From Quantum Materials to Quantum Information: Symposium on Trans-Scale Quantum Science and Quantum Materials Synthesis (QMQI2024)

 

Registration fee
30,000 JPY

Application Deadline
For full consideration, please apply before July 17, 2024.   CLOSED

Final deadline for payment of registration fee [accepted participants only]
September 15th, 2024.   

Please apply for the symposium using the application form below.    A limited number of spaces are available, and accepted participants will be notified around the beginning of September.   Only accepted participants will need to complete payment of the registration fee.   

If you would like to give a contributed talk or a poster presentation, please provide detatils within the application form.

Application form link: Closed

 

Schedule

1. Application Deadline
For full consideration, please ensure that your application is submitted by July 17, 2024.  

2. Selection Process
After the application deadline, our team will carefully review all submitted applications. In the event that the number of applications exceeds the available spots, participants will be selected accordingly.

3. Notification of Acceptance
Once the application review is complete, we will notify all applicants about the status of their application, expected by the beginning of September. If you are accepted as a participant, you'll receive a link to pay the registration fee. Registration will start the beginning of September and close on September 30.

This is part of the workshop operating budget and a breakdown cannot be provided.

 

Invited speakers are listed below. We will also accept a limited number of contributed talks.

1. Francesco Buscemi (Nagoya University, Japan)
2. Jak Chakhalian (Rutgers University, USA)
3. Cui-Zu Chang (The Pennsylvania State University, USA)
4. Joseph Checkelsky (Massachusetts Institute of Technology, USA)
5. Sang-Wook Cheong (Rutgers University, USA)
6. Giulio Chiribella (The University of Hong Kong, Hong Kong)
7. David Elkouss (OIST, Japan)
8. Chang-Beom Eom (University of Wisconsin-Madison, USA)
9. Tomas Jungwirth (Institute of Physics of the Czech Academy of Sciences, Czechia)
10. Bella Lake (HZB, Germany)
11. Maxmilian Lock (IQOQI, Vienna)
12. David Mandrus (University of Tennessee, USA)
13. Emilia Morosan (Rice University, USA)
14. Masaya Nakagawa (The University of Tokyo, Japan)
15. Masaki Oshikawa (The University of Tokyo, Japan)
16. Stuart Parkin (Max Planck Institute of Microstructure Physics, Germany)
17. Frank Pollmann (TU Munich, Germany)
18. Sandu Popescu (University of Bristol, UK)
19. Ana Belen Sainz (Univeristy of Gdansk, Poland)
20. Leslie Schoop (Princeton University, USA)
21. Yoshinori Tokura (The University of Tokyo, Japan)
22. Jason Twamley (OIST, Japan)
23. Vilasini Venkatesh (Inria, Université Grenoble Alpes, France)
24. Mischa Woods (University of Grenoble Alpes, France)

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Program structure:

 Monday-11 November / SEASIDE HOUSE

8:30-8:50	Welcome coffee
8:50-9:00	Opening Remarks
9:00-9:40	Stuart Parkin　  Magnetic Tunnel and Josephson junctions using twisted van der Waals layers
9:40-10:20	Jak Chakhalian  Weyl fermions meet magnetic monopoles
10:20-10:50	Coffee Break
10:50-11:30	Emilia Moroson  Kramers Nodal Lines, Weyl Fermions and Large Anomalous Hall Effect in SmAlSi and InxTaS2
11:30-11:50	Kouta Kondou  Demonstration of current-driven fast magnetic octupole domain-wall motion in noncollinear antiferromagnets
11:50-12:30	Tomas Jungwirth  From superfluid He-3 to altermagnets
12:30-14:30	Lunch & Discussions
14:30-15:10	Sang-Wook Cheong(TBC)  Altermagnetism and Kinetomagnetism
15:10-15:30	Tomoya Higo  Current-induced perpendicular switching of non-collinear antiferromagnetic order
15:30-16:00	Coffee Break
16:00-16:20	Igor Herbut  SO(8) unification theory of interacting electrons in graphene
16:20-16:40	Han Yan  Designing Light in an Artificial Universe
16:40-17:00	Poster Preview (Asakura, Lu, Singhania, Yamada)
17:00-18:00	Poster Session 1
18:00-20:00	Dinner

 Tuesday-12 November / SEASIDE HOUSE

9:00-9:40	Joseph Chechelsky  Natural Superlattice Design of Modulated Superconductors
9:40-10:20	Cui-Zu Chang  Interface-Induced Superconductivity in Quantum Anomalous Hall Insulators
10:20-10:50	Coffee Break
10:50-11:30	Leslie Schoop  Which Material is worth Studying? (from the viewpoint of quantum materials)
11:30-11:50	Grigorii Skorupskii  Designing Giant Hall Response in Layered Topological Semimetals
11:50-12:30	Chang-Beom Eom  Synthesis of Electronic-Grade Quantum Heterostructures
12:30-14:30	Lunch & Discussions
14:30-15:10	David Mandrus  Complex Magnetic Phase Diagram in the Kagome Metal LuMn6Sn6
15:00-15:10	Sang-Wook Cheong  Announcement of next QMS symposium
15:10-15:30	Akito Sakai  Novel quantum many-body state in quadrupole Kondo lattice PrV2AI20|
15:30-16:00	Coffee Break
16:00-16:20	Margarita Drovnova  Evolution of spin glass state in pyrochlore-structured spinel oxide Zn(Fe,Ga)2O4
16:20-16:40	Daniel MacNally  Inside Nature Materials: An Editors Perspective
16:40-17:00	Poster Preview (Gauntam, Ji, Mine, Patil)
17:00-18:00	Poster Session 2
18:00-19:30	Dinner (BBQ) [Taxis to hotels available from 19:30]

 Wednesday-13 November / B250 (Center Building)

8:50-9:00	Introduction
9:00-9:40	Yoshi Tokura  Dynamic transition and Galilean relativity of current-driven skyrmions
9:40-10:20	Frank Pollmann  Exploring the dynamics of quantum phases of matter on quantum processors
10:20-10:50	Coffee Break [Group Photo]
10:50-11:30	Bella Lake  Investigating quantum states in spin chain materials
11:30-11:50	Tokuro Shimokawa  Can experimentally-accessible measures of entanglement distinguish quantum spin liquid and random singlet states?
11:50-12:30	Masaki Oshikawa  Measurement-induced entanglement between quantum spin chains
12:30-13:30	Lunch
13:30-14:30	Campus Tour
14:30-18:30	Excursion (Nakajin Castle, Churaumi Aquarium)
18:30-20:30	Banquet at the main tank of Churaumi Aquarium

