arXiv subjects

Haoyang Gao

Publications and source records attributed to Haoyang Gao.

9 recordsLinked to original sources

arXiv2026

Nanoscale magnetometry via collective many-body dynamics in diamond

Many-body dynamics constitutes a promising approach for creating correlations between quantum particles which can be used for applications in sensing and metrology. However, utilizing this potential for substantial gains in practical settings is a challenging task with only a very few applications realized to date. Here, we demonstrate an approach to nanoscale magnetic sensing enabled by strongly interacting electronic spins in a room temperature solid. By coherently controlling collective many-body dynamics of a dipolar ensemble of $\sim 10^4$ nitrogen-vacancy (NV) centres in diamond with pulsed magnetic field gradients, we demonstrate practical metrological gain up to $7.9(2)\,\mathrm{dB}$ for magnetic signal detection and $8.8(3)\,\mathrm{dB}$ for magnetic noise sensing, fully accounting for experimental overheads. Finally, we combine these methods to demonstrate a momentum-space-resolved sensing modality that enables detection of spatially correlated magnetic noise at continuously tunable length scales down to 50 nanometers. These observations open the door toward practical applications of interaction-enhanced quantum sensors for nanoscale biological imaging and material characterization.

quant-ph↗

arXiv2025

Dressed-state Hamiltonian engineering in a strongly interacting solid-state spin ensemble

In quantum science applications, ranging from many-body physics to quantum metrology, dipolar interactions in spin ensembles are controlled via Floquet engineering. However, this technique typically reduces the interaction strength between spins, and effectively weakens the coupling to a target sensing field, limiting the metrological sensitivity. In this work, we develop and demonstrate a method for direct tuning of the native interaction in an ensemble of nitrogen-vacancy (NV) centers in diamond. Our approach utilizes dressed-state qubit encoding under a magnetic field perpendicular to the crystal lattice orientation. This method leads to a $3.2\times$ enhancement of the dimensionless coherence parameter $JT_2$ compared to state-of-the-art Floquet engineering, and a $2.6\times$ ($8.3~$dB) enhanced sensitivity in AC magnetometry. Utilizing the extended coherence we experimentally probe spin transport at intermediate to late times. Our results provide a powerful Hamiltonian engineering tool for future studies with NV ensembles and other interacting higher-spin ($S>\frac{1}{2}$) systems.

quant-ph↗

arXiv2025

Collective many-body dynamics in a solid-state quantum sensor controlled through nanoscale magnetic gradients

Coherent collective dynamics of strongly interacting qubits are a central resource in quantum information science, with applications from quantum computing and simulation to metrology. While electronic spins interact strongly via dipolar couplings in dense solid-state ensembles, imperfections and positional disorder pose major obstacles to coherent correlated behavior, limiting their usefulness. Here, we realize collective many-body dynamics by combining time-dependent magnetic field gradients with global coherent control of dense electron spin ensembles in diamond. We control and probe the dynamics of nanometer-scale spin spirals, and, by exploiting Hamiltonian engineering that enhances the microscopic symmetry of the interactions, we observe a disorder-resilient collective spin evolution. Our results establish a pathway to interaction-enhanced quantum metrology and nanoscale imaging of materials and biological systems under ambient conditions.

quant-ph↗

arXiv2025

Signal amplification in a solid-state quantum sensor via asymmetric time-reversal of many-body dynamics

Electronic spins of nitrogen vacancy (NV) centers in diamond constitute a promising system for micro- and nano-scale magnetic sensing, due to their operation under ambient conditions, ease of placement in close proximity to sensing targets, and biological compatibility. At high densities, the electronic spins interact through dipolar coupling, which typically limits but can also potentially enhance sensing performance. Here we report the experimental demonstration of many-body signal amplification in a solid-state, room temperature quantum sensor. Our approach utilizes time-reversed two-axis-twisting interactions, engineered through dynamical control of the quantization axis and Floquet engineering in a two-dimensional ensemble of NV centers. Strikingly, we observe that the optimal amplification occurs when the backward evolution time equals twice the forward evolution time, in sharp contrast to the conventional Loschmidt echo. These observations can be understood as resulting from an underlying time-reversed mirror symmetry of the microscopic dynamics, providing key insights into signal amplification and opening the door towards entanglement-enhanced practical quantum sensing.

