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Ran Qi

Publications and source records attributed to Ran Qi.

At least 19 recordsLinked to original sources

RoboHarness: Memory-Driven Orchestration of Heterogeneous Robot Policies for Long-Horizon Planning

Long-horizon robotic tasks require diverse capabilities that no single policy can reliably provide. Heterogeneous policies offer complementary strengths, but orchestrating them requires reasoning over uncertain capability boundaries and cross-policy distribution mismatch, which are largely overlooked by existing planning methods built on homogeneous, predefined skills with fixed applicability. We propose RoboHarness, a unified framework that encapsulates independently developed robot control systems as reusable agentic skills. Although instantiated in this work with VLAs, RL policies, and task-and-motion planning (TAMP) systems, RoboHarness is designed as a general framework compatible with a broader range of robot policies, such as navigation policies, model predictive controllers, and world-action models. RoboHarness uses multi-modal execution memory and online evidence to characterize policy capability boundaries for capability-aware decomposition and routing. To stabilize policy handoffs, its Memory Bridge retrieves execution trajectories associated with the next policy, estimates its in-distribution state region, and guides the robot toward that region without joint policy retraining. Extensive experiments on three public benchmarks, 500 customized tasks, and 135 real-robot experiments demonstrate effective capability-aware routing and stable policy orchestration, yielding substantial improvements in zero-shot long-horizon planning and out-of-distribution robustness.

cs.RO

Non-Resonant Boundary Time Crystals from Quantum Synchronization Breakdown

Quantum synchronization (QS) in dissipative systems is often inferred from smooth phase locking, leaving open whether its breakdown constitutes a genuine nonequilibrium transition. Here we introduce a Liouvillian framework that classifies driven-dissipative dynamics by the structure of the undriven dissipative background and show that QS breaks down via a Hopf-type dynamical phase transition into a boundary time crystal (BTC). The character of this transition is determined by the background attractor: systems with a self-sustained oscillator (SSO) support robust non-resonant BTCs, whereas those with a polar fixed point (PFP) sustain BTCs only at resonance and lose them under detuning. We identify sharp dynamical and spectral signatures of the QS-BTC transition and thereby establish, within U(1)-symmetric collective-spin Lindbladians driven by a single coherent tone, a background-based allowed/forbidden criterion that unifies QS, its breakdown, and time-crystalline order within a single Liouvillian framework.

quant-ph

Mediated Transmission of Quantum Synchronization in Star Networks

Synchronization transmission describes the emergence of coherence between two uncoupled oscillators mediated by their mutual coupling to an intermediate one. In classical star networks, such mediated coupling gives rise to remote synchronization--where nonadjacent leaf nodes synchronize through a nonsynchronous hub--and to explosive synchronization, characterized by an abrupt collective transition to coherence. In the quantum regime, analogous effects can arise from the interplay between 1:1 phase locking and 2:1 phase-locking blockade in coupled spin-1 particles. In this work, we investigate a star network composed of spin-1 particles. For identical oscillators, symmetric and asymmetric dissipation lead to distinct transmission behaviors: remote synchronization and quasi-explosive synchronization appear in different coupling regimes, a phenomenon absent in classical counterparts. For nonidentical networks, we find that at large detuning remote synchronization emerges in the weak-coupling regime and evolves into quasi-explosive synchronization as the coupling increases, consistent with classical star-network dynamics. These findings reveal the rich dynamical characteristics of mediated quantum synchronization and point toward new possibilities for exploring synchronization transmission in larger and more complex quantum systems.

quant-ph

Universal Manipulation of Quantum Synchronization in Spin Oscillator Networks

Quantum synchronization (QS) in open many-body systems offers a promising route for controlling collective quantum dynamics, yet existing manipulation schemes often rely on dissipation engineering, which distorts limit cycles, lacks scalability, and is strongly system-dependent. Here, we propose a universal and scalable method for continuously tuning QS from maximal synchronization under isotropic interactions to complete synchronization blockade (QSB) under fully anisotropic coupling in spin oscillator networks. Our approach preserves intrinsic limit cycles and applies to both few-body and macroscopic systems. We analytically show that QS arises solely from spin flip-flop processes and their higher-order correlations, while anisotropic interactions induce non-synchronizing coherence. A geometric QS measure reveals a macroscopic QSB effect in the thermodynamic limit. The proposed mechanism is experimentally feasible using XYZ interactions and optical pumping, and provides a general framework for programmable synchronization control in complex quantum networks and dynamical phases of matter.

