# Questions tagged [quantum-information]

Quantum information is the study of the informational content of quantum states. The most common object of study is the "qubit", the information in a two-state quantum system such as spin-1/2 or photon polarization.

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### How to efficiently get the largest probabilities / amplitudes of a quantum state stored as an MPS?

Let's say, that we have the following pure, superposition state $$|\psi \rangle = \frac{1}{\sqrt{2}}|000001 \rangle + \frac{1}{2}|101101 \rangle + \frac{1}{2}|100100 \rangle$$ stored in the MPS form....
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### Formalism to go from distinguishable to indistinguishable states in quantum mechanics, and the probability combination rules?

I was wondering how can we go from an analyzed system of particles, where we have considered them to be distinguishable, to results about the same particles where we consider them indistinguishable. ...
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### How do I find the exchange energy from the effective Hamiltonian?

I've just recently started studying noise in singlet-triplet qubits and the exchange interaction (as a function of detuning ${\epsilon}$ and tunnel coupling ${t_c}$) seems fundamental in many studies. ...
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### Orthogonal states evolution

I'm a bit little confused about orthogonality in QM. $<a|b>=0$ what does physically mean? Let's suppose that $<a|b>=0$ and for $t=0$ the system is in state a. Is there a possibility to ...
1 vote
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### Projection Postulate of Quantum Mechanics. Where does the Projection occur in the detection process?

This question is about a specific instance of the measurement problem. Let's say we excite a single emitter producing a single photon (described by state $|\psi_{i}>$), which then "travels&...
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### What does an effect algebra mean in terms of familiar quantum concepts?

I've heard of this particular representation of quantum theory before and been trying to toy with it for some time: https://en.wikipedia.org/wiki/Effect_algebra but I am not quite sure how to directly ...
1 vote
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### Choi-Jamialkoski Theorem in Phase damping channel [closed]

I am trying to replicate the solution I have to this problem provided by the instructor in the class where I am trying to use the Choi-Jamialkoski theorem to prove that Phase damping channel is ...
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### What does $\langle -z|$ mean in this expression $\langle -z|\rho|z\rangle$?

In some formulas of the Wigner function, there is an expression $\langle -z|\rho|z\rangle$ where $|z\rangle$ represents a coherent state. I don't understand what $\langle - z|$ means. Some other ...
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### Adiabatic elimination in the presence of single-photon transitions

I am trying to derive an effective Hamiltonian for a system that includes both periodic drives near resonance with certain transitions (that should lead to one-photon transitions) and pairs of drives ...
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### To verify the completely positivity: about conditionally completely positive

I'm reading the paper Assessing Non-Markovian Quantum Dynamics, by M.M. Wolf (PRL 101, 150402 (2008), arXiv:0711.3174). It mentions how to decide whether a generator is a valid Lindbladian generator, ...
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### Non Markovain dynamics [duplicate]

What are the examples of the practical implementations of studying the non-Markovian dynamics of such open quantum system (e.g. quantum dot)?
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### How does a disentangler disentangle a short ranged entangled (SRE) states in multi-scale entanglement renormalization ansatz (MERA) circuit?

I encounter a problem in understanding the role of disentanglers in Multi-scale entanglement renormalization ansatz (MERA). I do understand that without disentanglers, some short ranged entangled (SRE)...
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1 vote
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### Informations about non-Markovianity? [closed]

What are the examples of the practical implementations of studying the non-Markovian dynamics of such open quantum system (e.g. quantum dot)?
1 vote
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### Quantum dots applications [closed]

I wanna find some interesting project for my master thesis concerning quantum dots, meanwhile I'm learning open quantum dynamics (Markovian & non-Markovain). Is there some ideas to combine these ...
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### Derivation of Nielsen and Chuang's Eq. (8.127) and (8.128) [closed]

In subsection 8.3.6 "Phase damping" of Nielsen and Chuang (2010), the Hamiltonian is given as $$H = \chi a^\dagger a(b+b^\dagger) \tag{8.126}\label{8.126}$$ and $U = \exp(-iH\Delta t)$, ...
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### Looking for reference material in quantum algebra

I want to reconstruct some problems to take my study further deeper that are closely aligned with information retrieval in the form of quantum algebra. but I wonder if there are very limited books ...
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### Post-measurement state after homodyne measurements of part of the system

Let us have an $N$ mode Gaussian state and B denote the last mode (for simplicity I just consider a two-modes state) It is said in articles (and for example How to find the covariance matrix after a ...
1 vote
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### Is there a physical intuition behind the disentanglement of Werner states and the sudden death of entanglement?

It is possible to write two-qubit Werner states in terms of a mixture between a Bell state and the maximally mixed state: \begin{equation} \rho_W = \lambda |\Psi_-\rangle \langle\Psi_-| + \frac{1-\...
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### Is my simplistic understanding of a Qubit, Superposition and Entanglement correct? [closed]

I've gone through a number of Lenny Susskind's lectures on entanglement (both just for the joy of it and to better understand quantum mechanics) where he delves into the idea of a qubit. For the sake ...
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### Nielsen and Chuang give 4 nomenclatures / definitions for projective measurements - are they equal?

What this question is about (the 4 nomenclatures in short): Nielsen, M.A. and Chuang, I.L. state in their famous book (see http://dx.doi.org/10.1017/CBO9780511976667, p. 87 ff.) that there are 4 ...
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### How many apparent horizons could the universe have?

I was reading a paper written by Nobel laureate George Smoot, Go with the Flow, Average Holographic Universe, which assumes the holographic principle as true and conjectures that our universe would be ...
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