arXiv subjects

Ningyuan Jia

Publications and source records attributed to Ningyuan Jia.

13 recordsLinked to original sources

arXiv2026

Revealing Hidden Correlations in a Fermi-Hubbard system via Interaction Ramps

We observe an enhanced visibility of charge-density-wave correlations in a cold-atom realization of the attractive Hubbard model following a rapid boost of the interaction strength. The interaction boost associates nonlocal pairs into doublons which mark the center of mass of the original pairs. The enhancement is largest in the strongly correlated regime where pairing is nonlocal. We distinguish the unpaired Fermi liquid from the pseudogap phase of preformed pairs by analyzing atom-resolved spin-charge correlations after the ramp. The technique we establish here may facilitate the observation of exotic forms of pair order in spin-imbalanced systems, and of stripe order in the dual case of the doped repulsive Hubbard model.

cond-mat.quant-gas↗

arXiv2025

Competition of fermion pairing, magnetism, and charge order in the spin-doped attractive Hubbard gas

The tension between fermion pairing and magnetism affects numerous strongly correlated electron systems, from high-temperature cuprates to twisted bilayer graphene. Exotic forms of fermion pairing and superfluidity are predicted when attraction between fermions competes with spin doping. Here, we follow the evolution of fermion pairing and charge and spin order in a spin-imbalanced attractive Hubbard gas of fermionic $^{40}$K atoms, covering a wide range of densities, magnetizations, and interactions with single-atom resolution. At low spin imbalance and weak interactions, we find a mixture of nonlocal fermion pairs coexisting with itinerant excess fermions. For stronger interactions an effective hard-core Bose-Fermi mixture emerges. Spin doping drives a crossover from charge-density wave correlations to a Fermi liquid of polarons. Beyond a certain spin imbalance and interaction strength, we find evidence for the onset of combined spin- and pair-density wave order, a possible precursor for the existence of magnetized superfluidity in the attractive Hubbard system.

cond-mat.quant-gas↗

arXiv2025

In search of exotic pairing in the Hubbard model: many-body computation and quantum gas microscopy

Pair density waves and exotic superconductivity have long been of strong interest, and have attracted much recent attention. We present a joint theoretical and experimental exploration of possible signatures of fermion pairing with finite center-of-mass momentum, or the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) order. Experimentally a doped and spin-imbalanced attractive two-dimensional Hubbard model is realized with a cold atomic gas in an optical lattice, and quantum gas microscopy is used to probe its properties. Computationally we study the same model with state-of-the-art constrained-path (CP) auxiliary field quantum Monte Carlo (AFQMC). Direct comparisons between experiment and computation on various short-range magnetic and charge correlations show excellent agreement. We then investigate these correlations, as well as pairing correlation functions, systematically to low temperatures with CP-AFQMC, and determine parameter regimes in density and magnetization where signatures of FFLO order may be observed. We show that the temperature at which precursors of such orders appear is already within reach of the current experiment. We discuss routes for direct experimental detection and measurements of such states.

cond-mat.quant-gas↗

arXiv2024

Experimental Demonstration of Logical Magic State Distillation

Realizing universal fault-tolerant quantum computation is a key goal in quantum information science. By encoding quantum information into logical qubits utilizing quantum error correcting codes, physical errors can be detected and corrected, enabling substantial reduction in logical error rates. However, the set of logical operations that can be easily implemented on such encoded qubits is often constrained, necessitating the use of special resource states known as 'magic states' to implement universal, classically hard circuits. A key method to prepare high-fidelity magic states is to perform 'distillation', creating them from multiple lower fidelity inputs. Here we present the experimental realization of magic state distillation with logical qubits on a neutral-atom quantum computer. Our approach makes use of a dynamically reconfigurable architecture to encode and perform quantum operations on many logical qubits in parallel. We demonstrate the distillation of magic states encoded in d=3 and d=5 color codes, observing improvements of the logical fidelity of the output magic states compared to the input logical magic states. These experiments demonstrate a key building block of universal fault-tolerant quantum computation, and represent an important step towards large-scale logical quantum processors.

quant-ph↗

arXiv2024

Large-scale quantum reservoir learning with an analog quantum computer

Quantum machine learning has gained considerable attention as quantum technology advances, presenting a promising approach for efficiently learning complex data patterns. Despite this promise, most contemporary quantum methods require significant resources for variational parameter optimization and face issues with vanishing gradients, leading to experiments that are either limited in scale or lack potential for quantum advantage. To address this, we develop a general-purpose, gradient-free, and scalable quantum reservoir learning algorithm that harnesses the quantum dynamics of neutral-atom analog quantum computers to process data. We experimentally implement the algorithm, achieving competitive performance across various categories of machine learning tasks, including binary and multi-class classification, as well as timeseries prediction. Effective and improving learning is observed with increasing system sizes of up to 108 qubits, demonstrating the largest quantum machine learning experiment to date. We further observe comparative quantum kernel advantage in learning tasks by constructing synthetic datasets based on the geometric differences between generated quantum and classical data kernels. Our findings demonstrate the potential of utilizing classically intractable quantum correlations for effective machine learning. We expect these results to stimulate further extensions to different quantum hardware and machine learning paradigms, including early fault-tolerant hardware and generative machine learning tasks.

