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Questions tagged [circuit-model]

For questions about using the circuit-model of quantum computing, versus, for example, the quantum annealing model or the measurement-based model. Questions which are using the circuit-model but are not specifically asking about it probably should not have this tag.

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1answer
60 views

List of known circuits and their expected output

I've written an API which takes in a circuit scaffold, according to some specifications, and outputs the results of simulating the circuit. The circuit constraints are that the measurements are ...
3
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4answers
488 views

What circuit or operation corresponds to the tensor product?

What Clifford gate circuit operating on states $|\psi_1\rangle$ and $|\psi_2\rangle$ prepares the state $|\Psi\rangle=|\psi_1\rangle \otimes |\psi_2\rangle$ ?
2
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1answer
83 views

How to you encode a network as an adjacency-list in the quantum-gate model?

I have a network problem that I believe would be represented as an adjacency-list on a quantum circuit. Typically, the list is up for traversing from various perspectives (e.g., shortest-path between ...
5
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2answers
81 views

Reversible computation without inverting the circuit

I know that if you have a circuit $U$ that transforms $A → B$, it's possible to construct an inverse, ${U\dagger}(B) → A$. Is it also possible to transform the states with $T_{i,o}$ so that I can use ...
0
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1answer
76 views

What's the matrix representation of this 3 qubit circuit?

How do I calculate the matrix representation of this part of a teleportation circuit? It must be a matrix of dimension 8.
3
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3answers
74 views

Can we do adiabatic quantum computing with a quantum circuit model and how?

This is a question that must be asked a lot but is it possible? And if in theory possible, what are the challenges to do it, and what are the drawbacks?
3
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0answers
52 views

Circuit to construct a $n$-qubit state which is a superposition of states with only a single qubit being $\lvert1\rangle$ [duplicate]

So the question came up in a book I am working through. Given a circuit with $n$ qubits, construct a state with only $n$ possible measurement results, each of which has only $1$ of $n$ qubits as $1$, ...
2
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3answers
102 views

Calculating measurement result of quantum swap circuit

Consider the following circuit, where $F_n$ swaps two n-qubit states. If the inital state is $|0\rangle \otimes |\psi\rangle \otimes |\phi\rangle = |0\rangle|\psi\rangle|\phi\rangle$, the state ...
6
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3answers
71 views

$R_z$ gate representations

Why is the $R_z$ gate sometimes written as: $$ R_{z}\left(\theta\right)=\begin{pmatrix}1 & 0\\ 0 & e^{i\theta} \end{pmatrix}, $$ while other times it is written as: $$ R_{z}\left(\theta\...
5
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2answers
39 views

Fault tolerant quantum measurement: how is implemented the “majority vote”

As a fundamental component for a quantum computation, the measurement needs to be implemented in a fault tolerant way. As indicated in Chuang and Nielsen Quantum Computation and Quantum Information, ...
6
votes
1answer
159 views

Decomposition of arbitrary 2 qubit operator

As you know, universal quantum computing is the ability to construct a circuit from a finite set of operations that can approximate to arbitrary accuracy any unitary operation. There also exist some ...
6
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3answers
93 views

Generalization for $n$ quantum teleportations

In Breaking Down the Quantum Swap, it is stated: Thanks to the CNOT, we can implement a xor-swap on a quantum computer. All we need to do is chain three CNOTs back and forth. In a comment to a ...
5
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1answer
49 views

Classical XOR gate in Quantum Circuit

Can we use classical XOR gate in a quantum circuit? Or are there any alternatives for XOR gate?
8
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6answers
326 views

How to construct a multi-qubit controlled-Z from elementary gates?

For the implementation of a certain quantum algorithm, I need to construct a multi-qubit (in this case, a three-qubit) controlled-Z gate from a set of elementary gates, as shown in the figure below. ....
4
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4answers
223 views

How to re-create the following circuit image?

What would be the best way to re-create the following image of the HHL quantum circuit without compromising on image quality (the image is from this review paper)? Using qasm2circ I can create the ...
5
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1answer
70 views

Arbitrary powers of NOT and SWAP

The square-root of not and square-root of swap gates are often singled out for discussion of gates displaying important properties relating to quantum computers. How do I define arbitrary (non-...
7
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2answers
117 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)?
5
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3answers
149 views

Showing the equivalence of two simple {NOT, CNOT} circuits

As a beginner, for exercise purpose, I’ve studied this two quantum circuits. They are equivalent, and for 2 qubits it’s easy to write the unitary transformation matrix. Looking for another method I ...
6
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1answer
117 views

SWAP gate(s) in the $R(\lambda^{-1})$ step of the HHL circuit for $4\times 4$ systems

Context: On the 5th page of the paper Quantum circuit design for solving linear systems of equations (Cao et al, 2012) there's this circuit: Schematic: A brief schematic of what's actually ...
2
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1answer
69 views

Photonic Circuit Idea (Does this already exist?)

