About

Yoram Alhassid is the Frederick Phineas Rose Professor of Physics at Yale University. He is a theoretical physicist with broad expertise in many-body nuclear theory, cold atom physics, mesoscopic physics, and nanoscience. His research contributions include the development of novel methods for understanding the statistical properties of quantum many-body systems, such as atomic nuclei, cold atomic Fermi gases, and quantum dots. Prof. Alhassid has developed powerful auxiliary-field quantum Monte Carlo (AFMC) methods in Fock space, enabling the microscopic study of heavy nuclei and nuclear reactions relevant to stellar nucleosynthesis and nuclear reactor design. His work extends to cold atomic Fermi gases, where he has implemented controlled lattice AFMC methods to study thermodynamics and pairing correlations, including the calculation of the contact in the unitary Fermi gas. Additionally, his research explores mesoscopic systems and nanostructures, developing statistical theories of quantum dots and investigating pairing correlations in nano-scale metallic grains. He received his Ph.D. from the Hebrew University of Jerusalem in 1979, and his distinguished career includes awards such as the Aharon Katzir prize, the Alfred P. Sloan Foundation fellowship, and the Alexander von Humboldt Senior Scientist Award. He has held positions as a scientific director at the Max Planck Institute for Complex Systems and organized interdisciplinary programs at leading institutions, contributing significantly to the advancement of many-body physics.

Research topics

• Quantum mechanics
• Physics
• Condensed matter physics
• Nuclear physics
• Statistics
• Statistical physics
• Theoretical physics
• Thermodynamics

Selected publications

• Supplemental Data Files for "Nuclear state and level densities of actinides in the shell-model Monte Carlo"

  Open MIND · 2026-02-10

  articleSenior author

  Additional data files, Python scripts, and plots for the article "Nuclear State and Level Densities of Actinides in the Shell-Model Monte Carlo" by Dallas DeMartini and Yoram Alhassid.

  DOI

• Supplemental Data Files for "Nuclear state and level densities of actinides in the shell-model Monte Carlo"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-10

  articleOpen accessSenior author

  Additional data files, Python scripts, and plots for the article "Nuclear State and Level Densities of Actinides in the Shell-Model Monte Carlo" by Dallas DeMartini and Yoram Alhassid.

  PublisherDOI

• Low-energy enhancement of the magnetic dipole radiation in odd-mass lanthanides

  Physical review. C · 2025-03-11 · 1 citations

  articleOpen accessSenior author

  We compute the magnetic dipole ($M1$) $\ensuremath{\gamma}$-ray strength functions ($\ensuremath{\gamma}\mathrm{SF}\text{s}$) for the odd-mass lanthanides $^{143--151}\mathrm{Nd}$ and $^{147--153}\mathrm{Sm}$ using the shell-model Monte Carlo method in combination with the static-path approximation and the maximum-entropy method. In particular, we quantify the statistical uncertainties in the calculated $M1\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}\mathrm{SFs}$ and show that they are under control for the excitation energies relevant to the experiments despite a Monte Carlo sign problem that originates in the projection onto an odd number of neutrons. We identify a low-energy enhancement (LEE) in the $M1\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}\mathrm{SFs}$ of these odd-mass lanthanides, which was recently observed experimentally in some of them. We also find a scissors mode resonance (SR) in the strongly deformed isotopes. We observe that the decrease in the LEE strength with neutron number along an isotopic chain is compensated for by an increase in the SR strength in the deformed nuclei. We compare our results with recent experiments.

  PublisherOA PDFDOI

• Direct local parametrization of nuclear state densities using the back-shifted Bethe formula

  Nuclear Physics A · 2025-02-14 · 1 citations

  articleOpen accessSenior authorCorresponding

  Level densities are often parametrized using the back-shifted Bethe formula (BBF) for nuclei that have experimental data for s-wave neutron resonance average spacings and a complete discrete level sequence at low excitation energies. However, these parametrizations require additional modeling of the dependence of the spin-cutoff parameter on excitation energy. Here we avoid the need to model the spin distribution of level densities by using the experimental data to parametrize directly the state densities, for which the BBF does not depend on the spin-cutoff parameter. This approach allows for a local parameterization of state densities that is independent of the spin-cutoff parameter. We provide these parameters in a tabulated form for applications in nuclear reaction calculations and for testing microscopic approaches to state densities.

