arXiv subjects

Yanting Cheng

Publications and source records attributed to Yanting Cheng.

18 recordsLinked to original sources

arXiv2026

Shallow Unitary Circuits for Kramers-Wannier Dualities

The quantum Kramers-Wannier (KW) duality is a fundamental transformation mapping short-range entangled (SRE) states to long-range entangled (LRE) states. While spatially local unitary circuits require linear-in-system-size depth to implement this duality, the ultimate speed limit for purely unitary circuits equipped with nonlocal connectivity remains an open question. Here, we explicitly construct logarithmic depth, spatially nonlocal unitary circuits that realize the exact $\mathbb{Z}_2$ KW dualities in both one and two spatial dimensions. We further generalize the construction to arbitrary $\mathbb{Z}_n$ KW dualities. Unlike algorithms tailored to prepare specific target states, our circuits implement complete duality maps. Within the symmetric (charge-neutral) sector, these dualities exactly transform arbitrary non-fixed-point SRE states into their corresponding LRE duals. Consequently, our results establish an efficient, purely coherent pathway for exploring phase transitions and topological dualities on modern quantum platforms.

quant-ph↗

arXiv2026

Scar Full Eigenstate Thermalization Hypothesis

The eigenstate thermalization hypothesis (ETH) provides a fundamental mechanism for emergent statistical mechanics in isolated chaotic quantum systems, asserting that individual energy eigenstates behave as pseudorandom vectors within an energy window. This enables a complete characterization of nontrivial correlations among matrix elements in the energy eigenbasis, as described by the full ETH ansatz. Nevertheless, this description breaks down in systems exhibiting quantum many-body scars, which host non-thermal eigenstates with extensive energy. In this Letter, we address this problem by formulating the \textit{scar full ETH}, which captures correlations among matrix elements involving scar states. The corresponding scaling forms and factorization properties are established using typicality arguments. Multi-time correlation functions for scar states are then organized in terms of both thermal and scar cumulants, providing a nontrivial reorganization of higher-order correlations. We numerically demonstrate the validity of this framework in the paradigmatic model of quantum scars, the PXP model. Our results pave the way for a systematic understanding of intriguing correlations in systems with quantum many-body scars.

quant-ph↗

arXiv2025

Spacetime Supersymmetry in the Truncated Lattice Schwinger Model

Gauge theories in (1+1)D have attracted renewed attention partially due to their experimental realizations in quantum simulation platforms. In this work, we revisit the truncated lattice massive Schwinger model and the truncated lattice Abelian-Higgs model in (1+1)D, where to facilitate quantum simulation, the electric field eigenvalues are truncated to a finite subset while preserving the exact gauge and global symmetries. We uncover previously overlooked universal features in these models, including the emergence of a supersymmetric quantum critical point when the Maxwell term's coefficient changes sign. Our primary focus is the truncated lattice Schwinger model at $\theta=0$, a model not equivalent to familiar spin models. We find that upon reversing the sign of the Maxwell term, the second-order charge conjugation symmetry breaking transition (or confinement-deconfinement transition in a sense) can become first-order. Furthermore, the two types of transitions are connected by a supersymmetric critical point in the tricritical Ising universality class. In the case of truncated Abelian-Higgs model at $\theta=0$, which we find to be equivalent to the quantum Blume-Capel model, the very existence of a symmetry-breaking phase requires a negative-sign Maxwell term. Similarly, there is a tricritical Ising point separating first-order and second-order phase transitions.

cond-mat.quant-gas↗

arXiv2024

Emergent Gauge Theory in Rydberg Atom Arrays

Rydberg atom arrays have emerged as a novel platform exhibiting rich quantum many-body physics and offering promise for universal quantum computation. The Rydberg blockade effect plays an essential role in establishing many-body correlations in this system. In this review, we will highlight that the lattice gauge theory is an efficient description of the Rydberg blockade effect and overview recent exciting developments in this system from equilibrium phases to quantum dynamics. These developments include realizing exotic ground states such as spin liquids, discovering quantum many-body scar states violating quantum thermalization, and observing confinement-deconfinement transition through quantum dynamics. We emphasize that the gauge theory description offers a universal theoretical framework to capture all these phenomena. This perspective of Rydberg atom arrays will inspire further the future development of quantum simulation and quantum computation in this platform.

