# Questions tagged [bb84]

For questions related to quantum cryptography protocol BB84.

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### Where can I find a detailled exposition of the Information theoretic part of BB84?

I understand the general idea of information reconciliation and advantage distillation, but I can't find any exposition of the algorithm used, unlike the quantum part of the protocol which is well ...
4 votes
1 answer
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### Eavesdropping in case of the BB84 Protocol

I try to understand eavesdropping in case of the BB84 protocol (lets assume we have single photons, no noise etc.). Alice and Bob generate a classical random bit $a_i'$ and $b_i'$. Alice generates an ...
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### Heisenberg Uncertainty Principle for BB84 Protocol using Paulis Spin Matrices

I am doing a term project on the BB84 Protocol and it makes use of the Heisenberg Uncertainty Principle. I think I understand the principle in theory. If we have two non-commuting observables, then we ...
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### BB84 Protocol doubt

I was studying BB84 protocol from lecture notes by John Watrous. I had some doubts which i thought of asking. Here is the protocol. Alice prepares strings $x=(01110100)$ and $y=(11010001)$. based on ...
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4 votes
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### Show That an Intercept and Resend Attack on all qubits reduces mutual information

Exercise 5.3.3 With no eavesdropping the mutual information $H(A:B)$ between the substring of $\mathcal R$ held by Alice and $\mathcal R'$ held by Bob is $1$ bit. Show that if Eve is performing an ...
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### Doubt in CSS error correction step

At the end of page 3 in Simple proof of security of the BB84 QKD, the following equation (equation 4) is given :  \begin{array}{r} \frac{1}{2^{n}\left|C_{2}\right|} \sum_{z}\left[\sum_{w_{1}, w_{2} ...
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1 answer
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### Doubt in Simple proof of Security of the BB84 QKD

I am not able to understand an argument from Simple proof of Security of the BB84 QKD; I need your help. In page 2 it is mentioned that "Alice can measure her half of the encoded EPR pairs before ...
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4 votes
3 answers
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### How are eavesdroppers detected when using BB84 in the presence of noise?

I would like to expand upon this question: What is the probability of detecting Eve's tampering, in BB84? Let's say that when the receiver (colloquially referred to as Bob) receives a qubit and ...
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1 vote
2 answers
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### Show when $a_k$ and $b_k$ are correlated when measuring in different bases, in the BB84 protocol

I'm trying to answer the following question about the BB84 protocol from Nielsen and Chuang's Introduction to Quantum Information. As I understand it, the string $b$ is determining whether we are ...
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### What is the probability of detecting Eve's tampering, in BB84?

Alice sends a 0 in computational basis I understand that theres a $\frac12$ probability that eve guesses the basis wrong, and can go with Hadamard. So it's $\frac12$ chance Eve will pick computational ...
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### Can quantum state tomography break bb84?

I am currently reading through this paper and read some of the wikipedia pages on weak measurement and quantum tomography and I am curious if weak measurement could be used to break BB84 quantum key ...
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### Any good resources for learning about quantum networks and how to do a simulation of BB84 protocol?

I'm a communication engineering student. And I'm thinking of doing my project on BB84 protocol but I don't know where to start. As a beginner, are there any documents or tutorials about quantum ...
3 votes
1 answer
201 views

### Can Eve randomly guess the correct bases in the BB84 exchange of a one-time pad?

I'm learning about Quantum Key Distribution, and just learned about the BB84 exchange. I learned that it can be used to exchange a key for a one-time pad, which would allow for information-...
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### Is there a notion of “computational security” in quantum cryptography?

In classical cryptography, security proofs are often based on the (assumed) computational hardness of some mathematical problem. Using the principles of quantum mechanics might provide means to design ...
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### Is it a good idea to publish a research paper about the simulation of BB84 protocol?

I'm an engineering student. As my end of year project I've simulated BB84 protocol using simulaqron(python). I'm thinking about publishing a paper about this simulation. I haven't published any ...
2 votes
1 answer
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### Hadamard gate with two inputs in the circuit for the BB84 protocol?

I am reading the book "Quantum Computing verstehen" by Matthias Homeister. At the moment i'm having a look at the BB84 protocol (which is described in kind of an abstract way). In this chapter a ...
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### Is the BB84 protocol an example of "quantum supremacy"?

This is a fairly broad question, I hope it fits here. I am wondering if the BB84 protocol is an example of "quantum supremacy", ie. something a quantum computer can do but something that is assumed a ...
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5 votes
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### In the BB84 protocol, for what error thresholds can Alice and Bob not establish secure bits?

Suppose Alice and Bob can communicate over a quantum channel. The quantum channel is noiseless in the absence of eavesdropping, a condition that cannot be guaranteed. They can also communicate over a ...
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### Why Alice and Bob don't get the same result when they measure in the same basis?

I'm simulating the BB84 protocol using simulaqron. My problem is that when Alice and Bob measure in the same basis, they don't get the same result. How can I fix this error? . BB84.py ...
1 vote
1 answer
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### How to deal with noise in BB84 protocol?

BB84 protocol works followingly: Alice generate $N$ random qubits $a_i$ in state either $|0\rangle$ or $|1\rangle$ . These will be a key. Then she prepares $N$ random bits $b_{i}$. If $b_i=0$, an ...
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2 votes
1 answer
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### How does a rectilinear filter used for QKD-BB84 detect both horizontal and vertical polarizations?

When using the BB84 algorithm for QKD, you arbitrarily choose which of two filters (bases) to use when detecting a photon: rectilinear or diagonal. If you choose rectilinear, you can detect ...
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### What is the quantum state transmitted to Bob in BB84 protocol?

Sender (Alice) wants to exchange private encryption key with Bob using BB84 protocol. She generate a binary string (1010100010010111),and encode using Hadamard gate and identity gate (HHHIIHIHHIIIHIIH)...
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### Show that if $b'$ and $b$ are uncorrelated, then $a'$ and $a$ are uncorrelated

Let $a'_k$ be Bob's measurement result of qubit ${\Psi_{a_kb_k}}$, assuming a noiseless channel with no eavesdropping. Show that when $b'_k\neq b_k$, $a'_k$ is random and completely uncorrelated ...
4 votes
1 answer
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### Does the Lieb-Robinson bound constrain the speed of entanglement information transmission?

I just learned from the existence of the theoretical Lieb-Robinson bound, which indicates that the speed at which information can be propagated in non-relativistic quantum systems cannot exceed this ...
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### What authentication protocol to use for BB84 and other QKD protocols?

Just like other classical and quantum key distribution protocols, BB84 is vulnerable to "man"-in-the-middle attacks, where Eve pretends to be Bob to Alice, and Eve pretends to be Alice to ...
3 votes
1 answer
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### Counting channel uses of the lossy bosonic channel or definition of channel uses

The PLOB-bound ("Fundamental Limits of Repeaterless Quantum Communications") gives an asymptotic upper bound on the secret-key rate per used lossy bosonic channel. However, I'm not sure how to count ...
1 vote
1 answer
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### Comprehension questions on quantum cryptography especially BB84

I have recently read a lot about the BB84 protocol, I have used three primary sources, the original work, a QK book, and a diploma thesis. My questions refer to the photons sent by Alice, the base of ...
11 votes
1 answer
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### How many bits do Alice and Bob needs to compare to make sure the channel is secure in BB84?

I was trying to self-study qmc by reading the Quantum Computing A Gentle Introduction book, in section 2.4 it talks about the quantum key distribution protocol BB84. After (I thought) I understood it ...
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