuss the effects of environmental decoherence, and show that already with existing technology one could observe the persistence of DTC spatiotemporal order over hundreds periods, with parametric improvements to come as the technology advances in the future. 

9 Sep 7AM (AEST) and 5PM  (EST)

Kris Helmerson (Monash University)

Evolution of large-scale flow from turbulence in a two-dimensional superfluid 

In two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices [1], in which the persistent large-scale vortices correspond to negative temperature states. We have confirmed Onsager's model in an experiment on a superfluid gas of atoms [2]. By dragging grid barriers, formed by an array of laser beams, through an oblate atomic gas Bose-Einstein condensate we generate non-equilibrium distributions of vortices. We subsequently use velocity-selective Bragg scattering and absorption imaging to identify the sign of the circulation and location of the vortices in order to determine the vortex distributions and resultant flow fields. We observe signatures of an inverse energy cascade, in the subsequent evolution of the superfluid, driven by the evaporative heating of vortices, leading to steady-state configurations of clustered vortices characterized by negative absolute temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven out of equilibrium.

[1] L. Onsager, Il Nuovo Cimento 6,. 279 (1949).

[2] S. P. Johnstone et al., Science, 364,, 12670 (2019)

26 Aug 10AM (AEST)  and 8PM (EST) 

Kin Fai Mak (Cornell University)

Simulating Hubbard model physics in semiconductor moiré superlattices

The Hubbard model, first formulated by physicist John Hubbard in the 1960s, is a simple theoretical model of interacting quantum particles in a lattice. The model is thought to capture the essential physics of high-temperature superconductors, magnetic insulators, and other complex emergent quantum many-body ground states. Although the Hubbard model is greatly simplified as a representation of most real materials, it has nevertheless proved difficult to solve accurately except in the one-dimensional case. Physical realizations of the Hubbard model in two or three dimensions, which can act as quantum simulators, therefore have a vital role to play in solving the strong-correlation puzzle. In this talk, I will discuss our recent efforts on simulating Hubbard model physics in semiconductor moiré superlattices. As a result of the strong Coulomb interactions, an abundance of correlated phases of matter, including the Mott insulating state, charge-ordered states, stripe phases and electronic liquid crystals, emerges. I will also discuss the magnetic phase diagram of the system and implications for future studies.