18 votes

Advantage of quantum key distribution over post-quantum cryptography

Quantum key distribution requires that you wholesale replace your entire communications infrastructure built out of 5 EUR ethernet cables and 0.50 EUR CPUs by multimillion-euro dedicated fiber links ...
Squeamish Ossifrage's user avatar
15 votes
Accepted

Advantage of quantum key distribution over post-quantum cryptography

If it is proven that a given asymmetric encryption protocol relies on a problem which cannot be solved efficiently even by a quantum computer, then quantum cryptography becomes largely irrelevant. ...
glS's user avatar
  • 23.9k
7 votes
Accepted

Why is the efficiency of Ekert 91 Protocol 25%?

I emailed Artur Ekert to seek help for this quesiton, and he replied: There are different variants of the E91 protocol that may give you different efficiencies. In my original version the ...
Lynn's user avatar
  • 311
5 votes

In what ways can qubits be used for applications that do not require entanglement?

One (obvious) application is the generation as True Random Number Generators, e.g. IDQ, or you can download some here Free True Random Numbers (please do not use these for security relevant ...
Fleeep's user avatar
  • 374
4 votes

In what ways can qubits be used for applications that do not require entanglement?

Certainly not exhaustive, but to get the ball rolling... One possible application is blind quantum computation. In this, there is a user who wants to complete a computation, but only has the ...
DaftWullie's user avatar
  • 56.8k
4 votes

Why is the efficiency of Ekert 91 Protocol 25%?

TL;DR: The efficiency is 2/9, not 25%. The Ekert 91 protocol involves many rounds. In each round, Alice and Bob share a Bell pair $$ (|00\rangle+|11\rangle)/\sqrt{2} $$ They both choose randomly ...
DaftWullie's user avatar
  • 56.8k
4 votes
Accepted

What is meant with "reconciliation" in CV QKD?

I assume the paper you are reading is referring to information reconciliation. Information reconciliation is a vital part of post-processing in QKD, to limit (or erase in the best-case scenario) the ...
JSdJ's user avatar
  • 5,399
3 votes
Accepted

The Methodology of Quantum Key Distributions Systems

1. Existing Products I've not yet come across commercial systems using entanglement based schemes. The commercial products I've seen, like ID Quantique and MagiQ seem to be using BB84/B92 type ...
Jonathan Trousdale's user avatar
3 votes
Accepted

Doubt in CSS error correction step

We can think of an $n$-bit string as a "mask" that specifies a set of positions where the bit string is $1$. For an $n$-bit string $x$ denote with $s(x)\subset\{0, 1, \dots, n-1\}$ the set ...
Adam Zalcman's user avatar
  • 21.7k
3 votes
Accepted

Implementing BB84 protocol with easily-obtained consumer hardware

I am glad you enjoyed my experiments! :) I'd be happy to talk more about how I ran that project --- dm me at twitter.com/crazy4pi314. To your question, I don't know of any good papers or articles on ...
Dr. Sarah Kaiser's user avatar
2 votes

What role do Hecke operators and ideal classes perform in “Quantum Money from Modular Forms?”

CW from self-answer Reviewing Farhi et al. on quantum money from knots, one can say that the Markov chain applied by the verification algorithm that walks along the Reidemeister graph is far from ...
2 votes

What is the difference between quantum key distribution and quantum key exchange?

Quantum key distribution (QKD) is a secure communication method that enables two parties to produce a shared random secret key known only to them, which can then be used to encrypt and decrypt ...
Gokul Alex's user avatar
2 votes

Lattice based cryptography vs BB84

Post-quantum crypto schemes run on classical computers and are hoped to be secure against quantum attacks. Quantum key distribution such as bb84 or e91 run on quantum hardware (although does not ...
DaftWullie's user avatar
  • 56.8k
2 votes
Accepted

Doubt in Simple proof of Security of the BB84 QKD

I'm not sure that I would claim the two situations are entirely equivalent - if Alice and Bob share Bell pairs, there are extra things they could do (e.g. testing Bell inequalities), but in terms of ...
DaftWullie's user avatar
  • 56.8k
2 votes

Major Security proofs available for Device-Independent QKD

The progress in DIQKD security proofs has been quite rapid in recent years. In particular, the approach of Vazirani and Vidick is no longer what the community uses. The two major approaches that I ...
Rammus's user avatar
  • 5,435
2 votes

Can we do error correction for entangled particles?

