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# Questions tagged [quantum-gate]

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

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### Qiskit cant run circuit with reset gate with error

In qiskit if i have a reset gate in a circuit. If i want to add noise to the circuit it wont transpile. For example: ...
• 31
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1 answer
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### qiskit statevector ordering issue

I am currently studying Qiskit. I don't understand the two pictures below while studying. When I apply circuit.x(1), the X gate should be applied to the second qubit, resulting in the state |01>. ...
• 131
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### Equivalence of two unitary transformation with respect to local operations

Suppose that $U_1$ and $U_2$ are two (entangling) operators that act on a quantum system consisting of several subsystems. Is there any criterion to tell if these two are equivalent up to applying ...
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### How to determine the single-qubit phase?

In some works it is suggested to find the qubit phase by the following method: Apply $X/2$ (or $Y/2$) gate - preparing the qubit in superposition. Detune the qubit by flux pulse, for example here ...
• 259
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### Does the $\text{CNOT}$ gate activate if the control qubit is $-|1⟩?$

I understand how the $\text{CNOT}$ gate works intuitively: However, say we have a circuit where the $Z$ gate is applied to $|1⟩$, which turns $|1⟩ \to -|1⟩$. Then, there is a $\text{CNOT}$ gate with ...
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### References for mapping qudit gates to qubits equivalent

Let's assume that I'm modelling a d-levels qudit as a set of n qubits, where $d = 2^n$. I would need to map the application of quantum gates on the qudit to a set of operations of the relative qubits ...
• 11
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### general way to decompose a CZ gate on $n$-qubit system

Suppose I have a CZ(i,j) gate (or CNOT) acting on qubit $i$ and $j$, on a $n$-qubit system. Is there a general way to decompose this gate into a set of gates that only involve single-qubit gates and ...
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### A measure of entanglement created by a unitary operation

Let $U$ be a unitary matrix acting on a 3-qubit system. If there is no correlation among any pairs of the three qubits, the unitary operation can be represented as $U = U_1 \otimes U_2 \otimes U_3$, ...
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### How do qubits interact to form logic gates?

How do qubits interact to form, say, CNOT gates? There are very few comprehensive explanations of how quantum computing works. They all use obscure metaphors that don’t make sense (like Schrödinger’s ...