 Thursday-14 November / SEASIDE HOUSE

9:00-9:40	Guilio Chiribella  Energy and nonequilibrium requirements of quantum information processing
9:40-10:20	Vilasini Venkatesh  Quantum circuits for Wigner’s Friends: consistent logical and causal reasoning without absolute measurement events
10:20-10:50	Coffee Break
10:50-11:10	Matthias Salzger  A decompositional framework for process theories in spacetime
11:10-11:30	Philip Taranto  Characterising the Hierarchy of Multi-time Quantum Processes with Classical Memory
11:30-12:10	Ana Belen Sainz  Activation of post-quantum steering
12:10-12:30	John Selby  Generalised contextuality as a necessary resource for universal quantum computation
12:30-14:30	Lunch & Discussions
14:30-15:10	Masaya Nakagawa  Topological Maxwell's demon
15:10-15:30	Stefan Eccles  Why ETH?
15:30-16:00	Coffee Break
16:00-16:40	David Elkouss  Towards implementing useful quantum network applications
16:40-17:00	Poster Preview (Hokkyo, Sabharwal, Raj)
17:00-18:00	Poster Session 3
18:00-19:30	Dinner [Taxis to hotels available from 19:30]

Friday-15 November / SEASIDE HOUSE

9:00-9:40	Sandu Popescu  TBA
9:40-10:20	Francesco Buscemi  Observing Microscopic Systems on a Macroscopic Scale: from Quantum Bayes' Rule to the Second Law
10:20-10:50	Coffee Break
10:50-11:10	Zane Rossi  Parallel Quantum Signal Processing via Polynomial Factorization
11:10-11:30	Yunlong Xiao  Quantum Uncertainty Principles for Measurements with Interventions
11:30-12:10	Maxiliam Lock  Emergence of a second law of thermodynamics in isolated quantum systems
12:10-12:30	Koji Inui  Inverse Hamiltonian design of highly-entangled systems
12:30-14:30	Lunch & Discussions
14:30-15:10	Mischa Woods  Quantum Frequential Computing: a quadratic runtime advantage for all Computation
15:10-15:30	Michele Dall'Arno  Bayesian inference of quantum devices
15:30-16:00	Coffee Break
16:00-16:40	Jason Twamley  Towards macroscopic quantum superpositions using magnetically levitated systems: exploring the links between gravity and quantum and thermodynamics
16:40-17:00	Poster Preview (Fukushima, Matsui, Niwa)
17:00-18:00	Poster Session 4
18:00-19:30	Dinner (BBQ) [Taxis to hotels available from 19:30]

 

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Venue
Primary venue (Mon/Tue/Thu/Fri): OIST Seaside House (7542 Onna, Onna-son, Kunigami-gun, Okinawa, Japan)

Secondary venue (Wed): Conference Room B250, Center Building, OIST Main Campus (1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa, Japan 904-0495)

Airport
Access to Okinawa s will arrive at the Naha airport in Okinawa.

Access to Seaside House
by Taxi
by Bus
Between OIST main Campus and Seaside House

It is possible to reach Seaside House or The Peridot Smart Hotel Tancha Ward using local bus #120 from Naha airport. 

 

On-Campus Accommodation [shared]
Guest Rooms at Seaside House

22 twin rooms, for two people to share, are available in Seaside House.   The use of these rooms is restricted to  participants in the symposium.   However, rooms will be provided free of charge to students and other participants who need support for accomodation.   Please request accomodation in Seaside House through the Application Form.

Off-Campus Accommodations

THE PERIDOT Smart Hotel Tancha Ward

A block of rooms have been reserved in the Peridot Smart Hotel.    These are available on a first-come-first served basis at a discounted rate of JPY 13,200 per night.   (Additional charges will appy for particpants traveling family).   Transport to the workshop will be provided.  Please request accomodation in Peridot Smart Hotel through the Application Form.

Rizzan Sea Park Hotel Tancha Bay

Participants wishing to stay in the Rizzan Sea Park Hotel should make their own booking directly from the hotel, or through an online booking website such as Agoda, Booking.com or Expedia.  Please request accomodation in Peridot Smart Hotel through the Application Form.

Transport will be provided between the Rizzan Sea Park Hotel and Seaside House, at the start and finish of each day of the program.    Participants who choose to stay in other hotels will be  responsible for making their own transport arrangements to Seaside House.

 

 Hotel and Travel Agency Scammers

Workshop organizers and invited speakers are often contacted by number of "travel agencies" to which OIST is not related, based on the publicly available information on the web. Please refrain from replying to those agencies unless OIST organizers or secretariat have explicitly contacted you beforehand. When in doubt, please send a copy of any email communication to the OIST Conference and Workshop Section: workshop@oist.jp

 

Sponsors

 

Contact & FAQ

Secretariat

• Email: QMQI2024 [at] oist.jp
• Mail: 1919-1 Tancha, Onna-son, Okinawa 904-0495 JAPAN

 

contributed talks below

Invited talks

 

Francesco Buscemi

Observing Microscopic Systems on a Macroscopic Scale: from Quantum Bayes' Rule to the Second Law

 

Jak Chakhalian

Weyl fermions meet magnetic monopoles

Magnetic Weyl semimetals represent an exciting class of materials whose properties are defined by the presence of Weyl nodes - special points in the band structure where bands intersect, each carrying a chiral topological charge. This unique feature gives rise to various intriguing phenomena, including the chiral anomaly and Fermi arcs observable on the material's surface or interface. The introduction of magnetism to these systems further enriches their behavior, leading to phenomena with chirality naturally entwined into their response. At the same time, spin ice is a frustrated magnetic system where spins obey the so-called "ice rules" with two-in/two-out spin configurations per tetrahedron. This motif creates a highly degenerate ground state with no long- range order and emergent electrodynamics, such as excitations resembling magnetic monopoles. In this talk, we will explore new approaches to addressing pivotal challenges in the subfield: (1) the development of new synthetic templates with complex many-body interactions inspired by magnetic rare-earth pyrochlore iridates and spin-ice pyrochlore titanates, and (2) the discovery of exotic states and phenomena arising from the Kondo coupled magnetic states of spin ice with Weyl fermions. This includes a possible realization of the quantum electronic nematic state. We will focus on the experimental feasibility of validating these exotic states within a novel class of oriented heterostructures with highly frustrated Kagome interfaces.

Cui-Zu Chang

Interface-Induced Superconductivity in Quantum Anomalous Hall Insulators

When two different electronic materials are brought together, the resultant interface often shows unexpected quantum phenomena, including interfacial superconductivity and Fu-Kane topological superconductivity (TSC). In this talk, I will first briefly talk about our recent progress on the quantum anomalous Hall (QAH) effect in magnetic topological insulator (TI) multilayers. Next, I will focus on our recent discovery of interfacial superconductivity in QAH/iron chalcogenide heterostructures. We employed molecular beam epitaxy (MBE) to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic TI with the QAH state and an antiferromagnetic iron chalcogenide (FeTe). We discovered emergent interface-induced superconductivity in these heterostructures and demonstrated the trifecta occurrence of superconductivity, ferromagnetism, and topological band structure in the QAH layer, the three essential ingredients of chiral TSC. The unusual coexistence of ferromagnetism and superconductivity can be attributed to the high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. The QAH/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics, constituting an important step toward scalable topological quantum computation.

