17

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 and specialized computers that actually just do classical secret-key cryptography anyway. Plus you have to authenticate the shared secret keys you negotiate ...


10

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. The point is that, as of today, no one was able to do this. Indeed, such a result would be a serious breakthrough, as it would prove the existence of $\text{NP}$ ...


5

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 settings used for the keys bits were indeed chosen with the probability 2/9, but others optimised it in all kind of ways. So at least 2/9 is the probability of ...


5

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 application). In order to build such a TRNG, from a quantum circuit perspective, all you need is a single qubit, a Hadamard gate and a measurement. Although there might ...


4

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 capability of producing single-qubit (non-entangled) states. These are sent to a server who can (locally) entangle them for the purposes of performing a measurement-...


3

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 (50:50 outcomes). you can perform a Bell test on the state to verify its nature. Using a maximally entangled state gives you the property of the 50:50 outcomes (...


3

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 the setup, but you can get a pretty reasonable demo of polarization-encoded BB84 with a few pretty common components: polarized laser pointer some half wave ...


2

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 which of 3 measurements to make. Alice chooses between the measurement bases $Z$, $(X+Z)/\sqrt{2}$ and $X$. Bob chooses between $(X+Z)/\sqrt{2}$, $X$ and $(X-Z)/\...


2

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 require the full power of a quantum computer) and is provably secure (subject to certain underlying assumptions about lab security etc) against quantum attack.


2

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 messages. Quantum key distribution is only used to produce and distribute a key, not to transmit any message data. The algorithm most commonly associated with QKD is ...


1

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 have a maximum of 6. If everything works perfectly, all 6 bits should be equal. Of course, in the real world, there are experimental imperfections and it could ...


1

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 tester prior to discussing multi-qubit entanglement in lecture 5. In the Elitzur-Vaidman tester, a single qubit in a superposition can be used to probe and ...


1

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 on the secret key rate is computed as a regularisation, where one considers the infinite limit of $ n \rightarrow \infty$ transmissions across the channel in ...


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