FOR 5522 PhD School on Nonergodic Quantum Dynamics

Session

Poster Session

24 Sept 2024, 16:15

HS 2 (Max Born Hörsaal) (Faculty of Physics)

Description

Catering (Drinks and Snacks)

47. A novel method to classify continuous phase transitions in isolated quantum spin systems

Phase transitions play an important role in all branches of physics, from cosmology to the quark-gluon plasma, as they allow to study the structure of different systems. An important subclass are continuous phase transitions, which are usually related to symmetries and critical phenomena, and allow to classify different systems into universality classes. Each class is characterized by a set of...

59. An internal clock perspective of the dynamics of disordered quantum many body systems

Generically isolated quantum many-body systems reach a thermal equilib-
rium state upon unitary time evolution, which is explained by the Eigenstate
thermalization hypothesis. But, when disorder is added to these systems, the
dynamics becomes extremely slow. These systems are believed to evade ther-
malization even after very long time evolution. Our work sheds light on the slow
dynamics...

45. An internal clock perspective of the dynamics of disordered quantum many body systems

Generically isolated quantum many-body systems reach a thermal equilib-
rium state upon unitary time evolution, which is explained by the Eigenstate
thermalization hypothesis. But, when disorder is added to these systems, the
dynamics becomes extremely slow. These systems are believed to evade ther-
malization even after very long time evolution. Our work sheds light on the slow
dynamics...

55. Can prethermal quantum machines beat thermal ones?

Quantum heat engines operate through quasistatic transformations, and a common assumption is that the working medium is in instantaneous thermal equilibrium. However, several many-body systems offer long-lived prethermal states: can we use them to operate quantum engines with enhanced efficiency? This work considers the quantum Otto cycle, which consists of two adiabatic strokes and two...

48. Characterizing the Entanglement of Mixed States in Anyonic Systems

Entanglement of mixed quantum states can be quantified using the partial transpose and its corresponding entanglement measure, the logarithmic negativity. Recently, the notion of partial transpose has been extended to systems of anyons, which are exotic quasiparticles whose exchange statistics go beyond the bosonic and fermionic case. Studying the fundamental properties of this anyonic partial...

79. Constrained dynamics in synthetic dimensions of ultracold polar molecules

In this work, we explore nonequilibrium dynamics in the system of ultracold polar molecules with synthetic dimensions trapped in a 1D optical lattice. In the system, the excitation of rotational states of the molecule plays a role of a particle that can hop along the synthetic dimension, and two nearest neighbor molecules interact when the synthetic distance is one between them. We numerically...

70. Delocalization in a partially disordered interacting many-body system

We study a partially disordered one-dimensional system with interacting particles. Concretely, we impose a disorder potential to only every other site, followed by a clean site. Our numerical analysis of eigenstate properties is based on the entanglement entropy. Most importantly, at large disorder, there exist eigenstates with large entanglement entropies and significant correlations between...

75. Dynamical screening in and Floquet theory for X-ray spectroscopies

We develop a Floquet theory tailored for resonant inelastic X-ray scattering (RIXS) and present first results employing our formalism. In particular, there are two effects of a periodic driving: (i) the dipolar light-matter transition can be interpreted as a non-local operator, (ii) elastic-like resonances and orbital excitations in the RIXS signal show different selection rules on the Floquet...

46. Entanglement dynamics and eigenstate correlations in strongly disordered quantum many-body systems

The many-body localised phase of quantum systems is an unusual dynamical phase wherein the system fails to thermalise and yet, entanglement grows unboundedly albeit very slowly in time. We present a microscopic theory of this ultraslow growth of entanglement in terms of dynamical eigenstate correlations of strongly disordered, interacting quantum systems in the many-body localised regime....

34. Entanglement phases, localization and multifractality of monitored free fermions in 2D

We investigate the entanglement structure and wave function characteristics of continuously monitored free fermions with $U(1)$-symmetry in 2D. Using exact numerical simulations, we establish the phenomenology of the entanglement transition and explore the similarities and differences with Anderson-type localization transitions. At weak monitoring, we observe characteristic $L\log(L)$...