Guilio Chiribella

Energy and nonequilibrium requirements of quantum information processing

Quantum computing and other quantum technologies require an accurate processing of information at the quantum scale. At the fundamental, accurate quantum information processing requires physical resources, such as clean qubits in states that deviate from the thermal equilibrium state. When quantum information is encoded into quantum systems with nontrivial energy spectrum, accurate processing also requires a supply of energy and quantum coherence across different energy levels. In this talk I will present two results on the intrinsic resource requirements of quantum information processing. The first is a direct link between information processing tasks and the amount of nonequilibrium resources required to implement them. The second is a quantification of the initial amount of energy that has to be provided in order to execute a desired quantum computation, and provides the quantum analogue of a classic result by Fredkin and Toffoli on reversible classical computing.

Joseph Chechelsky

Natural Superlattice Design of Modulated Superconductors

Connecting theoretical models for exotic quantum states to real materials is a key goal in quantum materials synthesis. Two-dimensional model systems have been proposed to host a wide variety of exotic phases- historically a number of techniques have been used to realize these including thin film growth and mechanical exfoliation. We describe here our recent progress in experimentally realizing 2D model systems using bulk crystal synthesis including modulated superconducting states. We discuss their structures and the new phenomena that they support. We comment on the perspective for realizing further 2D model systems in complex material structures and their connections to other methods for realizing 2D systems.

Sang-Wook Cheong

Altermagnetism and Kinetomagnetism
 

David Elkouss

Towards implementing useful quantum network applications

Very recently we have seen the first proof of principle demonstrations of entanglement-based quantum networks. However, analogous to quantum computers, near-term quantum networks will feature noisy devices communicating at modest rates. Here, I will present some recent ideas for performing communication and computation applications with near-term quantum networks. Finally, I will discuss the potential of quantum networks for performing quantum cryptographic applications beyond quantum key distribution.

Chang-Beom Eom

Synthesis of Electronic-Grade Quantum Heterostructures

Modern quantum materials are inherently sensitive to point defects, and require a new synthesis route to produce epitaxial oxide thin films and interfaces clean enough to probe fundamental quantum phenomena. The recent discovery of robust superconductivity at KTaO3 (111) and KTaO3 (110) heterointerfaces on KaTaO3 bulk single crystals offers new insights into the role of incipient ferroelectricity and strong spin-orbit coupling. Electronic grade epitaxial thin film platforms will facilitate investigation and control of the interfacial superconductivity and understanding the fundamental mechanisms of the superconductivity in KTaO3. The major challenge of research on KTaO3 system is that it is difficult to grow high-quality KTaO3 epitaxial thin films due to potassium volatility. Recently, we have developed the hybrid PLD method for electronic grade KTaO3 thin film growth, which successfully achieves this by taking advantage of the unique capabilities of PLD to instantly evaporate Ta2O5 in a controlled manner and evaporation of K2O to maintain sufficient overpressure of volatile species. We successfully synthesized heteroepitaxial KTaO3 thin films on 111-oriented KTaO3 bulk single crystal substrates with a SmScO3 template by hybrid PLD, followed by a LaAlO3 overlayer. Electrical transport data show a superconducting transition temperature of ~ 1.35K. We anticipate that the ability to synthesize high-quality epitaxial complex oxides such as KTaO3 that contain volatile elements will provide a new platform for exploring new physics and technological applications arising from unique characteristics such as large spin-orbit coupling. This works has been done in collaboration with Jieun Kim, Jungwoo Lee, Muqing Yu, Neil Campbell, Shun-Li Shang, Jinsol Seo, Zhipeng Wang, Sangho Oh, Zi-Kui Liu, Mark S. Rzchowski, Jeremy Levy.

Tomas Jungwirth

From superfluid He-3 to altermagnets

The Pauli exclusion principle combined with interactions between fermions is a unifying basic mechanism that can give rise to quantum phases with spin order in diverse physical systems. Transition-metal ferromagnets, with isotropic ordering respecting crystallographic rotation symmetries and with a net magnetization, are a relatively common manifestation of this mechanism, leading to numerous practical applications, e.g., in spintronic information technologies. In contrast, superfluid 3He has been a unique and fragile manifestation, in which the spin-ordered phase is anisotropic, breaking the real-space rotation symmetries, and has vanishing net magnetization. The recently discovered altermagnets share the spin-ordered anisotropic vanishing-magnetization nature of superfluid 3He. Yet, altermagnets appear to be even more abundant than ferromagnets, can be robust, and are projected to offer superior scalability for spintronics compared to ferromagnets. The talk revisits the decades of research of the spin-ordered anisotropic phases with vanishing net magnetization including, besides superfluid 3He, also theoretically conceived Pomeranchuk instabilities of Fermi liquids [1,2]. While all sharing the same extraordinary character of symmetry breaking, we highlight the distinctions in microscopic physics which set altermagnets apart and enable their robust and abundant material realizations. We show coordinate-space and momentum-space microscopies, experimentally demonstrating and exploring the altermagnetic ordering in MnTe [3,4]. References [1] L. Smejkal, J. Sinova, T. Jungwirth, Physical Review X (Perspective) 12, 040501(2022). [2] T. Jungwirth, R. M. Fernandes, E. Fradkin, A. H. MacDonald, J. Sinova, L. Smejkal, (Perspective) arXiv:2411.00717 [3] O. J. Amin et al., Nature in press, arXiv:2405.02409. [4] J. Krempasky et al., Nature 626, 517 (2024).

Bella Lake

Investigating quantum states in spin chain materials

The antiferromagnetic spin-1/2 spin chain with Heisenberg-Ising (XXZ) anisotropy is a rich source of novel phenomena. Good physical realizations are the compounds SrCo2V2O8 and BaCo2V2O8 where the Co2+ ions have effective spin-1/2 and are coupled by antiferromagnetic interactions into chains while collinear long-range magnetic order occurs below TN ~ 5 K due to weak interchain coupling. In a longitudinal magnetic field applied along the easy axis, the magnetic order is suppressed and using inelastic neutron scattering and optical spectroscopy we find the evidence for complex bound states of magnetic excitations, known as Bethe strings. Furthermore, the characteristic energy, scattering intensity and linewidth of the observed string states exhibit excellent agreement with precise Bethe ansatz calculations. Our results confirm the existence of the long-sought Bethe string excitations predicted almost a century ago. Application of transverse magnetic field along the direction perpendicular to the easy axis induces a quantum phase transition where the antiferromagnetic order is destroyed at a three-dimensional quantum critical point. The evolution of the excitations is investigated as a function of field revealing a complex series of modes and continuua. At a particular field still within the antiferromagnetically ordered phase we find a sequence of excitations whose energies match the lightest three E8 particles corresponding to the maximal exceptional Lie E8 algebra.

