# Tag Info

## Hot answers tagged quantum-circuit

Accepted

### An impossible quantum adder claimed by a journal article?

it's from International Journal of Theoretical Physics - reputable journal Consider this paper your lesson in how reliable "reputability" is. Look at Figure 5 from the paper: Specifically ...
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### What's meant by the depth of a quantum circuit?

The depth of a circuit is the longest path in the circuit. The path length is always an integer number, representing the number of gates it has to execute in that path. For example, the following ...
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### How to check if a quantum circuit can be constructed for a given matrix representation?

Correct, unitarity is a sufficient and necessary condition. From Nielson and Chuang page 18: Amazingly, this unitary constraint is the only constraint on quantum gates. Any unitary matrix specifies a ...
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### How to distinguish between collapsed and uncertain qubits in a quantum circuit?

Consider a quantum circuit on one qubit initialized in the state $|0\rangle$ and consisting of two Hadamard gates where we can insert a measurement between the Hadamards. The input state is $|0\rangle$...
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### Building a controlled NOT gate which is controlled by the qubit it is acting on

The operation you want is impossible, because it is not reversible. It sends both |1> and |0> to |0>, so afterwards if you see |0> you can't tell if it came from |1> or from |0>. So ...
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### How could one implement a circuit using Grover's algorithm to solve a linear system of equations?

You certainly could use Grover's search. You would create 2 registers. This first, of 3 qubits, would effectively store the $\{s_0,s_1,s_2\}$. This is the standard register for Grovers on which you ...
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### Superposition of quantum circuits

As Davit Khachatryan's answer points out, the task is impossible / ill-defined, since the desired target state is generally not normalized and it depends on the relative global phases of the two ...
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### How to check if a quantum circuit can be constructed for a given matrix representation?

Right. But when you build a quantum computer, you want to have a certain set of gates that you want to implement, and all other gates (unitary matrices) can be built from that set of gates. This is ...
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### Qiskit - Circuit drawing aesthetics - Can I force the measurements in my circuit to show at the end?

You can add a barrier before the measure ...
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