quant-ph

Agentic Aerial Cinematography: From Dialogue Cues to Cinematic Trajectories

We present Agentic Aerial Cinematography: From Dialogue Cues to Cinematic Trajectories (ACDC), an autonomous drone cinematography system driven by natural language communication between human directors and drones. The main limitation of previous drone cinematography workflows is that they require manual selection of waypoints and view angles based on predefined human intent, which is labor-intensive and yields inconsistent performance. In this paper, we propose employing large language models (LLMs) and vision foundation models (VFMs) to convert free-form natural language prompts directly into executable indoor UAV video tours. Specifically, our method comprises a vision-language retrieval pipeline for initial waypoint selection, a preference-based Bayesian optimization framework that refines poses using aesthetic feedback, and a motion planner that generates safe quadrotor trajectories. We validate ACDC through both simulation and hardware-in-the-loop experiments, demonstrating that it robustly produces professional-quality footage across diverse indoor scenes without requiring expertise in robotics or cinematography. These results highlight the potential of embodied AI agents to close the loop from open-vocabulary dialogue to real-world autonomous aerial cinematography.

cs.RO

Observation of high partial-wave Feshbach resonances in $^{39}$K Bose-Einstein condensates

We report the new observation of several high partial-wave (HPW) magnetic Feshbach resonances (FRs) in $^{39}$K atoms of the hyperfine substate $\left|F=1,m_{F}=-1\right\rangle$. These resonances locate at the region between two broad $s$-wave FRs from 32.6 G to 162.8 G, in which Bose-Einstein condensates (BECs) can be produced with tunable positive scattering length obtained by magnetic FRs. These HPW FRs are induced by the dipolar spin-spin interaction with s-wave in the open channel and HPW in the closed channel. Therefore, these HPW FRs have distinct characteristics in temperature dependence and loss line shape from that induced by spin-exchange interaction with HPWs in both open and closed channels. Among these resonances, one $d$-wave and two $g$-wave FRs are confirmed by the multichannel quantum-defect theory (MQDT) calculation. The HPW FRs have significant applications in many-body physics dominated by HPW pairing.

cond-mat.quant-gas

Non-equilibrium Dynamics of Fermi Polarons Driven by Time-dependent Interaction

We systematically studied the dynamics of Fermi polarons driven by time-dependent scattering length using a time-dependent variational method. Starting from the non-interacting initial state, we calculated the evolution behavior of the contact, energy, and quasiparticle residue of this system as the scattering length $a_s(t)$ increases from zero. In the short-time evolution, we obtained analytical results, verifying that when $a_s(t)$ grows as $\sqrt{t}$, the contact $C(t)$ and energy $E(t)$ exhibit the maximum growth rate. Furthermore, we numerically solved the long-time evolution, when $a_s(t)$ is diven with a strength $\beta$ and a power $\alpha$ as $a_s(t) = {\sqrt{2}\beta}/{k_F} {(\epsilon_Ft)}^{\alpha}$. For large driving strength, due to the interference between the polaron states and the non-interacting states, $C(t)$ and $Z(t)$ exhibit oscillatory behavior; For small $\beta$, the oscillatory behavior disappears due to the decay of the repulsive polaron into the continuum, and $C(t)$ and $Z(t)$ gradually relax to zero. The energy always saturates over long times for different driving strength. Additionally, our method is applicable to any time-dependent form of the scattering length.

cond-mat.quant-gas

Synthetic Mutual Gauge Field in Microwave-Shielded Polar Molecular Gases

The recent breakthrough of realizing the Bose-Einstein condensate of polar molecules and degenerate Fermi molecules in three dimensions relies crucially on the microwave shielding technique, which strongly suppresses the collision loss between molecules. In this letter, we show that the cooperation of microwave shielding and dipolar interaction naturally leads to the emergence of a synthetic gauge field. Unlike that studied in cold atoms before, this gauge field couples to the relative motion of every two molecules instead of single-particle motion, therefore being a mutual gauge field. In this case, every molecule carrying a synthetic charge sees the other molecule as carrying the source of the magnetic field, and the spatial distribution of the magnetic field is reminiscent of a solenoid attached to the molecule. In other words, in addition to microwave-shielded interaction, another part of the interaction between two molecules behaves as a charge interacting with a solenoid, which was missed in the previous discussion. We argue that the physical manifestation of this gauge field is breaking time-reversal symmetry in the collective spatial motion of molecules. Finally, we discuss the challenges in quantitatively studying such a quantum many-body system.

cond-mat.quant-gas

Rabi Oscillation of High Partial Wave Interacting Atoms in Deep Optical Lattice

Motivated by the recent experiment of p-wave interacting $^{40}\mathrm{K}$ atom gases in a deep optical lattice, we investigated the Rabi oscillation for any partial wave interacting quantum gases in a deep optical lattice. We first review the solution for two particles interacting by any partial wave in a harmonic trap by using pseudopotential. We generalize the model used in recent work to any partial wave cases, repeated some of the theoretic and experiment results for p-wave interacting $^{40}\mathrm{K}$ atoms in a deep optical lattice and show the results for the d-wave case. Our results may be useful for future experiments and may stimulate further theoretic investigation.

