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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Understanding a Physics Paper on Quantum Teleportation of Continuous variables
The paper I am trying to understand is here:
http://pra.aps.org/abstract/PRA/v49/i2/p1473_1
The paper describes the quantum teleportation protocol in a general case with continuous dynamical ...
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430 views
Entanglement spectrum
What does it mean by the entanglement spectrum of a quantum system? A brief introduction and a few key references would be appreciated.
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116 views
OAM states for wireless communications
Can someone give me an overview of how OAM states are used in communications?
Using Orbital Angular Momentum States seems like a hot topic for communications. I read a few articles about the basic ...
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235 views
Mathematically challenging areas in Quantum information theory and quantum cryptography
I am a physics undergrad and thinking of exploring quantum information theory. I had a look at some books in my college library. What area in QIT, is the most mathematically challenging and rigorous? ...
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185 views
Entanglement: Is it possible to prepare and reset probabilities to send information?
I'm pretty certain that the answer to the question in the title is a no, but I don't understand why. I have some basic misunderstanding of quantum processes that I’d like clarified in the form of ...
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fiber optic second order PMD as an operator on the tensor product Hilbert space
Second order polarization mode dispersion (SOPMD) is a coupling mechanism between polarization and frequency. Take our photon to be the following tensor product:
$\psi = \int \gamma_{\omega} | ...
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decoherence free subspace of a single photon
Take the state vector for a single photon as
$\psi = \int \gamma_{\omega} | \omega \rangle \otimes (\alpha |H \rangle + \beta | V \rangle )d \omega$
$H, V, \omega$ are the horizontal polarization, ...
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55 views
Experimental realization of Quantum Teleportation of Spin, not polarization, not ions or atoms
I've looked everywhere in databases my school provides, to google searches, to the questions asked in physics forums, and here. As I understand, the original QT (quantum teleportation) protocol ...
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187 views
Can we make a Maxwell's Demon using Quantum Computers?
Although I'm reasonably sure that quantum computing advances will not lead to the ability to construct a machine that globally violates the 2nd law of thermodynamics, it feels like a difficult ...
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124 views
Using Quantum Teleportation in a way to have the effect of matter teleportation
So, I understand that quantum teleportation is the transfer of a quantum state from one particle or system of particles and its correlations to another receiving system consisting of particle(s). ...
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318 views
Extending the idea of superdense coding
I was reading through the superdense coding protocol, that lets A convey two classical bits to B by sending one qubit (assuming B sends A a qubit beforehand). So B creates a 2-qubit state and sends ...
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Concurrence in higher dimensions?
Does anybody know of any calculation of the concurrence for some mixed state other than the qubit-qubit case (which was solved by Wootters)?
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319 views
What is the difference between Quantum teleportation and Radio waves?
Quantum teleportation over 143 kilometres using active feed- forward
What is the difference between Quantum teleportation and radio waves?
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513 views
Can quantum annealing be used for factorization?
It is known that there is a famous quantum factorization algorithm by Peter Shor. The algorithm is thought to be suitable only for quantum gate computer.
But can a an adiabatic quantum computer ...
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661 views
What is postselection?
I was reading some questions here.
I couldn't understand what it means by postselection.
What is postselection? What is its use/significance? Where did it came from?
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Quantum entanglement faster than speed of light?
recently i was watching a video on quantum computing where the narrators describes that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster ...
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2answers
131 views
Quantum Mechanics in terms of *-algebras
I'm currently trying to find my way into the geometric description of Quantum Mechanics. I therefor started reading:
Geometry of state spaces. In: Entanglement and Decoherence (A. Buchleitner et ...
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61 views
Question on the preservation of information via mapping to free field states
In Hawking's paper, "Breakdown of predictability in gravitational collapse", the crux of Hawking's argument is as follows:
...,one can extend the principle to treatments in which the gravitational ...
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What is spontaneous symmetry breaking in QUANTUM systems?
Most descriptions of spontaneous symmetry breaking, even for spontaneous symmetry breaking in quantum systems, actually only give a classical picture.
According to the classical picture, spontaneous ...
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knowledge of an internal observer
I would like to discuss the consequences of the concept of an internal observer in quantum theory. If we assume that we have a universe that evolves unitarily at a global scale and an observer is ...
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Is Shor's algorithm a demonstration of the many worlds interpretation?
David Deutsch is very fond of pointing out Shor's integer factorization algorithm is a demonstration of the many worlds interpretation. As he often asked, where else did all the exponentially many ...
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Information relationship to Special Relativity
How do we write mathematically that "information" cannot go faster than light? And along a similar line of thought, how do we relate "information" with special relativity. Lastly, what is the ...
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180 views
Anybody have example of two-qubit non-Pauli and non-Clifford quantum gate?
A lot of known quantum gates are in the Pauli group (I,X,Z,Y) or in the Clifford group (H,P,Cnot). I need examples of the quantum gates that aren't in this groups. Also, are there are matlab functions ...
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1answer
147 views
Proof of Pauli group preservation by Clifford group conjugation?
A well know result is that Clifford group preserve the Pauli group under conjugation or, in other words:
$C(P_{1} \otimes P_{2})C^{\dagger} = P_{3} \otimes P_{4}$, with $C \in$ Clifford group and ...
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61 views
Matrix separability preservation under conjugation?
Someone know any paper about matrix separability preservation under conjugation? A well know result is that Clifford group preserve the Pauli group under conjugation or, in other words:
$C(P_{1} ...
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285 views
number of microstates associated with two-level quantum systems
this is a very simple question, but apparently one that has no simple answer, at least from standard quantum mechanics theory
I'm trying to figure the number of simple quantum states (microstates) of ...
