scholarly journals Towards space from Hilbert space: finding lattice structure in finite-dimensional quantum systems

2018 ◽  
Vol 6 (2) ◽  
pp. 181-200 ◽  
Author(s):  
Jason Pollack ◽  
Ashmeet Singh
Keyword(s):  
Hilbert Space ◽  
Lattice Structure ◽  
Quantum Systems ◽  
Finite Dimensional

Reducibility Criteria and a Construction Method for the Analysis of Open Quantum Systems

2019 ◽  
Vol 26 (02) ◽  
pp. 1950010
Author(s):  
Takeo Kamizawa
Keyword(s):  
Hilbert Space ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Computational Method ◽  
System Structure ◽  
Diagonal Form ◽  
Open Quantum ◽  
Complete Reducibility ◽  
Finite Dimensional ◽  
Block Diagonal Form

The analysis of an open quantum system can be by far difficult if the dimension of the system Hilbert space is large or infinite. However, in some cases the dynamics on a finite-dimensional Hilbert space can be decomposed into a block-diagonal form, which simplifies the system structure. In this presentation, we will study several criteria for the complete reducibility and, in addition, a computational method for a basis of each simplified component to apply for the analysis of open quantum systems. An important point of these tools is that they are “effective” methods (one can complete the task in a finite number of steps).

scholarly journals Length filtration of the separable states

2016 ◽  
Vol 472 (2195) ◽  
pp. 20160350 ◽  
Author(s):  
Lin Chen ◽  
Dragomir Ž. Ðoković
Keyword(s):  
Hilbert Space ◽  
Quantum System ◽  
Simple Formula ◽  
Jacobian Matrix ◽  
Critical Length ◽  
Quantum Systems ◽  
Separable States ◽  
Single Qubit ◽  
Finite Dimensional ◽  
Pure Product

We investigate the separable states ρ of an arbitrary multi-partite quantum system with Hilbert space H of dimension d . The length L ( ρ ) of ρ is defined as the smallest number of pure product states having ρ as their mixture. The length filtration of the set of separable states, S , is the increasing chain ∅ ⊊ S 1 ′ ⊆ S 2 ′ ⊆ ⋯ , where S i ′ = { ρ ∈ S : L ( ρ ) ≤ i } . We define the maximum length, L max = max ρ ∈ S L ( ρ ) , critical length, L crit , and yet another special length, L c , which was defined by a simple formula in one of our previous papers. The critical length indicates the first term in the length filtration whose dimension is equal to Dim   S . We show that in general d ≤ L c ≤ L crit ≤ L max ≤ d 2 . We conjecture that the equality L crit = L c holds for all finite-dimensional multi-partite quantum systems. Our main result is that L crit = L c for the bipartite systems having a single qubit as one of the parties. This is accomplished by computing the rank of the Jacobian matrix of a suitable map having S as its range.

A note on normal operators

1963 ◽  
Vol 59 (4) ◽  
pp. 727-729 ◽  
Author(s):  
S. J. Bernau ◽  
F. Smithies
Keyword(s):  
Hilbert Space ◽  
Linear Operator ◽  
Adjoint Operator ◽  
Spectral Theorem ◽  
Unitary Operators ◽  
Unitary Space ◽  
Bounded Linear ◽  
Finite Dimensional ◽  
Normal Operators ◽  
Finite Dimensional Case

We recall that a bounded linear operator T in a Hilbert space or finite-dimensional unitary space is said to be normal if T commutes with its adjoint operator T*, i.e. TT* = T*T. Most of the proofs given in the literature for the spectral theorem for normal operators, even in the finite-dimensional case, appeal to the corresponding results for Hermitian or unitary operators.

scholarly journals When are maps preserving semi-inner products linear?

