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Questions tagged [open-quantum-systems]

The study of open quantum systems is concerned with understanding and predicting the dynamics of quantum systems that are coupled significantly to their surroundings, leading to effects such as dissipation and decoherence.

All quantum systems are coupled to their surroundings to some extent. In some cases, this coupling is so weak that the system can be treated as approximately isolated, so that the usual laws of unitary quantum evolution apply. However, in many cases, the influence of the environment cannot be ignored and the system no longer evolves unitarily, in which case the quantum system is called open. The study of open quantum systems is concerned with understanding and predicting the dynamics of such open systems, including the most important effects arising due to their unavoidable interaction with the environment, such as decoherence and energy dissipation.

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What is an open quantum system?

What is an open quantum system? The simple quantum textbook examples like Simple Harmonic Oscillator potential and H-atom, seem to me open quantum systems, since the particle interacts with the potential. How is exactly the problem of open quantum…
Seeker
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How to efficiently check if a superoperator is Lindbladian?

Superoperators are linear maps on the vector space of linear operator. The Lindbladian superoperators are the important subset that can be expressed in the form $$\mathcal{L}[\rho] = -i (H \rho - \rho H) + \sum_i L_i\rho L_i^\dagger -…
Jess Riedel
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What is the relationship between the Drude form and the exponential form of Ohmic spectral density?

I have been studying open quantum systems for some time now. I have learnt about something known as spectral density that confers information about the physical structure and are found in the definition of the correlation functions. Now, the…
TanMath
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How to determine the collapse operator for a Lindblad equation

Given a Hamiltonian $H$, how can I relate the collapse operator for the Lindblad equation to a given environmental effect? Also, how can I relate the constant $\gamma$ in front of the sum of the collapse operators to the full Hamiltonian? For…
TanMath
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Semi-group in quantum open systems

In the literature of Open Quantum System, one often comes across the following ($t_2>t_1,>0$): Semi-group property of a map: $A(t_1+t_2,0) = A(t_2,0) A(t_1,0)$. What does this mean physically, and why the name semi-group?
user238110
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Physics behind assumptions in deduction of quantum master equation

In Breuer's book, he deduces quantum master equation using following steps: $(1). \frac{d}{dt}\rho(t)=-i[H_{I},\rho(t)]$ then the solution for equ.(1) can be written as $(2).{\rho(t)}=\rho(0)-i\int_{0}^{t}ds[H_{I},\rho(t)]$ By plugging equ(2) to…
xiang sun
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Why does the Redfield equation model thermal relaxation while the Lindblad equation does not?

In open quantum systems, we model a process known as thermal relaxation. What is this process, and why is it that only the Redfield equation models this process, and the Lindblad equation doesn't?
TanMath
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Equation of motion for various operators in open quantum systems

I am trying to reproduce the calculations presented on page 4 in arXiv:1511.03347. The Hamiltonian (Eq. 2.4) is given by $H= \hbar \omega (a^{\dagger} a + \frac{1}{2}) - B \sqrt{\frac{\hbar g}{2 \omega}} (a^{\dagger} + a) $, where $a^{\dagger}(a)$…
Shasa
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Markov Approximation and Master Equation Derivation

In deriving the master equation, I am coming across the Markov Approximation which says: Suppose environment $E$ and system $S$ interact and exchange some energy with each other. Then $E$ would recover back to thermal equilibrium faster than $S$…
Eesh Starryn
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Is hermicity of the reduced density matrix preserved here?

I am following along Breuer and Petruccione's book . I would like to know if the property $\rho^{\dagger} = \rho$ is preserved for evolution that is described by the Born Approximation. For a Hilbert space $\mathscr{H}_s \otimes \mathscr{H}_{b}$…
QuantumEyedea
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Why do bath correlations decay?

When deriving a Lindblad equation (for example Breuer chapter 3), one crucial assumption is that $\tau_b$, the reservoir correlation function decay time, is (in short) the smallest relevant time scale. What I cannot understand is why these…
peep
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Projection of master equation onto eigenstates

I'm trying to understand the paper: "Quantum dot cavity-QED in the presence of strong electron-phonon interactions" by Wilson Ray and A. Imamoglu (https://journals.aps.org/prb/abstract/10.1103/PhysRevB.65.235311). I have arrived at the following…
Cedric Chia
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Example of an infinite volume Lindblad system

What is an explicit example of a Lindbladian \begin{align*} L(\rho) = - i \lbrack H_A, \rho \rbrack + G \sum_{j} V_j \rho V_j^* - \frac{1}{2}(V_j^* V_j \rho + \rho V_j^* V_j) \end{align*} acting on the space of trace class operators on some Hilbert…
Frederik Ravn Klausen
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Can quantum systems interact with multiple environments of different types?

If it can, how can we write the Hamiltonian of the total System is it just (for example with N bath) $$ H_{tot} = H_{s} + H_{B_{1}} + H_{B_{2}} + ... + H_{B_{N}} + H_{I_{1}} + H_{I_{2}} + ... +H_{I_{N}} $$ And can environments be a different…
Hezzuappu
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Does there exist a relation between the eigen-energies of two subsystems of a closed system?

I am rather new to the field of open quantum systems and I have a seemingly basic question for which I somehow cannot find a complete answer. Consider a closed system which we divide into two subsystems A and B which have empty intersection and…
WLV
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