cond-mat.quant-gas

Two Ultracold Atoms in a Quasi-Two-Dimensional Box Confinement

We investigate the scattering and two-body bound states of two ultracold atoms in a quasi-two-dimensional (quasi-2D) confinement, with the confinement potential being an infinite square well (box potential) in the transverse ($z$-) direction, and the motion of the atoms in the $x$-$y$ plane being free. Specifically, we calculate the effective 2D scattering length and 2D effective range of the low-energy scattering, as well as the energy and the transverse-excited-mode probability of the bound states. Comparing these results with those obtained under a harmonic transverse confinement potential, we find that in most of the cases the 2D effective range for the box confinement is approximately 0.28 of the one for the harmonic confinement. Moreover, the transverse-excited-mode probability of the bound states for the box confinement is also much lower than the one for the harmonic confinement. These results suggest that the transverse excitation in the box confinement is notably weaker than the one in a harmonic confinement. Therefore, achieving quasi-2D ultracold gases well-described by pure-2D effective models, particularly those with 2D contact interaction, is more feasible through box confinement. Our results are helpful for the quantum simulation of 2D many-body physics with ultracold atoms, e.g., the suppression of 2D effective range may lead to an enhancement of quantum anomaly in two-dimensional Fermi Gases. Additionally, our calculation method is applicable to the two-body problems of ultracold atoms in other types of quasi-2D confinements.

cond-mat.quant-gas

Single Particle Spectroscopies of $p$-wave and $d$-wave Interacting Bose Gases in Normal Phase

Motivated by experiments of interacting quantum gases across high partial wave resonance, we investigated the thermodynamic properties as well as single particle spectrums of Bose gases in normal phase for different interaction strengths both for $p$-wave and $d$-wave interactions. The equation of state, contact density, momentum distributions, and self-energies of single particle Green's functions are obtained in the spirit of ladder diagram approximations. Radio frequency (RF) spectrum, as an important experimental approach to detect Feshbach molecules or interaction effect, is calculated at different temperatures. A reversed temperature dependence on the BEC side and BCS side is identified for both $p$-wave and $d$-wave interactions. An estimation for the signal of RF spectra under typical experimental conditions is also provided.

cond-mat.quant-gas

Accelerating Relaxation Dynamics in Open Quantum System with Liouvillian Skin Effect

We investigate a non-Hermitian model featuring non-reciprocal gradient hoppings. Through an in-depth analysis of the Liouvillian spectrum and dynamics, we confirm the emergence of the Liouvillian skin effect resulting from the non-reciprocal nature of hoppings in this model. Furthermore, we observe that the presence of gradient hopping strength leads to an accelerated relaxation time for the system. Through numerical investigations of the Liouvillian gap, relaxation time, and steady-state localization length, we discover that the relaxation time in this model cannot be explained by the currently established relationship associated with the Liouvillian skin effect. This discrepancy highlights the need for further exploration and theoretical advancements to fully comprehend the intricate mechanisms underlying quantum relaxation processes. Motivated by these findings, we propose a theoretical approach to realize this non-Hermitian model in an atomic system with a sideband structure by employing adiabatic elimination technique. These results contribute to our deeper comprehension of quantum relaxation dynamics and provide theoretical backing for the development of techniques aimed at controlling quantum relaxation processes.

quant-ph

Absence of Correlations in Dissipative Interacting Qubits: a No-Go Theorem

Exact solutions of model problems are elusive but potent tools for understanding many body interacting systems. We study a system of dissipative qubits with the Heisenberg interaction and obtain, for qubits under a certain condition, an exact steady state solution to the Lindblad master equation describing its dynamics. The physical content of such a solution is a remarkable no-go theorem, which states that for qubits possessing identical ratios of the damping and gain rates, no correlation can be established between them in the steady state. Two consequences of this theorem are discussed in the context of quantum synchronization of qubits. The first is a complete blockade of quantum synchronization of qubits under the aforementioned condition, an effect reminiscent of, but having a much broader scope than, that found in dissipated Kerr-anharmonic oscillators. The second, and a more important consequence is the possibility of reducing a complex all-to-all qubit network to a much simpler one-to-all network by engineering the dissipation. Such a reduction is desired because it provides an effective tool to optimize the quantum synchronization of a complex qubit network. Finally, we propose two concrete experimental schemes to implement our model and to test our predictions.

quant-ph

Interacting Bose gas across a narrow Feshbach resonance

We use a two-channel model to investigate an interacting Bose gas across a narrow Feshbach resonance within a field path integral approach. The ground state properties show strong deviation from that of a broad Feshbach resonance or a single channel interaction. The deviation can be interpreted by the strong energy dependence of two-body scattering length near a narrow Feshbach resonance. As the density increases, the chemical potential and energy per particle are found to saturate while the inverse compressibility and phonon velocity undergo a significant reduction. We also take Gaussian fluctuations into account and calculate the ground state energy correction as well as the quantum depletion.

