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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Quantum GCD circuit: Clearing ancillae

I am currently trying to implement a circuit for computing the greatest common divisor in the Quantum Computing Language. In my work, I partially proceed from the paper Quantum Circuits for GCD ...
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Pure State Entanglement and Private Communication

My question is about the relation between two protocols of transmitting a quantum message through a Quantum channel using entanglement (entanglement Transmission or generation for this question) and ...
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156 views

What does it mean physically if pentagon identity or hexagon identity doesn't have any answers?

Imagine I write a fusion rule for some anyons on a paper. Then, I try to solve Pentagon identity and Hexagon identity, imagine finally I find out for example the Hexagonal equation doesn't have any ...
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Measurement without collapse

Does anybody have a reference for Cini's model of Quantum Measurement theory. I have a background of Quantum Mechanics (Ballentine level). Also I don't have access to Cini's paper.
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current measurement of entanglement [on hold]

From my reading about measurement of entanglement, I know the research towards to concurrence. May I know if there any new measurement used now? thanks you
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measurement of tripartit qubit state

From general schmidt decomposition, GSD, the state of tripartite is classify by five parameter as below: |V>=a|000>+b|100>+c|110>+d|101>+e|111>. how can I determine the value of parameter a,b,c,d,e? ...
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Can the absence of information provide which-way knowledge?

This seems an incredibly basic question, but one I've been unable to find an answer to on PSE; if this is a duplicate please point me in the right direction. Concerning a simple Young's double-slit ...
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Could my idea of Faster-Than-Light communication using quantum entangled particles be feasible? [duplicate]

I am most likely completely off but I have an idea on how we might be able to exchange information using spins only (provided that we prepare for the exchange of information): We communicate using ...
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39 views

Two black holes prepared from different initial states

I have asked a similar question, I would like to reformulate it in more details. Here is a thought experiment: Assuming we can create black holes by squeezing photons, we can then prepare two ...
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395 views

Heisenberg XXX time evolution operator for three qubits

I've a problem to reproduce the result in equation (4) on page three of this paper: http://arxiv.org/abs/0802.2588. So far I've understood that they apply a Heisenberg XXX interaction between ...
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34 views

Reference for statistical mechanics from information theoretic view

I am interested in knowing if some one here knows book/notes for statistical mechanics from the information theoretic viewpoint.
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85 views

Is a larger black hole a faster or a slower processor?

For a remote observer, a black hole with mass $M$ has a temperature $T=1/M$. Now I am confused with the problem: A larger black hole can achieve a task faster or slower if it's regarded as a kind ...
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Has Jaynes's argument against Bell's theorem been debunked?

As a student of theoretical physics I'm well acquainted with the multitude of crackpot ideas attempting to circumvent Bell's theorem regarding local hidden variable theories in quantum physics. ...
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Temperature influence in Optical Quantum Computing

I've recently been looking into the (perhaps a bit outdated but still very interesting) field of linear optical quantum computing. Using photons as information carriers, and using objects like ...
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133 views

Is the translational information all that matters, or do we need to take into account internal states?

For anyone in this community that's familiar with quantum teleportation, I need desperate help. I am currently working on my senior thesis and my goal is to teleport a molecule. Background: So in ...
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39 views

Black hole evaporation, mass or bit?

Usually when we talk about black hole evaporation, mass or energy is taken as the target and the evaporation time is computed based on mass loss in a given time period. Is there any work to analysis ...
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63 views

A question about the universal quantum cloning machine (UQCM)

In the recent paper Replicating the benefits of Deutschian closed timelike curves without breaking causality, a quantum state cloner based on open timelike curve (OTC) was mentioned. There to clone ...
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What's the entanglement of a typical state of multiple qubits?

For a n-qubit system, with n a large number, under free (random) unitary evolution starting from a product state, what's the entanglement distribution of a typical state of the system? Here the ...
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How does one arrive at the two qubit matrix that represents a gate? [on hold]

The two qubit CNOT gate is represented by a 2x2 matrix. However, it is also represented pictorally. How does one arrive at that matrix representation? I am not looking for "take a diagonal matrix and ...
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Resources on estimation of environment model for environemnt induced quantum decoherence

I am curious to see what literature exists about estimation of a quasi-classical environment interacting with a quantum system causing decoherence in system states. There has been in general a lot ...
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97 views

Hilbert Schmidt inner product

I am desperately trying to solve the following problem, and would really appreciate help! Suppose $R$ and $Q$ are two quantum systems with the same Hilbert space $\mathcal{H}$ with ...
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Complex vector on Block sphere [closed]

I've the following problem. Given this vector on a 3D complex space: $$\\\\ {\phi_{1}} = \begin{matrix}% 1/2(-1, & i\sqrt{2}, &1)^{T} \end{matrix}\\ $$ Is it possible to draw it on the ...
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1answer
87 views

Quantum computing, NP complexity [closed]

Hi I have a very limited knowledge of quantum physics and its bothering me trying to understand quantum computing. I want understand how a qubit can return usable data faster then a regular bit, how ...
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2answers
70 views

Does quantum entangled particle release energy when its “twin” is measured? [closed]

So I was just thinking a bit, and I came up with a couple of questions. As we all know the scenario: We have two quantum entangled particles. Let's call them A and B. We like to measure the state of ...
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Physical interpretation of applying a unitary operator to a state

When we apply one of the Pauli matrices $\sigma_y$ on one of its eigen-vectors $| \odot \rangle$, what does the eigen-value tell us about $| \odot \rangle$? Is this considered a measurement of $| ...
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Quantum computing with biological matter? [closed]

As a biologist with physics background I wonder whether there is a way to use biological matter to create quantum computers or at least to advance the field somewhat. Usually, my first feeling would ...
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2answers
227 views

Hartle and Hawking's universal wavefunction

My apologies in advance if this question is poorly worded or doesn't make any sense, however I have just finished reading into this theory and it seems as though Hawkings No Boundary Universe is ...
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1answer
158 views

What is the significance of being equivalent up to local isometry?

