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Questions tagged [communication]

Quantum communication is a generalization of quantum cryptography. It refers to protocols and techniques for transmission of an unknown quantum state (of a quantum system) from one place to another.

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Does no-cloning imply zero capacity of antidegradable channels?

I read that (paraphrasing, see below) "antidegradable channels have zero capacity because of the no-cloning theorem". Is there a formal derivation of the capacity of an antidegradable ...
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Does measurement in different bases allow for FTL communication?

Imagine for a moment that we could distinguish between arbitrary quantum states. We’ll show that this implies the ability to communicate faster than light, using entan- glement. Suppose Alice and Bob ...
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Why does this not break the security of quantum teleportation

Reposted from my post on the physics stack exchange, apparently this is a better place. I am taking an course on quantum mechanics, and we have just encountered the quantum teleportation protocol that ...
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How can a third party learn the coefficient of a shared $2n$-qubits state using a classical message from each one?

Suppose Alice and Bob share the $2n$-qubits state $$|\phi _{x,y,b} \rangle = \frac{1}{2}(|x\rangle + (-1)^b |y\rangle)$$ where $x,y$ are $2n$-length strings of $0$ and $1$, $b$ is a bit, and $x \ne y$....
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Pseudo telepathy with 3 people that share the state $\frac{1}{2}(|000\rangle -|011\rangle-|101\rangle-|110\rangle)$

The problem is similar to the pseudo-telepathy where Alice, Bob and Charlie are given bits $a,b,c \in \{0,1\}$ such that $a \oplus b \oplus c=0$, and their goal is to output the bits $A,B,C$ without ...
Gabi G's user avatar
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Classical capacity of quantum channel - Holevo quantity vs accessible information of a channel

Just above Eq (20.7) in Mark Wilde's book, while discussing the classical capacity of a quantum channel, he says: These results then suggest that the ultimate classical capacity of the channel is the ...
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Can you project on an orthogonal basis for a multipartite system using only local measurements and classical communication?

Say Alice possesses one qubit, and Bob two, and that the joint state is $|\psi_{A, B_1, B_2}\rangle = \alpha|n_1\rangle + \beta |n_2\rangle$, where $|n_1\rangle$ and $|n_2\rangle$ are orthonormal ...
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What is a "quantum communication link"?

The IBM roadmap for scaling their quantum computers refer to a quantum communication link to combine together multiple smaller quantum chips. What is the technology that enables connecting together ...
Jim Haddocc's user avatar
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Increasing quantum channel capacity

I have a few confusions regarding quantum communication. Please bear with me as I ask what might appear to be basic or naive questions: In the case of classical communication the capacity of wireless ...
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Distributing entanglement using entanglement swapping

I've read papers that consider the problem of sharing entanglement between A and C with an intermediate B. A and B share an entangled state and so do B and C. Then, entanglement swapping is used to ...
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Entangling two particles at a distance

Entangled quantum particles are very interesting as they only make sense if you look only at the math. Usually, when we talk of "entangling" two qubits, we mean that we have two qubits, $A$ ...
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Average-case error and worst-case error in entangment-assisted classical communication

I am reading this paper where one considers a quantum channel $\mathcal{N}$. We are interested in the maximum rate at which we can send classical messages over this channel in the one-shot setting i.e....
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Possible applications for small photonic cluster-states

Assume I have a "resource state generator", enabling me to produce photonic cluster states in arbitrary shape with O(1-10) photons. Are there any possible applications for such a device in ...
Yaron Jarach's user avatar
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Is it advantageous for a state to have higher Bell CHSH violation?

For a density matrix $\hat \rho$, one can construct a "Bell operator" $\hat B$, such that the violation of the inequality $\langle \hat B \rangle \le 2$ is a clear indication of quantum ...
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Can $2^n$ bits be sent with $n$ instances of quantum teleportation?

So, right now these are two pieces of information I've been told are correct: Quantum teleportation can send a single qubit from Alice to Bob, with two classical bits $n$ qubits can store $2^n$ ...
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Is it well known classical communication over a quantum channel at a rate below its classical channel capacity can have an exponentially small error?

Classical channel capacity $C(\mathcal N)$ of a quantum channel $\mathcal N$ is defined to be a rate below which any classical communication can succeed with an arbitrarily small error. Specifically, ...
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Do quantum teleportation require transmission media?

It said on wikipedia: Because classical information needs to be sent, quantum teleportation cannot occur faster than the speed of light. So does it mean quantum communication specifically ...
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Does a noiseless quantum channel violate no-cloning theorem?

