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Our research lies at the intersection of quantum information, quantum magnetism, and topological phenomena. Our work is strongly driven by the interest in connecting theoretical models with experimentally observable phenomena, keeping our understanding closely anchored in physical reality. We seek to fully harness opportunities offered by nature by exploring quantum phenomena across different degrees of freedom, and by distilling complex many-body physics into simple, minimal models that provide clear and intuitive insights.
Summaries of some of our works are below.
Quantum computing and quantum communication based on mobile topological spin textures
Quantum computing and quantum communication based on mobile topological spin textures
Key idea: Harness the quantum coherence in the magnetic system for quantum computing!
Related publications:
Ji Zou†, S. Bosco, B. Pal, S. Parkin, J. Klinovaja, D. Loss; Phys. Rev. Research 5 (3), 033166 (2023)
Ji Zou†, S. Bosco, J. Klinovaja, D. Loss; arXiv:2409.14373 (2024)
G. Qu, Ji Zou, D. Loss, T. Hirosawa; arXiv:2412.11585 (2024)
A. Background: Researchers have shown that domain wall (DW) motion is highly tunable, with velocities exceeding 1000 m/s under the right conditions. At the same time, nanoscale DWs—now achievable in the lab—hold the potential to exhibit quantum behavior at low temperatures. With these breakthroughs converging, the time is now to push the classical racetrack into the quantum realm!
B. Where we store the quantum information: Chirality!
The DW can have different chiralities, as shown in the figure. The key idea is to harness this chirality degree of freedom as a pseudospin for quantum information encoding!
Just like superconducting flux qubits use macroscopic quantum states (supercurrents flowing in opposite directions) to store information, we use spin winding with opposite chiralities for encoding!
C. Unique advantages!
1) Highly Mobile: Unlike conventional stationary qubits (e.g., superconducting qubits), domain walls (DWs) are mobile, making them a powerful solid-state flying qubit for quantum communication.
2) Long-Distance Entanglement: As shown in the figure, mobile DWs can entangle distant spin qubits and enable efficient two-qubit gates across long distances—paving the way for scalable quantum computation!
3) Ultrafast Quantum Gates: Novel approach to qubit control—by manipulating its motion! Thanks to the spin Berry phase effect, which induces a strong intrinsic spin-orbit coupling, the qubit's motion is directly linked to its spin dynamics. This enables ultrafast gate operations on the scale of 0.1 ns!
4) Easily scalable: Multiple DWs can be created on a single racetrack, enabling high-density qubit arrays. Even more exciting, the racetrack can potentially extend into 3D architectures, paving the way for ultra-compact processors!
Open Quantum System: from Bell state generation to magnon diode effect
Open Quantum System: from Bell state generation to magnon diode effect
Key idea: Harness quantum correlations in condensed matter systems to control classical and quantum information.
Related publications:
Ji Zou†, S. Bosco, E. Thingstad, J. Klinovaja, D. Loss; Phys. Rev. Lett. 132 (3), 036701(2024)
Ji Zou†, S. Bosco, D. Loss; npj Quantum Information 10 (1), 46 (2024)
Ji Zou, S. Zhang, Y. Tserkovnyak; Phys. Rev. B. 106, L180406 (2022)
Ji Zou, S. K. Kim, Y. Tserkovnyak; Phys. Rev. B 101, 014416 (2020)
T. Yu, Ji Zou, B. Zeng, J. W. Rao, K. Xia; Physics Reports 1062, 1-86 (2024)
A. Motivation: We have a wide variety of condensed matter systems, including magnets, superconductors, topological materials, and more exotic phases like spin liquids. These systems exhibit diverse orders and unique quantum properties. A natural question arises: can we harness these properties for (quantum) information processing?
It is intriguing to consider coupling a qubit system to a many-body system, opening up new opportunities to leverage many-body effects to engineer qubits. A basic question to explore is whether quantum correlations from a many-body system can be imprinted onto a qubit.
B. Unexpected results!
Qubit-Magnet Hybrid System: Quantum correlations in the magnetic system give rise to dissipative coupling and correlated decoherence in the qubit system. Remarkably, this interaction enables the formation of long-lived Bell states for two qubits—and even more intriguingly, it can generate a long-lived chiral W state for three qubits!
Beyond Qubits—Macrospin Dynamics: When replacing qubits with larger spins (macrospins), we uncover even richer physics. The correlated decay induced by the environment can give rise to a nonreciprocal interaction between macrospins, leading to a striking magnon diode effect in certain scenarios!
C. Future directions!
So far, we have explored a simple yet already exciting setup—two qubits coupled to an ordered magnet—revealing fascinating physics. But this is just the beginning!
Even more exciting phenomena can emerge when a collection of qubits is coupled to exotic quantum systems with rich correlations. Imagine leveraging topologically nontrivial materials or highly entangled phases like quantum spin liquids, whether in equilibrium or driven far from it. This opens up an entirely new frontier at the intersection of many-body physics, topology, and quantum technologies—a direction ripe for exciting discoveries!
Topological Magnetic Textures and Their Transport
Topological Magnetic Textures and Their Transport
Key idea: Harness topological excitations in magnetic systems for robust information transmission!
Related publications:
Ji Zou, S. Zhang, Y. Tserkovnyak; Phys. Rev. Lett. 125, 267201 (2020)
Ji Zou, S. K. Kim, Y. Tserkovnyak; Phys. Rev. B 99, 180402(R) (2019)
Y. Tserkovnyak, Ji Zou, Phys. Rev. Research 1, 033071 (2019)
Y. Tserkovnyak, Ji Zou, S. K. Kim, S. Takei, Phys. Rev. B 102, 224433 (2020)
A. Motivation: Spin waves (magnons) are a natural choice for carrying information in magnetic systems. But a fundamental challenge remains—magnons are inherently lossy quasiparticles, limiting long-range signal transfer.
But what if we could harness something more robust? Magnetic systems also host topological excitations—such as vortices and skyrmions—which are protected by topology and inherently conserved. We have a hope to achieve highly stable and long-range information transmission!
B. Nice findings!
We investigated the transport of topologically nonlocal textures—such as vortices and hedgehogs—in magnets. Remarkably, we found that signal decay improves from exponential (as in magnons) to algebraic, thanks to the robust conservation of these topological textures!
Even more striking, we demonstrated that this conservation holds at the quantum level, paving the way for a quantum hydrodynamic framework for these nonlocal textures, even on a quantum lattice!
C. Future directions?
A fascinating direction is extending our quantum hydrodynamics framework for topological charges to quantum spin liquids. Beyond its theoretical appeal, this approach holds practical significance—transport measurements could provide a powerful experimental tool for identifying quantum spin liquids, a long-sought challenge in condensed matter physics.
Equally exciting is the opportunity to unravel new phases and emergent hydrodynamics of topological spin textures in Moire magnets, where tunable interactions could unlock new quantum phenomena!
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