Maxiliam Lock

Emergence of a second law of thermodynamics in isolated quantum systems

The second law of thermodynamics states that the entropy of an isolated system can only increase over time. This appears to conflict with the reversible evolution of isolated quantum systems under the Schrödinger equation, which preserves the von Neumann entropy. Nonetheless, one finds that the expectation values of many observables approach a fixed value -- their equilibrium value. This ultimately raises the question: in what sense does the entropy of an isolated quantum system increase over time? For classical systems, one introduces the assumption of a low entropy initial state along with the concept of ignorance about the microscopic details of the physical system, leading to a statistical interpretation of the second law. By considering the observables through which we examine quantum systems, both these assumptions can be incorporated, building upon recent studies of the equilibration on average of observables. While the statistical behaviour of observable expectation values is well-established, a quantitative connection to entropy increase has been lacking so far. In deriving novel bounds for the equilibration of observables, and considering the entropy of the system relative to observables, we recover a variant of the second law: the entropy with respect to a given observable tends towards its equilibrium value in the course of the system's unitary evolution. These results also support recent findings which question the necessity of non-integrability for equilibration in quantum systems. We further illustrate our bounds using numerical results from the paradigmatic example of a quantum Ising model on a chain of spins. There, we observe entropy increasing up to equilibrium values, as well as fluctuations which expose the underlying reversible evolution in accordance with the derived bounds.

David Mandrus

Complex Magnetic Phase Diagram in the Kagome Metal LuMn6Sn6

 

Emilia Morosan

Kramers Nodal Lines, Weyl Fermions and Large Anomalous Hall Effect in SmAlSi and InxTaS2

Kramers nodal lines (KNLs) are a special type of Weyl line degeneracies that connect time reversal invariant momenta (TRIM). KNLs are robust to spin orbit coupling (SOC), and are inherent to all non-centrosymmetric achiral crystal structures. In this talk, I will present magneto-transport and ARPES experimental data together with DFT calculations, pointing to the existence of novel KNLs in SmAlSi. SmAlSi develops an incommensurate spin density wave order at low temperatures. I will show evidence for the symmetry-protected KNLs, as well as Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. In the AFM state, angle-dependent quantum oscillations (AQOs) provide evidence for the Weyl points, while large AHE is observed in both the AFM and the PM states. We propose a new mechanism to explain AHE in non-FM materials, based on magnetic field-induced Weyl-nodes evolution in non-centrosymmetric Weyl semimetals. I will then contrast the properties of SmAlSi with those of the intercalated transition metal dichalcogenides InxTaS2 (ITS). The ITS compounds showcase the cleanest FS with a single KNL crossing the Fermi level, and also feature superconducting ground states below Tc between 0.6 K and 2.5 K (when x = 1/2, 2/3 or 1). Our AQOs and ARPES data on InTaS2 point to the existence of pinch points enforced by KNL, reminiscent of 2D massless Dirac fermions on the surface of 3D topological insulators. So when the pinch points with (2n+1) (n = integer) Berry curvature are gapped by superconductivity, they are expected to produce nontrivial vortex spectra hosting chiral Majorana zero modes.

Masaya Nakagawa

Topological Maxwell's demon

Topology has played a pivotal role in quantum material science since the discovery of topological phases of matter. Here, topology is intimately related to robust properties of materials that are insensitive to local perturbations such as disorder. Meanwhile, Maxwell's demon has been a long-standing problem in statistical physics, and its in-depth understanding has culminated in the development of a research area that integrates thermodynamics with information theory. In this presentation, we propose a novel platform of topological phases that utilizes Maxwell's demon [1]. In particular, we construct a topological Maxwell's demon that achieves unidirectional charge transport robust against disorder, noise, and decoherence. We also provide a general theory of topological Maxwell's demons, which provides a guiding principle for topology-based design of quantum feedback control. [1] Masaya Nakagawa and Masahito Ueda, arXiv:2403.08406.

Masaki Oshikawa

Measurement-induced entanglement between quantum spin chains

We discuss the entanglement between two critical spin chains induced by the Bell-state measurements, when each chain was independently in the ground state before the measurement. This corresponds to a many-body version of “entanglement swapping”. We employ a boundary conformal field theory (CFT) approach and describe the measurements as conformal boundary conditions in the replicated field theory. We show that the swapped entanglement exhibits a logarithmic scaling, whose coefficient takes a universal value determined by the scaling dimension of the boundary condition changing operator. We apply our framework to the critical spin-1/2 XXZ chain and determine the universal coefficient by the boundary CFT analysis, which is verified by a numerical calculation.

Stuart Parkin

Magnetic Tunnel and Josephson junctions using twisted van der Waals layers

Tunnel junctions are essential for spintronic and superconducting devices for memory and logic applications. We discuss some of our recent work on magnetic tunnel junctions (MTJs) and Josephson junctions (JJs) formed using 2D van der Waals (vdw) materials. In particular, the properties of conventional nano-scale MTJs using ferromagnetic or ferrimagnetic electrodes are dominated by magnetostatic fields that must be eliminated. This is possible using the concept of a synthetic antiferromagnet (SAF) [1, 2]. Recently we have demonstrated how a bilayer of the van der Waals antiferromagnetic CrSBr acts just like a SAF in tunnel junctions formed from two “natural” SAFs. Whilst individual CrSBr layers are ferromagnetic with a strong in-plane magnetic anisotropy, these layers are coupled antiferromagnetically so that a bilayer acts just like a SAF. By twisting two bilayers we show that the natural antiferromagnetic coupling between these layers becomes very small, thereby allowing for an all antiferromagnetic tunnel junction that exhibits two non-volatile states in zero magnetic field [3]. We show from theoretical modelling that the origin of the tunnelling magnetoresistance is via the accumulated k-dependent transmission through the individual semiconducting CrSrBr layers which depends on the twist angle [3]. The recent discovery of a Josephson Diode effect (JDE) gives a major impetus to superconducting logic. We have observed a JDE in JJs formed from several 2D van der Waals layer, including NiTe2 [4], PtTe2 [5] and WTe2 [6]. An important question is the origin of the JDE and when it is intrinsic and when extrinsic. Vertical Josephson junctions formed from WTe2 show a JDE with a large non-reciprocity in the critical supercurrent when a small magnetic field is applied perpendicular to the supercurrent within the plane of the WTe2 flake. The diode effect strongly depends on the orientation of the magnetic field within the plane of the WTe2 with respect to the crystal structure of the WTe2 [6]. These results clearly indicate that the JDE in these devices has an intrinsic origin. JJs with twisted WTe2 layers further support this conclusion [6]. Such an effect could have important applications as a novel magnetic field detector at cryogenic temperatures, for example, to “read” magnetic domain walls in a cryogenic racetrack memory [7]* . * Funded through an European Research Council Advanced Grant “SUPERMINT” (2022-2027).