quant-ph↗

arXiv2022

Direct observation of non-local fermion pairing in an attractive Fermi-Hubbard gas

Pairing of fermions lies at the heart of superconductivity, the hierarchy of nuclear binding energies and superfluidity of neutron stars. The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a "pseudo-gap" region where pairs form already above the superfluid critical temperature. We here directly observe the non-local nature of fermion pairing in a Hubbard lattice gas, employing spin- and density-resolved imaging of $\sim$1000 fermionic ${}^{40}$K atoms under a bilayer microscope. Complete fermion pairing is revealed by the vanishing of global spin fluctuations with increasing attraction. In the strongly correlated regime, the fermion pair size is found to be on the order of the average interparticle spacing. We resolve polaronic correlations around individual spins, resulting from the interplay of non-local pair fluctuations and charge-density-wave order. Our techniques open the door toward in-situ observation of fermionic superfluids in a Hubbard lattice gas.

cond-mat.quant-gas↗

arXiv2021

Quantum Register of Fermion Pairs

Fermions are the building blocks of matter, forming atoms and nuclei, complex materials and neutron stars. Our understanding of many-fermion systems is however limited, as classical computers are often insufficient to handle the intricate interplay of the Pauli principle with strong interactions. Quantum simulators based on ultracold fermionic atoms instead directly realize paradigmatic Fermi systems, albeit in "analog" fashion, without coherent control of individual fermions. Digital qubit-based quantum computation of fermion models, on the other hand, faces significant challenges in implementing fermionic anti-symmetrization, calling for an architecture that natively employs fermions as the fundamental unit. Here we demonstrate a robust quantum register composed of hundreds of fermionic atom pairs trapped in an optical lattice. With each fermion pair forming a spin-singlet, the qubit is realized as a set of near-degenerate, symmetry-protected two-particle wavefunctions describing common and relative motion. Degeneracy is lifted by the atomic recoil energy, only dependent on mass and lattice wavelength, thereby rendering two-fermion motional qubits insensitive against noise of the confining potential. We observe quantum coherence beyond ten seconds. Universal control is provided by modulating interactions between the atoms. Via state-dependent, coherent conversion of free atom pairs into tightly bound molecules, we tune the speed of motional entanglement over three orders of magnitude, yielding $10^4$ Ramsey oscillations within the coherence time. For site-resolved motional state readout, fermion pairs are coherently split into a double well, creating entangled Bell pairs. The methods presented here open the door towards fully programmable quantum simulation and digital quantum computation based on fermions.

cond-mat.quant-gas↗

arXiv2020

Doublon-hole correlations and fluctuation thermometry in a Fermi-Hubbard gas

We report on the single atom and single site-resolved detection of the total density in a cold atom realization of the 2D Fermi-Hubbard model. Fluorescence imaging of doublons is achieved by splitting each lattice site into a double well, thereby separating atom pairs. Full density readout yields a direct measurement of the equation of state, including direct thermometry via the fluctuation-dissipation theorem. Site-resolved density correlations reveal the Pauli hole at low filling, and strong doublon-hole correlations near half filling. These are shown to account for the difference between local and non-local density fluctuations in the Mott insulator. Our technique enables the study of atom-resolved charge transport in the Fermi-Hubbard model, the site-resolved observation of molecules, and the creation of bilayer Fermi-Hubbard systems.

cond-mat.quant-gas↗

arXiv2019

Observation of Laughlin states made of light

Much of the richness in nature emerges because the same simple constituents can form an endless variety of ordered states. While many such states are fully characterized by their symmetries, interacting quantum systems can also exhibit topological order, which is instead characterized by intricate patterns of entanglement. A paradigmatic example of such topological order is the Laughlin state, which minimizes the interaction energy of charged particles in a magnetic field and underlies the fractional quantum Hall effect. Broad efforts have arisen to enhance our understanding of these orders by forming Laughlin states in synthetic quantum systems, such as those composed of ultracold atoms or photons. In spite of these efforts, electron gases remain essentially the only physical system in which topological order has appeared. Here, we present the first observation of optical photon pairs in the Laughlin state. These pairs emerge from a photonic analog of a fractional quantum Hall system, which combines strong, Rydberg-mediated interactions between photons and synthetic magnetic fields for light, induced by twisting an optical resonator. Photons entering this system undergo collisions to form pairs in an angular momentum superposition consistent with the Laughlin state. Characterizing the same pairs in real space reveals that the photons avoid each other, a hallmark of the Laughlin state. This work heralds a new era of quantum many-body optics, where strongly interacting and topological photons enable exploration of quantum matter with wholly new properties and unique probes.