A quantum channel is defined as CPTP map from Alice to Bob $\mathcal{N}: \mathcal{H}_A \to \mathcal{H}_B$. In particular, a noiseless quantum channel is such that $\mathcal{N}(\rho_A) = \rho_A$. My ...
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$2$ ebits $+$ $1$ bit $ = 2$ bits?

The Set-Up Let's say Alice and Bob share $k$ ebits, i.e., they have one-qubit each of each of the $k$ Bell states $\frac{\vert 00\rangle+\vert 11\rangle}{\sqrt{2}}$. Now, Alice wants to send $2n$ bits ...
FreeAssange's user avatar
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Is it possible to prevent quantum communication detection?

From what I understood, one of the advantages of quantum communication is that one can (mathematically/physically) prove that the quantum communication/message has not been intercepted/tampered with. (...
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Entanglement-assisted communication ability of a quantum depolarizing channel vs. a classical binary symmetric channel

Consider a quantum qubit depolarizing channel which takes a quantum state $\rho$ to output $$N(\rho) = (1-p)\rho + p\frac{\mathbb{1}_2}{2}.$$ If I restrict $\rho$ to be either $\vert0\rangle\langle 0\...
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What type of attack(individual attack, collective attack, coherent attack) is a PNS attack?

While studying the attack method of QKD, I found that intercept and resend attack is an example of an individual attack. What are the examples of collective attack and coherent attack? Specifically, ...
James Thomas's user avatar
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Is there a non-deterministic protocol for entanglement generation between distant parties?

I'm aware that one can imperfectly clone entanglement that's shared between two parties (i.e. Bell pairs) using deterministic quantum cloning machines to produce two, lower fidelity entangled states. ...
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How does the teleportation step work in entanglement dilution?

Consider the entanglement dilution protocol for pure states, as described in Preskill's notes (Link to pdf, see around page 32). The context is that Alice and Bob share $k=n(S(\rho_A)+\delta)$ Bell ...
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Efficient Protocol for Entanglement Purification

By using entanglement purification, we can produce a high-fidelity entangled state from several pieces of low-fidelity entangled states. From my study, there is a protocol proposed by Bennett et al. ...
Syed Emad Uddin's user avatar
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1 answer
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Can joint measurement be achieved in two labs far apart?

Consider the following scenario: Alice and Bob are in two labs far apart, and they each have one qubit. Can joint measurement (for bipartite projective measurement, they are measurements that cannot ...
narip's user avatar
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What are conceptual open problem in quantum communications and cryptography?

I recently heard that most of the challenges in quantum communications nowadays are related to "practical" engineering implementations and there are no longer "real" conceptual ...
Marco Fellous-Asiani's user avatar
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3 answers
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Is it possible to have Quantum Teleportation Protocol without using classical channel?

I'm still learning Quantum Information right now, especially with Quantum Teleportation (QT). I have found an interesting article suggesting a Simplified Protocol of QT that doesn't need classical ...
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What is the difference between CV QKD and DV QKD?

I know what QKD is, as a concept but I recently found papers mentioning continuous-variable quantum key distribution , and discrete-variable quantum key distribution . So I would like to know what is ...
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Quantum communications and "knowledge" of receiving a qubit

Question from a computer scientist (not a physicist). Imagine two nodes on a quantum network. Alice sends Bob a qubit in some state of superposition over a quantum channel. Is Bob able to sense that ...
Quantum SPCA Cat Protectors's user avatar
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1 answer
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What is the difference between having a single-qubit state and knowing a result of a measurement you want to perform on it?

In the quantum teleportation protocol Alice can send Bob an unknown quantum state $|\psi\rangle$. If the only thing Bob does with $|\psi\rangle$ is to measure it in some basis, I guess it would be ...
Nikita Nemkov's user avatar
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1 answer
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Complexity of quantum circuits in a specific protocol

Consider the following simultaneous communication problem. Alice and Bob do not share any entanglement or any common randomness, and cannot communicate directly with each other. As inputs, $x$ is ...
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Optimality of teleportation for entanglement-assisted quantum channel coding

Setting: Consider a quantum channel $N_{A\rightarrow B}$ between Alice and Bob. Let Alice and Bob also share arbitrary amounts of entanglement assistance through the state $\phi_{A_EB_E}$ (these can ...
user1936752's user avatar
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Tradeoff between error and rates of quantum communication

Suppose Alice and Bob share $n$ copies of a noiseless quantum channel $I_{A\rightarrow B}$ which can be used to send quantum states and $H_A\cong H_B$ i.e. the input and output Hilbert spaces are the ...
user1936752's user avatar
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How to prove that $\frac{| x_0 \rangle + | x_1 \rangle}{\sqrt{2}}$ hides one of $x_0$ or $x_1$?