quant-ph↗

arXiv2024

Two-axis twisting using Floquet-engineered XYZ spin models with polar molecules

Polar molecules confined in an optical lattice are a versatile platform to explore spin-motion dynamics based on strong, long-range dipolar interactions. The precise tunability of Ising and spin-exchange interactions with both microwave and dc electric fields makes the molecular system particularly suitable for engineering complex many-body dynamics. Here, we used Floquet engineering to realize interesting quantum many-body systems of polar molecules. Using a spin encoded in the two lowest rotational states of ultracold KRb molecules, we mutually validated XXZ spin models tuned by a Floquet microwave pulse sequence against those tuned by a dc electric field through observations of Ramsey contrast dynamics, setting the stage for the realization of Hamiltonians inaccessible with static fields. In particular, we observed two-axis twisting mean-field dynamics, generated by a Floquet-engineered XYZ model using itinerant molecules in 2D layers. In the future, Floquet-engineered Hamiltonians could generate entangled states for molecule-based precision measurement or could take advantage of the rich molecular structure for quantum simulation of multi-level systems.

cond-mat.quant-gas↗

arXiv2023

Controlling local thermalization dynamics in a Floquet-engineered dipolar ensemble

Understanding the microscopic mechanisms of thermalization in closed quantum systems is among the key challenges in modern quantum many-body physics. We demonstrate a method to probe local thermalization in a large-scale many-body system by exploiting its inherent disorder, and use this to uncover the thermalization mechanisms in a three-dimensional, dipolar-interacting spin system with tunable interactions. Utilizing advanced Hamiltonian engineering techniques to explore a range of spin Hamiltonians, we observe a striking change in the characteristic shape and timescale of local correlation decay as we vary the engineered exchange anisotropy. We show that these observations originate from the system's intrinsic many-body dynamics and reveal the signatures of conservation laws within localized clusters of spins, which do not readily manifest using global probes. Our method provides an exquisite lens into the tunable nature of local thermalization dynamics, and enables detailed studies of scrambling, thermalization and hydrodynamics in strongly-interacting quantum systems.

quant-ph↗

arXiv2023

Robust Hamiltonian Engineering for Interacting Qudit Systems

We develop a formalism for the robust dynamical decoupling and Hamiltonian engineering of strongly interacting qudit systems. Specifically, we present a geometric formalism that significantly simplifies qudit pulse sequence design, while incorporating the necessary robustness conditions. We experimentally demonstrate these techniques in a strongly-interacting, disordered ensemble of spin-1 nitrogen-vacancy centers, achieving over an order of magnitude improvement in coherence time over existing pulse sequences. We further describe how our techniques enable the engineering of exotic many-body phenomena such as quantum many-body scars, and allow enhanced sensitivities for quantum metrology. These results enable the engineering of a whole new class of complex qudit Hamiltonians, with wide-reaching applications in dynamical decoupling, many-body physics and quantum metrology.

quant-ph↗

arXiv2022

Out-of-equilibrium criticalities in graphene superlattices

In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy whereas the filled bands underneath contribute little to conduction. Here we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics resembling those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common for all graphene-based superlattices.

cond-mat.other↗

arXiv2019

Plasmonic Drag in a Flowing Fermi Liquid

Collective modes in two-dimensional electron fluids show an interesting response to a background carrier flow. Surface plasmons propagating on top of a flowing Fermi liquid acquire a non-reciprocal character manifest in a $\pm k$ asymmetry of mode dispersion. The nonreciprocity arises due to Fermi surface polarization by the flow. The flow-induced interactions between quasiparticles make collective modes of the system uniquely sensitive to subtle "motional" Fermi-liquid effects. The flow-induced Doppler-type frequency shift of plasmon resonances, arising due to electron interactions, can strongly deviate from the classical value. This opens a possibility to directly probe motional Fermi-liquid effects in plasmonic near-field imaging experiments.

cond-mat.mes-hall↗