Frank Pollmann

Exploring the dynamics of quantum phases of matter on quantum processors

The interplay of quantum fluctuations and interactions can yield to novel quantum phases of matter with fascinating properties. Understanding the physics of such system is a very challenging problem as it requires to solve quantum many body problems—which is generically exponentially hard on classical computers. In this context, universal quantum computers are potentially an ideal setting for simulating the emergent quantum many-body physics. Here we discuss applications to the study the dynamics of topologically ordered systems: We first prepare the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measure a topological entanglement entropy near the expected value of ln(2) and detect anyonic statistics of the fractionalised excitations. We then introduce a magnetic field and study the dynamics of the confinement transition.

Sandu Popescu

TBA

 

Ana Belen Sainz

Activation of post-quantum steering

In this talk we will discuss the phenomenon of Einstein, Podolsky, and Rosen (EPR) steering, and its relation to Bell nonclassicality. We will focus on the so-called non-signalling resources (those that could in principle be achieved in non-signalling theories) in both Bell and EPR experiments, in particular those which cannot be realised with a quantum setup (called post-quantum). Previous work shows how EPR scenarios allow for postquantum resources which, from the viewpoint of the associated Bell scenario, generate only correlations compatible with quantum theory. In this talk we will see how one can activate the post-quantumness of such EPR resources by placing them in a larger Bell-like network, so that the observed correlations may violate a Bell inequality beyond what's possible in a quantum experiment. That is, we will show how to activate post-quantum steering so that it can now be witnessed as post-quantum correlations in a Bell scenario. This talk is based on the preprint arXiv:2406.10570.

Leslie Schoop

Which Material is worth Studying? (from the viewpoint of quantum materials)

Quantum materials are hoped to change technology in various aspects. However, most of the desired applications are hindered by the lack of suitable materials. While we know tens of thousands of crystalline organic compounds, we studied only a tiny fraction of those for their potential as quantum materials. As synthesis of such materials, especially in single crystal form, can be challenging, a brute force experimental study of all know crystalline inorganic compounds is not feasible. In my group, we are developing simple concepts that guide to find those materials worth growing and studying. We are using concepts from chemistry to understand, predict and synthesize new quantum materials. In this talk, I will show how simple concepts derived from the theory of chemical bonding allow us to make predictions about electronic structures of materials, which we can then use to find new topological materials. We then can combine this with structural building blocks containing magnetic elements to design materials with non-colinear or even non-coplanar magnetism. Thinking about the degree of delocalization in a chemical bond can be helpful to find kagome or linear-chain materials with band structures that better resemble simple tight binding models. I will give a general overview how powerful chemical concepts are in materials discovery and highlight a flute of materials that were discovered in this light.

Yoshinori Tokura

Dynamic transition and Galilean relativity of current-driven skyrmions

The coupling of conduction electrons and magnetic textures leads to quantum transport phenomena described by emergent electromagnetic fields. For magnetic skyrmions (spin-swirling particle-like objects), an emergent magnetic field is produced by their topological structure (quantized scalar spin chirality), re-sulting in the conduction electrons exhibiting the topological Hall effect (THE). When the skyrmion lattice (SkL) acquires a drift velocity under the flow of conduction electrons, an emergent electric field is also generated. The resulting emergent electrodynamics dictate the magnitude of the THE by the relative motion of the SkL and conduction electrons. Here, we report the emergent electromagnetic phenomena induced by SkL motion in a centrosymmetric (achiral) crystal of Gd2PdSi3. With increasing current excitation, we observe the dynamic transition of the SkL motion from the pinned state to the creep state, and finally to the flow state, in which the THE is completely suppressed. We argue that the Galilean relativity required for the total can-cellation of the THE may not be generally obvious in complex multiband systems like the present compound, but it may be generally recovered in the flow state. Furthermore, the observed THE voltages are large enough to enable real-time measurement of the SkL velocity-current profile, showing the inertial-like motion of the SkL in the creep state, appearing as the current hysteresis of the skyrmion velocity. We discuss the possibility of emergent electromagnetic induction arising from the dynamics of nano-magnetic structures induced by current excitation.

Jason Twamley

Towards macroscopic quantum superpositions using magnetically levitated systems: exploring the links between gravity and quantum and thermodynamics
 

Vilasini Venkatesh

Quantum circuits for Wigner’s Friends: consistent logical and causal reasoning without absolute measurement events

Observers in quantum theory are typically treated classically, but Extended Wigner’s Friend Scenarios (EWFS) go beyond by modeling agents as unitarily evolving quantum systems. This has led to no-go arguments suggesting significant implications for logic, causality, and events. In particular, Frauchiger and Renner argue that quantum agents reasoning about each others’ knowledge can arrive at logical contradictions, while the Local-Friendliness theorem highlights a failure of absoluteness of observed measurement events in EWFS (under certain meta-physical assumptions) which poses challenges for causality. This raises a crucial question: Can we reliably make scientific predictions and reason consistently about the world when applying quantum theory universally, without assuming absolute measurement outcomes or violating causality? We provide a positive answer by developing a generalised quantum circuit framework for EWFS that enables quantum agents to make consistent predictions and scientifically reason within a well-defined causal structure. By mapping Heisenberg cuts to distinct quantum channels, our framework resolves all Frauchiger-Renner-type paradoxes in quantum theory and ensures that fundamentally different and relational perspectives in an EWFS are consistently captured in a single quantum circuit without altering the principles of unitary quantum theory, the Born rule or classical logic. Furthermore, although our framework can consistently account for non-absolute events, we also demonstrate that an objective notion of measurement events emerges in real-world experiments where agents do not perform general quantum operations on each others’ memories. This offers a unified approach to overcoming logical and causal challenges in EWFS without assuming absolute measurement events, and a concrete formalism to understand the emergence of objectivity and inter-agent agreement.

Mischa Woods

Quantum Frequential Computing: a quadratic runtime advantage for all Computation


 

Contributed talks

Michele Dall'Arno

Bayesian inference of quantum devices

We consider the scenario in which a black box with buttons and light bulbs is given so that, if any button is pressed a certain number of times, the corresponding probability distribution on the light bulbs lighting up can be observed. We model the black box as a prepare-and-measure setup, that is, an unspecified state is prepared upon the pressure of any button, and an unspecified measurement is performed on such a state. We consider the problem of the Bayesian inference of, say, the measurement (but, of course, we could consider the dual problem of inferring the states), that is, we aim at finding the measurement that maximizes the Bayesian posterior probability density, given the observations, for any given prior probability density on states and measurements.Our main result is to characterize such optimal measurements in the informationally complete (IC) case when uniform probability densities (i.e. maximal ignorance) are assumed on states and measure-ments, as it is natural in the first iteration of the Bayesian inference. In particular, we prove that any measurement that produces the observations upon the input of a 2-design set of states is optimal, thus settling in closed-form the case of non-overcomplete measurements, for which the only 2-design is the symmetric, informationally complete (SIC) set of states. Being data-driven, the inferential setup we consider offers a solution to the chicken-or-egg problem of usual quantum tomography, that is, the fact that the tomography of a measurement requires the knowledge of the input states, whereas the tomography of the states requires the knowledge of the measurement, in a neverending loop.

