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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
  • 26k
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
Accepted

Can weak measurements or quantum state tomography break bb84?

No, weak measurement and quantum tomography don't break BB84. I recommend that you create an explicit quantum circuit that implements the weak measurement or the quantum tomography, and check for ...
Craig Gidney's user avatar
  • 39.8k
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

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
  • 59.9k
4 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
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
  • 59.9k
4 votes

Can weak measurements or quantum state tomography break bb84?

Tomography generally speaking uses a collection of measurements to reproduce an underlying state. So you experimentally reproduce the same situation over and over, collect statistics and find the most ...
Steven Sagona's user avatar
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
  • 5,559
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

Non maximally entangled states for QKD

In schemes like E91, the idea behind using an entangled state is that: in a particular measurement basis (for both parties), the measurement outcomes are perfectly correlated but completely random (...
DaftWullie's user avatar
  • 59.9k
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
  • 23.2k
3 votes
Accepted

What is the difference between CV QKD and DV QKD?

It's the dimension of the Hilbert spaces. In DV-QKD you have a finite dimensional Hilbert space (like a qubit). Thus your measurement outcomes come from a finite set. On the other hand a CV-QKD ...
Rammus's user avatar
  • 5,988
3 votes
Accepted

Misunderstanding of QKD BB84 protocol

This looks like a mistake in the image to me (or a reflection of Alice and Bob using faulty procedures to convert bits to qubits and vice versa, which seems much less likely). Under ideal conditions, ...
Mariia Mykhailova's user avatar
3 votes
Accepted

How to correctly describe state preparation?

For applications such as BB84, it really doesn't matter which of the two descriptions you use, because from everybody's perspective apart from Alice, they do not have access to the first system, and ...
DaftWullie's user avatar
  • 59.9k
3 votes
Accepted

Doubt in understanding the use of Uhlmann's Theorem in BB84 security proof

The relation in 1. is essentially a statement of Uhlmann's theorem. Ulmann's theorem states: Given two density matrices $\rho$ and $\sigma$, we have that the fidelity $F(\rho, \sigma)$ is given by $$F(...
xzkxyz's user avatar
  • 451
3 votes

Why isn't quantum error correction used in quantum key distribution protocols like BB84?

I do not feel an expert on this topic but I have recently encountered QKD protocol variants that make use of quantum error correction, so maybe you will find this interesting: in Chapter 12.6 of the ...
Miriam K.'s user avatar
  • 165
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
  • 59.9k
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
2 votes

How do I compare the secret key rate (kbps) with the secret key rate per channel use?

Indeed, the PLOB bound is an ultimate upper bound for repeaterless quantum communications, and is thus derived by averaging over $n\rightarrow \infty$ uses of the communications channel - Hence why ...
Cei328's user avatar
  • 101
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
  • 59.9k
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
  • 5,988
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
  • 39.8k
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

What is the difference between CV QKD and DV QKD?

One example to understand it, if someone finds it useful, is the following: Most QKD is done by sending light through a channel. In DV-QKD we send single photons through the channel, one at a time. We ...
Troncho Col's user avatar
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

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
  • 59.9k

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