cond-mat.quant-gas↗

arXiv2018

Probing the Berry Curvature and Fermi Arcs of a Weyl Circuit

The Weyl particle is the massless fermionic cousin of the photon. While no fundamental Weyl particles have been identified, they arise in condensed matter and meta-material systems, where their spinor nature imposes topological constraints on low-energy dispersion and surface properties. Here we demonstrate a topological circuit with Weyl dispersion at low-momentum, realizing a 3D lattice that behaves as a half-flux Hofstadter model in all principal planes. The circuit platform provides access to the complete complex-valued spin-texture of all bulk- and surface- states, thereby revealing not only the presence of Weyl points and the Fermi arcs that connect their surface-projections, but also, for the first time, the Berry curvature distribution through the Brillouin zone and the associated quantized Chiral charge of the Weyl points. This work opens a path to exploration of interacting Weyl physics in superconducting circuits, as well as studies of how manifold topology impacts band topology in three dimensions.

cond-mat.quant-gas↗

arXiv2018

Interacting Floquet polaritons

Ordinarily, photons do not interact with one another. However, atoms can be used to mediate photonic interactions, raising the prospect of forming synthetic materials and quantum information systems from photons. One promising approach uses electromagnetically-induced transparency with highly-excited Rydberg atoms to generate strong photonic interactions. Adding an optical cavity shapes the available modes and forms strongly-interacting polaritons with enhanced light-matter coupling. However, since every atom of the same species is identical, the atomic transitions available are only those prescribed by nature. This inflexibility severely limits their utility for mediating the formation of photonic materials in cavities, as the resonator mode spectrum is typically poorly matched to the atomic spectrum. Here we use Floquet engineering to redesign the spectrum of Rubidium and make it compatible with the spectrum of a cavity, in order to explore strongly interacting polaritons in a customized space. We show that periodically modulating the energy of an atomic level redistributes its spectral weight into lifetime-limited bands separated by multiples of the modulation frequency. Simultaneously generating bands resonant with two chosen spatial modes of an optical cavity supports "Floquet polaritons" in both modes. In the presence of Rydberg dressing, we find that these polaritons interact strongly. Floquet polaritons thus provide a promising new path to quantum information technologies such as multimode photon-by-photon switching, as well as to ordered states of strongly-correlated photons, including crystals and topological fluids.

cond-mat.quant-gas↗

arXiv2017

A Strongly Interacting Polaritonic Quantum Dot

Polaritons are an emerging platform for exploration of synthetic materials [1] and quantum information processing [2] that draw properties from two disparate particles: a photon and an atom. Cavity polaritons are particularly promising, as they are long-lived and their dispersion and mass are controllable through cavity geometry [3]. To date, studies of cavity polaritons have operated in the mean-field regime, using short-range interactions between their matter components [4]. Rydberg excitations have recently been demonstrated as a promising matter-component of polaritons [5], due to their strong interactions over distances large compared to an optical wavelength. In this work we explore, for the first time, the cavity quantum electrodynamics of Rydberg polaritons, combining the non-linearity of polaritonic quantum wires with the zero-dimensional strong coupling of an optical resonator. We assemble a quantum dot composed of $\sim 150$ strongly interacting, Rydberg-dressed $^{87}$Rb atoms in a cavity, and observe blockaded polariton transport as well as coherent quantum dynamics of a single polaritonic super-atom. This work establishes a new generation of photonic quantum information processors and quantum materials, along with a clear path to topological quantum matter [6].

cond-mat.quant-gas↗

arXiv2015

Time Reversal Invariant Topologically Insulating Circuits

From studies of exotic quantum many-body phenomena to applications in spintronics and quantum information processing, topological materials are poised to revolutionize the condensed matter frontier and the landscape of modern materials science. Accordingly, there is a broad effort to realize topologically non-trivial electronic and photonic materials for fundamental science as well as practical applications. In this work, we demonstrate the first simultaneous site- and time- resolved measurements of a time reversal invariant topological band-structure, which we realize in a radio frequency (RF) photonic circuit. We control band-structure topology via local permutation of a traveling wave capacitor-inductor network, increasing robustness by going beyond the tight-binding limit. We observe a gapped density of states consistent with a modified Hofstadter spectrum at a flux per plaquette of $ϕ=π/2$. In-situ probes of the band-gaps reveal spatially-localized bulk-states and de-localized edge-states. Time-resolved measurements reveal dynamical separation of localized edge-excitations into spin-polarized currents. The RF circuit paradigm is naturally compatible with non-local coupling schemes, allowing us to implement a Möbius strip topology inaccessible in conventional systems. This room-temperature experiment illuminates the origins of topology in band-structure, and when combined with circuit quantum electrodynamics (QED) techniques, provides a direct path to topologically-ordered quantum matter.

cond-mat.mes-hall↗