Publications

Order by: publication date number of citations

• The Floquet Baxterisation

  Yuan Miao, Vladimir Gritsev, Denis V. Kurlov

  SciPost Phys. 16, 078 (2024) · published 18 March 2024 | Toggle abstract · pdf

  Quantum integrability has proven to be a useful tool to study quantum many-body systems out of equilibrium. In this paper we construct a generic framework for integrable quantum circuits through the procedure of Floquet Baxterisation. The integrability is guaranteed by establishing a connection between Floquet evolution operators and inhomogeneous transfer matrices obtained from the Yang-Baxter relations. This allows us to construct integrable Floquet evolution operators with arbitrary depths and various boundary conditions. Furthermore, we focus on the example related to the staggered 6-vertex model. In the scaling limit we establish a connection of this Floquet protocol with a non-rational conformal field theory. Employing the properties of the underlying affine Temperley-Lieb algebraic structure, we demonstrate the dynamical anti-unitary symmetry breaking in the easy-plane regime. We also give an overview of integrability-related quantum circuits, highlighting future research directions.

• The resistance of quantum entanglement to temperature in the Kugel-Khomskii model

  Valerii E. Valiulin, Andrey V. Mikheyenkov, Nikolay M. Chtchelkatchev, Kliment I. Kugel

  SciPost Phys. Core 6, 025 (2023) · published 4 April 2023 | Toggle abstract · pdf

  The Kugel-Khomskii model with entangled spin and orbital degrees of freedom is a good testing ground for many important features in quantum information processing, such as robust gaps in the entanglement spectra. Here, we demonstrate that the entanglement can be also robust under effect of temperature within a wide range of parameters. It is shown, in particular, that the temperature dependence of entanglement often exhibits a nonmonotonic behavior. Namely, there turn out to be ranges of the model parameters, where entanglement is absent at zero temperature, but then, with an increase in temperature, it appears, passes through a maximum, and again vanishes.

• Stochastic representation of the quantum quartic oscillator

  Gennaro Tucci, Stefano De Nicola, Sascha Wald, Andrea Gambassi

  SciPost Phys. Core 6, 029 (2023) · published 14 April 2023 | Toggle abstract · pdf

  Recent experimental advances have inspired the development of theoretical tools to describe the non-equilibrium dynamics of quantum systems. Among them an exact representation of quantum spin systems in terms of classical stochastic processes has been proposed. Here we provide first steps towards the extension of this stochastic approach to bosonic systems by considering the one-dimensional quantum quartic oscillator. We show how to exactly parameterize the time evolution of this prototypical model via the dynamics of a set of classical variables. We interpret these variables as stochastic processes, which allows us to propose a novel way to numerically simulate the time evolution of the system. We benchmark our findings by considering analytically solvable limits and providing alternative derivations of known results.

• Finite-time bounds on the probabilistic violation of the second law of thermodynamics

  Harry J. D. Miller, Martí Perarnau-Llobet

  SciPost Phys. 14, 072 (2023) · published 17 April 2023 | Toggle abstract · pdf

  Jarzynski's equality sets a strong bound on the probability of violating the second law of thermodynamics by extracting work beyond the free energy difference. We derive finite-time refinements to this bound for driven systems in contact with a thermal Markovian environment, which can be expressed in terms of the geometric notion of thermodynamic length. We show that finite-time protocols converge to Jarzynski's bound at a rate slower than $1/\sqrt{\tau}$, where $\tau$ is the total time of the work-extraction protocol. Our result highlights a new application of minimal dissipation processes and demonstrates a connection between thermodynamic geometry and the higher order statistical properties of work.

• Influence of the Pauli principle on two-cluster potential energy

  Yuliya A. Lashko, Victor S. Vasilevsky, Gennady F. Filippov

  SciPost Phys. Proc. 3, 021 (2020) · published 25 February 2020 | Toggle abstract · pdf

  We study effects of the Pauli principle on the potential energy of two-cluster systems. The object of the investigation is the lightest nuclei of p-shell with a dominant $\alpha$-cluster channel. For this aim we construct matrix elements of two-cluster potential energy between cluster oscillator functions with and without full antisymmetrization. Eigenvalues and eigenfunctions of the potential energy matrix are studied in detail. Eigenfunctions of the potential energy operator are presented in oscillator, coordinate and momentum spaces. We demonstrate that the Pauli principle affects more strongly the eigenfunctions than the eigenvalues of the matrix and leads to the formation of resonance and trapped states.