Background : I am reading the paper device independent outlook on quantum mechanics. The author mentions the concept of two pure states being equivalent up local isometry. From what I understood two ...
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106 views

Understanding the quantum eraser from a quantum information stand point

Is there a way to understand the quantum eraser experiment in terms of quantum information? In particular, is there a quantum circuit that would function as a quantum eraser experiment? The issue I'm ...
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104 views

Understanding the delayed choice quantum eraser from a quantum information stand point

A continuation of Understanding the quantum eraser from a quantum information stand point What quantum circuit would correspond to delayed choice? In particular, the decision of whether to not to ...
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1answer
61 views

Entanglement, superposition, and propositional logic [duplicate]

From what I am understanding, there is entanglement in a system if there is a correlation between elements of that system. For an example that I found, If you have only two cards and know that one is ...
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272 views

Quantum and classical scaling of memory

In the literature of Quantum Computation (QC), when discussing the simulation of quantum systems, one usually comes across comparisons with the classical digital analog such as: "Classically the size ...
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51 views

Approximate cloning of a qubit, given multiple starting copies

Suppose I'm given several clones of a qubit in a pure unentangled state. That is to say, I'm given the state $(a \left|0\right\rangle + b \left|1\right\rangle)^{\otimes n}$. My goal is to make $d$ ...
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Second order quantum coherence function

I have one question from the course of quantum optics. In general the second order quantum coherence in time is defined as, $$g^{(2)}(\tau)=\frac{\left\langle ...
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Shape of the state space under different tensor products

I am currently studying generalized probabilistic theories. Let me roughly recall how such a theory looks like (you can skip this and go to "My question" if you are familiar with this). Recall: In a ...
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336 views

How are the field operator and quantum state after a beam splitter and a polarizing beam splitter individually?

How are the field operator $\hat{a}$, $\hat{a}^\dagger$ and the quantum state (like coherent state $|\alpha>$, Fock state $|n>$) changed after a beam splitter and a polarizing beam splitter ...
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Tensor product of Hadamard operators

The Hadamard Operator on one qubit is: \begin{align*} H = \tfrac{1}{\sqrt{2}}\left[\,\left(\color{darkgreen}{|0\rangle + |1\rangle}\right)\color{darkblue}{\langle ...
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Hamiltonian of a quantum harmonic oscillator

On page 286-287 of Nielsen Chuang's Quantum Information and Quantum Computation (10th edition) book, the Hamiltonian for a quantum harmonic oscillator is approximated as $H=a^\dagger a.$ What are the ...
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58 views

Why doesn't the quantum eraser violate the no-deletion theorem?

In the quantum eraser experiment and its variants, you basically have a double slit experiment, where you detect which slit the photon went through, but then forget this information. My question is, ...
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Atomic system satisfying a simple level scheme

I have a simple two level system with an allowed dipole transition between the levels. The top level is also allowed to decay to another third level (looks a bit like a lambda system). Could someone ...
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1answer
51 views

How do we imagine a Hadamard gate acting on the Bloch Sphere? [closed]

We can rewrite the Hadamard gate as $R_x(-\pi/2)R_z(-\pi/2)R_x(-\pi/2)$. I am trying to visualize the effect of applying the Hadamard gate to $|+\rangle$ on the Bloch sphere. The X gate takes ...
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Can Quantum Measurement Be Detected After The Fact?

My question is simple and has a crude drawing associated with it. I was watching some videos of the quantum erasure experiments and being a computer scientist have researched quantum encryption ...
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80 views

Proof of Uhlmann Theorem [closed]

In p228, Chapter 9 of Mark Wilde's text , in the course of proving Uhlmann's theorem for quantum fidelity, it claims $$\sum_{i,j} <i|^R <i|^A (U^R \otimes (\sqrt{\rho}\sqrt{\sigma})^A) |j>^R ...
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Quantum circuit and Witness preserving amplification for QMA

My question is about the witness preserving amplification scheme for QMA proposed by Marriott and Watrous in 2005 (see http://arxiv.org/abs/cs/0506068 and ...
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2answers
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Difference between DMRG (density matrix renomalization group) and MPS (matrix product states)?

I am learning DMRG recently. I noticed there are many papers both in the DMRG approach and MPS (such as variational matrix product state (VMPS) by F.Verstraete and J.I.Cirac) approach. In my eyes, ...
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How to understand the relationship between these two geometrical structures?

During my study of quantum information processing, I occasionally meet two different geometrical structures: (a) The geometry of the Hilbert space of quantum state, where the superposition and ...
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Is it possible to make a state tomography of an entangled state only by measurements on subsystems?

As far as I can understand, to make a state tomography of a composite system, a properly selected set of joint measurements should be carried out on the composite system to estimate the density matrix ...
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93 views

How to understand the measurement on entangled state in the following cases? [closed]

Assuming an EPR pair AB, event MA is a measurement on A. My questions are: (1) At MB and MB' (depending on where B is located), if we try to describe the state of B (but not measure B yet), ...
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102 views

What is entanglement entropy? and all those stories about counting [closed]

In Quantum mechanics entanglement is a concept that informs us about nature of states. It is a statement about non-product states, thus correlations. This is my rather foolish view of ...
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279 views

Quantum algorithm for checking if element exists

I am currently having hard times while facing an interesting idea, which could speed up many present quantum algorithms, but I am not sure whether my thought is not misleading, or more precisely, ...