Thomas D. Cohen
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The organizations/institutes from the scholar's latest article
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Thomas D. Cohen has a total of 132 co-authors. Here are the top co-authors by number of shared publications:
- Richard F. Lebed
Arizona State University
38 shared publications - Aleksey Cherman
Department of Physics University of Maryland 20742-4111 College Park MD
13 shared publications - Vojtěch Krejčiřík
Maryland Center for Fundamental Physics Department of Physics University of Maryland 20742-4111 College Park MD
9 shared publications - Yiming Cai
Maryland Center for Fundamental Physics Department of Physics University of Maryland College Park MD USA
8 shared publications - Daniel C. Dakin
Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
7 shared publications - Elizabeth S. Werbos
Department of Physics University of Maryland 20742-4111 College Park MD
7 shared publications
Latest Publications
- Open Access
- 1 October 2026
- Published by American Physical Society (APS) in Physical Review C
- Vol. 114 (4) , 045202
Massive Thirring / sine-Gordon model with nonzero current density
This paper determines the zero-temperature equation of state for the massive Thirring / sine-Gordon model. This demonstrates recently derived model-independent upper and lower bounds on the zero-temperature equation of state with fixed number density from systems with a nonzero current density. That approach is potentially valuable as Monte Carlo calculations with a current density avoid the sign problem in the Euclidean formulation. An advantage to illustrating these bounds in the massive Thirring/sine-Gordon model is that the relevant calculations with both a number density and a current density can be done using a Bethe ansatz. For this model, optimal bounds constrain the energy density as a function of number density by a factor of two from above and below at high densities for all choices of couplings. The lower bound becomes exact at low densities, while the upper bound approaches the worst constraint of a factor of 4.90 .
- 1 October 2026
- Published by American Physical Society (APS) in Physical Review C
- Vol. 114 (4) , 045202
Open AccessMassive Thirring / sine-Gordon model with nonzero current density
This paper determines the zero-temperature equation of state for the massive Thirring / sine-Gordon model. This demonstrates recently derived model-independent upper and lower bounds on the zero-temperature equation of state with fixed number density from systems with a nonzero current density. That approach is potentially valuable as Monte Carlo calculations with a current density avoid the sign problem in the Euclidean formulation. An advantage to illustrating these bounds in the massive Thirring/sine-Gordon model is that the relevant calculations with both a number density and a current density can be done using a Bethe ansatz. For this model, optimal bounds constrain the energy density as a function of number density by a factor of two from above and below at high densities for all choices of couplings. The lower bound becomes exact at low densities, while the upper bound approaches the worst constraint of a factor of 4.90 .
- Open Access
- 23 June 2026
- Published by Springer Nature in The European Physical Journal A
- Vol. 62 (6) , 122
Numerical study of computational cost of maintaining adiabaticity for long paths
Recent work [1] argued that the scaling of a dimensionless quantity $$Q_D$$ with path length is a better proxy for quantifying the scaling of the computational cost of maintaining adiabaticity than the timescale. It also conjectured that generically the scaling will be superlinear (although special cases exist in which it is linear). The quantity $$Q_D$$ depends only on the properties of ground states along the Hamiltonian path and the rate at which the path is followed. In this paper, we demonstrate that this conjecture holds for simple Hamiltonian systems that can be studied numerically. In particular, the systems studied exhibit the behavior that $$Q_D$$ grows approximately as $$L \log L$$ where L is the path length when the threshold error is fixed.- 23 June 2026
- Published by Springer Nature in The European Physical Journal A
- Vol. 62 (6) , 122
Open AccessNumerical study of computational cost of maintaining adiabaticity for long paths
Recent work [1] argued that the scaling of a dimensionless quantity $$Q_D$$ with path length is a better proxy for quantifying the scaling of the computational cost of maintaining adiabaticity than the timescale. It also conjectured that generically the scaling will be superlinear (although special cases exist in which it is linear). The quantity $$Q_D$$ depends only on the properties of ground states along the Hamiltonian path and the rate at which the path is followed. In this paper, we demonstrate that this conjecture holds for simple Hamiltonian systems that can be studied numerically. In particular, the systems studied exhibit the behavior that $$Q_D$$ grows approximately as $$L \log L$$ where L is the path length when the threshold error is fixed. - 7 May 2026
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 136 (18) , 181901
Method to Obtain Bounds on the Equation of State of Cold Nuclear Matter from Imaginary Chemical Potentials
The sign problem in numerical calculations of the QCD Euclidean space path integral of QCD with a chemical potential vanishes if the chemical potential is imaginary. Moreover, calculations of the partition function with imaginary chemical potentials are equivalent to calculations with Lagrange multipliers enforcing the current density. At zero temperature, Lorentz boosts allow one to deduce properties of systems with both number density and current density from properties of systems with a current density alone; this allows both upper and lower bounds to be determined for the equation of state in the form of energy density as a function of number density.
