About

Professor Han Pu leads a research group focused on theoretical ultracold atomic physics. The group's research explores the fascinating behaviors exhibited by atoms and molecules when cooled to extremely low temperatures, a regime governed by the principles of Quantum Mechanics. This field investigates the unique quantum phenomena that emerge under such ultracold conditions, contributing to a deeper understanding of atomic and molecular physics. For more detailed information on the group's current research activities, additional resources are available on their Research page. The group is also connected to broader ultracold physics efforts at Rice University through the Rice Laboratory for Ultracold Physics (RLUP).

Research topics

• Physics
• Quantum mechanics
• Theoretical physics
• Condensed matter physics

Selected publications

• Monogamy-of-entanglement-inspired protocol for quantifying bipartite entanglement using spin squeezing

  Physical review. A/Physical review, A · 2025-05-28

  preprintOpen accessSenior author

  Quantum entanglement is an essential resource for quantum science and technology. However, entanglement detection and quantification, via typical entanglement measures such as linear entanglement entropy or negativity, can be a very challenging task. Here we propose a protocol to detect bipartite entanglement in a system of $N$ qubits inspired by the concept of monogamy of entanglement, where, given a total system in a pure state with some bipartite entanglement between two subsystems, subsequent unitary evolution and measurement of one of the subsystems may be used to quantify the entanglement between the two. To address the difficulty of detection, we propose to use spin squeezing to quantify the entanglement within the individual subsystem. Knowing that the relation between spin squeezing and some entanglement measures is not one-to-one, we give some suggestions on how a judicious choice of squeezing Hamiltonian can lead to better results in our protocol. For systems with a small number of qubits, we derive analytical results and show how our protocol can work optimally for GHZ states. For larger systems, we show how the accuracy of the protocol can be improved by a proper choice of the squeezing Hamiltonian. Our protocol presents an alternative for entanglement detection in platforms where state tomography is inaccessible or hard to perform. Additionally, the ideas presented here can be extended beyond spin-only systems to expand their applicability.

  PublisherOA PDFDOI

• Breakdown of the single-mode description of ultradilute quantum droplets in binary Bose mixtures: A perspective from a microscopic bosonic pairing theory

  Physical review. A/Physical review, A · 2025-02-10

  article

  In his seminal proposal of quantum droplets in binary Bose mixtures [D. Petrov, Phys. Rev. Lett. 115, 155302 (2015)], Petrov suggested that the density ratio ${n}_{2}/{n}_{1}$ of the two bosonic components is locked to an optimal value, which is given by the square root of the ratio of the two intraspecies scattering lengths, i.e., $\sqrt{{a}_{11}/{a}_{22}}$. Due to such density locking, quantum droplets can be efficiently described by using an extended Gross-Pitaevskii equation within the single-mode approximation. Here, we find that this single-mode description necessarily breaks down in the deep quantum droplet regime, when the attractive interspecies scattering length ${a}_{12}$ significantly deviates away from the threshold of mean-field collapse (i.e., $\ensuremath{-}\sqrt{{a}_{11}{a}_{22}}$). By applying a bosonic pairing theory, we show that the density ratio is allowed to fluctuate in a sizable interval. Most importantly, the optimal density ratio would be very different from $\sqrt{{a}_{11}/{a}_{22}}$, in the case of unequal intraspecies scattering lengths (${a}_{11}\ensuremath{\ne}{a}_{22}$). Our finding might provide a plausible microscopic explanation of the puzzling low critical particle number of quantum droplets, as experimentally observed. Our predicted interval of the density ratio, as a function of the interspecies scattering length, could also be experimentally examined in cold-atom laboratories in the near future.