I create a quantum state $| \psi \rangle = \frac{| x_0 \rangle + | x_1 \rangle}{\sqrt{2}}$ for a randomly chosen $x_0,x_1$ of 50 bits. I give this quantum state $|\psi \rangle$ to you and you return ...
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What was the meaning of Lossless Quantum compression?

I was reading few questions regarding lossless quantum compression on stack exchange, then out of curiosity, I started reading this article. After reading I end up being confused about what does ...
User1086's user avatar
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States used in lossless quantum compression?

I was reading about quantum compression in this article and have some doubts regarding an example mentioned. Specifically, I have two questions: In example they represented $|a\rangle = \dfrac{1}{\...
John Jones's user avatar
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What are examples of zero capacity quantum channels with Choi rank less than $d$?

All the currently known examples of quantum channels with zero quantum capacity are either PPT or anti-degradable. These notions can be conveniently defined in terms of the Choi matrix of the given ...
mathwizard's user avatar
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Can someone elaborate how to use Qutrits to do teleportation? And the unitary operation Bob needs to do? [duplicate]

I can understand doing teleportation by using qubits, however, I am stuck there when it comes to qutrits and the operation Bob needs to perform. Suppose Alice and Bob are sharing the most entangled ...
NewtoQC's user avatar
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How are inputs during the quantum communication between Alice and Bob placed in the Galois Field?

I have to write a report on "Classical Interaction Cannot Replace a Quantum Message" by Gavinsky (arxiv link). The author gave a lecture, and at 14:55 explains that a communication problem ...
Asjad Sohail's user avatar
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2 answers
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Why do quantum networks matter?

I'm very new to quantum computing, sorry if this is a dumb question. I was reading in some lecture notes I found online that a quantum network could be created by using teleportation multiple times to ...
John L.'s user avatar
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If Alice and Bob share only classical communication resources, is shared entanglement always equivalent to shared randomness?

If Alice and Bob share only classical communication resources such as noisy or perfect classical channels, is shared entanglement always equivalent to shared randomness? In other words, must there be ...
JRT's user avatar
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Teleportation followed by measurement: Lowering communication cost

Suppose Alice and Bob have access to shared entanglement and a classical channel and wish to simulate the following quantum protocol. Alice sends over to Bob an $n$-qubit state which is not known to ...
user1936752's user avatar
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Non-ideal coin tossing

Can someone please check if the following makes sense? We have a non-ideal coin-tossing scheme as follows. Alice and Bob know what $|0\rangle,|1\rangle$ are. Bob wins when the coin is 1. Honest Alice ...
user777's user avatar
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Non-ideal bit commitment and coin tossing

Can someone please explain rigorously the reasoning behing non-ideal ($\epsilon$-concealing and $\delta$-binding) bit commitment scheme and the impossibility of coin tossing. What is bias in coin ...
user777's user avatar
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2 answers
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Proof of the no-communication theorem

Let $A, B$ be (finite-dimensional) Hilbert spaces, and $\rho$ some mixed state of $A \otimes B$. I am trying to show that a measurement performed on the '$A$-subsystem' does not affect $\rho^B = \text{...
Pedro's user avatar
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Quantum teleportation and the reality of quantum states

This question is perhaps philosophical but it's been confusing me. Suppose Alice is teleporting some qubit state $|\phi\rangle$ to Bob via the quantum teleportation protocol. After Alice applies the ...
Pedro's user avatar
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Distributed quantum computing with classical communication

I'm interested in the field of distributed quantum computing, i.e. using multiple smaller quantum devices/circuits to cooperate to be able to perform some task that would require a larger device (...
Ilan Rozen's user avatar
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Simulating a Quantum Network over a real Classical Network Using Simulaqron

I'm trying to simulate a quantum network over a real classical network using the Simulaqron framework. I know the documentations says this is possible but I am having trouble finding examples of how ...
Scott Oshiro's user avatar
1 vote
1 answer
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Entanglement and teleportation transmission costs

Let say we have a product state $$|\phi^+\rangle_{12}|\phi^+\rangle_{34}$$ with particles (1,4) belong to $A$ and (2,3) belong to $B$. Where $A$ and $B$ are say at distance of $L$ from each other. ...
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