  PublisherOA PDFDOI

• Precision thermodynamics of the strongly interacting Fermi gas in two dimensions

  arXiv (Cornell University) · 2025-11-25

  preprintOpen accessSenior author

  The two-species cold atomic Fermi gas with attractive short-range interactions in two spatial dimensions undergoes a Bardeen-Cooper-Schrieffer (BCS) to a Bose-Einstein Condensate (BEC) crossover as a function of $\ln (k_F a)$, where $a$ is the scattering length. However, the nature of this crossover in the strong coupling regime $\ln(k_F a) \sim 1$ remains poorly understood. In this work we use canonical-ensemble auxiliary-field quantum Monte Carlo methods on discrete lattices to calculate several thermodynamical quantities in the strongly interacting regime, and eliminate systematic errors by extrapolating to continuous time and taking the continuum limit. In particular, we present results for the condensate fraction, spin susceptibility, contact, energy equation of state, and the free energy staggering gap. We identify signatures of a pseudogap regime, in which pairing correlations survive above the critical temperature for superfluidity, in the spin susceptibility and in the free energy staggering gap. These results can be used as a benchmark for future experiments.

  PublisherDOI

• Low-energy enhancement in the magnetic dipole radiation of actinide nuclei

  ArXiv.org · 2025-11-14

  preprintOpen accessSenior author

  Contains the data files and plotting scripts used for creating the article "Low-energy enhancement in the magnetic dipole radiation of actinide nuclei" by Cade Rodgers, Dallas DeMartini and Yoram Alhassid

  PublisherOA PDFDOI

• Precision thermodynamics of the strongly interacting Fermi gas in two dimensions

  The European Physical Journal Special Topics · 2025-10-28

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Correction to: Compound-Nuclear Reactions

  Springer proceedings in physics · 2025-01-01

  book-chapterOpen access
  PublisherOA PDFDOI

• Pseudogap regime of the unitary Fermi gas with lattice auxiliary-field quantum Monte Carlo in the continuum limit

  arXiv (Cornell University) · 2024-08-29

  preprintOpen accessSenior author

  The unitary Fermi gas (UFG) is a strongly correlated system of two-species (spin-1/2) fermions with a short-range attractive interaction modeled by a contact interaction and has attracted much interest across different disciplines. The UFG is considered a paradigm for strongly correlated superfluids and has been investigated extensively, with generally good agreement found between theory and experiment. However, the extent of a pseudogap regime above the critical temperature $T_c$ for superfluidity is still debated both theoretically and experimentally. Here we study thermodynamic properties of the UFG across the superfluid phase transition using finite-temperature lattice auxiliary-field quantum Monte Carlo (AFMC) methods in the canonical ensemble of fixed particle numbers. We extrapolate our lattice AFMC results to the continuous time and continuum limits, thus removing the systematic error associated with the finite filling factor of previous AFMC studies. We determine the critical temperature to be $T_c=0.16(1)\, T_{F}$. For the largest particle number studied $N=114$, the energy-staggering pairing gap is suppressed above a pairing scale temperature of $T^{*}\approx 0.2\,T_F$. The spin susceptibility displays moderate suppression above $T_c$ with a spin gap temperature of $T_s\approx 0.2 \,T_F$. We also calculate a free energy-staggering pairing gap, which shows substantially reduced statistical errors when compared with the energy-staggering gap, allowing for a clear signature of pairing correlations in the finite-size system. All results indicate that the pseudogap regime is narrow, with pseudogap signatures emerging at temperatures below $T^{*}\approx 0.2 \, T_F$. The reduced statistical errors of the free energy gap enable an extrapolation at low temperatures, allowing an estimate of the zero-temperature pairing gap $Δ_E = 0.576(24) \, ε_F$.

  PublisherOA PDFDOI

• Magnetic dipole <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math>-ray strength functions in the crossover from spherical to deformed neodymium isotopes

  Physical review. C · 2024-11-13 · 4 citations

  articleOpen accessSenior author

  The $\ensuremath{\gamma}$-ray strength function is an important input into Hauser-Feshbach calculations of neutron capture in compound nuclear reactions. Experiments suggest an enhancement of the strength function at low energy, but this enhancement has not been reproduced in models of heavy nuclei as conventional shell-model methods become computationally intractable. Using shell-model Monte Carlo methods, the authors have successfully reproduced the low-energy enhancement (LEE) for magnetic dipole transitions in neodymium isotopes, while also illuminating the role of the scissors and spin-flip modes in these $M1$ transitions. If the LEE persists in heavy neutron-rich nuclei, thus significantly enhancing the radiative neutron-capture rates of nuclei near the neutron drip line, it would likely have profound effects on $r$-process nucleosynthesis.

  PublisherOA PDFDOI

Frequent coauthors

• H. Nakada

  Chiba University

  38 shared

• Brian Bush

  National Renewable Energy Laboratory

  35 shared

• C. N. Gilbreth

  28 shared

• P. Fanto

  Yale University

  28 shared

• C. Özen

  Los Alamos National Laboratory

  27 shared

• Konstantin N. Nesterov

  25 shared

• G. F. Bertsch

  24 shared

• F. Iachello

  24 shared

Awards & honors

• Aharon Katzir Prize
• Chaim Weizmann Fellow
• Alfred P. Sloan Foundation fellowship in physics
• Fellow of the American Physical Society
• Alexander von Humboldt Senior Scientist Award