• Variational quantum gate optimization at the pulse level

  Sean Greenaway, Francesco Petiziol, Hongzheng Zhao, Florian Mintert

  SciPost Phys. 16, 082 (2024) · published 22 March 2024 | Toggle abstract · pdf

  We experimentally investigate the viability of a variational quantum gate optimization protocol informed by the underlying physical Hamiltonian of fixed-frequency transmon qubits. Through the successful experimental optimization of two and three qubit quantum gates the utility of the scheme for obtaining gates based on static effective Hamiltonians is demonstrated. The limits of such a strategy are investigated through the optimization of a time-dependent, Floquet-engineered gate, however parameter drift is identified as a key limiting factor preventing the implementation of such a scheme which the variational optimization protocol is unable to overcome.

• Roy Glauber and asymptotic diffraction theory

  Per Osland

  SciPost Phys. Proc. 3, 016 (2020) · published 25 February 2020 | Toggle abstract · pdf

  This is a review of Glauber's asymptotic diffraction theory, in which diffractive scattering is described in terms of interference between semiclassical amplitudes, resulting from a stationary-phase approximation. Typically two such amplitudes are sufficient to accurately describe elastic scattering, but the stationary points are located at complex values of the impact parameter. Their separation controls the interference pattern, and their offsets from the real axis determine the overall fall-off with momentum transfer. Asymptotically, at large momentum transfers, the stationary points move towards singularities of the profile function. I also include some reminiscences from our collaboration.

• Recent progress on the study of nucleon structure from lattice QCD and future perspectives

  Constantia Alexandrou

  SciPost Phys. Proc. 3, 015 (2020) · published 25 February 2020 | Toggle abstract · pdf

  We review the progress achieved within the last five years in the simulations of lattice QCD, as well as in the analysis for selected quantities probing nucleon structure. In particular, we discuss results on the nucleon electromagnetic form factors, $\sigma$-terms, the momentum fraction carried b quark in the nucleon and the helicity and transversity. All quantities are obtained using simulations generated with quark masses fixed to their physical values. In addition, we review the on-going effort to extract parton distribution functions (PDFs) directly from lattice QCD using the quasi-PDFs approach.

• Self-binding of one-dimensional fermionic mixtures with zero-range interspecies attraction

  Jules Givois, Andrea Tononi, and Dmitry S. Petrov

  SciPost Phys. 14, 091 (2023) · published 3 May 2023 | Toggle abstract · pdf

  For sufficiently large mass ratios the attractive exchange force caused by a single light atom interacting with a few heavy identical fermions can overcome their Fermi degeneracy pressure and bind them into an $N+1$ cluster. Here, by using a mean-field approach valid for large $N$, we find that $N+1$ clusters can attract each other and form a self-bound charge density wave, the properties of which we fully characterize. Our work shows that there are no fundamental obstacles for having self-bound states in fermionic mixtures with zero-range interactions.

• Quantum-inspired tempering for ground state approximation using artificial neural networks

  Tameem Albash, Conor Smith, Quinn Campbell, Andrew D. Baczewski

  SciPost Phys. 14, 121 (2023) · published 19 May 2023 | Toggle abstract · pdf

  A large body of work has demonstrated that parameterized artificial neural networks (ANNs) can efficiently describe ground states of numerous interesting quantum many-body Hamiltonians. However, the standard variational algorithms used to update or train the ANN parameters can get trapped in local minima, especially for frustrated systems and even if the representation is sufficiently expressive. We propose a parallel tempering method that facilitates escape from such local minima. This methods involves training multiple ANNs independently, with each simulation governed by a Hamiltonian with a different "driver" strength, in analogy to quantum parallel tempering, and it incorporates an update step into the training that allows for the exchange of neighboring ANN configurations. We study instances from two classes of Hamiltonians to demonstrate the utility of our approach using Restricted Boltzmann Machines as our parameterized ANN. The first instance is based on a permutation-invariant Hamiltonian whose landscape stymies the standard training algorithm by drawing it increasingly to a false local minimum. The second instance is four hydrogen atoms arranged in a rectangle, which is an instance of the second quantized electronic structure Hamiltonian discretized using Gaussian basis functions. We study this problem in a minimal basis set, which exhibits false minima that can trap the standard variational algorithm despite the problem's small size. We show that augmenting the training with quantum parallel tempering becomes useful to finding good approximations to the ground states of these problem instances.