# Tag Info

Accepted

### Is 216 qumodes photonic quantum processor equivalent to 216 qubits superconducting quantum processor, in terms of computational power?

My name is Isaac and I work at Xanadu. That’s a really good question! Generally speaking, you can argue that 216 qumodes are more powerful than 216 superconducting (SC) qubits since qumodes encode ...
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### Is there a quantum gate that can turn any superposition $|\varphi \rangle$ into a unit column vector $|00\cdots 1\cdots 0\rangle$

It depends on what you mean. For a given state $|\varphi\rangle$, it is always possible to find a gate $U_\varphi$ such that $U_\varphi|\varphi\rangle=|i\rangle_{10}$ for some given $i$. However, it ...
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### Are the SDG and TDG gates hermitian?

A matrix $A$ is a Hermitian if and only if $$A = A^\dagger$$ So if $A^\dagger$ is Hermitian then that means $A^\dagger = (A^\dagger)^\dagger = A$ and so of course $A$ is hermitian. By the way, by ...
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Accepted

### what's the point of the first barrier in this circuit?

Correct, quoting What is a "barrier" in Qiskit Circuits?: The barrier acts as a directive for circuit compilation to separate pieces of a circuit so that any optimizations or re-writes are ...
• 1,833
Accepted

### Can someone explain to me what is T gate and tdg like im five?

tdg is the method used to apply $T^\dagger$ (read T dagger). Thus, there are no differences between these two. For a quantum gate $U$, $U^\dagger$ is the inverse of ...
• 2,671
Accepted

### Quantum gates with 1 qubit output

Indeed, it is useful to consider these types of situations. Sometimes we might measure a qubit and throw it away, leaving us one less qubit than before in our system. The issue you bring up is, what ...
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### How can I write if conditions on quantum registers using qiskit

If "some operations" in your question means quantum operations, then you can use Gate.c_if() to apply a gate based on a value in a classical register as ...
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### Definitions of a quantum circuit's depth and connectivity

Let me try to provide a more precise definition of connectivity in a quantum circuit. Every quantum circuit defines a graph (network), with vertices (nodes) given by qubits. There is an edge $q_1 q_2$ ...
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1 vote

### Is there a general way to parametrize 2-qubit unitaries?

What I propose here could possibly be simplified further, but that's at least a first direction. First, any unitary can be written as $U=e^{-it/\hbar \widetilde{H}}$ for some $t$ and $\widetilde{H}$ (...
1 vote

### Finite subgroup of $U(4)$ containing a non-Clifford gate and all local Cliffords

Here's an example for the real Pauli and Clifford groups : $$P_1=<X_1,Z_1>; |P_1|=8;$$ $$P_2=<X_1,Z_1,X_2,Z_2>; |P_2|=32;$$ $$C_1=<X_1,Z_1,H_1>; |C_1|=16;$$ C_1^{\otimes 2}=<X_1,...
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1 vote
Accepted

### Definitions of a quantum circuit's depth and connectivity

I would like to give explicit definitions of the circuit depth and connectivity. I assume that the meaning of terms like vector state, quantum circuit, wires, and 1- and 2-qubit gates is understood. I'...
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1 vote
Accepted

### Speed of Superconducting Qubit Architectures

Google's Sycamore processor for which they claimed quantum supremacy (https://doi.org/10.1038/s41586-019-1666-5) performs two-qubit operations in 12 ns, so that would be some 80 MHz. Of course ...
• 161
1 vote

### How to write a code to separate two qubits?

Maybe it should be useful tu use qutip to better understand what you desire (if you are familiar with python) by visualizing exactly the 2 qubits and its state vectors (which I believe is what you ...
1 vote

### Is there a gate sending $|0\rangle^{\otimes n}$ to a state where some amplitudes are zero?

you can check out qiskit textbook, https://qiskit.org/textbook/ch-gates/phase-kickback.html https://qiskit.org/textbook/ch-quantum-hardware/density-matrix.html#5.-Mixed-States-in-the-Bloch-Sphere-- ...
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1 vote

### Is digital quantum computing more powerful than the analog one?

As someone else said, you're right depending on how you define "analog quantum computing" because it's a bit of an overloaded term. Quantum annealers work by slowly changing a Hamiltonian ...
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