  PublisherDOI

• Floquet geometric squeezing in fast-rotating condensates

  Physical review. A/Physical review, A · 2025-01-14 · 2 citations

  articleSenior author
  PublisherDOI

• Interpreting convolutional neural networks' low-dimensional approximation to quantum spin systems

  Physical Review Research · 2025-01-23

  articleOpen access

  Convolutional neural networks (CNNs) have been employed along with variational Monte Carlo methods for finding the ground state of quantum many-body spin systems with great success. However, it remains uncertain how CNNs, with a model complexity that scales at most linearly with the number of particles, solve the “curse of dimensionality” and efficiently represent wavefunctions in exponentially large Hilbert spaces. In this work, we use methodologies from information theory, group theory and machine learning, to elucidate how CNN captures relevant physics of quantum systems. We connect CNNs to a class of restricted maximum entropy (MaxEnt) and entangled plaquette correlator product state (EP-CPS) models that approximate symmetry constrained classical correlations between subsystems. For the final part of the puzzle, inspired by similar analyses for matrix product states and tensor networks, we show that the CNNs rely on the spectrum of each subsystem's entanglement Hamiltonians as captured by the size of the convolutional filter. All put together, these allow CNNs to simulate exponential quantum wave functions using a model that scales at most linear in system size as well as provide clues into when CNNs might fail to simulate Hamiltonians. We incorporate our insights into a new training algorithm and demonstrate its improved efficiency, accuracy, and robustness. Finally, we use regression analysis to show how the CNNs solutions can be used to identify salient physical features of the system that are the most relevant to an efficient approximation. Our integrated approach can be extended to similarly analyzing other neural network architectures and quantum spin systems.

  PublisherOA PDFDOI

• Delocalized Excitation Transfer in Open Quantum Systems with Long-Range Interactions

  PRX Quantum · 2025-10-01 · 1 citations

  articleOpen access

  The interplay between coherence and system-environment interactions is at the basis of a wide range of phenomena, from quantum information processing to charge and energy transfer in molecular systems, biomolecules, and photochemical materials. In this work, we use a Frenkel exciton model with long-range interacting qubits coupled to a damped collective bosonic mode to investigate vibrationally assisted transfer processes in donor-acceptor systems featuring internal substructures analogous to light-harvesting complexes. We find that certain delocalized excitonic states maximize the transfer rate and that the entanglement is preserved during the dissipative transfer over a wide range of parameters. We investigate the reduction in transfer caused by static disorder, white noise, and finite temperature and study how transfer efficiency scales as a function of the number of dimerized monomers and the component number of each monomer, finding which excitonic states lead to optimal transfer. Finally, we provide a realistic experimental setting to realize this model in analog trapped-ion quantum simulators. Analog quantum simulation of systems comprising many and increasingly complex monomers could offer valuable insights into the design of light-harvesting materials, particularly in the nonperturbative intermediate parameter regime examined in this study, where classical simulation methods are resource intensive.

  PublisherDOI

• Floquet geometric squeezing in fast-rotating condensates

  arXiv (Cornell University) · 2025-01-06

  preprintOpen accessSenior author

  Constructing and manipulating quantum states in fast-rotating Bose-Einstein condensates (BEC) has long stood as a significant challenge as the rotating speed approaching the critical velocity. Although the recent experiment [Science, 372, 1318 (2021)] has realized the geometrically squeezed state of the guiding-center mode, the remaining degree of freedom, the cyclotron mode, remains unsqueezed due to the large energy gap of Landau levels. To overcome this limitation, in this paper, we propose a Floquet-based state-preparation protocol by periodically driving an anisotropic potential. This protocol not only facilitates the single cyclotron-mode squeezing, but also enables a two-mode squeezing. Such two-mode squeezing offers a richer set of dynamics compared to single-mode squeezing and can achieve wavepacket width well below the lowest Landau level limit. Our work provides a highly controllable knob for realizing diverse geometrically squeezed states in ultracold quantum gases within the quantum Hall regime.

