Research
Some Recent Publications
Spectroscopic signatures of fractionalization in octupolar quantum spin ice
Félix Desrochers, Yong Baek Kim
Recent investigations on the dipolar-octupolar compounds Ce2Zr2O7 and Ce2Sn2O7 suggest that they may stabilize so-called π-flux octupolar quantum spin ice (π-O-QSI), a novel three-dimensional quantum spin liquid hosting emergent photons. In this Letter, we thoroughly investigate O-QSI using an extension of gauge mean-field theory. This framework produces a phase diagram consistent with previous studies and an energy-integrated neutron scattering signal with intensity-modulated rod motifs, as reported in experiments and numerical studies. We predict that the dynamical spin structure factor of π-O-QSI is characterized by a broad continuum with three distinctive peaks as a consequence of the two mostly flat spinon bands. These three peaks should be measurable by high-resolution inelastic neutron scattering. Such spectroscopic signatures would be clear evidence for the realization of π-flux quantum spin ice.
Phys. Rev. Lett. 132, 066502 (2024)
Fractional matter coupled to the emergent gauge field in a quantum spin ice
Victor Porée, Han Yan, Félix Desrochers, Sylvain Petit, Elsa Lhotel, Markus Appel, Jacques Ollivier, Yong Baek Kim, Andriy H. Nevidomskyy, Romain Sibille
Quantum spin ice (QSI) is a theoretically well-established example of quantum spin liquid and described by an emergent quantum electrodynamics, with excitations behaving like photon and matter quasiparticles. Our experimental colleagues use backscattering neutron spectroscopy to achieve extremely high resolution of the time-dependent magnetic response of the candidate QSI material Ce2Sn2O7. The experiments find a gapped spectrum featuring peaks that match theories for pair production and propagation of fractional matter excitations (spinons). We show that the multiple peaks are a specific signature of the π-flux phase of QSI, providing spectroscopic evidence for fractionalization in a three-dimensional quantum spin liquid.
arXiv:2304.05452
Intertwined van-Hove Singularities as a Mechanism for Loop Current Order in Kagome Metal
Heqiu Li, Yong Baek Kim, Hae-Young Kee
Recent experiments on Kagome metals AV3Sb5 (A=Cs,Rb,K) indicated spontaneous time-reversal symmetry breaking in the charge density wave state in the absence of static magnetization. The loop current order (LCO) is proposed as its cause, but a microscopic model explaining the emergence of LCO through electronic correlations has not been firmly established. We show that the coupling between van-Hove singularities (vHS) with distinct mirror symmetries is a key ingredient to generate LCO ground state.
Phys. Rev. Lett. 132, 146501 (2024)
Bosonization of Non-Fermi Liquids
SangEun Han, Félix Desrochers, Yong Baek Kim
Understanding non-Fermi liquids in dimensions higher than one remains one of the most formidable challenges in modern condensed matter physics. Inspired by recent work on the bosonization of Fermi surfaces [Delacretaz, Du, Mehta, and Son, Physical Review Research, 4, 033131 (2022)], we present a procedure for bosonizing non-Fermi liquids. Our method involves parameterizing the generalized fermionic distribution function through a bosonic field that describes frequency-dependent local variations of the chemical potential in momentum space. We propose an effective action that produces the collisionless quantum Boltzmann equation as its equation of motion and can straightforwardly be used for any dimension and Fermi surface of interest. Even at the quadratic order, this action reproduces highly non-trivial results obtainable only through involved analysis with alternative means.
arXiv:2306.14955
Joe Huxford, Dung Xuan Nguyen, Yong Baek Kim
We examine the condensation and confinement mechanisms exhibited by a deformed toric code model proposed in [Castelnovo and Chamon, Phys. Rev. B, 2008]. The model describes both sides of a phase transition from a topological phase to a trivial phase. Our findings reveal an unconventional confinement mechanism, namely the confined magnetic charge can still be displaced without any energy cost, albeit only via the application of non-unitary operators that reduce the norm of the state. This peculiar phenomenon can be attributed to a previously known feature of the model: it maintains the non-trivial ground state degeneracy of the toric code throughout the transition. We describe how this degeneracy arises in both phases in terms of spontaneous symmetry breaking of a generalized (1-form) symmetry and explain why such symmetry breaking is compatible with the trivial phase. The present study implies the existence of subtle considerations that must be addressed in the context of recently posited connections between topological phases and broken higher-form symmetries.
SciPost Phys. 15, 253 (2023)
Measurement-induced entanglement phase transitions in variational quantum circuits
Roeland Wiersema, Cunlu Zhou, Juan Felipe Carrasquilla, Yong Baek Kim
We investigate the entanglement transition in variational quantum circuits endowed with intermediate projective measurements. We provide evidence that the transition belongs to the same universality class of random unitary circuits. Importantly, the transition coincides with a "landscape transition" from severe to mild/no barren plateaus in the classical optimization. Our work paves an avenue for greatly improving the trainability of quantum circuits by incorporating intermediate measurement protocols in currently available quantum hardware.
SciPost Phys. 14, 147 (2023)
Fractonic Quantum Phases in Breathing Pyrochlore Lattice
SangEun Han, Adarsh Patri, Yong Baek Kim
We provide a realistic quantum model of quadratic spin interactions on the breathing pyrochlore lattice, inspired by a classical spin model studied earlier. We show that the emergent "charge" excitations in this model can only arise as a cluster, not as a standalone excitation, and move in a sub-dimensional space. The charges may reside at the boundary of membrane objects, which represent vacuum fluctuations. It is shown that the ground state degeneracy is sub-extensive and explicitly depends on the lattice geometry. We discuss the implications of these results in light of the rank-2 tensor gauge theory.
Phys. Rev. B 105, 235120 (2022)
Exploring entanglement and optimization within the Hamiltonian Variational Ansatz
Roeland Wiersema, Cunlu Zhou, Yvette de Sereville, Juan Felipe Carrasquilla, Yong Baek Kim, Henry Yuen
We consider a quantum variational algorithm for near-term quantum computers. By studying quantum entanglement in the quantum circuit, we show that the Hamiltonian variational ansatz have many desirable properties.
PRX Quantum 1, 020319 (2020)
Theory of two-dimensional nonlinear spectroscopy for the Kitaev spin liquid
Wonjune Choi, Ki Hoon Lee, Yong Baek Kim
It is shown that 2D coherent non-linear spectroscopy can be used to detect unambiguous signatures of the Majorna fermions and visons in the spin-half Kitaev quantum spin liquid.
Physical Review Letters 124, 117205 (2020)