2021 ◽  
Author(s):  
Paweł Wójcik
Keyword(s):  
Hilbert Space ◽  
Infinite Dimensions ◽  
Normed Spaces ◽  
Linear Isometry ◽  
Inner Products ◽  
Finite Dimensional ◽  
Uniformly Smooth ◽  
Non Linear ◽  
Extra Assumption ◽  
Continuous Injection

AbstractWe observe that every map between finite-dimensional normed spaces of the same dimension that respects fixed semi-inner products must be automatically a linear isometry. Moreover, we construct a uniformly smooth renorming of the Hilbert space $$\ell _2$$ ℓ 2 and a continuous injection acting thereon that respects the semi-inner products, yet it is non-linear. This demonstrates that there is no immediate extension of the former result to infinite dimensions, even under an extra assumption of uniform smoothness.

Quantum systems with finite Hilbert space

2004 ◽  
Vol 67 (3) ◽  
pp. 267-320 ◽  
Author(s):  
A Vourdas
Keyword(s):  
Hilbert Space ◽  
Quantum Systems

scholarly journals Paths of unitary access to exceptional points

2021 ◽  
Vol 2038 (1) ◽  
pp. 012026
Author(s):  
Miloslav Znojil
Keyword(s):  
Hilbert Space ◽  
Phase Transitions ◽  
Quantum Phase Transitions ◽  
Quantum Systems ◽  
Point Of View ◽  
Explicit Description ◽  
Direct Access ◽  
Exceptional Point ◽  
Exceptional Points ◽  
Innovative Idea

Abstract With an innovative idea of acceptability and usefulness of the non-Hermitian representations of Hamiltonians for the description of unitary quantum systems (dating back to the Dyson’s papers), the community of quantum physicists was offered a new and powerful tool for the building of models of quantum phase transitions. In this paper the mechanism of such transitions is discussed from the point of view of mathematics. The emergence of the direct access to the instant of transition (i.e., to the Kato’s exceptional point) is attributed to the underlying split of several roles played by the traditional single Hilbert space of states ℒ into a triplet (viz., in our notation, spaces K and ℋ besides the conventional ℒ ). Although this explains the abrupt, quantum-catastrophic nature of the change of phase (i.e., the loss of observability) caused by an infinitesimal change of parameters, the explicit description of the unitarity-preserving corridors of access to the phenomenologically relevant exceptional points remained unclear. In the paper some of the recent results in this direction are summarized and critically reviewed.

scholarly journals Modelling equilibration of local many-body quantum systems by random graph ensembles

Quantum ◽  
2020 ◽  
Vol 4 ◽  
pp. 273 ◽  
Author(s):  
Daniel Nickelsen ◽  
Michael Kastner
Keyword(s):  
Hilbert Space ◽  
Random Matrices ◽  
Network Theory ◽  
Maximum Flow ◽  
Quantum Systems ◽  
Complex Matrix ◽  
Many Body ◽  
Random Matrix Ensembles ◽  
Matrix Ensembles ◽  
Exact Diagonalisation

We introduce structured random matrix ensembles, constructed to model many-body quantum systems with local interactions. These ensembles are employed to study equilibration of isolated many-body quantum systems, showing that rather complex matrix structures, well beyond Wigner's full or banded random matrices, are required to faithfully model equilibration times. Viewing the random matrices as connectivities of graphs, we analyse the resulting network of classical oscillators in Hilbert space with tools from network theory. One of these tools, called the maximum flow value, is found to be an excellent proxy for equilibration times. Since maximum flow values are less expensive to compute, they give access to approximate equilibration times for system sizes beyond those accessible by exact diagonalisation.

scholarly journals On the Generation of Random Ensembles of Qubits and Qutrits Computing Separability Probabilities for Fixed Rank States

2018 ◽  
Vol 173 ◽  
pp. 02010 ◽  
Author(s):  
Arsen Khvedelidze ◽  
Ilya Rogojin
Keyword(s):  
Quantum Systems ◽  
Separable State ◽  
Mixed States ◽  
Finite Dimensional ◽  
Fixed Rank

The generation of random mixed states is discussed, aiming for the computation of probabilistic characteristics of composite finite dimensional quantum systems. In particular, we consider the generation of random Hilbert-Schmidt and Bures ensembles of qubit and qutrit pairs and compute the corresponding probabilities to find a separable state among the states of a fixed rank.

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