cond-mat.quant-gas

Solutions of the Schr\"{o}dinger equation for anisotropic dipole-dipole interaction plus isotropic van der Waals interaction

By generalizing Bo Gao's approach [Phys. Rev. A 58, 1728 (1998)] for solving the Schr\"{o}dinger equation for an isotropic van der Waals (vdW) potential to the systems with a multi-scale anisotropic long-range interaction, we derive the solutions for the Schr\"{o}dinger equation for an anisotropic dipole-dipole interaction plus an isotropic attractive vdW potential, i.e., ${C_d(1-3\cos^2\theta)}/{r^3}-{C_6}/{r^6}$, which is projected to the subspace with angular momentum $l\leq l_{\rm cut}$, with $l_{\rm cut}$ being an arbitrary angular-momentum cutoff. Here $\theta$ is the polar angle of the coordinate $\boldsymbol{r}$ and $r=|\boldsymbol{r}|$. The asymptotic behaviors of these solutions for $r\rightarrow 0$ and $r\rightarrow \infty$ are obtained. These results can be used in the research of collisions and chemical reactions between ultra-cold polar molecules in a static electric field. Our approach to derive the solutions can be applied to the systems with a general long-range potential $\sum_{\lambda= 2}^{\lambda_{\rm max}} {V_\lambda(\theta,\varphi)}/{r^\lambda}$, with $\varphi$ being the azimuthal angle of $\boldsymbol{r}$, and thus can be used in various problems on molecule-molecule interaction.

cond-mat.quant-gas

Exact Solutions and Quantum Defect Theory for van der Waals Potentials in Ultracold Molecular Systems

In this paper, we have provided exact two-body solutions to the 2D and 3D Schr\"odinger equations with isotropic van der Waals potentials of the form \(\pm 1/r^6\). Based on these solutions, we developed an analytical quantum defect theory (QDT) applicable to both quasi-2D and 3D geometries, and applied it to study the scattering properties and bound-state spectra of ultracold polar molecules confined in these geometries. Interestingly, we find that in the attractive (repulsive) van der Waals potential case, the short-range interaction can be effectively modeled by an infinite square barrier (finite square well), which leads to narrow and dense (broad and sparse) resonance structures in the quantum defect parameter. In the quasi-2D attractive case, shape resonances can appear in an ordered fashion across different partial waves, characterized by sharp phase jumps as the scattering energy is varied. Furthermore, the low-energy analytical expansions derived from QDT show excellent agreement with the exact numerical results, validating the accuracy and usefulness of our analytical approach in describing two-body physics governed by long-range van der Waals interactions.

cond-mat.quant-gas

Maximum Energy Growth Rate in Dilute Quantum Gases

In this letter we study how fast the energy density of a quantum gas can increase in time, when the inter-atomic interaction characterized by the $s$-wave scattering length $a_\text{s}$ is increased from zero with arbitrary time dependence. We show that, at short time, the energy density can at most increase as $\sqrt{t}$, which can be achieved when the time dependence of $a_\text{s}$ is also proportional to $\sqrt{t}$, and especially, a universal maximum energy growth rate can be reached when $a_\text{s}$ varies as $2\sqrt{\hbar t/(πm)}$. If $a_\text{s}$ varies faster or slower than $\sqrt{t}$, it is respectively proximate to the quench process and the adiabatic process, and both result in a slower energy growth rate. These results are obtained by analyzing the short time dynamics of the short-range behavior of the many-body wave function characterized by the contact, and are also confirmed by numerical solving an example of interacting bosons with time-dependent Bogoliubov theory. These results can also be verified experimentally in ultracold atomic gases.

cond-mat.quant-gas

Observation of state-to-state hyperfine-changing collision in a Bose-Fermi mixture of $^6$Li and $^{41}$K atoms

Hyperfine-changing collisions are of fundamental interest for the studying of ultracold heteronuclear mixtures. Here, we report the state-to-state study of the hyperfine-changing-collision dynamics in a Bose-Fermi mixture of $^6$Li and $^{41}$K atoms. The collision products are directly observed and the spin-changing dynamics is measured. Based on a two-body collision model, the experimental results are simultaneously fitted from which the spin-changing rate coefficient of $ 1.9(2)\times 10^{-12}~\rm{cm^3\cdot s^{-1}}$ is gained, being consistent with the multi-channel quantum defect theory calculation. We further show that the contact parameter of $^6$Li-$^{41}$K mixture can be extracted from the measured spin-changing dynamics. The obtained results are consistent with the first order perturbation theory in the weakly-interacting limit. Our system offers great promise for studying spin-changing interactions in heteronuclear mixtures.

cond-mat.quant-gas