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arXiv2023

Observation of microscopic confinement dynamics by a tunable topological $\theta$-angle

The topological $\theta$-angle is central to the understanding of a plethora of phenomena in condensed matter and high-energy physics such as the strong CP problem, dynamical quantum topological phase transitions, and the confinement--deconfinement transition. Difficulties arise when probing the effects of the topological $\theta$-angle using classical methods, in particular through the appearance of a sign problem in numerical simulations. Quantum simulators offer a powerful alternate venue for realizing the $\theta$-angle, which has hitherto remained an outstanding challenge due to the difficulty of introducing a dynamical electric field in the experiment. Here, we report on the experimental realization of a tunable topological $\theta$-angle in a Bose--Hubbard gauge-theory quantum simulator, implemented through a tilted superlattice potential that induces an effective background electric field. We demonstrate the rich physics due to this angle by the direct observation of the confinement--deconfinement transition of $(1+1)$-dimensional quantum electrodynamics. Using an atomic-precision quantum gas microscope, we distinguish between the confined and deconfined phases by monitoring the real-time evolution of particle--antiparticle pairs, which exhibit constrained (ballistic) propagation for a finite (vanishing) deviation of the $\theta$-angle from $\pi$. Our work provides a major step forward in the realization of topological terms on modern quantum simulators, and the exploration of rich physics they have been theorized to entail.

cond-mat.quant-gas↗

arXiv2022

Gauge theory description of Rydberg atom arrays with a tunable blockade radius

We discuss a Rydberg atom chain with a tunable blockade radius from the gauge theoretic perspective. When the blockade radius is one lattice spacing, this system can be formulated in terms of the PXP model, and there is a $\mathbb{Z}_2$ Ising phase transition known to be equivalent to a confinement-deconfinement transition in a gauge theory, the lattice Schwinger model. Further increasing the blockade radius, one can add a next-nearest neighbor (NNN) interaction into the PXP model. We discuss the interpretation of NNN interaction in terms of the gauge theory and how finite NNN interaction alters the deconfinement behavior and propose a corresponding experimental protocol. When the blockade radius reaches two lattice spacing, the model reduces to the PPXPP model. A novel gauge theory equivalent to the PPXPP model is formulated, and the phases in the two formulations are delineated. These results are readily explored experimentally in Rydberg quantum simulators.

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arXiv2022

Tunable Confinement-Deconfinement Transition in an Ultracold Atom Quantum Simulator

The one-dimensional lattice Schwinger model has recently been realized by using bosons in optical lattices. This model contains both confinement and deconfinement phases, whose phase diagram is controlled by the mass of the matter field and the topological angle. Since varying the mass of matter field is straightforward experimentally, we propose how to tune the topological angle, allowing accessing the entire phase diagram. We propose that direct experimental evidence of confinement and deconfinement can be obtained by measuring whether a physical charge is localized around a fixed gauge charge to screen it. We also discuss the PXP model realized in the Rydberg atoms array, which is equivalent to the lattice Schwinger model when all local gauge charges are fixed as zero. Although the gauge charges are fixed, we can alternatively probe the confinement and the deconfinement in the PXP model by studying the relative motion of a pair of a physical charge and an anti-charge. Our scheme can be directly implemented in these two relevant experimental platforms of ultracold atom quantum simulators.

cond-mat.quant-gas↗

arXiv2021

Variational Approach to Quantum Spin Liquid in a Rydberg Atom Simulator

Recently the Rydberg blockade effect has been utilized to realize quantum spin liquid on the kagome lattice. Evidence of quantum spin liquid has been obtained experimentally by directly measuring non-local string order. In this letter, we report a BCS-type variational wave function study of the spin liquid state in this model. This wave function is motivated by mapping the Rydberg blockade model to a lattice gauge theory, where the local gauge conservations replace the role of constraints from the Rydberg blockade. We determine the variational parameter from the experimental measurement of the Rydberg atom population. Then we compare the predictions of this deterministic wave function with the experimental measurements of non-local string order. Combining the measurements on both open and closed strings, we extract the fluctuations only associated with the closed-loop as an indicator of the topological order. The prediction from our wave function agrees reasonably well with the experimental data without any fitting parameter. Our variational wave function provides a simple and intuitive picture of the quantum spin liquid in this system that can be generalized to various generalizations of the current model.