I have had a few ideas for circuits that I would like to get feedback on (do such things already exist, what utility they serve, etc). Any suggestions on how I might graphically render these? ...
5
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1answer
114 views

Quantum Arithmetic

I'm looking at this paper and try to implement the Quantum adders they define myself. Suppose we have a number $b=b_{n-1}\dots b_1b_0$ and they want to add a constant number $a=a_{n-1}\dots a_1a_0$. ...
11
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3answers
1k views

How can I build a circuit to generate an equal superposition of 3 outcomes for 2 qubits?

Given a $2$ qubit-system and thus $4$ possible measurements results in the basis $\{|00\rangle$, $|01\rangle$, $|10\rangle$, $|11\rangle\}$, how can I prepare the state, where: only $3$ of these $4$ ...
11
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1answer
763 views

How to interpret a quantum circuit as a matrix?

If a circuit takes more than one qubit as its input and has quantum gates which take different numbers of qubits as their input, how would we interpret this circuit as a matrix? Here is a toy example:...
11
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2answers
191 views

Jones Polynomial

There are many fairly standard quantum algorithms that can all be understood within a very similar framework, from Deutsch's algorithm Simon's problem, Grover's search, Shor's algorithm and so on. ...
6
votes
1answer
232 views

How to apply single and two qubit gates to 2 qubits multiple times?

Let's say we have the following quantum circuit: Let's say we input the state $|00\rangle$ . Both of the $H$ gates produce the output $1/\sqrt{2}$, but which one of the following $2$ vectors is the ...
8
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2answers
233 views

Shortest sequence of universal quantum gates that correspond to a given unitary

Question: Given a unitary matrix acting on $n$ qubits, can we find the shortest sequence of Clifford + T gates that correspond to that unitary? For background on the question, two important ...
21
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2answers
3k views

What is quantum gate teleportation?

Quantum state teleportation is the quantum information protocol where a qubit is transferred between two parties using an initial shared entangled state, Bell measurement, classical communication and ...
6
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1answer
367 views

How exactly does Simon's algorithm solve the Simon's problem?

Problem Statement: We are given a $2-1$ function $f:\{0,1\}^{n}\to\{0,1\}^{n}$ such that: there is a secret string $s\in\{0,1\}^{n}$ such that: $f(x)=f(x\oplus s)$. Challenge: find $s$. Simon's ...
6
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3answers
135 views

Do the 'fundamental circuit elements' have a correspondence in quantum technologies?

Capacitors, Inductors and Resistors are well-known circuit components. Since the proposal of Leon Chua in 1971, the Memristor joined them as a fundamental component. I am wondering whether these ...
10
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3answers
204 views

What would be the simplest addition that would make the D-Wave architecture universal?

The D-Wave system, as I understand it, allows us to program Ising models and to find their ground states. In this form, it is not universal for quantum computation: it can not simulate a circuit model ...
16
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3answers
811 views

How do I add 1+1 using a quantum computer?

This can be seen as the software complement to How does a quantum computer do basic math at the hardware level? The question was asked by a member of the audience at the 4th network of the Spanish ...
13
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2answers
962 views

Do multi-qubit measurements make a difference in quantum circuits?

Consider the unitary circuit model of quantum computation. If we need to generate entanglement between the input qubits with the circuit, it must have multi-qubit gates such as CNOT, as entanglement ...
10
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1answer
136 views

What do double wires mean in quantum circuits, and how do they relate to if statements?

The circuit can be translated to the following code: ...
11
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2answers
310 views

Circuit of controlled-Unitary gate

Suppose we have a circuit decomposition of a unitary $U$ using some universal gate set (for example CNOT-gates and single qubit unitaries). Is there a direct way to write down the circuit of the ...
14
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2answers
240 views

Why is it important to eliminate the garbage qubits?

Most reversible quantum algorithms use standard gates like Toffoli gate (CCNOT) or Fredkin gate (CSWAP). Since some operations require a constant $\left|0\right>$ as input and the number ...
20
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2answers
467 views

How is the oracle in Grover's search algorithm implemented?

Grover's search algorithm provides a provable polynomial speed-up for unsorted database search. The algorithm is usually expressed by the following quantum circuit: In most representations, a crucial ...
17
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2answers
392 views

Why can't quantum annealing be described by a gate model?

This is a question I was inspired to ask based on this question, which notes that quantum annealing is an entirely different model for computation than the usual circuit model. I've heard this before, ...