# Questions tagged [quantum-gate]

For questions regarding usage, performance, implementation, application or theory related to quantum gates.

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### How the simulator work?

Recently I focused on how to simulate in classical computer, and I found Qiskit offers qasmsimulator and statevector simulator. ...
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### Is there anything Quantikz can do that Tikz cannot do?

I am learning how to draw quantum circuits. I was checking the options available and I could see that Tikz and Quantikz are suitable for making circuits diagrams but I want to know if there are some ...
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### How can we construct a square root of NOT gate in Qiskit and IBMQ circuit composer using universal gates?

I have tried it with decomposing controlled S then conjugating with H gate. But I want to construct it using a minimum number of gates.
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### Applying a gate to all line qubits without explicitly listing them in Cirq

Say we have a custom gate CG, defined by a unitary matrix U, and line qubits qubits in Cirq. ...
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### Visualizing custom gates in Cirq

I'm trying to visualize a custom gate in Cirq. I have through this page, which briefly mentions how to create custom gates in Cirq. However, I'm getting errors when trying to visualize it. My current ...
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### How can a half-wave plate affect the position qubit and not the polarization qubit of a photon?

I recently was watching these 2 videos on Coursera which show how to build a simple quantum computer that can implement the simplest case of the Deutsch-Jozsa algorithm (which uses only 2 qubits). ...
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### Expectation value of an operator error: Composition is not defined over operators of different dimensions,

I am trying to calculate the expectation value of a customized operator on two similar but differently constructed states $\phi = \phi_2 =\frac{1}{\sqrt{2}}\left( |001⟩ + |011⟩\right)$ which consist ...
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### How to calculate destabilizer group of toric and other codes

Some papers use the "destabilizer group" for more efficient simulations; see for example (page 3): https://www.scottaaronson.com/showcase2/report/ted-yoder.pdf "In addition to ...
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### Is there a quantum operation to change a phase $e^{(0.q_0 q_1 q_2 q_3)}$ into $e^{(0.q_1 q_2 q_3)}$?

Given a set of four qubits, say $q_{0},q_{1},q_{2},q_{3}$ which represent a $4$-bit binary number with $q_{0}$ as the MSB. After applying QFT on these qubits the phase of $q_{0}$using the concept of ...
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### import error :No module named 'qiskit_aqua'

I have an error when I use Quantum SVM kernel algorithm from Qiskit aqua. This is my code section with imports: ...
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### Difference between $Rz$ and $R1$ gate [closed]

You are given an operation that implements a single-qubit unitary transformation: either the Rz gate or the R1 gate. The operation will have Adjoint and Controlled variants defined. Your task is to ...
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### How to find a circuit for the roots of QFT?

After reading about using quantum gates instead of ancillas, it asserts that every quantum circuit has a square root. Theoretically, they do, but is there a practical method to generate the quantum ...
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### What is the shortest sequence of decomposition a given single-qubit unitary gate

Given a single-qubit unitary matrix, can we find the shortest sequence of Clifford + T gates that correspond to that unitary? According to Fast and efficient exact synthesis of single qubit unitaries ...
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### Why is a different convention used for the $Rz$ implementation on IBM Q?

A $z$ rotation gate is defined as $$Rz(\theta)=\mathrm{e}^{-i\frac{\theta}{2}Z}= \begin{pmatrix} \mathrm{e}^{-i\frac{\theta}{2}} & 0 \\ 0 & \mathrm{e}^{i\frac{\theta}{2}} \end{pmatrix},$$ ...
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### How to append an Instruction to a QuantumCircuit with variable length of QuantumRegisters as qargs?

I think it is a bug but I'm not really sure. Basically, what I'm trying to do is the following: I have an Oracle Instruction which I want to append to my QuantumCircuit, looks as follows: ...
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### How to solve these questions? [duplicate]

Link: v.ht/qhash. Here are some of the best questions available on the net, if anyone could code them in Q#, then it would be great. By solving you will gain experience on qubits, quantum gates, ...
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### Screening procedure in an iterative qubit coupled cluster (iQCC) ansatz

The paper Iterative Qubit Coupled Cluster approach with efficient screening of generators describes a new screening procedure for generators of the QCC ansatz. How does one get from defining the ...
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### Is it possible to express u1(λ) through the gates rx, ry, rz while maintaining the phase? In Qiskit for example

Is it possible to express gate u1(λ) through the gates rx, ry, rz while maintaining the phase? Both in principle and in practice (in Qiskit for example)? The single gate rz(λ) is not suitable, because ...
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### Example of a quantum algorithm better than its classical counterpart which involves only $1$ qubit?

I was reading over the proof of the Deutsch-Jozsa algorithm, which in its simplest case, involves at least 2 qubits. Is there an example of a quantum algorithm that is better than it's classical ...
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### How to approximate $Rx$, $Ry$ and $Rz$ gates?

Quantum Inspire is a quantum computing platform provided by QuTech. It consists of two real quantum processors - Starmon-5 and Spin-2. Whereas it is possible to use rotation gates $Rx$, $Ry$ and $Rz$ ...
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### Show that these two expressions for the oracle transformation are equivalent

Suppose $x \in \{0,1\}^n$. The standard way to make a query is with an oracle $O_x$ that given an input $|i,b \rangle$ returns $|i,b \oplus x_i \rangle$. Via the phase kick-back trick, this can be ...
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### Efficient implementation of exponential of projector

If I have an $n$ qubit system and a projector $P$ such as $P_0 = \left|0\right>^{\otimes n}\left<0\right|^{\otimes n}$ (as an example) on those qubits, is there an efficient way to implement the ...
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### How to decompose unitary quantum gate in current simulator or emulator?

I have a question about how to decompose a unitary quantum gate in a currently existing simulator or emulator. I have read some papers about SK algorithm and other algorithms which aim to decompose ...
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### A question about a real programmable quantum computer

In the theory of universal quantum gates,I have known a common universal gate set is the Clifford + T gate set, which is composed of the CNOT, H, S and T gates. Then there is a concept called "...
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### Show that a $CZ$ gate can be implemented using a $CNOT$ gate and Hadamard gates

Show that a $CZ$ gate can be implemented using a $CNOT$ gate and Hadamard gates and write down the corresponding circuit. Recall from Quantum Information Theory that $Z=HXH$. As $CNOT$ is a ...
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### Question about the practical use of super dense coding in information transmission [duplicate]

Question about the practical use of super dense coding in information transmission: We know that by using super dense coding it is possible to transmit 2n classical bits transmitting n qubits, ...
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### How to spot the matrix representation of the quantum NOT operation

Applying the above construction to AND we get the map $(x1,x2,y) \rightarrow (x1,x2,y⊕(x1∧x2))$ for $x1,x2,y \in \{0,1\}$. The unitaryoperator which implements this is then simply the map \$|x1〉|x2〉|y&...
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### Do all physical architectures for quantum computers use the same universal gate sets?

Now I have understood that physical implementation of quantum computer need a universal quantum gate set like Clifford+T to realize any unitary quantum gate. However, I don't know if it is all the ...