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Questions tagged [quirk]

Quirk is an open-source drag-and-drop quantum circuit simulator for exploring and understanding small quantum circuits. It was developed by Craig Gidney.

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22 votes
3 answers
4k views

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 ...
D-Brc's user avatar
  • 413
9 votes
2 answers
280 views

Topological Circuit Simulator

Does something like Quirk exist for topological (eg. braided) circuits? Alternatively, any ideas on how @CraigGidney is getting these circuits (or something similar)?
user820789's user avatar
  • 3,302
2 votes
2 answers
348 views

Why does entanglement of 3 qubits break this?

Another user asked about the Ekert Quantum Key Distribution protocol: Alice and Bob each randomly choose one of three bases separated by $120^{\circ} $ in which to measure, and then later compare the ...
Frank Yellin's user avatar
2 votes
2 answers
505 views

Problem with commutation of $e^{-iH_1t}$ and $e^{-iH_2t}$, where $H_1$ commutes with $H_2$

I'm given with a Hamiltonian, $H=H_1+H_2$, where $H_1=\sigma_x\otimes\sigma_z$ and $H_2=\sigma_y\otimes\sigma_y$, and want to built a circuit which will implement $e^{-iHt},t=\pi/6$. We see that as $\...
Omkar 's user avatar
  • 331
5 votes
0 answers
560 views

Error: Simulation of "Quantum algorithm for linear systems of equations" for $4\times 4$ systems on Quirk (without SWAP) - Global phase

Following @DaftWullie's answer I tried to simulate the circuit given in Fig. 4 of the paper (arXiv pre-print): Quantum circuit design for solving linear systems of equations (Cao et al, 2012), on ...
Sanchayan Dutta's user avatar
4 votes
2 answers
244 views

What is wrong with my circuit for the fourth-root of $X$?

For learning purposes I would like to hand-craft my own circuit for the fourth-root of $X$, using $S$, $T$, and $\sqrt X$ gates. Note that $\sqrt[4]X$ is of order eight while $\sqrt X$ is of order ...
Mark Spinelli's user avatar
2 votes
1 answer
159 views

Problem with eigenvalue evaluation algorithm application on matrix $U$

Once I get to the end of the algorithm, I can't understand how to calculate the eigenvalue using formulas. Bear in mind that it is an exercise to be carried out with pen and paper. the matrix of $U$ ...
Francescov20's user avatar
1 vote
1 answer
158 views

How to store error caused by circuit manipulation

Given that is equivalent to I am interested into not performing the last CNOT. Rather, I want to keep track of the error I intentionally introduced by removing it. I am trying to do this by means of ...
Daniele Cuomo's user avatar