Margarita Drovnova

Evolution of spin glass state in pyrochlore-structured spinel oxide Zn(Fe,Ga)2O4

Spin glass state is of great interest due to its spin dynamics and frustration, potentially illustrating fundamental roles of both in connection to spin liquid states. Theoretical treatises of spin glass are centralized around Edwards-Anderson’s replica theory and Parisi’s replica symmetry breaking, which have provided a hierarchical framework to understand the free energy landscape [1]. However, while the replica theory provides a mathematical framework of idealized spin glass, real systems in general do not conform to this picture. It is unclear how they, with microscopic differences such as metal or insulator, RKKY or FM/AF type of super-exchange interaction, long- or short-range natures of the interaction, and Ising or Heisenberg spins, are compared to the ideal situation. It is believed disorder and frustration are two attributes of spin glasses, but it remains unclear whether there are different types of spin glasses, or to what level ideal spin glasses would be inert to microscopic differences [1]. In addition, similarly to the spin liquid state, the unique signatures of the disordered spin state have not been explained and clearly identified experimentally. Here we discuss how B-site diluted ZnFe2O4 spinel can serve as an ideal model system to reveal bona fide experimental signatures of spin glasses. For pure ZnFe2O4 in the clean limit, Fe3+ spins are S=5/2 classic Heisenberg spins located on a pyrochlore sublattice and order antiferro-magnetically in a three-dimensional checkerboard pattern [2, 3]. As Fe3+ are replaced by non-magnetic Ga3+ ions, similar in size within 5%, on the B-site, the long-range order is turned into short range order and characteristics of spin glass states emerge. Doping of Ga3+ generates a spin glass that is based on antiferromagnetic insulator, with short-range exchange interaction, and well above the site percolation limit, all different from canonical spin glass states in dilute, RKKY-interaction dominated metallic alloys. Our growth technique cleanly removes the inversion disorder (Fe3+ occupying the A-site) and only introduces randomness in the B-site occupancy between Fe3+ and Ga3+ ions. With our fine control of disorder, we demonstrate that a dramatical contrast in correlated spin behavior exists between 5 and 11% of Fe replacement. Using heat capacity, AC magnetic susceptibility, and neutron diffuse scattering, we explore this contrast in spin glass in three different time regimes. Our combined macroscopic and microscopic probes reveal a strong connection between the low-energy excitation and the spatial range of spin order. [1] K. Binder, A. P. Young, Rev. Mod. Phys. 58, 801 (1986). [2] M.G. Dronova et al. PNAS 119, e2208748119 (2022). [3] M.G. Dronova et al. Phys, Rev. B 109, 064421 (2024).

Stefan Eccles

Why ETH?

The eigenstate thermalization hypothesis (ETH) provides the prevailing framework for understanding thermalization in closed quantum systems. An informal expectation is that many “simple” and “local” observables in chaotic systems take the ETH form, and therefore thermalize. However, a complete understanding of which observables and in which systems the ETH form obtains is lacking. I will present a framework for addressing this question in finite systems based on the spectral properties of observables, and a corresponding Hamiltonian decomposition and perturbation problem.

Igor Herbut

SO(8) unification theory of interacting electrons in graphene

It is well known that electrons on honeycomb or pi-flux lattices obey effective massless Dirac equation at low energies and at the neutrality point and suffer quantum phase transitions into various Mott insulators and superconductors at strong two-body interactions. We show that 35 out of 36 such order parameters that provide Lorentz-invariant mass-gaps to Dirac fermions can be organized into a single irreducible tensor representation of the underlying SO(8) symmetry of the two-dimensional Dirac Hamiltonian for the spin-1/2 lattice fermions. The minimal interacting Lagrangian away from the neutrality point has the SO(8) symmetry reduced to U(1)×SU(4) by finite chemical potential, and it contains two independent interaction terms. When the Lagrangian is nearly SO(8)-symmetric and the ground state insulating at the neutrality point we show it turns superconducting at the critical value of the chemical potential through a ``flop" between the tensor components. The theory is exactly solvable in the limit of large number of fermions. A lattice Hamiltonian that should exhibit this transition and the consequences for the celebrated Gross-Neveu model will be discussed, time permitting.

Tomoya Higo

Current-induced perpendicular switching of non-collinear antiferromagnetic order

There has been a surge of interest in antiferromagnetic (AF) materials due to their favorable properties for device applications, including a vanishingly small stray field and faster spin dynamics than their ferromagnetic counterparts. These interesting properties have inspired the development of materials under various concepts, such as topological electronic structures, non-collinear magnetism, and altermagnetism [1]. The non-collinear antiferromagnet (AFM) Mn3Sn [2], a prominent example of time-reversal symmetry-breaking AFMs, is a magnetic Weyl semimetal possessing a large and controllable Berry curvature in the momentum space due to its unique magnetic and electronic structures. Recently, several methods have been found to electrically manipulate the non-collinear AF order and Berry-curvature-induced responses [3]. However, the antiferromagnetic domains could be partially switched, and thus, a more efficient switching mechanism was required. In this study [4], we prepare epitaxial heterostructures of a heavy-metal/Mn3Sn bilayer on MgO substrates by molecular beam epitaxy (MBE). The sample exhibits a sizable Hall conductivity of σH ~ 40 Ω-1cm-1 at room temperature, reaching the largest reported signal in the Mn3Sn bulk single crystals [2]. The current-induced switching experiments demonstrate the full (100%) switching of the non-collinear AF domain, and AHE signals with a relatively small write current of 14 MA/cm2. We find epitaxial tensile strain in the Mn3Sn layer causes the perpendicular magnetic anisotropy (PMA) [5] and enables the full electrical switching of the domains of the perpendicularly oriented magnetic order parameter in the AF order. Given the high reliability and efficiency of the perpendicular and full SOT switching, our realization of low-power switching using PMA and their efficient coupling to spin current forms a significant basis for further development of AF spintronics. [1] Jungwirth et al., Nat. Nano. 11, 231 (2016); Baltz et al., RMP 90, 015005 (2018); Nakatsuji & Arita, Annu. Rev. Condens. Matter. 13, 119 (2022); Šmejkal et al., PRX 12, 040501 (2022). [2] Nakatsuji, Kiyohara, & Higo, Nature 527, 212 (2015); Kuroda+, Tomita+ et al., Nat. Mater. 16, 1090 (2017). [3] Tsai+, Higo+ et al., Nature 580, 608 (2020); Takeuchi et al., Nat. Mater. 20, 1364 (2021).