  PublisherOA PDFDOI

• Quantum Simulation of Charge and Exciton Transfer in Multi-mode Models with Engineered Reservoirs

  Research Square · 2025-07-31 · 1 citations

  preprintOpen access
  PublisherOA PDFDOI

• Quantum simulation of charge and exciton transfer in multi-mode models using engineered reservoirs

  Nature Communications · 2025-12-05

  articleOpen access

  Quantum simulation enables studies of open-system dynamics in non-perturbative regimes by programming electronic, vibrational, and environmental interactions on comparable energy scales. Trapped ions offer this capability, combining spins, phonons, and tunable dissipation on one platform. We demonstrate an open-system quantum simulation of charge and exciton transfer in a multi-mode linear vibronic coupling model. Using tailored spin-phonon interactions with reservoir engineering, we emulate a system with two dissipative vibrational modes coupled to donor and acceptor sites and track its non-equilibrium dynamics. We continuously tune the system from the charge transfer regime to the vibrationally assisted exciton transfer regime and find that degenerate modes enhance transfer rates at large energy gaps, while non-degenerate modes activate pathways that reduce the energy-gap dependence. Thus, the presence of one additional vibration introduces interfering pathways and reshapes non-perturbative excitation transfer. Our results establish a scalable, hardware-efficient route to simulate vibronic processes with engineered environments. Recent developments in trapped-ion platforms are opening towards quantum simulation of chemical dynamics. Here, the authors demonstrate independent control of spin-phonon coupling and reservoir engineering in a two-mode trapped-ion system to simulate excitation transfer dynamics.

  PublisherOA PDFDOI

• Quantum Simulation of Charge and Exciton Transfer in Multi-mode Models using Engineered Reservoirs

  ArXiv.org · 2025-05-28

  preprintOpen access

  Quantum simulation offers a route to study open-system molecular dynamics in non-perturbative regimes by programming the interactions among electronic, vibrational, and environmental degrees of freedom on similar energy scales. Trapped-ion systems possess this capability, with their native spins, phonons, and tunable dissipation integrated within a single platform. Here, we demonstrate an open-system quantum simulation of charge and exciton transfer in a multi-mode linear vibronic coupling model. Employing tailored spin-phonon interactions alongside reservoir engineering techniques, we emulate a system with two dissipative vibrational modes coupled to donor and acceptor electronic sites and follow its non-equilibrium dynamics. We continuously tune the system from the charge transfer (CT) regime to the vibrationally assisted exciton transfer (VAET) regime by controlling the vibronic coupling strengths. We find that degenerate modes enhance CT and VAET rates at large energy gaps, while non-degenerate modes activate slow-mode pathways that reduce the energy-gap dependence, thus enlarging the window for efficient transfer. These results show that the presence of one additional vibration introduces interfering vibrationally assisted pathways and reshapes non-perturbative quantum excitation transfer. Our work establishes a scalable and hardware-efficient route to simulating chemically relevant, many-mode vibronic processes with engineered environments, guiding the design of next-generation organic photovoltaics and molecular electronics.

  PublisherOA PDFDOI

• Enhanced photocatalytic performance of titanium dioxides by modulating defect contents and carbon deposits through a simple gas–solid interface reaction

  New Journal of Chemistry · 2025-01-01 · 2 citations

  article1st authorCorresponding

  TiO 2 modified with a deposited carbon layer and oxygen vacancy defects, exhibits excellent photocatalytic degradation of RhB under visible light due to the narrowed bandgap and fast charge separation and transfer.

  PublisherDOI

Recent grants

• Manipulating Spinor Quantum Gases

  NSF · $283k · 2019–2022

• Superfluid Atomic Bosons, Fermions and Their Mixtures

  NSF · $180k · 2012–2015

• Superfluid Atomic Bosons, Fermions and Their Mixtures

  NSF · $204k · 2009–2012

• Manipulating Ultracold Atoms --- from One to Many

  NSF · $305k · 2015–2019

• Manipulating Spinor Quantum Gases --- Spin, Charge and Their Interplay

  NSF · $300k · 2022–2025

Frequent coauthors

• N. P. Bigelow

  University of Rochester

  55 shared

• Guang‐Can Guo

  University of Science and Technology of China

  41 shared

• Hui Hu

  36 shared

• Xiang-Fa Zhou

  Hefei University

  33 shared

• Zheng-Wei Zhou

  32 shared

• Hong Y. Ling

  Rowan University

  32 shared

• Lei Jiang

  Linyi University

  31 shared

• Pierre Meystre

  University of Arizona

  29 shared