arXiv subjects

Luheng Zhao

Publications and source records attributed to Luheng Zhao.

5 recordsLinked to original sources

arXiv2025

Statistical Localization in a Rydberg Simulator of $U(1)$ Lattice Gauge Theory

Lattice gauge theories (LGTs) provide a framework for describing dynamical systems ranging from nuclei to materials. LGTs that host concatenated conservation laws can exhibit Hilbert space fragmentation, where each subspace may be labeled by a conserved quantity with nonlocal operator support. It is expected that nonlocal conservation laws will not impede thermalization locally. However, this expectation has recently been challenged by the notion of statistical localization, wherein particular motifs of microscopic configurations may remain frozen in time due to strong Hilbert space fragmentation. Here, we report the first experimental signatures of statistically-localized behavior. We realize a novel constrained LGT model using a facilitated Rydberg atom array, where atoms mediate the dynamics of electric charge clusters whose nonlocal pattern of net charges remains invariant. By experimentally reconstructing observables sampled from a temporal ensemble, we probe the spatial distribution of each conserved quantity. We find that as a result of strong Hilbert space fragmentation, the expectation values of all conserved quantities remain locally distributed in typical quantum states, even though they are described by nonlocal string-like operators. Our work opens the door to high-energy explorations of cluster dynamics and low-energy studies of strong zero modes that persist in infinite-temperature topological systems.

quant-ph↗

arXiv2024

Observation of quantum thermalization restricted to Hilbert space fragments

Quantum thermalization occurs in a broad class of systems from elementary particles to complex materials. Out-of-equilibrium quantum systems have long been understood to either thermalize or retain memory of their initial states, but not both. Here we achieve the first coexistence of thermalization and memory in a quantum system, where we use both Rydberg blockade and facilitation in an atom array to engineer a fragmentation of the Hilbert space into exponentially many disjointed subspaces. We find that the kinetically constrained system yields quantum many-body scars arising from the $\mathbb{Z}_{2k}$ class of initial states, which generalizes beyond the $\mathbb{Z}_{2}$ scars previously reported in other quantum systems. When bringing multiple long-range interactions into resonance, we observe quantum thermalization restricted to Hilbert space fragments, where the thermalized system retains characteristics of the initial configuration. Intriguingly, states belonging to different subspaces do not thermalize with each other even when they have the same energy. Our work challenges established ideas of quantum thermalization while experimentally resolving the longstanding tension between thermalization and memory. These results may be applied to control entanglement dynamics in quantum processors and quantum sensors.

quant-ph↗

arXiv2023

Floquet-Tailored Rydberg Interactions

The Rydberg blockade is a key ingredient for entangling atoms in arrays. However, it requires atoms to be spaced well within the blockade radius, which limits the range of local quantum gates. Here we break this constraint using Floquet frequency modulation, with which we demonstrate Rydberg-blockade entanglement beyond the traditional blockade radius and show how the enlarged entanglement range improves qubit connectivity in a neutral atom array. Further, we find that the coherence of entangled states can be extended under Floquet frequency modulation. Finally, we realize Rydberg anti-blockade states for two sodium Rydberg atoms within the blockade radius. Such Rydberg anti-blockade states for atoms at close range enables the robust preparation of strongly-interacting, long-lived Rydberg states, yet their steady-state population cannot be achieved with only the conventional static drive. Our work transforms between the paradigmatic regimes of Rydberg blockade versus anti-blockade and paves the way for realizing more connected, coherent, and tunable neutral atom quantum processors with a single approach.

quant-ph↗

arXiv2021

D1 magic wavelength tweezers for scaling atom arrays

D1 magic wavelengths have been predicted for the alkali atoms but are not yet observed to date. We experimentally confirm a D1 magic wavelength that is predicted to lie at 615.87 nm for $^{23}$Na, which we then use to trap and image individual atoms with 80.0(6)% efficiency and without having to modulate the trapping and imaging light intensities. We further demonstrate that the mean loading efficiency remains as high as 74.2(7)% for a 1D array of eight atoms. Leveraging on the absence of trap intensity modulation and lower trap depths afforded by the D1 light, we achieve an order-of-magnitude reduction on the tweezer laser power requirements and a corresponding increase in the scalability of atom arrays. The methods reported here are applicable to all the alkalis, including those that are attractive candidates for dipolar molecule assembly, Rydberg dressing, or are fermionic in nature.

physics.atom-ph↗

arXiv2019

Numerical Study of Evaporative Cooling in the Space Station

In this paper, we numerically studied the effects of mechanical vibration and magnetic fields on evaporative cooling process carried in space station by direct simulation Monte Carlo method. Simulated with the vibration data of international space station, we found that the cooling process would suffer great atomic losses until the accelerations reduced tenfold at least. In addition, if we enlarge the s-wave scattering length five times by Feshbach resonance, the PSD increased to 50 compared to 3 of no magnetic fields situation after 5 seconds evaporative cooling. We also simulated the two stages crossed beam evaporative cooling process (TSCBC) under both physical impacts and obtain $4\times10^5$ $^{85}$Rb atoms with a temperature of 8 pK. These results are of significance to the cold atom experiments carried out on space station in the future.

cond-mat.quant-gas↗