Local spin and open quantum systems: clarifying misconceptions, unifying approaches

Local Spin and Open Quantum Systems: Clarifying Misconceptions, Unifying Approaches

10.26434/chemrxiv.13200245.v1 ◽

2020 ◽

Author(s):

Angel Martín Pendás ◽

Evelio Francisco

Keyword(s):

Quantum Control ◽

Open Systems ◽

Open Quantum Systems ◽

Real Space ◽

Quantum Systems ◽

Spin Coupling ◽

Molecular Systems ◽

Open Quantum ◽

Local Spin

We now show that Clark and Davidson local spins operators are perfectly defined subsystem operators if a fragment is taken as an open quantum system (OQS). Open systems have become essential in quantum control and quantum computation, but have not received much attention in Chemistry. We have already shown (J. Chem. Theory Comput. 2018, 15, 1079) how real space OQSs can be defined in molecular systems and how they offer new insights relating quantum mechanical entaglement and chemical bonding. The OQS account of local spin that we offer yields a rigorous, yet easily accessible way to rationalize local spin values. A fragment is found in a mixed state direct sum of sectors characterized by different number of electrons that occur with different probabilities. The local spin is then a weighted sum of otherwise standard S(S+1) values. With OQS glasses, it is obvious that atomic or fragment spins should not vanish. Our approach thus casts doubts on any procedure used to annihilate them, like those used by Mayer and coworkers. OQS local spins allow for a fruitful use of models. One can propose easily sector probabilities for localized, covalent, ionic, zwitterionic, etc. situations, and examine their ideal local spins. We have mapped all 2c-2e cases, and shown how to do that in general multielectron cases. The role of electron correlation is also studied by tuning the Hubbard U/t parameter for H chains. Correlation induced localization changes the spin-coupling patterns even qualitatively, and show how the limiting antiferromagnet arises.

Download Full-text

Local Spin and Open Quantum Systems: Clarifying Misconceptions, Unifying Approaches

10.26434/chemrxiv.13200245 ◽

2020 ◽

Author(s):

Angel Martín Pendás ◽

Evelio Francisco

Keyword(s):

Quantum Control ◽

Open Systems ◽

Open Quantum Systems ◽

Real Space ◽

Quantum Systems ◽

Spin Coupling ◽

Molecular Systems ◽

Open Quantum ◽

Local Spin

We now show that Clark and Davidson local spins operators are perfectly defined subsystem operators if a fragment is taken as an open quantum system (OQS). Open systems have become essential in quantum control and quantum computation, but have not received much attention in Chemistry. We have already shown (J. Chem. Theory Comput. 2018, 15, 1079) how real space OQSs can be defined in molecular systems and how they offer new insights relating quantum mechanical entaglement and chemical bonding. The OQS account of local spin that we offer yields a rigorous, yet easily accessible way to rationalize local spin values. A fragment is found in a mixed state direct sum of sectors characterized by different number of electrons that occur with different probabilities. The local spin is then a weighted sum of otherwise standard S(S+1) values. With OQS glasses, it is obvious that atomic or fragment spins should not vanish. Our approach thus casts doubts on any procedure used to annihilate them, like those used by Mayer and coworkers. OQS local spins allow for a fruitful use of models. One can propose easily sector probabilities for localized, covalent, ionic, zwitterionic, etc. situations, and examine their ideal local spins. We have mapped all 2c-2e cases, and shown how to do that in general multielectron cases. The role of electron correlation is also studied by tuning the Hubbard U/t parameter for H chains. Correlation induced localization changes the spin-coupling patterns even qualitatively, and show how the limiting antiferromagnet arises.

Download Full-text

Relaxation of interacting open quantum systems

Uspekhi Fizicheskih Nauk ◽

10.3367/ufnr.2018.06.038359 ◽

2018 ◽

Vol 189 (05) ◽

Author(s):

Vladislav Yu. Shishkov ◽

Evgenii S. Andrianov ◽

Aleksandr A. Pukhov ◽

Aleksei P. Vinogradov ◽

A.A. Lisyansky

Keyword(s):

Open Quantum Systems ◽

Quantum Systems ◽

Open Quantum

Download Full-text

Open quantum systems & decoherence

Physics Subject Headings (PhySH) ◽

10.29172/fce63f544c304bd4b3b61a4d58bdaceb ◽

2018 ◽

Keyword(s):