- 7 May 2026
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 136 (18) , 181901
Method to Obtain Bounds on the Equation of State of Cold Nuclear Matter from Imaginary Chemical Potentials
The sign problem in numerical calculations of the QCD Euclidean space path integral of QCD with a chemical potential vanishes if the chemical potential is imaginary. Moreover, calculations of the partition function with imaginary chemical potentials are equivalent to calculations with Lagrange multipliers enforcing the current density. At zero temperature, Lorentz boosts allow one to deduce properties of systems with both number density and current density from properties of systems with a current density alone; this allows both upper and lower bounds to be determined for the equation of state in the form of energy density as a function of number density.
- Open Access
- 17 April 2026
- Published by Springer Nature in The European Physical Journal D
- Vol. 80 (4) , 41
Practical limitations of the switching theorem for adiabatic state preparation
The viability of adiabatic quantum computation depends on the slow evolution of the Hamiltonian. The adiabatic switching theorem provides an asymptotic series for error estimates in 1/ T , based on the lowest nonzero derivative of the Hamiltonian and its eigenvalues at the endpoints. Modifications at the endpoints in practical implementations can modify this scaling behavior, suggesting opportunities for error reduction by altering endpoint behavior while keeping intermediate evolution largely unchanged. Such modifications can significantly reduce errors for long evolution times, but they may also require exceedingly long timescales to reach the hyperadiabatic regime, limiting their practicality. This paper explores the transition between the adiabatic and hyperadiabatic regimes in simple low-dimensional Hamiltonians, highlighting the impact of modifications of the endpoints on approaching the asymptotic behavior described by the switching theorem. Graphical
- 17 April 2026
- Published by Springer Nature in The European Physical Journal D
- Vol. 80 (4) , 41
Open AccessPractical limitations of the switching theorem for adiabatic state preparation
The viability of adiabatic quantum computation depends on the slow evolution of the Hamiltonian. The adiabatic switching theorem provides an asymptotic series for error estimates in 1/ T , based on the lowest nonzero derivative of the Hamiltonian and its eigenvalues at the endpoints. Modifications at the endpoints in practical implementations can modify this scaling behavior, suggesting opportunities for error reduction by altering endpoint behavior while keeping intermediate evolution largely unchanged. Such modifications can significantly reduce errors for long evolution times, but they may also require exceedingly long timescales to reach the hyperadiabatic regime, limiting their practicality. This paper explores the transition between the adiabatic and hyperadiabatic regimes in simple low-dimensional Hamiltonians, highlighting the impact of modifications of the endpoints on approaching the asymptotic behavior described by the switching theorem. Graphical
- Open Access
The Silver Blaze Problem in QCD
This article provides a pedagogical introduction to the Silver Blaze problem. This problem refers to the difficulty of reconciling to perspectives on QCD with a chemical potential. The first is the phenomenological fact that at $T=0$ QCD remains in its ground state -- the vacuum -- with all physical observables unchanged whenever the magnitude of a chemical potential is less than some critical value. The second is the fact that in functional integral treatments, the inclusion of any nonzero chemical potential changes all eigenvalues of the Dirac operator for every gauge configuration, leading to a natural expectation that the functional determinants also changes, which leads to the expectation that physical observables should be altered. The problem amounts to explaining why nothing happens below the critical chemical potential. By focusing on the eigenvalues of $γ_0$ times the Dirac operator rather than the Dirac operator itself, it is possible to show that for QCD with two flavors and identical quark masses, an isospin chemical potential with a magnitude less than $m_π$ (and no baryon chemical potential), or a baryon chemical potential of less than $\frac{3}{2} m_π$ (and no isospin chemical potential), the functional integerals at $T=0$ themselves remain unchanged in all configurations that contribute to the functional integral with non-vanishing weight. However, for $μ_{\rm crit}μ_B > \frac{3}{2} m_π$, the Silver Blaze phenomenon arises due to functional determinants having nontrivial phases that lead to cancellations between different gauge configurations. The mechanism leading to such cancellations remains unknown.Open AccessThe Silver Blaze Problem in QCD