54. Entanglement transitions in unitary circuit games with free fermions

In the recently introduced unitary circuit games, a competition between two unitary parties, an "entangler" and a "disentangler," can lead to an entanglement phase transition, with a behavior that differes from measurement-induced transitions. In this work, we study unitary circuit games within the framework of free fermion (matchgate) dynamics. First, we examine the game for braiding...

84. Entanglement-based approaches in studying highly correlated 1D spin systems using DMRG

For my poster I would like to show recent works:

First part shows joined work [1] with Clio Agrapidis and Satoshi Nishimoto we investigate the low-energy properties of the dimerized frustrated ferromagnetic (FM) $J_1−J_1'−J_2$ model with the density matrix renormalization group method. We show the ground state phase diagram spanned by a wide range of $J_1'/J_1$ and $J_2/|J_1|$features...

67. Erbium-Lithium: towards a new quantum mixture experiment

In this Erbium-Lithium mixture experiment, we want to realize a quantum gas mixture of erbium and lithium. Remarkably for this mixture is the heavy mass imbalance with a factor of 28, where thermalisation properties will be interesting to observe.

As an additional constrain, we want to trap erbium in a shallow trap at 1064 nm, whereas lithium shall be in a narrow trap at 841 nm, where a...

58. Evidence for simple "arrow of time functions" in closed quantum systems

Through an explicit construction, we assign to any infinite temperature autocorrelation function $C(t)$ a function $\alpha^R(t)$, called "arrow of time function". The construction of $\alpha^R(t)$ from $C(t)$ requires the first $2R$ temporal derivatives of $C(t)$ at times $0$ and $t$. For correlation functions of few body observables we numerically observe the following: There is a...

83. Fading Ergodicity

Eigenstate thermalization hypothesis (ETH) represents a breakthrough in many-body physics since it allows to link thermalization of physical observables with the applicability of random matrix theory (RMT). Recent years were also extremely fruitful in exploring possible counterexamples to thermalization, ranging, among others, from integrability, single-particle chaos, many-body localization,...

74. Fractionalized Prethermalization in the hole doped Hubbard model

Prethermalization phenomena in driven systems are generally understood via a local Floquet Hamiltonian obtained from a high frequency expansion. It turns out that this picture is insufficient for systems with emergent fractionalized excitations. A first example is a driven Kitaev spin liquid which realizes a quasistationary state with vastly different Temperatures of the matter and flux...

72. Fractonic dynamics in breathing pyrochlore

Fracton quantum matter is characterized by excitations with constrained mobility. It remains an open challenge to identify suitable material candidates for such systems. Recently, breathing pyrochlore lattices have been argued as potential candidates for realizing fractonic constraints. Here, we study the dynamics of excitations in a toy model on such a breathing pyrochlore lattice. We show,...

76. Highly-entangled stationary states from strong symmetries

We find that the presence of strong non-Abelian conserved quantities can lead to highly entangled stationary states even for unital quantum channels. We derive exact expressions for the bipartite logarithmic negativity, Rényi negativities, and operator space entanglement for stationary states restricted to one symmetric subspace, with focus on the trivial subspace. As Abelian examples, we show...

63. Imaging dynamics of the confinement transition in a lattice gauge theory

Lattice models can be employed to understand a wide range of phenomena, from elementary particles in high energy physics to effective descriptions of many-body interactions in materials. In these models, studying the emergent phases and their dynamical properties can be extremely challenging as it requires solving many-body problems that are generally beyond the perturbative limit.Using a 2D...

50. Interacting Quantum Hard Disks

The study of quantum matter with extended volume restrictions has revealed intriguing dynamical properties. In our recent investigation, we discovered that the two-dimensional quantum hard disk model exhibits Hilbert space fragmentation and quantum many-body scars. This phenomenon results in non-thermal behavior in the dynamics for specific initial conditions. In this work, we extend this...