Koji Inui

Inverse Hamiltonian design of highly-entangled systems

Solving inverse problems to identify Hamiltonians with desired properties holds promise for the discovery of fundamental principles. In quantum systems, quantum entanglement plays a pivotal role in not only characterizing the quantum nature but also developing quantum technology like quantum computing. Nonetheless, the design principles of the quantum entanglement are yet to be clarified. Here we apply an inverse design framework using automatic differentiation to quantum spin systems, aiming to construct Hamiltonians with large quantum entanglement. We show that the method automatically finds the Kitaev model with bond-dependent anisotropic interactions, whose ground state is a quantum spin liquid, on both honeycomb and square-octagon lattices. On triangular and maple-leaf lattices with geometrical frustration, it generates numerous solutions with spatially inhomogeneous interactions rather than converging to a specific model, but it still helps to construct unprecedented models. The comparative study reveals that bond-dependent anisotropic interactions, rather than isotropic Heisenberg interactions, amplify quantum entanglement, even in systems with geometrical frustration. The present study paves the way for the automatic design of new quantum systems with desired quantum nature and functionality. https://arxiv.org/abs/2402.15802

Kouta Kondou

Demonstration of current-driven fast magnetic octupole domain-wall motion in noncollinear antiferromagnets

Antiferromagnets have the natural advantages of ultrafast magnetization dynamics and negligible stray fields compared with ferromagnets, thus appealing for next-generation spintronics devices with ultrafast operations. However, even the fundamental study of the magnetization dynamics in antiferromagnets has been challenging because of their insensitive magneto-electric responses. Recently, remarkable progress has been reported that antiferromagnets enabled us to detect and manipulate their antiferromagnetic domain states by utilizing the noncollinear spin structure in Mn3X (X = Sn, Ge) [1-7]. Here, we focused on current-driven magnetic domain wall motion which is one of the crucial topics in the spintronics field. Then, we show a first observation of current-driven fast domain-wall motion with a low current density in single crystal Mn3X wires [8]. It implies extremely high mobility compared with typical ferromagnets, an an important character for ultrafast operation devices. Interestingly we found the strong dependence of domain wall structure for the propagation speed. To understand such novel current-induced spin dynamics, we theoretically extended the spin-torque phenomenology for domain-wall dynamics from collinear to noncollinear magnetic systems. These findings open a new route to developing a mechanism for antiferromagnetic domain-wall-based applications. References [1] S. Nakatsuji et al., Nature 527, 212–215 (2015). [2] T. Higo, et al., Nat. Photon. 12, 73–78 (2018). [3] H. Tsai, et al., Nature 580, 608–613 (2020). [4] Y. Takeuchi et al., Nat. Mater. 20, 1364–1370 (2021). [5] T. Higo, et al., Nature 607, 474–479 (2022).

Zane Rossi

Parallel Quantum Signal Processing via Polynomial Factorization
 

Akito Sakai

Novel quantum many-body state in quadrupole Kondo lattice PrV2AI20

Unconventional metals characterized by the T-linear resistivity, which is recently called “Planckian dissipation”, have been discovered in various strongly correlated materials especially near quantum critical points. On the other hand, the quadrupole version of the Kondo effect can provide another type of novel metallic state. Namely, when conduction electrons screen the local f-electrons' quadrupole, conduction electrons’ spin degree of freedom acts as an additional internal degree of freedom (channel). As a result of this “two-channel Kondo” problem, the ground state is over-screened non-Fermi liquid even in the single impurity limit, characterized by the fractionalized residual entropy related to the Majorana zero mode [1]. Such exotic coupling may induce further interesting phenomena in real materials with lattice periodicities [2-4]. A cubic Pr-based rare-earth compound PrV2Al20 is the quadrupole Kondo lattice system where both strong c-f hybridization and quadrupole active nonmagnetic crystalline electric field ground state (cubic Γ3) are realized. Besides, PrV2Al20 exhibits anomalous metallic behavior characterized by ρ~T^0.5, double-multipolar transition at T_Q ∼ 0.7 and T* ~0.6 K, and superconductivity at Tc ∼ 0.05 K [5, 6]. Although various experiments are performed, the origin of the multipole order in PrV2Al20 is not yet well understood. In this presentation, I will present the novel quantum many-body state in PrV2Al20, especially for the multipole ordered phases. References [1] D. L. Cox, Phys. Rev. Lett., 59, 1240 (1987). [2] S. Hoshino, J. Otsuki, and Y. Kuramoto Phys. Rev. Lett. 107, 247202 (2011). S. Hoshino and Y. Kuramoto Phys. Rev. Lett. 112, 167204 (2014). [3] K. Inui and Y. Motome Phys. Rev. B 102, 155126 (2020). [4] S.E. Han, D. J. Schultz, and Y. B. Kim Phys. Rev. B 106, 155155 (2022). [5] A. Sakai and S. Nakatsuji, J. Phys. Soc. Jpn., 80, 063701 (2011). [6] M. Tsujimoto et al., Phys. Rev. Lett. 113, 267001 (2014).

Matthias Salzger

A decompositional framework for process theories in spacetime

There has been a recent surge in interest in quantum foundations coming from incorporating ideas from general relativity and quantum gravity. In particular, the field of indefinite causal order has emerged and is now an important research topic in its own right. Many of the tools that we use in quantum foundations and information, are, however, totally agnostic as to the underlying spacetime in which the quantum systems live. To give a practical example, whenever we draw a quantum circuit we are not taking into account the connectivity of the physical qubits which will realize this circuit. In this work, we aim to address this limitation. In particular, we show how to extend the formalism of process theories (a framework to study both quantum and post-quantum theories) to incorporate a background causal structure arising from a fixed spacetime. We discuss when processes are embeddable in spacetime under certain constraints. To this end, we introduce the concept of implementations of a process, which are decompositions of the process. A process is then embeddable if one of its implementations can be embedded in such a way that all the processes are localized and all wires follow time-like paths. The set of all implementations of a process is a rather unwieldy object but we show that there exists a subset with useful properties which tells us everything we need to know about the remaining implementations and the embeddability of a process. We call this subset minimal representatives. Future directions include plans to define and analyse the compositional structure of the framework more rigorously, extending the framework to indefinite causal structures, studying exotic causal influence and using the minimal representatives to probe the decompositional structure of quantum theory and beyond.

John Selby

Generalised contextuality as a necessary resource for universal quantum computation

A universal and well-motivated notion of classicality for an operational theory is explainability by a generalised-noncontextual ontological model. I will here explain what notion of classicality this implies within the framework of generalised probabilistic theories. I then prove that for any locally tomographic theory, every such classical model is given by a complete frame representation. Using this powerful constraint on the space of possible classical representations, I will then prove that the stabilizer subtheory has a unique classical representation—namely Gross's discrete Wigner function. This provides deep insights into the relevance of Gross's representation within quantum computation. It also implies that generalised contextuality is also a necessary resource for universal quantum computation within the state injection model. Based on https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.120403

Tokuro Shimokawa

Can experimentally-accessible measures of entanglement distinguish quantum spin liquid and random singlet states?