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108 views
Fast algorithm for maximizing the quantum fidelity
Consider the following optimization problem: Given a quantum state $\sigma$, a constant $b$ and a Hermitian operator $A$, find
$\underset{\rho} \max F(\rho,\sigma)$
subject to $\text{Tr}(\rho ...
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Does quantum fingerprinting really argue for the exponential size of wavefunctions?
Does quantum fingerprinting really argue for the exponential size of wavefunctions? Quantum fingerprinting is the idea that an exponentially long classical string can be encoded in a linear number of ...
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232 views
Defining entanglement in subspaces of tensor product
I have asked the question in math.stackexchange, but perhaps it should be more relevant here. Hence I am re-posting it with necessary reediting.
Let $\mathcal{H}=\mathbb{C}^n$ be a Hilbert space. A ...
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Can double entanglement preserve correlations?
We have 2 EPR experiments running in parallel, with Alice having one leg of each (a1,a2) and Bob the other leg of each (b1,b2). Thus (a1,b1) are anticorrelated, as are (a2,b2). Thus also (a1,a2) are ...
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217 views
Physical meaning of the sign basis in quantum mechanics
If we take a hydrogen atom as qubit, let
$\lvert0\rangle$ = unexcited state
$\lvert1\rangle$ = excited state
then what is the meaning of measuring the qubit value in the sign basis? If the atom may ...
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416 views
Interpretation of “superqubits”
Two very intriguing papers recently appeared on the arXiv, claiming that one can use "superqubits" -- a supersymmetric generalization of qubits -- to violate the Bell inequality by more than standard ...
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4answers
548 views
Can superdeterminism resolve contextuality, entanglement and Shor's algorithm in quantum mechanics?
Superdeterminism is the idea that the apparent freedom for the choice of experimental apparatuses and their settings are nothing but an illusion. Contextuality is the dependence of the properties of a ...
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589 views
Conservation of energy in quantum teleportation
Consider the quantum state teleportation protocol of Bennett et. al.
How does one prove that this protocol would never violate the conservation of energy? At the face of it, it doesn't seem to be ...
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248 views
Did anyone claim that quantum theory meant lasers would never work
I've been reading 'How the Hippies saved Physics', which describes a design for a superluminal communication device, of which the crucial part was a laser which duplicated an incoming photon many ...
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Entanglement of qubits circuit- Bell states
I know that the quantum circuit $\text{CNOT}\; (H \otimes I)$, where $\text{CNOT}$ is the controlled-not gate and $H$ the Hadamard gate, takes the computational basis of two qubits ...
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State of the entangled particles at the event horizon of black hole
Looking through the article of Samir Mathur http://arxiv.org/abs/0909.1038
he assumes that the entangled particles created at the event horizon have all the state ...
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1answer
924 views
What are the benefits of quantum information “teleportation”?
I read occasionally popular science articles and from time to time encounter issues about quantum information teleportation. (this one for example http://www.physorg.com/news193551675.html)
So far I ...
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What is a completely positive map *physically*?
I am sure this question is really stupid, but I could not refrain from asking it in this forum. This can be considered as a continuation of this question.
...
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are pinch-off bubbles valid solutions to general relativity?
are bubbles of spacetime pinching-off allowed solutions to general relativity? With "pinch-off bubble" i really mean a finite 3D volume of space whose 2D boundary decreases until it reaches zero and ...
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166 views
At what time exactly does decoherence happen? and retrodating
Take a qubit initialized to $|0\rangle$. Apply a Hadamard transform to it. Measure it with an apparatus along the $|0\rangle,\, |1\rangle$ basis. If zero, spare a living cat. If 1, kill the cat. ...
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262 views
Areas of computer science required for quantum computing
What knowledge of computer science should I have, to be able to pursue research in quantum computing. I am a Physics undergrad and would take three core courses in QM, before the completion of my ...
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Why are there only perfectly anti-correlated quantum states, not perfectly correlated?
The singlet state of two qubits is anticorrelated in every basis. For example, in the Pauli bases, it can be expressed,
$\frac{1}{\sqrt{2}} ( | 01 \rangle - | 10 \rangle) = \frac{1}{\sqrt{2}} ( | +- ...
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Extending mixed states to pure state
Let us consider any pure state $|\psi\rangle\in\mathbb{C^n\otimes C^n\otimes C^n}$. Its reduced bipartite density matrix represent a pure state or mixed state depending on whether $|\psi\rangle$ is ...
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1answer
183 views
Schmidt decomposition of coupled oscillators
Consider a system of two coupled oscillators, with Hamiltonian ($\hbar = m = 1$):
\begin{align}
\mathcal{H} = \frac{1}{2}(p_1^2 + \omega_0^2 x_1^2) + \frac{1}{2}(p_2^2 + \omega_0^2 x_2^2) ...
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Separable states of maximum non-classical correlations
Although there is no standard measure of entanglement, the GHZ states
$|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$
are often deemed as maximally entangled states of ...
2
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2answers
135 views
Bell states entanglement
I'm trying to learn about the Bell state $\frac{1}{\sqrt{2}}|00\rangle+\frac{1}{\sqrt{2}}|11\rangle$. Question 10.1 in Algorithms asks us to show that this cannot be decomposed into the tensor product ...
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Known properties of a specific class of quantum states
Recently, I have been studying a quantum protocol for the "Hidden Matching" problem that makes use of states that can be expressed as
$|\psi\rangle=\frac{1}{\sqrt{n}}\sum_{i=1}^n ...
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162 views
What is the code distance in quantum information theory?
What is the code distance in quantum information theory?
Code distance seems to be a very important concept in fault tolerant
quantum computation and topological quantum computation.
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What is “code” in “toric code”?
When I first heard people talking about using Kitaev's toric code to do topological quantum computation, I was thinking how many lines does the toric code have. Then I was told that
the "code" really ...