77. Krylov locallization as a probe of ergodicity-breaking

Krylov complexity has recently gained attention where the growth of operator complexity in time is measured in terms of the off-diagonal operator Lanczos coefficients. The operator Lanczos algorithm reduces the problem of complexity growth to a single-particle semi-infinite tight-binding chain (known as the Krylov chain). Employing the phenomenon of Anderson localization, we propose the...

43. Lindblad dynamics from spatio-temporal correlation functions in nonintegrable spin-1/2 chains with different boundary conditions

We investigate the Lindblad equation in the context of boundary-driven magnetization transport in spin-1/2 chains. Our central question is whether the nonequilibrium steady state of the open system, including its buildup in time, can be described on the basis of the dynamics in the closed system. To this end, we rely on a previous study [Heitmann et al., Phys. Rev. B 108, L201119 (2023)], in...

40. Long-living prethermalization in nearly integrable spin ladders

Relaxation rates in nearly integrable systems usually increase quadratically with the strength of the perturbation that breaks integrability. We show that the relaxation rates can be significantly smaller in systems that are integrable along two intersecting lines in the parameter space. In the vicinity of the intersection point, the relaxation rates of certain observables increase with the...

64. Loss-induced quantum information jet in an infinite temperature Hubbard chain

Information propagation in the one-dimensional infinite temperature Hubbard model with a dissipative particle sink at the end of a semi-infinite chain is studied. In the strongly interacting limit, the two-site mutual information and the operator entanglement entropy exhibit a rich structure with two propagating information fronts and superimposed interference fringes. A classical reversible...

53. Measurement-induced charge sharpening in 'Bayes non-optimal' U(1) circuits

Ref. [1] introduced measurement-induced charge-sharpening in quantum circuits with qubits undergoing $U(1)$ dynamics alongside 'bath' qudits. Here the charge variance of the density matrix undergoes a (purportedly KT) transition before the entanglement transition. In the $d \rightarrow \infty$ limit, the transition can be described by stat-mech model of constrained hard-core walkers.

We...

36. Non-Equilibrium Quantum Lakes from Counter-Diabatic Driving

One paradigmatic route to exploring states of matter in analog quantum simulators is to perform adiabatic parameter sweeps. However, the presence of small gaps along the sweep, either due to unavoidable quantum phase transitions or competing orders, generically poses an obstacle to preparing desired ground states. Recently, it was shown that the slightly non-equilibrium nature of dynamical...

61. Polynomially filtered exact diagonalization in quantum many body systems

The polynomially filtered exact diagonalization (POLFED) appeared (2020, Sierant) as an efficient method to extract eigenstates and eigenvalues at the middle of the spectrum for system sizes beyond exact diagonalization. The shift-and-invert method already provided those features but because of the filling-in phenomena can not reach as large system sizes as one would want. POLFED enables us to...

49. Quantum hard disks on a lattice

We formulate a quantum version of the hard-disk problem on lattices, which exhibits a natural realization in systems of Rydberg atoms. We find that quantum hard disks exhibit unique dynamical quantum features. In 1D, the crystal melting process displays ballistic behavior as opposed to classical sub-diffusion. For 2D, crystal structures remain intact against most defects, whereas classically...

78. Quantum impurity coupled to the SYK bath

We study a non-equilibrium behavior of an impurity connected to the SYK bath. From the Kadanoff-Baym equations for a noninteracting impurity, we see that the only relevant property for the impurity occupation is a combination of hybridisation and density of states of the bath. These parameters can be adjusted in order to model the impurity connected to any bath of interest. Using this...

51. Quantum many-body physics of MWIS-encoding gadgets

We study the quantum dynamics of the encoding scheme proposed in [Nguyen et al., PRX Quantum 4, 010316 (2023)], which is designed to encode optimization problems on graphs with arbitrary connectivity into Rydberg atom arrays.
Here, a graph vertex is represented by a wire of atoms, and the (crossing) crossing-with-edge gadget is placed at the intersection of two wires to (de)couple the wire...