This article provides a pedagogical introduction to the Silver Blaze problem. This problem refers to the difficulty of reconciling to perspectives on QCD with a chemical potential. The first is the phenomenological fact that at $T=0$ QCD remains in its ground state -- the vacuum -- with all physical observables unchanged whenever the magnitude of a chemical potential is less than some critical value. The second is the fact that in functional integral treatments, the inclusion of any nonzero chemical potential changes all eigenvalues of the Dirac operator for every gauge configuration, leading to a natural expectation that the functional determinants also changes, which leads to the expectation that physical observables should be altered. The problem amounts to explaining why nothing happens below the critical chemical potential. By focusing on the eigenvalues of $γ_0$ times the Dirac operator rather than the Dirac operator itself, it is possible to show that for QCD with two flavors and identical quark masses, an isospin chemical potential with a magnitude less than $m_π$ (and no baryon chemical potential), or a baryon chemical potential of less than $\frac{3}{2} m_π$ (and no isospin chemical potential), the functional integerals at $T=0$ themselves remain unchanged in all configurations that contribute to the functional integral with non-vanishing weight. However, for $μ_{\rm crit}μ_B > \frac{3}{2} m_π$, the Silver Blaze phenomenon arises due to functional determinants having nontrivial phases that lead to cancellations between different gauge configurations. The mechanism leading to such cancellations remains unknown. - 23 May 2025
- Published by American Physical Society (APS) in Physical Review C
- Vol. 111 (5)
Hypertriton puzzle in relativistic heavy-ion collisions
- 23 May 2025
- Published by American Physical Society (APS) in Physical Review C
- Vol. 111 (5)
Hypertriton puzzle in relativistic heavy-ion collisions
- 11 April 2025
- Published by American Physical Society (APS) in Physical Review A
- Vol. 111 (4) , 042612
Asymptotic errors in adiabatic evolution
The adiabatic theorem in quantum mechanics implies that if a system is in a discrete eigenstate of a Hamiltonian and the Hamiltonian evolves in time arbitrarily slowly, the system will remain in the corresponding eigenstate of the evolved Hamiltonian. Understanding corrections to the adiabatic result that arise when the evolution of the Hamiltonian is slow, but not arbitrarily slow, has become increasingly important, especially since adiabatic evolution has been proposed as a method of state preparation in quantum computing. This paper identifies two regimes, an adiabatic regime in which corrections are generically small and can depend on details of the evolution throughout the path and a hyperadiabatic regime in which the error is given by a form similar to an asymptotic expansion in the inverse of the evolution time with the coefficients depending principally on the behavior at the endpoints. However, the error in this hyperadiabatic regime is neither given by a true asymptotic series nor solely dependent on the endpoints: The coefficients combine the contributions from both endpoints, with relative phase factors that depend on the average spectral gaps along the trajectory, multiplied by the evolution time. The central result of this paper is to identify a quantity, referred to as the typical error, which is obtained by appropriately averaging the error over evolution times that are small compared to the evolution time itself. This typical error is characterized by an asymptotic series and depends solely on the endpoints of the evolution, remaining independent of the details of the intermediate evolution.
- 11 April 2025
- Published by American Physical Society (APS) in Physical Review A
- Vol. 111 (4) , 042612
Asymptotic errors in adiabatic evolution
The adiabatic theorem in quantum mechanics implies that if a system is in a discrete eigenstate of a Hamiltonian and the Hamiltonian evolves in time arbitrarily slowly, the system will remain in the corresponding eigenstate of the evolved Hamiltonian. Understanding corrections to the adiabatic result that arise when the evolution of the Hamiltonian is slow, but not arbitrarily slow, has become increasingly important, especially since adiabatic evolution has been proposed as a method of state preparation in quantum computing. This paper identifies two regimes, an adiabatic regime in which corrections are generically small and can depend on details of the evolution throughout the path and a hyperadiabatic regime in which the error is given by a form similar to an asymptotic expansion in the inverse of the evolution time with the coefficients depending principally on the behavior at the endpoints. However, the error in this hyperadiabatic regime is neither given by a true asymptotic series nor solely dependent on the endpoints: The coefficients combine the contributions from both endpoints, with relative phase factors that depend on the average spectral gaps along the trajectory, multiplied by the evolution time. The central result of this paper is to identify a quantity, referred to as the typical error, which is obtained by appropriately averaging the error over evolution times that are small compared to the evolution time itself. This typical error is characterized by an asymptotic series and depends solely on the endpoints of the evolution, remaining independent of the details of the intermediate evolution.
