Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

Questions tagged [cloning]

Quantum cloning is a process that takes an arbitrary, unknown quantum state and makes an exact copy without altering the original state in any way. (Wikipedia)

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Toffoli gate as FANOUT

I was searching for examples of quantum circuits to exercise with Q# programming and I stumbled on this circuit: From: Examples of Quantum Circuit Diagrams - Michal Charemza During my introductory courses in quantum computation, we were taught…
D-Brc
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Advances on imperfect quantum copying

It is known by the no-cloning theorem that constructing a machine that is able to clone an arbitrary quantum state is impossible. However, if the copying is assumed not to be perfect, then universal quantum cloning machines can be generated, being…
Josu Etxezarreta Martinez
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Approximate Cloning

Question Consider two single qubit states $\left\{|\alpha_0\rangle,|\alpha_1\rangle\right\}$ which are not orthogonal or parallel, i.e. $\left|\langle\alpha_0|\alpha_1\rangle\right|\ne0,1$. Additionally, consider the unitary operation:…
Chris Long
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No-cloning theorem and distinguishing between two non-orthogonal quantum states revisited

There are a couple of posts on this question, but I think they are not satisfactory. The question is Nielsen and Chuang's QCQI, Exercise 1.2, page 57, which asks "Explain how a device which, upon input of two non-orthogonal states correctly…
Anna Naden
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Cloning classical data encoded into qubits

How is it possible to maintain classical data encoded into qubits, which often contains copies of information, given that the no cloning theorem prevents cloning information?
pinkdroid
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Is their a way to perfectly clone coherent state and squeezed states?

Coherent state and squeezed states can be swapped why cloning coherent states can't be perfect to clone we obtain $$|\cos(|z|)b\rangle \otimes |\sin(|z|)b\rangle,$$ If we set $|z| = \pi/4$ then $$|b\rangle \otimes |0\rangle = |b/\sqrt 2\rangle…
pahuldeep singh
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Classical and quantum limits to classical copying?

The no-cloning theorem can be sharpened to give quantitative bounds on the fidelity with which an arbitrary quantum state can be copied. Is there a similar picture available for classical copying? This breaks down into two Questions: In classical…
Tim Campion
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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. What I want to know is, does there exist some…
Visipi
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Compute the output of this Approximate Quantum Cloning three-qubit circuit

Above is a circuit for "Approximate Quantum Cloning" The preparation state is given by $$|\psi\rangle =\alpha|0\rangle+\beta|1\rangle$$ The gates labelled $\theta_i$ denote single qubit rotations given by…
Dwye
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How to show that BB84 is safe against imperfect cloning?

One of the reasons why BB84 is usually considered safe is due to the no-cloning principle. However, as far as I know imperfect cloning of quantum states is possible. I've been thinking about a potential attack on the BB84 where Eve makes imperfect…
Miriam K.
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does there exist a quantum approximate cloning method that does not modify the initial qubit (the one whose state we want to clone)?

I am currently trying to implement circuit (in Qiskit if that is relevant) to approximate a state of a qubit without measuring it (basically I want to "attach it" to a qubit and have some approximate idea about it's state while not collapsing it's…
puma
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Symmetric Universal Quantum Cloning Machine (UQCM) $N \to M$ for unknown states

Does it exist a schematic diagram of the quantum circuit implementing the symmetric UQCM $N \to M$ for unknown states? If yes, does anyone know a Qiskit implementation of it?
L. Lenzini
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Shared entanglement to copy orthogonal states

Assume that Alice and Bob are allowed to share entanglement and are spatially separated. Alice is given an unknown state and asked to measure this in the computational basis to obtain $\vert 0\rangle$ or $\vert 1\rangle$. Is there some way for Bob…
user1936752
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No-cloning theorem and distinguishing between two non-orthogonal quantum states revisited revisited

There are many posts to this question from Nielson and Chuang's Quantum Computation and Quantum Information Exercise 1.2 page 57. It is required to prove that if a hypothetical device exists, which could distinguish between two non-orthogonal…
Manit Agarwal
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What are the best algorithms to achieve probabilistic quantum cloning?

I am aware that there are algorithms that can clone states with unit fidelity but with a positive probability of failure. What would be the best known algorithms to create a perfect clone of an arbitrary unknown single qubit state with minimum…
Fabio Dias
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