82. Scaling theory of many-body ergodicity breaking

Scaling theory of localization in noninteracting systems established validity of one-parameter scaling hypothesis in the entire range from the ergodic to localized states.
It is expected that in the presence of interactions, the many-body ergodicity breaking transition gives rise to the breakdown of the one-parameter scaling.
Here, we argue that the one-parameter scaling hypothesis may still...

65. Scarred circuits - implementing integer subspaces within digital chaotic quantum dynamics

Weak ergodicity breaking describes scenarios where a subpart of the Hilbert space does not thermalise under generic time evolution. In Hamiltonian systems, this corresponds to so-called quantum many-body scar states, which are eigenstates of the Hamiltonian but disobey the eigenstate thermalisation hypothesis. Here, we extend the concept to chaotic quantum circuits by implementing conditioned...

62. Scattering theory of chiral edge modes in topological magnon insulators

The well known Quantum Hall effect states that when a finite sample of a conductor is placed in a magnetic field, it develops stable chiral modes strongly localized at the edge. These emergent quasiparticles explore a system of an effective lower dimension: a great deal of attention has been devoted to single-mode properties, but interactions among edge modes are strong and further enhanced by...

73. Search For Quantum Many-Body Scars in Anyon-Models

Hilbert spaces of chains of non-Abelian anyons are constrained by their fusion rules. These constraints may restrict the dynamics and lead to nontrivial thermalization behavior for such systems. As an examplary anyonic model with restricted thermalization, we suggest a one dimensional Fibonacci anyonic chain where the topological charges can perform braid moves around each other. We identify...

35. Space-time correlations in monitored kinetically constrained discrete-time quantum dynamics

State of the art quantum simulators permit local temporal control of interactions and midcircuit readout. These capabilities pave the way towards the exploration of intriguing non-equilibrium phenomena. We illustrate this by discussing a dissipative many-body model with kinetic constraints, which can for example be implemented on Rydberg quantum simulation platforms. The dynamics, which...

41. Temporal Entanglement Profiles in Dual-Unitary Clifford Circuits with Measurements

We study temporal entanglement in dual-unitary Clifford circuits with probabilistic measurements preserving spatial unitarity. We exactly characterize the temporal entanglement barrier in the measurement-free regime, exhibiting ballistic growth and decay and a volume-law peak. In the presence of measurements, we show that the initial ballistic growth of temporal entanglement with bath size is...

57. Thouless time in a spin-1/2 XX ladder

In this study, we try to calculate the Thouless time by analyzing the spectral form factor, survival probability, and diffusion constant within the context of a spin-$1/2$ $XX$ ladder model. We employ numerical methods to compare the Thouless time extracted from these different observables. However, our preliminary results indicate inconsistencies between the methods, prompting concerns about...

52. Ultracold bosons in 2D quasicrystalline and Aubry-Andre systems

Ultracold atoms in optical lattices provide an ideal medium for studies of interacting lattice physics, thanks to their flexible, clean and widely tuneable nature. As such, applying this medium to the investigation of quasiperiodic systems, and the rich physics associated with them, presents a promising avenue to probing a range of physical phenomena, not least those related to localization....

56. Universal dynamics in disordered two-dimensional systems: semiclassical approach

Understanding and predicting the temporal evolution of quantum systems is essential for the development of theoretical physics and modern quantum technologies. A significant group of models that have been intensively researched in recent years are non-ergodic systems of interacting particles. They open the way to future technological solutions such as quantum memories. In the relaxation...

69. What can we learn from time-dependent spectral functions?

The nonequilibrium dynamics of quantum many-body systems is a fascinating topic hosting a rich phenomenology. Going out of equilibrium, transient states can be realized, which are hard to obtain at equilibrium. One important tool for the investigation of such transient states is to examine the time evolution of spectral properties, like time-dependent band structures, single-electron spectral...