cond-mat.quant-gas↗

arXiv2021

Asymmetric Conductivity of the Kondo Effect in Cold Atomic Systems

Motivated by recent theoretical and experimental advances in quantum simulations using alkaline earth(AE) atoms, we put forward a proposal to detect the Kondo physics in a cold atomic system. It has been demonstrated that the intrinsic spin-exchange interaction in AE atoms can be significantly enhanced near a confinement-induced resonance(CIR), which facilitates the simulation of Kondo physics. Since the Kondo effect appears only for antiferromagnetic coupling, we find that the conductivity of such a system exhibits an asymmetry across a resonance of spin-exchange interaction. The asymmetric conductivity can serve as the smoking gun evidence for Kondo physics in the cold atom context. When an extra magnetic field ramps up, the spin-exchange process near the Fermi surface is suppressed by Zeeman energy and the conductivity becomes more and more symmetric. Our results can be verified in the current experimental setup.

cond-mat.quant-gas↗

arXiv2020

Many-body Dynamics with Time-dependent Interaction

Recent advances in optical Feshbach resonance technique have enabled the experimental investigation of atomic gases with time-dependent interaction. In this work, we study the many-body dynamics of weakly interacting bosons subject with an arbitrary time varying scattering length. By employing a variational ansatz, we derive an effective Hamiltonian that governs the dynamics of thermal particles. Crucially, we show that there exists a hidden symmetry in this Hamiltonian that can map the many-body dynamics to the precession of an SU(1,1) "spin". As a demonstration, we calculate the situation where the scattering length is sinusoidally modulated. We show that the non-compactness of the SU(1,1) group naturally leads to solutions with exponentially growth of Bogoliubov modes and causes instabilities.

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arXiv2019

Realizing the Hayden-Preskill Protocol with Coupled Dicke Models

Hayden and Preskill proposed a thought experiment that Bob can recover the information Alice throws into a black hole if he has a quantum computer entangled with the black hole, and Yoshida and Kitaev recently proposed a concrete decoding scheme. The parallel question is that after a small system is thermalized with a large system, how one can decode the initial state information with the help of two entangled many-body systems. Here we propose to realize this protocol in a physical system of two Dicke models, with two cavity fields prepared in a thermofield double state. We show that the Yoshida-Kitaev protocol allows us to read out the initial spin information after it is scrambled into the cavity. We show that the readout efficiency reaches a maximum when the model parameter is tuned to the regime where the system is the most chaotic, characterized by the shortest scrambling time in the out-of-time-ordered correlation function. Our proposal opens up the possibility of discussing this profound thought experiment in a realistic setting.

cond-mat.quant-gas↗

arXiv2019

Interaction Control of Ultracold Alkaline-Earth Atoms

Ultracold alkaline-earth atoms have now been widely explored for precision measurements and quantum simulation. Because of its unique atomic structure, alkaline earth atoms possess great advantages for quantum simulation and studying quantum many-body matters, such as simulating synthetic gauge field, Kondo physics and $SU(N)$ physics. To fully explore the potential of ultracold alkaline-earth atoms, these systems also need to be equipped with the capability of tuning the inter-atomic interaction to the strongly interacting regime. Recently several theoretical proposals and experimental demonstrations have shown that both spin-independent and spin-exchanging interaction can be tuned to resonance. In this perspective, we will review these progress and discuss the new opportunities brought by these interaction control tools for future quantum simulation studies with ultracold alkaline-earth atoms.

cond-mat.quant-gas↗

arXiv2017

Enhancing Kondo Coupling in Alkaline-Earth Atomic Gases with Confinement-induced Resonances in Mixed Dimensions

The Kondo effect describes the spin-exchanging interaction between localized impurity and the itinerant fermions. The ultracold alkaline-earth atomic gas provides a natural platform for quantum simulation of the Kondo model, utilizing its long-lived clock state and the nuclear-spin exchanging interaction between the clock state and the ground state. One of the key issue now is whether the Kondo temperature can be high enough to be reached in current experiment, for which we have proposed using a transverse confinement to confine atoms into a one-dimensional tube and to utilize the confinement-induced resonance to enhance the Kondo coupling. In this work, we further consider the $1+0$ dimensional scattering problem when the clock state is further confined by an axial harmonic confinement. We show that this axial confinement for the clock state atoms not only plays a role for localizing them, but also can act as an additional control knob to reach the confinement-induced resonance. We show that by combining both the transverse and the axial confinements, the confinement-induced resonance can be reached in the practical conditions and the Kondo effect can be attainable in this system.