The study of quantum spin liquid (QSL) state has been a central topic in the field of condensed matter physics since Anderson pioneered resonating valence bonds (RVB) as an alternative to low temperature magnetic order [1]. Tremendous efforts spanning half a century provided deep insights of the QSL states, however, the identification of QSL in experiments remains a challenge, particularly in materials with chemical or structural disorder, where there can be many different routes to a spin-disordered ground state, such as a random singlet (RS) state [2]. Entanglement properties might be useful in distinguishing QSL from other states. However, the entanglement entropy, commonly used in condensed matter physics nowadays, is theoretically very useful but difficult to apply at finite temperatures and is known to be extremely challenging to measure in real materials. An important question arises, are there experimentally-accessible entanglement measures that can solve the identification problem between QSL and RS states? In this talk, we show that experimentally-accessible measures of entanglement, one-tangle, two-tangle [3] and quantum Fisher information density [4], can distinguish QSL and RS states in a representative model of S=½ triangular-lattice Heisenberg antiferromagnets. Our non-biased numerical results based on exact-diagonalization-like algorithms reveal that the RS state is a multipartite entangled state as the QSL state, and that the difference between these two states is in the level of two-partite entanglement. We also find that the temperature dependence of the multipartite entanglement is powerful to solve this identification problem, and this finding is potentially applicable to inelastic neutron scattering measurements [5-7,8]. This work is a collaboration with Snigdh Sabharwal and Nic Shannon. [1] P. W. Anderson, Mat. Res. Bull. 8, 153 (1973). [2] K. Watanabe et al., J. Phys. Soc. Jpn. 83, 034714 (2014). [3] L. Amico et al., Phys. Rev. A 69, 022304 (2004). [4] P. Hauke et al., Nat. Phys. 12, 778 (2016). [5] P. Laurell et al., Phys. Rev. Lett. 127, 037201 (2021). [6] A. Scheie et al., Phys. Rev. B 103, 224434 (2021). [7] A. O. Scheie et al., Nat. Phys. (2023). [8] T. S., S. Sabharwal and Nic Shannon, in preparation.

Grigorii Skorupskii

Designing Giant Hall Response in Layered Topological Semimetals

Noncollinear and noncoplanar magnets are promising candidates for future data storage technologies. Of particular interest are materials that show electrical transport signatures originating from the magnetic order, such as Hall effect anomalies. Few materials are known to host those, and we have no clear chemical understanding of their origin. Here, we present a chemical design strategy that allowed us to discover a series of noncoplanar magnets Ln3Sn7 (Ln = Tb, Dy). Our strategy is based on targeting materials that combine several magnetic sublattices with dissimilar magnetic anisotropies, along with a square-net topological semimetal layer. Ln3Sn7 show high carrier mobilities upwards of 17,000 cm2/(V s), and, critically, display large anomalous Hall conductivities in excess of 40,000 S/cm, which is the highest value reported to date in a noncoplanar magnet.

Philip Taranto

Characterising the Hierarchy of Multi-time Quantum Processes with Classical Memory

Memory plays a vital role in various natural and engineered processes, from predicting weather patterns to financial markets and computational tasks. When memory is present but uncontrollable, it leads to complex non-Markovian noise, which is challenging to model accurately. On the other hand, a controlled memory becomes a powerful tool for information processing, as seen in systems like quantum dots, where tunable memory can enhance properties like charge transport and emission spectra, potentially benefiting technologies like photovoltaic cells and communication protocols. In the same vein as processes themselves, memory effects can be quantum or classical. They arise from interactions between a system of interest and its environment, with the latter acting as the memory carrier. Rapid dissipation of information leads to simple, memoryless processes; on the other hand, strong interactions with low dissipation often result in non-classical multi-time correlations. In between the two extremes of memorylessness and coherent quantum memory lies a class of quantum processes that offer significant application: quantum processes with classical memory. These are more powerful than memoryless ones and can be controlled over extended timeframes without being spoiled by decoherence or errors. Despite their potential, understanding the distinction between quantum and classical memory has thus far remained largely unexplored. Here, we systematically characterise the hierarchy of multi-time memory effects in quantum mechanics, in particular demonstrating the distinct behaviour between various types of possible memory effects. Many levels of the engendered hierarchy only emerge as discernible beyond the two-time setting, making our results genuinely multi-time phenomena. On the practical side, since noise in quantum devices—and thus the observed memory effects—will predominately be classical in the near future, our work provides a methodological framework upon which efficient and reliable quantum devices can be built.

Yunlong Xiao

Quantum Uncertainty Principles for Measurements with Interventions

Heisenberg's uncertainty principle implies fundamental constraints on what properties of a quantum system can we simultaneously learn. However, it typically assumes that we probe these properties via measurements at a single point in time. In contrast, inferring causal dependencies in complex processes often requires interactive experimentation - multiple rounds of interventions where we adaptively probe the process with different inputs to observe how they affect outputs. Here we demonstrate universal uncertainty principles for general interactive measurements involving arbitrary rounds of interventions. As a case study, we show that they imply an uncertainty trade-off between measurements compatible with different causal dependencies.

Han Yan

Designing Light in an Artificial Universe

Quantum spin ice (QSI) is a lattice spin-model realization of full-fledged quantum electrodynamics, including photons, electric charges, and magnetic monopoles. As one of the most interesting quantum spin liquids, a significant amount of experimental and theoretical investigation has been done in this field. I will present an overview of the quantum spin ice physics and also discuss our recent ongoing work [1] on how, in the so-called dipole-octupole QSI [2-6], one can experimentally have clean control of the dynamics of its emergent QED, including the transition between different symmetry-enriched phases, tuning the dispersion of photons and fine-structure constants, etc. One of the most straightforward experiments can achieve this: turning on the external magnetic field in the right direction. [1] Experimentally tunable QED in dipolar-octupolar quantum spin ice. HY, Alaric Sanders, Claudio Castelnovo, Andriy H Nevidomskyy, arXiv:2312.11641v1. [2] Thermodynamics of the dipole-octupole pyrochlore magnet Ce2Hf2O7 in applied magnetic fields. A Bhardwaj, V Porée, HY, et al., arXiv:2402.08723 [3] Dipolar-octupolar correlations and hierarchy of exchange interactions in Ce2Hf2O7. V Porée, A Bhardwaj, E Lhotel, S Petit, N Gauthier, HY, et al., arXiv:2305.08261 [4] Fractional matter coupled to the emergent gauge field in a quantum spin ice, V Porée, HY, F Desrochers et al., accepted for publication on Nature Physics [5] Experimental signatures of emergent quantum electrodynamics in Pr2Hf2O7 R Sibille, N Gauthier, HY et al., Nature Physics 14, 711–715 [6]Magnetic field effects in an octupolar quantum spin liquid candidate, B Gao, T Chen, HY, et al., PRB 106 (9), 094425