Error correcting codes work the same on entangled qubits as any other qubit. All Alice and Bob have to do is separately encode their qubit into a Shor code. They each run an encoding circuit, apply ...
Craig Gidney's user avatar
  • 34.9k
2 votes

Understanding the (2,3) threshold quantum secret sharing scheme in Cleve et al. 1999

add the value of the first share to the second (modulo three), and then add the value of the second share to the first means you first perform, on the 2 shares, the 2-qutrit unitary which maps $$|00\...
GotCarter's user avatar
  • 401
2 votes
Accepted

Why does entanglement of 3 qubits break this?

Why wouldn't it break it? Involving Eve requires, for example, putting a CNOT gate from one of the distributed qubits to some outside qubit. That CNOT operation doesn't commute with the controlled Y ...
Craig Gidney's user avatar
  • 34.9k
2 votes

E91 probability of wrong conclusion of eavesdropper

E91 doesn't really deal in such strong absolutes as you're talking about (although it's often a helpful way to talk about the protocol the first time you meet it). Instead, you measure a value $S$, in ...
DaftWullie's user avatar
  • 56.8k
2 votes

In the E91 protocol, how can Alice and Bob detect Eve if she waits to measure until A&B publish their bases?

Let us recall the Ekert-91 (E91) protocol. Initially Alice and Bob each independently receive respective elements of a plurality of Bell pairs (for example, generated by spontaneous parametric down-...
Mark Spinelli's user avatar
2 votes

In what ways can qubits be used for applications that do not require entanglement?

In lecture 4 of O'Donnell's series on quantum computing, he introduces the Elitzur-Vaidman bomb tester, which is an interesting application of the quantum Zeno effect. O'Donnell introduces the bomb ...
Mark Spinelli's user avatar
1 vote

Why does entanglement of 3 qubits break this?

Remember that, from the perspective of Alice and Bob, Eve's qubit(s) are an external system that they cannot control. The best description that they have of their system involves tracing out Eve's ...
DaftWullie's user avatar
  • 56.8k
1 vote
Accepted

Counting channel uses of the lossy bosonic channel or definition of channel uses

I think your misunderstanding is in the wording of the secret key rate; The PLOB-Bound offers an asymptotic, ultimate-upper bound on the secret key rate per use of a lossy bosonic channel. This bound ...
Cei328's user avatar
  • 101
1 vote

BB84 Protocol doubt

Let us work this out for your particular example, and see why it works in the general case. We have: $$ \begin{array}{c|c|c|c|c|c|c|c|c} \text{index}&1&2&3&4&5&6&7&8\\\...
Tristan Nemoz's user avatar
1 vote

Why is Measurement Device Independent (MDI) Quantum Key Distribution (QKD) truly MDI?

Actually, Charlie measures not the qubits themself, but the result of its interference. As there are currently no reliable quantum information medium other than photons, lets speak about photons: ...
totikom's user avatar
  • 196
1 vote

Quantum bit error rate

I do not know how the crosstalk matrix works. But the way I understand QBER is the following: QBER is the mismatch probability of the signals sent and receieved between Alice and Bob. Let Alice send ...
QuestionEverything's user avatar
1 vote

How are Franson Interferometers used to prove security in Photonic QKD Experiments?

What a Franson interferometer does is to superpose two-photon wavepackets generated at different times (within the coherence time of the pump, supposing we are generating a pair of entangled photons ...
Javier González M. del C.'s user avatar
1 vote

What is the intuition behind the following entanglement distillation protocol for continuous variable systems?

To see intuitively why this protocol increases the entanglement after each iteration, we can work out an example where our initial state is say $\lvert 00\rangle+\lvert 11\rangle$. Upon passing ...
Devjyoti Tripathy's user avatar
1 vote

BB84 and B92 protocols: what is maximum and minimum bits that Alice and Bob might agree on?

I’m not exactly sure what is meant by “the bits they agree on”, but I would interpret it slightly differently to you. If Alice and Bob don’t agree on the same basis, they discard those bits, so they ...
DaftWullie's user avatar
  • 56.8k
1 vote

What authentication protocol to use for BB84 and other QKD protocols?

In classical cryptography, the Diffie-Hellman key exchange is also susceptible to a man-in-the-middle attack, and to get around that, we use a digital signature algorithm, like RSA or ECDSA. You can ...
amihart's user avatar
  • 41

Only top scored, non community-wiki answers of a minimum length are eligible