cond-mat.quant-gas↗

arXiv2016

Quantum Defect Theory for Orbital Feshbach Resonance

In the ultracold gases of alkali-earth (like) atoms, a new type of Feshbach resonance, i.e., the orbital Feshbach resonance (OFR), has been proposed and experimentally observed in ultracold $^{173}$Yb atoms. When the OFR of the $^{173}$Yb atoms occurs, the energy gap between the open and closed channels is smaller by two orders of magnitudes than the van der Waals energy. As a result, quantitative accurate results for the low-energy two-body problems can be obtained via multi-channel quantum defect theory (MQDT), which is based on the exact solution of the Schr$\ddot{{\rm o}}$dinger equation with the van der Waals potential. In this paper we use the MQDT to calculate the two-atom scattering length, effective range, and the binding energy of two-body bound states for the systems with OFR. With these results we further study the clock-transition spectrum for the two-body bound states, which can be used to experimentally measure the binding energy. Our results are helpful for the quantitative theoretical and experimental researches for the ultracold gases of alkali-earth (like) atoms with OFR.

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arXiv2016

Orbital Feshbach Resonance: A "Wide" Narrow Resonance for Higher Transition Temperature Fermi Superfluid

In this letter we show that the recently theoretically predicted and experimentally observed "orbital Feshbach resonance" in alkali-earth-like Yb-173 atom is a narrow resonance in energy, while it is hundreds Gauss wide in term of magnetic field strength, taking the advantage that the magnetic moment difference between the open and closed channels is quite small. Therefore this is an ideal platform for the experimental realization of a strongly interacting Fermi superfluid with narrow resonance. We show that the transition temperature for the Fermi superfluid in this system, especially at the BCS side of the resonance, is even higher than that in a wide resonance, which is also due to the narrow character of this resonance. Our results will encourage experimental efforts to realize Fermi superfluid in the alkali-earth-like Yb-173 system, the properties of which will be complementary to extensively studied Fermi superfluids nearby a wide resonance in alkali K-40 and Li-6 systems.

cond-mat.quant-gas↗

arXiv2016

Orbital Feshbach Resonance with Small Energy Gap between Open and Closed Channels

Recently a new type of Feshbach resonance, i.e., orbital Feshbach resonance (OFR) was proposed for the ultracold alkali-earth (like) atoms, and experimentally observed in the ultracold gases of $^{{\rm 173}}$Yb atoms. Unlike most of the magnetic Feshbach resonances of ultracold alkali atoms, when the OFR of $^{{\rm 173}}$Yb atoms appears, the energy gap between the thresholds of the open channel (OC) and the closed channel (CC) is much smaller than the characteristic energy of the inter-atomic interaction, i.e., the van der Waals energy. In this paper we study the OFR in the systems with small CC-OC threshold gap. We show that in these systems the OFR can be induced by the coupling between the OC and either an isolated bound state of the CC or the scattering states of the CC. Moreover, we also show that in each case the two-channel Huang-Yang pesudopoential is always applicable for the approximate calculation of the low-energy scattering amplitude. Our results imply that in the theoretical calculations for these systems it is appropriate to take into account the contributions from the scattering states of the CC.

cond-mat.quant-gas↗

arXiv2015

Kondo Effect in Alkali-Earth Atomic Gases with Confinement-induced Resonance

Alkali-earth atoms have a long-lived electronic excited state, which can be localized in the Fermi sea of ground state atoms by an external potential and serve as magnetic impurities, due to the spin-exchange interaction between the excited and the ground state atoms. This can give rise to the Kondo effect. However, in order to achieve this effect in current atomic gas experiment, it requires the Kondo temperature to be increased to a sizable portion of the Fermi temperature. In this letter we propose that the spin-exchange interaction can be strongly enhanced by utilizing the confinement-induced resonance (CIR). We analyze this system by the renormalization group approach, and we show that nearby a CIR, the Kondo temperature can indeed be increased to the regime attainable by current experiments.

cond-mat.quant-gas↗

arXiv2015

Orbital Feshbach Resonance in Alkali-Earth Atoms

For a mixture of alkali-earth atomic gas in the long-lived excited state ${}^3P_0$ and ground state ${}^1S_0$, in addition to nuclear spin, another "orbital" index is introduced to distinguish these two internal states. In this letter we propose a mechanism to induce Feshbach resonance between two atoms with different orbital and nuclear spin quantum numbers. Two essential ingredients are inter-orbital spin-exchanging scattering and orbital dependence of the Land\'e g-factors. Here the orbital degrees of freedom plays similar role as electron spin degree of freedom in magnetic Feshbach resonance in alkali-metal atoms. This resonance is particularly accessible for ${}^{173}$Yb system. The BCS-BEC crossover in this system requires two fermion pairing order parameters, and displays significant difference comparing to that in alkali-metal system.

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