- 2 December 2024
- Published by American Physical Society (APS) in Physical Review A
- Vol. 110 (6)
Corrections to adiabatic behavior for long paths
- 2 December 2024
- Published by American Physical Society (APS) in Physical Review A
- Vol. 110 (6)
Corrections to adiabatic behavior for long paths
- 12 August 2024
- Published by American Physical Society (APS) in Physical Review A
- Vol. 110 (2) , 022417
Zeno effect suppression of gauge drift in quantum simulations
Quantum simulation of lattice gauge theories is a promising tool for the study of many complicated problems including ones with real-time dynamics. For gauge theories, however, there is a major challenge in maintaining gauge invariance during time evolution. Such theories have a full Hilbert space that is larger than the physical space—the set of states which are gauge invariant or equivalently respect the Gauss law. While an exact implementation of Hamiltonian dynamics starting in the physical Hilbert space will keep the system in the physical space, various types of errors will inevitably produce components outside of it. This work proposes a method of suppressing this gauge drift via the Zeno effect. As in the standard picture of the Zeno effect, our method relies on frequent projection onto the physical subspace. Additionally, a technique is discussed to reduce the speed of the gauge drift, which helps to reduce the required frequency of projections. We demonstrate our method on a gauge theory toy model.- 12 August 2024
- Published by American Physical Society (APS) in Physical Review A
- Vol. 110 (2) , 022417
Zeno effect suppression of gauge drift in quantum simulations
Quantum simulation of lattice gauge theories is a promising tool for the study of many complicated problems including ones with real-time dynamics. For gauge theories, however, there is a major challenge in maintaining gauge invariance during time evolution. Such theories have a full Hilbert space that is larger than the physical space—the set of states which are gauge invariant or equivalently respect the Gauss law. While an exact implementation of Hamiltonian dynamics starting in the physical Hilbert space will keep the system in the physical space, various types of errors will inevitably produce components outside of it. This work proposes a method of suppressing this gauge drift via the Zeno effect. As in the standard picture of the Zeno effect, our method relies on frequent projection onto the physical subspace. Additionally, a technique is discussed to reduce the speed of the gauge drift, which helps to reduce the required frequency of projections. We demonstrate our method on a gauge theory toy model.- Open Access
Efficient vacuum state preparation for quantum simulation of strongly interacting local quantum field theories
We present an efficient approach for preparing ground states in the context of strongly interacting local quantum field theories on quantum computers. The approach produces the vacuum state in a time proportional to the square-root of the volume, which is a square-root improvement in speed compared to traditional approaches. The approach exploits a novel method for traversing the path in parameter space in which the resources scale linearly with a path length suitably defined in parameter space. Errors due to practical limitations are controlled and do not exhibit secular growth along the path. The final accuracy can be arbitrarily improved with an additive cost, which is independent of the volume and grows slower than logarithmically with the overlap between the state produced and the exact ground state. We expect that the method could potentially hold practical value not only within the realm of quantum field theories but also in addressing other challenges involving long path lengths.
Open AccessEfficient vacuum state preparation for quantum simulation of strongly interacting local quantum field theories
We present an efficient approach for preparing ground states in the context of strongly interacting local quantum field theories on quantum computers. The approach produces the vacuum state in a time proportional to the square-root of the volume, which is a square-root improvement in speed compared to traditional approaches. The approach exploits a novel method for traversing the path in parameter space in which the resources scale linearly with a path length suitably defined in parameter space. Errors due to practical limitations are controlled and do not exhibit secular growth along the path. The final accuracy can be arbitrarily improved with an additive cost, which is independent of the volume and grows slower than logarithmically with the overlap between the state produced and the exact ground state. We expect that the method could potentially hold practical value not only within the realm of quantum field theories but also in addressing other challenges involving long path lengths.