Open Quantum Systems ◽

Quantum Systems ◽

Open Quantum

Download Full-text

Hamiltonian assignment for open quantum systems

Physical Review Research ◽

10.1103/physrevresearch.2.033251 ◽

2020 ◽

Vol 2 (3) ◽

Author(s):

Eugene F. Dumitrescu ◽

Pavel Lougovski

Keyword(s):

Open Quantum Systems ◽

Quantum Systems ◽

Open Quantum

Download Full-text

Perturbation Analysis of Quantum Reset Models

Journal of Statistical Physics ◽

10.1007/s10955-021-02752-y ◽

2021 ◽

Vol 183 (1) ◽

Author(s):

Géraldine Haack ◽

Alain Joye

Keyword(s):

Steady State ◽

Perturbation Analysis ◽

Open Quantum Systems ◽

Quantum Systems ◽

Markov Semigroup ◽

Coupling Constant ◽

Coupling Term ◽

Open Quantum ◽

Effective Dynamics ◽

A Chain

AbstractThis paper is devoted to the analysis of Lindblad operators of Quantum Reset Models, describing the effective dynamics of tri-partite quantum systems subject to stochastic resets. We consider a chain of three independent subsystems, coupled by a Hamiltonian term. The two subsystems at each end of the chain are driven, independently from each other, by a reset Lindbladian, while the center system is driven by a Hamiltonian. Under generic assumptions on the coupling term, we prove the existence of a unique steady state for the perturbed reset Lindbladian, analytic in the coupling constant. We further analyze the large times dynamics of the corresponding CPTP Markov semigroup that describes the approach to the steady state. We illustrate these results with concrete examples corresponding to realistic open quantum systems.

Download Full-text

Matrix Product State Simulations of Non-Equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures

Entropy ◽

10.3390/e23010077 ◽

2021 ◽

Vol 23 (1) ◽

pp. 77

Author(s):

Angus J. Dunnett ◽

Alex W. Chin

Keyword(s):

Finite Temperature ◽

Open Quantum Systems ◽

Quantum Systems ◽

Steady States ◽

Matrix Product ◽

Open Quantum ◽

Matrix Product State ◽

Wide Range ◽

Boson Model ◽

Non Equilibrium

Simulating the non-perturbative and non-Markovian dynamics of open quantum systems is a very challenging many body problem, due to the need to evolve both the system and its environments on an equal footing. Tensor network and matrix product states (MPS) have emerged as powerful tools for open system models, but the numerical resources required to treat finite-temperature environments grow extremely rapidly and limit their applications. In this study we use time-dependent variational evolution of MPS to explore the striking theory of Tamascelli et al. (Phys. Rev. Lett. 2019, 123, 090402.) that shows how finite-temperature open dynamics can be obtained from zero temperature, i.e., pure wave function, simulations. Using this approach, we produce a benchmark dataset for the dynamics of the Ohmic spin-boson model across a wide range of coupling strengths and temperatures, and also present a detailed analysis of the numerical costs of simulating non-equilibrium steady states, such as those emerging from the non-perturbative coupling of a qubit to baths at different temperatures. Despite ever-growing resource requirements, we find that converged non-perturbative results can be obtained, and we discuss a number of recent ideas and numerical techniques that should allow wide application of MPS to complex open quantum systems.

Download Full-text

Memory Effects in Quantum Dynamics Modelled by Quantum Renewal Processes

Entropy ◽

10.3390/e23070905 ◽

2021 ◽

Vol 23 (7) ◽

pp. 905

Author(s):

Nina Megier ◽

Manuel Ponzi ◽

Andrea Smirne ◽

Bassano Vacchini

Keyword(s):

Quantum Dynamics ◽

Open Quantum System ◽

Open Quantum Systems ◽

Phenomenological Approach ◽

Quantum Systems ◽

Renewal Processes ◽

Continuous Part ◽

Trace Distance ◽

Open Quantum ◽

And Control

Simple, controllable models play an important role in learning how to manipulate and control quantum resources. We focus here on quantum non-Markovianity and model the evolution of open quantum systems by quantum renewal processes. This class of quantum dynamics provides us with a phenomenological approach to characterise dynamics with a variety of non-Markovian behaviours, here described in terms of the trace distance between two reduced states. By adopting a trajectory picture for the open quantum system evolution, we analyse how non-Markovianity is influenced by the constituents defining the quantum renewal process, namely the time-continuous part of the dynamics, the type of jumps and the waiting time distributions. We focus not only on the mere value of the non-Markovianity measure, but also on how different features of the trace distance evolution are altered, including times and number of revivals.

Download Full-text